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  • 力学类中文核心期刊
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Abstract:
Abstract: In the numerical simulation study of Ultra-High Performance Concrete(Ultra-High Performance Concrete, UHPC), reasonable determination of its constitutive model parameters is the basis of improving the calculation accuracy and design reliability. This paper determined the parameters of HJC constitutive model of UHPC based on uniaxial compression test, SHPB test and existing tri-axial compression test and so on. In the process of parameters determination, the parameters of HJC constitutive model were divided into five categories. The yield surface parameters were determined by the static failure surface equation. The parameters of state equation were determined by P-μ relation. Damage parameters were determined according to relevant literature. The basic physical parameters were determined according to the test and so on. LS_DYNA was used to simulate the explosion test of the one-way slab. Firstly, the finite element model of the one-way slab was established. The HJC constitutive model was used for UHPC, and the linear reinforcement model was used for reinforcement material. The reinforcement and UHPC were connected by common joints. The air and explosive models were established, and the fluid-solid coupling method was used for calculation. By comparing the simulation results with the damage degree and the maximum deflection of the one-way slab in the test, the effectiveness of the determined parameters was verified. In order to further understand the anti-blast mechanism of UHPC members, the determined parameters were used to conduct numerical simulation research on the one-way slab explosion condition, and the influence of reinforcement and size effect on the explosion result was analyzed. Results show that during the explosion process, the maximum mid-span deflection of the one-way slab can be reduced by increasing the longitudinal reinforcement ratio, and the length of oblique cracks on the side of the one-way slab can be reduced by properly encrypted stirrups. UHPC one-way slab has obvious size effect, and the variation of thickness and length has the greatest influence on the explosion result.
Abstract:
With the rapid development of air transportation, the safe usability of aviation fuel is extremely important. However, during the storage, transportation and use of aviation fuel, it is very easy to form steam because of its good evaporation and combustion performance. In case of leakage, it will quickly form a flammable mixture with the air in the cabin, and combustion and explosion accidents may occur in case of fire source, and there are differences in the combustion and explosion parameters of aviation fuel in different compartment structures. In order to understand and grasp the hazard of aviation fuel combustion and explosion in different structural cabin, a numerical simulation study of aviation fuel vapor combustion and explosion in different structural aviation fuel cabin was conducted using CFD. The effects of different cabin structures on aviation fuel combustion and explosion were analyzed through the changes of parameters such as explosion overpressure time, explosion time and explosion temperature. The results show that when the premixed deflagration of aviation fuel vapor occurs in the closed aviation fuel cabin, the pressure changes are more uniform, the flame surface is spherical diffusion, and the combustion reaction mainly occurs on the flame surface. When the flame surface area increases or the flame propagation speed increases, the chamber pressure increases; Under the conditions of this numerical simulation, the maximum combustion and explosion pressure of aviation fuel in the closed compartment without partition and the closed compartment with incomplete partition are 0.76 MPa and 0.74 MPa respectively, that is, the special structures such as incomplete partition in the compartment have no significant effect on the maximum pressure generated by aviation fuel combustion and explosion; The existence of special structures such as diaphragms makes the air flow vortex in the cabin, increases the fuel consumption rate, and increases the propagation speed and pressure rise rate of the flame surface. The mass fraction of fuel in the cabin is determined by the flame surface.
Abstract:
To investigate the influence of multi-factor coupling on the explosion characteristics of methane, an explosive gas test platform with a 1.2 L cylindrical explosive device was designed and established. From the perspective of maximum explosion pressure, the effects of different equivalence ratios φ (0.6~1.4), initial temperatures T0 (25 ℃~200 ℃) and initial pressures p0 (0.1 MPa~0.5 MPa) on methane explosion characteristics were comprehensively analyzed. Based on the maximum explosion pressure data by the experiments, a nonlinear regression prediction model among the maximum explosion pressure of methane, equivalence ratio, initial temperature and initial pressure was developed by 1stOpt software. The results show that: under the coupling effect of initial temperature and initial pressure, the higher initial pressure becomes the more significant effect of initial temperature on the maximum explosion pressure. However, with the increasing of the initial temperature, the effect of initial pressure on the maximum explosion pressure is weakened. Under the coupling effect of initial pressure and equivalence ratio, and within the experimental conditions of the study, when φ<0.9 or φ>1.2, the higher initial pressure changes dramatically on the maximum explosion pressure. Under the coupling effect of initial temperature and equivalence ratio, and within the experimental conditions of the study, when φ>1.15, the higher initial temperature changes significantly on the maximum explosion pressure. In addition, comparing the prediction results of the 1stOpt prediction model with the experimental results, the relative error is less than 10%. It is indicated that the prediction model can provide high accuracy and good adaptability.
Abstract:
The most common hypervelocity propulsion systems are light gas guns. Especially, two-stage light gas gun is suitable for their ability to accelerate projectile at velocities ranging from 2 km/s to 9 km/s. However, velocities higher than 10 km/s are demanded eagerly for Ballistic Limit Equations on on-orbit impacts and meteoroids. In order to improve the launch performance of the light-gas guns, a concept of using density-gradient gas as the driven gas instead of single helium or hydrogen gas has been proposed. An analytical acceleration model of the projectile in the launch tube with constant
Abstract:
The complex terminal ballistic parameters of the warhead will affect the circumferential propagation law of the near ground explosive wave and the damage degree to the target. Studying the propagation law of the near ground explosive wave of the cylindrical charge has important engineering significance to accurately evaluate the damage efficiency. Based on AUTODYN-3D software, the near ground explosion of cylindrical charge with different terminal ballistic parameters is simulated and calculated, and the data of shock wave pressure in the front, back and side directions under the near ground explosion of cylindrical charge are obtained by modeling in two directions respectively; Thus, the influence of four parameters, namely, the velocity of the battle group, the impact angle, the height of the explosion center and the ratio of the length to diameter of the charge, on the propagation of the shock wave of the near ground explosion of the cylindrical charge is studied. The evolution process of the shock wave, the peak pressure and the height of the Mach stem are analyzed. The results show that the height of the explosion center is the main factor affecting the height of the shock wave Mach stem during static explosion, and the impact angle and the length diameter of the charge are the main factors affecting the difference in the height direction of the Mach stem. During dynamic explosion, the height of circumferential Mach stem can be increased, especially in the front; In addition, the peak value of forward shock wave increases linearly with the increase of dynamic detonation velocity. The results of orthogonal optimization show that the dynamic detonation velocity has the largest range to the front peak pressure of the cylindrical charge among the four variables; The impact angle has the largest range to the rear peak pressure; The height of explosion center has the greatest influence on the height of Mach stem. By studying the circumferential propagation law of the shock wave of near ground dynamic explosion of the cylindrical charge, the results show that reasonable adjustment of the charge parameters and the front of the near ground explosion can be used for reference to achieve the maximum damage or reduce the hyper-pressure damage in a certain direction.
Abstract:
To achieve large deformations of specimens at lower strain rates, the traditional Separate Hopkinson Press Bar (SHPB) experimental technique usually needs to use the long bar system. However, the machining of the bar and space limits the widespread application of the technique. This paper proposed a direct-impact double-loading Hopkinson press bar experimental technology. Stress wave reflected by a rigid wall at the end of the transmission bar is utilized to realize secondary loading. A wave separation algorithm is used to achieve effective separation and calculation of the superimposed waveforms. The loading of 1.2ms in a 4m-long bar system is available and the stress-strain relationship can be obtained accurately. Finite element model of secondary loading of direct-impact double-loading Hopkinson bar is established. Numerical results show that the experimental technique can effectively achieve secondary loading of the specimen, and the comparison with the numerical results obtained by the long bar system shows that the stress-strain relationship of the specimen obtained by the two methods is completely consistent. The stress-strain relationship calculated by the wave separation technique is the same as that obtained by direct extraction. Finally, this technique is utilized to test aluminum alloy specimens with large deformations of the specimens at 102 strain rate is achieved.
Abstract:

In order to improve the permeability of coal seam with high gas and low permeability and effectively control the disaster of coal and gas outburst, the mechanism of permeability enhancement of coal seam by shaped charge blasting is studied. Firstly, the comparative experiments of concrete cracking caused by shaped charge blasting and conventional blasting were carried out, and the sizes of concrete crushing area and fracture area after blasting were compared. Meanwhile, the strain data of the strain brick with time were collected by the super dynamic strain gauge. Then, ANSYS/LS-DYNA was used to reproduce the whole process of the formation, migration and penetration into concrete of shaped energy jet. The stress wave propagation characteristics of shaped charge blasting and conventional blasting were compared and analyzed. Finally, the coal seam antireflection tests were carried out in Pingmei No. 10 mine, and the gas volume fraction of the extraction hole after blasting is compared. Finally, the coal seam penetration enhancement tests of shaped charge blasting and conventional blasting were carried out in Pingmei No. 10 coal mine, and the gas volume fraction of the extraction hole after blasting was compared. The results show that after shaped charge blasting, the crack width of concrete in the direction of energy accumulation is 1.1 cm, the crack width of concrete in the direction of vertical energy accumulation is 0.4 cm, and the width of four main cracks formed in concrete after conventional blasting is 0.3 cm. Comparing the strain gauge peaks at the same distance, it is found that the strain gauge in the direction of energy accumulation is the maximum, followed by the direction of vertical energy accumulation, and the strain at the diagonal is the minimum. In addition, the strain peak value in the direction of energy accumulation is much larger than that of conventional blasting, and the strain peak value in the direction of vertical energy accumulation is basically equal to that of conventional blasting, while the strain peak value of the diagonal strain gauge is smaller than that of the conventional blasting. The numerical simulation results show that the crushing area of concrete after shaped charge blasting is "dumbbell type", and the area of crushing area is smaller than that of conventional blasting. While the fracture area is "spindle type", and the development of fracture degree is better. The field test shows that the gas volume fraction of the extraction hole after shaped charge blasting is significantly higher than that of conventional blasting. It can be seen that shaped charge blasting can effectively improve the permeability of coal seam with high gas and low permeability.

Abstract:
In order to study the dynamic mechanical behavior of coal rocks with characteristic bedding under complex ground conditions, the dynamic triaxial cyclic impact test on coal rocks with bedding (0°, 30°, 45°, 60° and 90°) was conducted using the 50 mm split Hopkinson pressure bar (SHPB) test system. Furthermore, the 3D profile scanner was utilized to quantify the fracture interface and investigate the bedding effect on the dynamic fracture process. The bedding angle effect and confining pressure effect on the dynamic properties of coal rock was investigated in combination with the dynamic parameters such as compressive strength, elastic modulus, energy distribution evolution and the fracture surface roughness variation. The research shows that when confining pressure is applied, the stress - strain curve of coal rock appears elastic aftereffect. The dynamic compressive strength and failure strain of bedding coal rock are 3.9~4.2 and 2.59~3.05 times higher than those without confining pressure, respectively. As the bedding angle increases, the dynamic compressive strength, elastic modulus and energy transmitted rate of coal rock displays the U-shaped distribution, which decreases first and then increases, reaching the minimum at 45°. Meanwhile, the energy absorbed rate and fracture surface roughness shows the ∩-shaped distribution of increasing first and decreasing then, and the damage variable showed the N-shaped distribution, reaching the maximum at 45°. The failure form with 45° bedding is the most serious, which is more prone to intergranular fracture and spalling fracture. However, the 90° bedding coal rock is more likely to absorb energy, and form transgranular fracture, resulting in a large number of mesoscopic fractures. The damage characteristics of coal rocks with the bedding angle can be summarized as the evolution of tensile damage (0°) - shear damage (30°, 45°, 60°) - splitting damage (90°). The relevant characteristic results obtained from the experiment can provide theoretical support for the safe and efficient exploitation of coalbed methane resources under the complex environment of practical working conditions.
Abstract:
Under the threat of terrorism attacks and military strikes, building columns of the perimeter frames are likely to suffer near-field near-ground explosion. To rapidly assess the dynamic responses and failure modes of the building columns under such blast scenarios, in this paper numerical simulation method is employed to investigate the distribution pattern of the shock waves on the front face of building columns under near-field near-ground blast scenarios, and a corresponding simplified blast load model is proposed. To this end, firstly, the existing experimental data of overpressure and impulse are selected to validate the numerical model for blast load. Then, a typical numerical model under near-field near-ground blast scenarios is established to study the effects of the scaled distance and scaled height of the spherical charges on the characteristic values of the shock waves acting at the building columns. Finally, formulae for the maximum reflected impulse and the representative value of the positive overpressure duration are derived based on regression analysis, and the blast load at each location of the column front face is represented by an equivalent triangular load model. The results indicate that when the scaled height of the charge is less than 0.3 m/kg1/3, the distribution of the maximum reflected impulse along the column length can be represented as a trilinear model and a bilinear model for the scaled distance of 0.4 m/kg1/3-0.6 m/kg1/3 and 0.6 m/kg1/3-1.4 m/kg1/3, respectively. Moreover, under a given scaled distance and a scaled height, with increasing the charge weight, the peak reflected overpressure remains constant but the maximum reflected impulse is proportional to the cubic root of the charge weight at the locations with the identical scaled height of the column.
Abstract:
A series of experiments were performed in a self-designed 5-m-long duct with a cross-section of 0.30 m × 0.30 m to investigate the effects of vent burst pressure (pv) on the flame propagation and pressure-time histories of 30 vol% hydrogen–air premixed gases. The explosion flames were recorded by a high-speed camera at a frequency of 2500 Hz. Five piezoelectric pressure transducers were employed to record the internal and external overpressure. The duct was evacuated using a vacuum pump before the experiment, and the premixed hydrogen-air gases with a concentration of 30% was prepared according to Dalton's law of partial pressure. The variation of the vent burst pressure was achieved by changing the thickness of the aluminum foil which was used as vent cover. The results show that the first three stages of the flame structure in the duct are hemispherical, finger-shaped and tulip flame, respectively. pv has a significant effect on the structure of tulip flame and its subsequent development. Three pressure peaks (pb, pout, pext) can be distinguished from the pressure-time histories monitored by the pressure transducer near the vent, corresponding to three different generation mechanisms: burst of the aluminum foil, venting of burned mixtures, and the external explosion, respectively. The three pressure peaks increase with an increase in pv. pb is the dominant pressure peak in most cases. The maximum internal overpressure increases as pv increases, and the position where the maximum internal overpressure is measured depends on pv. The maximum internal overpressure is obtained at the center of the duct (PT2) when pv ≤ 42 kPa, but near the open end of the duct (PT3) if pv > 42 kPa. When the flame reaches the vent, it ejects from the vent and then ignites the external combustible cloud. Therefore, the external explosion is triggered. pv significantly affects the flame evolution outside the duct, but there is no significant difference in the maximum length of the external flame at various pv. A non-monotonic trend between the maximum external overpressure and pv is observed.
Abstract:
In order to determine the critical vent area where a warhead can burn stably under fast cook-off, based on the law of mass conservation and the state equation of gases, the gas pressure rise inside the casing after the ignition of warhead charge was studied under the fast cook-off stimulation. A gas pressure rise model was established in the current work by considering the initial temperature of an explosive and gas venting in a warhead. A composition B explosive (Comp B) cylindrical warhead was used as the research object. The numerical calculation of the model was carried out by C language programming software, and it was developed to determine the AV0/SB ratio (critical vent area/external surface area of the explosive) at which the warhead could be in stable combustion after it was accidentally ignited, and the results were compared with experimental values. It is found that the change of pc (pressure inside the warhead casing) after the thermal stimulation and ignition of Comp B occurred in four stages of I~IV: increased sharply, then increased rapidly, decreased slowly, and finally, leveled off. The peak pressure of the warhead decreased linearly with the increase of AV/SB. When AV/SB corresponding to the peak pressure (pcmax) of 10 MPa in the warhead was taken as the critical AV/SB ratio, AV/SB could better separate the stable combustion reaction from the explosion reaction inside the warhead. The effects of the surface area of the explosive charge of the warhead, the initial temperature of the explosive, the air volume ratio, and the burning rate of the explosive on AV0/SB were investigated, and the model-predicted values at different temperatures were compared with experimental results. The surface area of the explosive charge has little effect on AV0/SB, and AV0/SB is positively correlated with the temperature and burning rate of the explosive and negatively correlated with the air volume ratio. The model-predicted values of AV0/SB at different temperatures are found to be in good agreement with experimental results. The proposed model can well predict the critical vent area of the Comp B warhead. Therefore, the findings of this study provide a theoretical basis for the design of thermally stimulated venting structures of ammunition.
Abstract:
Based on high-speed photography technology, the oblique water-entry experiments of high-speed projectile under multiple conditions are carried out. During the experiment, five experiments were conducted for each condition, and the same phenomenon appeared in the experiment. A self-programing is utilized to capture the image’s pixels and extract the experimental data for the experimental photographs. By analyzing the formation, development, and collapse processes of the oblique water-entry cavity of high-speed projectile, the evolution characteristics of projectile cavitation during tail-slapping are concluded. In addition, by comparing and analyzing the variations of the cavity size, and the velocity and acceleration of projectiles with different initial velocities of the water-entry of the projectile, the influence of the initial velocities of the water-entry of the projectile on cavitation evolution characteristics and water-entry motion traits is summarized. The results show that after the tail-slapping of the projectile, part of the projectile tail penetrates through the original cavity and gets wet, and a new tail-slapping cavity is generated backward from the projectile tail. The tail-slapping cavity fits closely with the original cavity. At the end of the tail-slapping, the location of the tail-slapping cavity under the water is basically unchanged. The tail-slapping cavity is pulled away from the surface of the original cavity of the projectile and collapses, while the original cavity at the same depth accelerates and collapses under the influence of the jet generated by the tail-slapping. With the increase of the initial velocities of the water-entry of the projectile, the size of the tail-slapping cavity and the length of the original gradually increase, and so does the maximum wet area of the tail. With the increase of the number of tail-slapping, the velocity attenuation amplitude and the energy loss of the projectile in each tail-slapping increase, and the capacity of the speed storage of the projectile decreases.
Abstract:
In order to explore the distribution of explosion strain field and fracture field of segmented charge explosion, used digital image correlation analysis (DIC) and computerized tomography (CT) scanning experiment analyzed the distribution of the explosion strain field and fracture field of the segment charge, established three-dimensional reconstruction model of "rock-explosion crack", described the spatial distribution of the location and shape of the explosion crack, and obtained the fractal dimension and damage degree of the explosion crack. The research results show that: the segment charge changes the full-field strain morphology of the medium caused by continuous charge. Under the condition of satisfying the damage effect of upper sublevel explosive on medium, the effect of lower sublevel explosive on medium is increased, at the same time, the time of blast stress wave is prolonged. It can be seen from the three-dimensional cracks of segmented charge and continuous charge explosion, the explosion crack mainly expands along the radial direction, the annular crack formed by axial stress and strain is not obvious, and the radial direction is the main direction of rock failure. When the charge ratio of the upper segment is 0.4, the strain peak value of the lower segment is larger, which better meets the demand of the rock mass for explosion energy in the lower segment in engineering practice. Under the same charging coefficient, the explosive cracks in the continuous charging structure do not run through the whole specimen, and the explosive cracks in the plugging section are less, under the segment charge structure, the upper sublevel of rock mass can better use the energy of explosive explosion to break rock because the position of explosive is improve. The overall damage degree of rock in segment charge is 23.5% higher than that in continuous charge, and the damage degree of rock in upper sublevel is 46.4% higher than that in continuous charge.
Abstract:
The failure law of shallow-buried reinforced concrete straight wall arch structure in soil under secondary explosion of conventional weapons was studied by explosion test and numerical simulation. Test structure adopts scale model based on similarity principle. Three groups of six shots were set up in the test. LS-DYNA is used to simulate the three groups of working conditions. By comparing the pressure of the measuring point in the soil, the speed of the structural measuring point, the structural deflection and other data, it is found that the simulation results are basically consistent with the experimental results. After comparing the numerical simulation results with the test, the numerical simulation conditions of the secondary explosion are expanded. When the comparison verifies that the numerical simulation is consistent with the experimental results, the secondary explosion conditions under the action of conventional weapons are simulated to study the dynamic response of structures under repeated impacts. Through calculation, it is found that when the proportional distance is set between 0.6 m/kg3 - 0.4 m/kg3, the damage of the structure is mainly caused by the overall damage. Combined with the macroscopic description of structural damage and the maximum deflection span ratio, the damage grade of the structure under the overall effect is divided. By discussing the initial damage of the structure and the failure law of reinforced concrete straight wall arch structure under different explosion sequences, the following conclusions are obtained: When the structure is damaged by explosion, such as cracking and bending, some concrete is out of work due to cracking or entering plasticity, resulting in the change of stiffness of the structure. The final damage degree of the structure is affected by the strike sequence, and the effect of initial explosion on the final damage of structure is greater than that of secondary explosion.
Abstract:
Safety separation distance is one of the key concerns in the engineering construction and research of hazards warehouses. In order to reduce the safety separation distance, a novel type of hazards warehouse was proposed based on the current codes and structure forms of existing hazards warehouses. The novel warehouse was mainly composed of a shallow-buried main body, a
Abstract:
With the development of the times, the demand for explosion-proof and impact resistant materials in the military and aerospace fields is increasing. As a traditional energy absorption and shock absorption protective material, polyurethane needs higher dynamic mechanical properties. One way to effectively improve the impact resistance of polyurethane materials is to add ceramic balls as reinforcing phase to polyurethane matrix. At present, the main research on ceramic ball reinforced materials is focused on the nano and micron size, and most of them are static mechanical properties and anti penetration properties. In order to study the effect of millimeter ceramic balls on the impact resistance of polyurethane composites under explosion load, the dynamic response of multi-size Al2O3 ceramic balls reinforced polyurethane matrix composites under small equivalent explosion load is simulated based on the ALE algorithm of LS-DYNA, and the deflection, velocity, acceleration The effects of appropriate explosion equivalent and ceramic ball size on the properties of composites were explored by absorbing energy and other parameters, and the correctness of numerical simulation was verified by using henrych's empirical formula of explosion overpressure in free field. The conclusions are as follows: the deflection of the center point of the back wave surface of the composite plate is smaller than that of the surrounding point within a certain time, and the velocity also shows the same trend; The acceleration of ceramic ball and polyurethane always keep the opposite direction, and the existence of ceramic ball reduces the amplitude of overall acceleration oscillation; With the increase of explosion equivalent, the deflection / velocity of the composite increased steadily and the energy absorption efficiency of polyurethane increased continuously; At the same area density, the smaller the ceramic ball size is, the stronger the deformation resistance of the composite plate is, the lower the sensitivity to the change of impact load is, and the overall acceleration fluctuation range becomes larger.
Abstract:
The formation of complex fracture networks in shale by cyclic impact loading is an important scientific problem for water-free fracturing technology of shale reservoirs such as explosive fracturing and high-energy-gas-fracturing. In this paper, two cyclic impact experiments based on the Hopkinson rod experimental system (SHPB) were conducted on freshly exposed black mud shale of the Wufeng Formation-Longmaxi Formation taken from Changning County, Sichuan Province, to investigated the kinetic response and damage evolution characteristics of the shale under different cyclic impact gas pressure and different cyclic impact gas pressure gradients, respectively, and to revealed the energy evolution law of cyclic impact shale using different impact gas pressure gradients under the condition of controlling the constant total incident energy. The main conclusions are as follows: With the increase of impact pressure, the number of times of impacts required to rupture the specimen decreases, the fragmentation and the peak stress increase; the specimen undergoes cyclic impact showing the mechanical response characteristics of compaction first and then gradual damage. The damage degree of shale specimens during cyclic impact were calculated by a dynamic damage model based on the Weibull distribution, and the results showed that the damage of the specimen gradually changes from slow deterioration to sudden damage by increasing the cyclic impact pressure. Different cyclic impact experiments with different impact gas pressure gradients were conducted, which showed that under the condition of constant total incident energy, different cyclic incident energy gradients could produce different damage effects, and the energy absorption ratio of the negative cycle impact gas pressure gradient and the positive cycle impact gas pressure gradient are greater than that of the zero gradients, and the absolute value of the pressure gradient shows a positive correlation with the energy absorption ratio. This indicates that under the same condition of total impact energy, increasing the absolute value of the cyclic impact gradient can produce better damage effect. The findings of the shale cyclic impact experiments can provide theoretical support for the technological design of multi-stage pulsed high-energy-gas-fracturing.
Abstract:
The self-driven rotary sprayer using ultra-high-pressure water jet is widely used in the rust removal of ship hulls, and its layout directly affects the efficiency and quality of ship derusting. Hitherto, the design of sprayer layout primarily depends on practical engineering experiences, due to the lack of support from accurate optimization techniques and theoretical analysis. In order to solve the layout optimization problem associated with self-driven rotary sprayers using ultra-high-pressure water jet, an improved elitist strategy genetic algorithm (ESGA) based on conventional genetic algorithm (GA) was proposed. By designing appropriate evolutionary operations, the ESGA algorithm can skip crossover and mutation operations on the fittest individuals in the population, and then directly copy the fittest individual to the next generation. Thus, the global convergence ability and robustness of the algorithm are improved effectively. By fully combining the sweep impinging performance and trajectory characteristics of rotary sprayer, a sweep impinging discrete-time model for self-driven
Abstract:
Abstract: Based on the working mechanism of local resonance materials, a filter concrete with stress wave attenuation characteristics is designed by embedding metal balls wrapped with elastic layer (filter units) in the concrete matrix.?First, the stress wave attenuation mechanism of filter concrete is analyzed by simplifying the filter concrete structure into the mass spring mechanical system.?Then, the propagation velocity and peak stress of stress wave in normal concrete model and filter concrete model under impact load are compared by using numerical simulation approach.?Through parameter analysis, the influence of the density of metal ball, elastic modulus and thickness of elastic layer on the energy storage effect of filter unit is studied. Finally, the spall damage patterns of normal concrete model and filter concrete model under impact load are compared.?The results show that the filter units can effectively reduce the stress wave propagation velocity and stress peak value in the concrete matrix.?The vibration of the metal balls and the deformation of the elastic layer make filter units have a good energy storage mechanism and effectively reduce the energy exerted by the impact load on the concrete matrix.?The larger the mass of the metal balls is, the better the energy storage effect of the filter unit is, while the elastic modulus and thickness of the elastic layer need to be designed through proper analysis to maximize the energy storage of the filter units.?The concrete matrix around the elastic layer has obvious stress concentration effect and local damage occurs, but the local damage of the filter concrete matrix dissipates a large amount of energy in the load, effectively reducing the degree of destruction near the free surface of the structure. Combined with the attenuation effect of the filter units on the stress wave, the filter concrete has good impact resistance.
Abstract:
A three-dimensional finite element (FE) model was developed to quantify the effect of attack angle on the penetration resistance of aramid laminates having varying thickness against flat-nosed projectile. The model was created through a macroscopic approach, which did not take into account the internal microscopic structure of the laminate and macroscopically equated each laminate as a homogeneous orthotropic anisotropic material. The validity of FE simulation results was compared with existing experimental data, with good agreement achieved in terms of residual velocities of the project and damage patterns of the aramid laminates. The validated FE model was subsequently employed to simulate the ballistic responses of 4 mm, 8 mm, and 16 mm target plates in the range of 0° ~ 30° attack angle. The residual velocity of the projectile, energy absorption rate of target, ballistic limit, and perforation energy threshold were calculated to characterize the ballistic performance of aramid laminates. By comparing the damage patterns of the aramid laminates and the contact forces applied to the project under different conditions, the mechanical mechanism by which the attack angle affected the ballistic performance of the aramid laminate at different impact velocities and different target thicknesses was explained. Within the studied working conditions, obtained results revealed that: the attack angle affects significantly the ballistic performance of aramid laminates, depending upon projectile impact velocity and target thickness; the ballistic limit and perforation energy threshold decrease with increasing attack angle, and the degree of such decrease is reduced as target thickness is increased; the residual velocity of projectile increases with increasing attack angle when the impact velocity is close to the ballistic limit and decreases with increasing attack angle when the velocity is well above the ballistic limit; the influencing mechanism of attack angle on ballistic
Abstract:
In order to improve the uniformity of the fragments of the fragmentation warhead and enhance the axial lethality of the warhead, it was proposed to use a wave shape controller to control the scattering direction of the fragments. The shape of the wave shape controller was designed based on the law of detonation wave reflection at the wave shape controller interface and the Shapiro formula. The LS-DYNA software and ALE algorithm were used to numerically calculate the scattering process of fragments, and the static explosion test of the warhead prototype was carried out to verify the rationality of using wave shape controller to improve the scattering characteristic of fragments. The difference in the fragment scattering process with and without the wave shape controller was compared. The law of fragment scattering velocity and scattering angle of the warhead was analyzed and summarized when there was no wave shape controller and when the wave shape controller materials were nylon, polyurethane and PTFE, respectively. The results show that wave shape controller can reduce the difference in the scattering velocity of fragments at the center and both ends
Abstract:
There is often a clearance of a certain thickness between two stacked metal flyers. When the double-layer metal flyers with clearance are loaded by detonation, the closing of clearance may affect the first and second loading wave form and shock intensity inside of the outer flyer, and then affect the free surface velocity of the outer flyer. In order to better grasp the motion characteristics under detonation loading, the law of the effect of clearance on the dynamic process needs to be studied. Firstly, the detonation driven two-layer steel flyers model is presented in which there is a certain thickness clearance between two steel flyers. In this model, the free surface of the outer flyer is loaded twice. By comparing the simulation results and experimental results of free surface velocity at different positions, it can be seen that the simulation can correctly catch the dynamic process. After then, the sources of the first and second loading in the outer flyer is given by the analysis of the simulated dynamic process. The first loading wave in the outer flyer comes from the clearance closing collision, and the second loading wave mainly comes from the sustained high pressure loading of detonation products. Finally, the simulation with different clearance thicknesses is carried out, and the effect of clearance thickness change is summarized. The simulated results of free surface velocity show that, with the increase of clearance thickness from 0.1 mm to more than 1 mm, the peak value of the first take-off free surface velocity first decreases and then remains unchanged, and the peak value of the second take-off free surface velocity first increases and then remains unchanged. The dynamic analysis show that, the size of the clearance thickness directly affects whether the inner steel flyer has enough time to develop into spallation on the clearance side after detonation loading. If the size of clearance is small, the inner flyer cannot develop into a spallation on clearance side, and the first loading wave form in the outer flyer is a triangular like wave. In this stage, with the increase of the clearance thickness, the first loading peak pressure decreases and the second loading peak pressure increases. If the size of clearance is large, the inner flyer can form a spallation with constant thickness and stable velocity on clearance side, and the first loading wave form in the outer flyer is an approximate square wave. In this stage, with the increase of clearance thickness, the peak pressure of the first and second loading is basically unchanged, but the time interval between the first and second loading decreases. The understanding has guiding significance for the interpretation of the free surface velocity measurement results in experiments, so as to better understand some unexpected physical phenomena caused by clearance in practical problems.
Abstract:
The calculation process of the break caused by the underwater close-range non-contact explosion of the ship is complex, involving many factors such as the hull frame, weapon charge, explosion distance and orientation, etc. the empirical formula is usually used in engineering practice. Based on the assumption that the ship is attacked by a "directional" warhead, the damage surface is approximately perpendicular to the damage axis, and the explosion process instantaneously meets the basic condition of approximate "energy conservation", the calculation method is given according
Abstract:
In order to control and prevent the safety risks caused by volatile gases during the storage and transportation of crude oil, the explosion limit of the ternary flammable gas mixture composed of volatile light hydrocarbons including CH4, C3H8 and C2H4 in crude oil was experimentally investigated in the 20L spherical explosive device. The experiment was carried out at 20°C and 0.1MPa, and the method of partial pressure was used to distribute the gases. Taking the rise of pressure over 5% as the criterion for explosion, each group of the experiments was repeated three times. Methods for predicting the explosion limit of the ternary flammable gas mixture based on Le Chatelier's law and the model of one-dimensional laminar premixed flame in Chemkin were proposed, and the reliability of the two methods was verified by the experiment. The results show that the explosion limit of the ternary flammable gas mixture is always within the explosion limit of these three pure components, which tends to approach the explosion limit of a certain pure component with its increase. The influence of the three pure components on the upper explosion limit is more pronounced than on the lower explosion limit, and the effect of C2H4 on the upper explosion limit is particularly obvious than the other two pure components. Both methods of prediction are highly consistent with the experimental regularity. The prediction of the lower explosion limit by Le Chatelier's law is relatively accurate. However, the deviation of the upper explosion limit increases with the raise of C2H4 due to its special characteristics of combustion, and the deviation decreases significantly after correction of Le Chatelier’s law; Although the prediction of the lower explosion limit in Chemkin, which predicts the lower explosion limit by calculating the laminar burning velocity near the lower explosion limit has a certain deviation, it’s within the allowable range of experimental deviations. Therefore, it can be used as a new method to predict the lower explosion limit of the ternary flammable gas mixtures, but the model of one-dimensional laminar premixed flame is not suitable for the prediction on the upper explosion limit.
Abstract:
To describe the dynamic mechanical properties of frozen sandy soil under active confining pressure state, a dynamic damage constitutive model, which could consider the effect of active confining pressure on the dynamic strength and deformation characteristics of frozen sandy soil, was established by connecting the plastic bodies on the nonlinear bodies of the Zhu-Wang-Tang model. The effects of damage parameters on the characteristics of stress-strain curves, yield point, peak stress, and peak strain were analyzed. In addition, the model parameters were determined based on the dynamic test data of frozen sandy soil. The applicability and accuracy of the established model were verified by comparing the model with the test data and analyzing its prediction errors under different test conditions. The results show that the damage parameters have no significant effect on the elastic stage and yield point of the dynamic stress-strain curves. However, it significantly affects the plastic and failure stages. The stress-strain curves predicted by the established constitutive model are in good agreement with the experimental results. The model is appropriate to predict the characteristics of large proportion of plastic stage and obvious yield point caused by active confining pressure. Moreover, it can also describe the enhancement effect of confining pressure on the dynamic compressive strength of frozen sandy soil. The prediction of the model on the peak stress and yield stress are better than that of peak strain and yield strain under different negative temperatures and active confining pressures.
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The physical mechanism of electrically exploding wires has caused much attention recently; fruitful experimental results have been reported by domestic researchers. Modeling and studying on the electrical metal wire explosion problems can help to understand the basic physics of Z pinches and other related magnetically driven plasma problems, and to evaluate the parameters of the equation of state and electrical conductivity. A zero-dimensional (0D) dynamical model of the underwater electrical wire explosion is developed; the single wire is modeled as a plasma cylinder undergoing self-similar radial motion with uniform density, temperature and pressure, while its velocity is varying linearly with radius. The kinetic equation and internal energy equation are derived from the hydrodynamic equations and used as the basic controlling equations. To close the 0D model, other parameters are supplemented, with the real gas quotidian equation of state(QEOS) model for pressure and internal energy, the modified Lee-More electrical conductivity model for resistivity, and an external circuit model for the current density. The boundary conditions are constructed from the shock Hugoniot relations in water, the pressure at the wire boundary is assumed to be equal to the water pressure behind the shock. The calculations are carried out from a cold start of wires with density and temperature in laboratory status. Results of the 0D model are validated by comparing with the results from simulations of one-dimensional (1D) magneto-hydrodynamic (MHD) model and experiments. Examples of electrical explosion of copper wires in water are taken in the applications, the rise time of the short-circuit current pulse is 5μs and the wires are varying from 50μm to 200μm in diameter. Results from the 0D-dynamical model are coincide well with the MHD simulation results and experimental data, typical discharging modes are achieved by varying the parameters of the wires. The 0D model can be used for parameters optimizing and data analysis in similar experiments.
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To study the explosion mechanism and the energy conversion process of the interaction between low melting point metal tin and water, a visual experiment platform which was composed of a high-frequency melting furnace, a high-speed camera, signal collectors and other equipment was built to monitor the contact reaction processes at different mass ratios of tin to water, like 5, 10, 15 and 20. Meanwhile, high melting point metal aluminum was selected for comparative experiments under the same experimental conditions to explore the differences in reaction characteristics between low melting point metal tin and high melting point metal aluminum during the steam explosion. Some mathematical calculation models were established to quantitatively analyze the shock wave energy in line with the law of conservation and explosive shock theory. The results show that two steam explosions were triggered when molten tin reacted with water at a mass ratio of 5; and in the comparative explosion experiments between molten tin with water and molten aluminum with water under the same experimental conditions, the reaction intensity and the duration during the explosion of molten metal with water are respectively related to the degree of fragmentation and thermal diffusivity. In addition, it is calculated that about 0.45% to 10.91% of the heat energy stored in the molten tin is converted into the explosion shock wave energy throughout the steam explosions. Moreover, the shock wave energy conversion rate is affected by the mass ratio; and this effect is reflected in that the energy conversion rate of the shock wave first increases and then decreases with the increase in mass ratio; when the mass ratio is 10, the energy conversion rate is the largest. It is
Abstract:
Polymer material has the characteristics of fast forming and good expansion performance. Its composite structure with gravel and reinforcement has obvious advantages in foundation treatment and urban road void removal and reinforcement. In this paper, polymer gravel slab and reinforced polymer slab were designed and manufactured, and experimental research under contact explosion impact was carried out. The damage characteristics of the two kinds of slabs were studied through the damage size and the measured shock wave data. Based on ANSYS / AUTODYN nonlinear explicit finite element program, the damage mode and damage diameter of reinforced polymer slab were studied, and compared with the test results to verify the accuracy and applicability of the established finite element model. The sensitivity of reinforced polymer slab to explosive quantity and slab thickness was analyzed parametrically, and the prediction formula of failure diameter of the top surface and bottom surface of reinforced polymer slab was put forward by using the multi-parameter regression analysis method. The results show that under the action of air contact explosion, the damage mode of polymer gravel slab is mainly local collapse and perforation at the contact part. Under the impact load of contact explosion, there are punching and cutting explosion pits on the top surface of the slab, tensile failure and collapse area on the bottom surface, and a through failure hole is formed in the center of the slab, in addition to some damage cracks; Under the action of air contact explosion, reinforced polymer slab mainly occurs crater damage on the top surface, spalling damage on the bottom surface and central punching perforation damage. The reinforced polymer slab has a good attenuation effect on the explosion shock wave. The diffuse reflection effect of the closed bubble in the polymer structure on the shock wave can absorb more energy to alleviate the explosion shock wave, which further shows that the polymer has the potential to be applied to the field of anti-explosion shock protection.
Abstract:
In order to study the influence mechanism of shaped charge liner on the perforation and damage fracturing effect of shaped charge penetrating shale reservoir, a three-dimensional model of "perforating charge-air-shale" was established. The cone angle of liner was set to 50 °, 60 °, 70 ° and 80 ° respectively, the thickness of liner was set to 0.5mm, 1.0mm and 1.5mm respectively, and the material of liner was set to copper, steel, titanium and tungsten respectively. The numerical calculation was carried out by using the ALE-Lagrange coupling method in the non-linear program (ANSYS/LS-DYNA).The ALE method was used to describe shell, explosive,liner and air , the Lagrange method was used to describe the shale reservoir. The systematic analysis was carried out from the aspects of jet velocity and shape, shale perforation effect and the fracture extension characteristics of shale. The results show that with the decrease of the cone angle of liner, the jet velocity and penetration depth increases, the pestle velocity and perforation diameter decreases. In a certain range with the decrease of the thickness of liner, the jet velocity, penetration depth and perforation inclination increases, the mass of the pestle decreases.The material of liner has a significant impact on the velocity of jet, pestle structure and shale perforation effect. Among them, the penetration depth of perforating charge with tungsten liner is the largest but the perforation diameter is the smallest, the penetration depth of perforating charge with titanium liner is the smallest but the perforation inclination is the largest, and the penetration depth of perforating charge with copper liner is slightly larger than that with steel liner, but the perforation diameter is slightly smaller. The charge with shell can significantly improve the jet velocity and penetration depth than the charge without shell. Because the detonation pressure has an obvious difference after the detonation wave is transmitted to the end of the explosive, which affects the jet velocity and penetration depth, the charge with shell has a greater jet velocity and penetration depth than the charge without shell. By comparing the fracture extension characteristics of shale in different groups, it is found that the fracture extension of shale mainly occurs in the stage of re reaming of pestle on shale. It is concluded that the material and structure of the liner have a significant influence on the shaped charge jet and its penetration effect, and then affect the formation and extention of damage fractures in shale. The fracture extension of shale can be promoted by reducing the initial perforation diameter of penetration, increasing the diameter of pestle and increasing the speed of pestle.
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The dynamic response and failure of the gradient metal foam sandwich beams subjected to high-velocity impact are studied experimentally. With the identical areal mass, five different core configurations are employed for the stepwise sandwich beams which are composed of three different densities of aluminum foams. All the sandwich beams are supported with a simply clamped boundary condition. Combing with the three-point bending, the impact resistance of the gradient sandwich beams in terms of dynamic deformation and failure modes are evaluated by considering the effects of core density gradient and impulsive intensity. The results show that the density gradient effect has a significant influence on the dynamic response and failure modes. The initial failure mode plays an important role in the structural response and the predominant energy absorption mechanism. The initial failure mode of the uniform and negative gradient sandwich structures is the overall bending deformation, while the local core compression is the initial failure mode for others. As the impulsive intensity is low, the gradient sandwich beam has superior impact resistance to the uniform counterpart. With the rapid core densification of the weak layer, the gradient sandwich beam shows inferior deflection resistance to the uniform counterpart with the elevating impulsive loading. Therefore, the optimal design of the core density gradient can efficiently improve the impact resistance of the sandwich beams under the high-velocity impact, which is a valuable reference for the engineering applications.
Abstract:
To study the ignition behavior of micro-mesoscopic hot spots in the matrix of pressed PBXs under GPa, 10μs-level slow-front ramp wave loading, a ramp wave loading device driven by non-shock initiation reaction of heavily constrained pressed PBX explosive was designed. The burning rate model of laminar combustion and the self-compiled two-dimensional axisymmetric finite difference program were used to analyze the characteristics of the pressure wave output by the device, the influence of the crushing degree of the donor explosive during the combustion process and the structural parameters of the device (the thickness of the case and the partition) on the output pressure wave were discussed. The calculation results show that the combustion specific surface area formed by the crushing of the donor explosive is the key factor affecting the pressure evolution of the non-shock initiation reaction. With larger combustion specific surface area comes greater ramp wave pressure. The ramp wave pressure can reach above GPa, and the corresponding rising front of the pressure wave can be reduced from tens of milliseconds to several milliseconds. The thickness of the case of the donor explosive, that is, the strength of constraint, has a significant effect on the pressure during non-impact initiation reaction. As the thickness of the interlayer increases, the output ramp wave pressure decays approximately exponentially. According to the calculation results, the structure design of the device was completed, and the ramp wave loading experiment was carried out on the tested PBX. The pressure at the incident interface of the tested explosive measured by PVDF is 1.6GPa, and the front of ramp wave is 25μs, which preliminarily proved the feasibility of realizing GPa, 10μs-level ramp wave pressure output by using the non-shock initiation reaction of heavily constrained pressed PBX explosives.
Abstract:
Under impact, aluminum foam undergoes significant plastic deformation, and the kinetic energy of the impactor is dissipated in the process, thereby protecting the structure from damage. The failure modes of aluminum foam sandwich structures under impact are complex, involving plastic deformation, panel failure, and cracking of the bonding interface. Traditional numerical simulation methods are difficult to solve these discontinuous problems. Peridynamic is a non-local numerical method that describes the mechanical behavior of materials by solving spatial integral equations. It has unique advantages in solving crack propagation, material failure, progressive damage of composite materials, and multi-scale problems. Although the basic bond-based peridynamic cannot describe plasticity, the ordinary state-based peridynamic decouples distortion and dilation, and can easily simulate the plastic deformation of materials. Therefore, based on ordinary state-based peridynamic, the Mises yield criterion and the linear isotropic hardening model were introduced to study the factors affecting the impact resistance of aluminum sandwich structures. Two-dimensional mesoscopic models of aluminum foam structure were established by the Monte Carlo method and impact was simulated using peridynamic. The influence of the porosity of aluminum foam on the impact resistance and damage mode of the sandwich structure was analyzed. The results show that good plastic deformation ability of aluminum foam sandwich structure is the main factor for its buffering and protection, and within a certain range, the higher the porosity of aluminum foam core, the better impact resistance of the sandwich structure. When the porosity of aluminum foam is increased from 0.4 to 0.7, the kinetic energy absorption rate of aluminum foam to the impactor is increased from 90% to 99%. The simulation results are in good agreement with the experimental results, which verifies the accuracy of the simulation results and the effectiveness of the analysis conclusions. Numerical simulation predicts the crack propagation morphology of the plexiglass backplate, and the results show that improving the porosity of aluminum foam can obtain better protection effect.
Abstract:
In order to investigate deeply the loading transmitting features within the warhead and the corresponding structural response characteristics in the drop impact condition, and promote the explosive safety assessment and the warhead structure design, the loading characteristics and structural response of warhead during the drop impact process were analyzed based on numerical simulation and shock wave analysis, in which the deformation and damage characteristics of the explosive subassembly were emphasized , and the influences of various factors, including drop posture, explosive configuration and drop height, etc., were discussed. In the numerical simulations materials were characterized by the viscoplasticity constitutive model combined with the accumulative damage model which considers the effects of strain rate and temperature, and the thermodynamic equation of state were employed to calculate the pressure in materials during the deformation process. The loading transmitting features in the warhead and the corresponding structural response were investigated through stress wave analysis, and then the influences of various factors on the structural response were discussed in detail. Firstly, the effect of drop posture was investigated by comparative analysis among five typical cases, i.e., tail-downward vertical drop, nose-downward vertical drop, horizontal drop, tail-downward inclined drop and nose-downward inclined drop. Secondly, the influence of warhead configuration was analyzed based on three configurations, i.e., 1 explosive segment warhead, 8 explosive segment warhead, and 8 explosive segments combined with separator warhead. Finally, the effect of drop height was also discussed, and in the discussion the height ranges from 3m to 40m. Related results indicates that during the drop impact process, the deformation of explosive subassembly is dominated by the stress wave propagation, rather than the interaction between explosive subassembly and warhead shell, correspondingly, the severest damage zone in explosive subassembly is located in its internal region instead of the outside region which contacts with the warhead shell. The transmission of stress wave between explosive subassembly and warhead shell, and the reflection as well as superposition of stress wave within the structures dominate the major deformation region in the explosive subassembly as well as the degree of deformation. Furthermore, the drop posture affects significantly the response characteristics and the deformation of explosive subassembly. The most dangerous drop posture which leads to high safety risk is, in order, tail-downward vertical drop, horizontal drop, nose-downward vertical drop, and inclined drop. The explosive configuration also acts an important role, the explosive segment interface is easily to induce the increase of deformation degree, however, it has little influence on the acceleration and the distribution of deformation region. The separator usually leads to high acceleration, and it changes the location of deformation region as well as the deformation degree. Comparatively, the drop height has little influence on the distribution feature of deformation zone, and it mainly affects the loading amplitude, the degree of deformation and the size of deformation zone, etc. These factors increase with increasing the drop height. The present method, which investigates the structural response of complex warhead based on numerical simulation integrated with stress wave analysis, has built an effective bridge linking the basic theory and the engineering application.
Abstract:
In this paper, the formation process of the Yilan crater is studied based on the iSALE-2D simulation code, and the Euler algorithm is used to carry out numerical simulation, and 8 groups of working conditions are simulated. According to the scaling law, it can be determined that the projectile diameter range is: 90m to 120m, and the projectile speed is: 12km/s, 15km/s.The simulation results of the corresponding working conditions are obtained after 150s of impact, including the crater diameter, depth and crater profile curve. The optimal impact conditions of the Yilan crater were studied, and the formation and distribution of the molten layer during the cratering process were statistically analyzed. Combined with the point source cratering similarity law model, the cratering radius relationship under the strength mechanism was obtained by fitting. The research results show that according to the comparison between the simulated data and the actual exploration data, a granite asteroid with a diameter of 120 m and an impact velocity of 12 km/s hits the surface vertically to form a crater with a shape similar to the Yilan crater. A crater with a final diameter of 1840m and a crater edge depth of 263m is formed, which is in good agreement with the exploration data of the Yilan crater. Three stages of crater formation are reproduced: contact and compression, excavation, and modification. The distribution of the impact melting layer of the target plate material during the formation of the crater under the simulated conditions is revealed. The material melts completely when the peak pressure exceeds 56GPa during the impact process, and this process is completed within 20ms. Most of the melt is distributed in layers and stacks at the bottom of the crater, and a small amount of melt is deposited on the surface of the target plate with the projectile in a discrete distribution. The mass of the completely melted material is about 24 times the mass of the projectile. The relative error between the simulation results and the fitted crater radius relational results under the conditions of 120m diameter and 12km/s impact speed is 10.3%.
Abstract:
To investigate the dynamical response and collision failure behavior of prefabricated RC box girder flyover with over-height vehicle, a recent actual engineering accident was taken as a case to carry out refined FE numerical analysis, and a double mass-parallel spring (DM-PS) simplified vehicle model was proposed to effectively simulate the non-centripetal collision between the over-height vehicle and bridge superstructures. The effectiveness of the proposed DM-PS model was fully assessed via comparison with two widely employed vehicle models, including full-scale (FS) model and simple rigid (SR) model. The results of comparison show that the failure characteristics of the collision area can be obtained via using the FS model, which is basically consistent with the photos of the accident scene; the S-R model overestimates the local damage of the structure and weakens the overall structural deformation; while the DM-PS model has high accuracy for predicting structural failure. Therefore, the proposed DM-PS model provides a simple and effective analysis means for the protection design of bridge structure subjected to over-height vehicle collision. On this basis, a detailed parameter analysis of the structural behavior is carried out based on the DM-PS model, and the effects of vehicle collision velocity, mass, position, and structural form are investigated in depth. It is show that the structural sensitivity of the impact dynamic behavior to collision velocity of the vehicle is significantly greater than that of the collision mass of the vehicle; the deformation and failure modes of mid-span collision and side-span collision are quite different, and the damage of side-span collision to one side base is more serious; the box plate and reinforced plate in the box girder can effectively improve the structural impact resistance. Numerical results and conclusions can provide a reference for the crashworthiness design of bridges. The critical information of the finite element analysis process is presented in detail.
Abstract:
In order to explore the effect of shaped charge opening angle on the effective utilization rate and shaped effect of bilinear shaped charge structure explosive, the boundary equation of effective shaped charge was deduced through the theory of instantaneous detonation hypothesis, and the shaped charge with different shaped charge angles was analyzed. Effective utilization of structural explosives. Through the physical model test of cement mortar, the law of crack formation of pre-cracked holes with different energy-gathering opening angles is studied. Using the LS-DYNA numerical simulation software,numerical models of different energy-gathering opening angles were established to reveal the penetration process of the bilinear energy-gathering structure charge jet with different energy-gathering opening angles. The research results show that the effective utilization rate of the energy-forming effect of explosives is the largest when the energy-gathering opening angle is 75°. When the opening angle of the energy-concentrating groove of the energy-concentrating structure is 75°, the pre-split hole formation effect is obviously better than that of the energy-concentrating structure capsule whose opening angle is 60°, and the stress concentration effect and penetration depth along the direction of the energy-concentrating groove are the best. the rock element on the blasthole wall first reaches the stress peak. The pre-split blasting field test of different lithology was carried out for the double-line shaped energy-concentrated structure charge with the energy-gathering opening angle of 75°. Under the condition that the hole spacing increased by 20%, the double-line The pre-split blasting effect of the shaped energy is better than that of the conventional pre-split blasting.
Abstract:
To investigate the damage effect of underwater explosions with different standoff differences on gravity dams and explore whether there is an “optimal standoff distance”, a fully-coupled explosive-water-air-gravity dam numerical model was established based on centrifuge model tests. The fully-coupled numerical model was validated by comparisons with centrifuge test results. Results demonstrated that the employed numerical model can well predict the dam failures and the effect of bubble pulse. Then, a numerical scheme with the inclusion of 60 numerical calculations was designed. For different calculations, the water depth was 600mm, the explosive mass was 2.2g, and the geometrical scaling factor of the gravity dam model was 1/80. The detonation depth ranged from 50 to 250mm with five detonation depths. Each detonation depth corresponded to 12 standoff distances, and the standoff distance ranged from 10 to 200mm, with the scaled standoff distance ranging from 0.077 to 1.54 m/kg1/3. Comparisons of damage degrees of gravity dams against underwater explosions with different standoff distances were conducted. Quantitative comparisons of dam average damage, element erosion rate, stress, and strain were also presented. Results demonstrates that for the overall structural failure of the gravity dam, such as the overall structural bending-induced tensile failure, there is an “optimal standoff distance” for the damage effects of underwater explosions on gravity dams, namely, with the increase of standoff distance, the damage degree of gravity dam increases firstly and then decreases. The quantitative results also indicates that with the increase of standoff distance, the average damage of the damage area in the dam upstream face, the element erosion rate, the average value of the maximum tensile stress of the dam heel, and the average value of the maximum tensile strain of the dam heel all increases firstly and then decreases and reaches their maximum values around a standoff distance of 40mm. With identical water depth, explosive mass, and geometrical model of gravity dam, the “optimal standoff distances” for the damage effects of underwater explosions near the water free surface with five different detonation depths on gravity dams are all near 40mm, which suggests that for underwater explosions near the water free surface, the detonation depth owns limited influences on the “optimal standoff distance”.
Abstract:
In order to study the anti-penetration performance of CFST(concrete-filled steel tubular)with honeycomb structure, six experiments on anti-penetration of CFST with honeycomb structure were conducted by using 125mm smooth bore. The failure pattern and penetration depth of target under different working conditions were measured, and the typical failure modes of CFST with honeycomb structure were analyzed, The difference of failure pattern of target under different ratio coefficient of target and projectile size and the influence of impact point and steel tube wall thickness on the anti-penetration performance of CFST with honeycomb structure were compared. Uniaxial compression tests on 7 groups of hexagonal concrete-filled steel tubular column with different wall thicknesses and 3 groups of Hexagonal concrete column were carried out. The enhancement effect of the hexagonal steel tube on the strength and ductility of the core concrete under different wall thicknesses were studied, and the relationship between the strength enhancement coefficient of the core concrete and the hoop coefficient was fitted. By improving the empirical formula for calculating the penetration depth of ordinary concrete, the formula for calculating the maximum penetration depth of CFST with honeycomb structure was obtained. The results show that the wall thickness is important factor that affects penetration depth, The greater the wall thickness, the smaller the penetration depth; The influence of the location of impact point on the penetration depth is complex and discrete; The location of impact point has a great influence on the failure pattern of the target surface; The existence of steel tube can effectively increase the strength and ductility of core concrete; The improved penetration depth formula can predict the maximum penetration depth of the projectile to the CFST with honeycomb structure.
2022-0003 re submission
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Abstract:
On the premise of good crushing effect, reducing the rock mass vibration above the bottom of the upward fan-shaped deep hole by reducing the peak pressure of the shock wave at the bottom of the hole is an effective measure to reduce the vibration and protect the superstructure. In order to determine the reasonable length of the air column at the bottom of the hole, the variation law of the length of the air column on the impact pressure of the hole wall when the air at the bottom of the hole is not coupled is studied by combining the theoretical research with the field model blasting dynamic test. Based on the theories of one-dimensional unsteady hydrodynamics and theoretical detonation physics, The action process and propagation law of shock wave in the blast hole after the explosion of bottom air interval charge column under the condition of cylindrical charge are discussed in stages. Considering the reflection and transmission of shock wave at the interface of different media, the parameters of shock wave front propagating in different directions and the initial shock pressure and action time acting on the hole wall in each stage are analyzed, Thus, the calculation formula and variation curve of pressure acting on the hole wall in each stage are obtained. In order to verify the above laws, six groups of 12 cylinder thick wall concrete models with different sizes were designed and made, and the bottom air interval blasting model tests were carried out. The air column lengths were 200mm, 400mm, 600mm, 800mm, 1000mm and 1200mm respectively. During the blasting process, the blast ultra high-speed multi-channel dynamic strain testing system was used to monitor the hole wall impact pressure, analyze the monitoring data and verify with the theoretical results, Finally, the variation curve of axial decoupling coefficient and hole wall impact pressure with time under the condition of uncoupled charge in air interval at the bottom of blast hole is obtained; Based on the dynamic compressive strength of rock, the reasonable length range of bottom axial air interval suitable for soft, medium and hard rocks is determined. In order to verify the rationality of the conclusion, the field industrial test is carried out, the charging blasting is carried out by using the air interval at the hole bottom, and the observation and photo analysis of the roof forming and blasting pile size after blasting are carried out. The research results show that the existence of air interval significantly increases the action time of impact pressure, The peak value of impact pressure decreases obviously; When k = 1.5 and the length of air column is 200mm, the attenuation ratio of peak pressure at the hole bottom is 73.4%; when k = 4 and the length of air column is 1.2m, the attenuation ratio of peak pressure at the hole bottom reaches 96.7%. When the air compartment is greater than 60cm, the area with low pressure value appears at the bottom of the blast hole. The reasonable bottom air interval length can not only ensure good blasting fragmentation, but also reduce blasting vibration by reducing the peak pressure at the hole bottom, so as to protect the stope roof and other protected objects.
Abstract:

In order to investigated the propagation process of underwater blasting shock wave in fish body and its effect on typical swim bladder fishes, the critical safety wave pressure model of typical fish was established and verified through theoretical analysis and field test. According to the transverse reflection pattern of one-dimensional elastic compression wave between different media, the relationship between critical safety wave pressure and body length of typical swim bladder fishes was clarified. The length and mechanical properties of swim bladder and fish body were measured using vernier caliper electronic and microcomputer tensile tester. Based on the measured data, the positive correlations of the length, width, wall thickness, and radial critical tensile stress of swim bladder with fish body length were determined, and the fish critical safety wave pressure model parameters were calibrated. The wave impedance ratio of water medium and swim bladder wall medium was 0.3~2. The width, wall thickness, shape, and radial critical tensile stress coefficients of swimming bladder were 0.04~0.09, 0.002, 0.6~1.1, and 60, respectively. The underwater blasting shock wave pressure and its effect on fishes were measured using blast wave tester, and the damage of fish was divided into three types: death, survival with influence, survival without influence. The fish critical safety wave pressure model was verified by the statistical results of fish damage. The results showed that the damage state of different body lengths fish under different shock pressure basically conformed with the maximum and minimum critical safety wave pressure that fish can withstand. The proposed fish critical safety wave pressure model can be used to describe the relationship between critical safety wave pressure and body length of swim bladder fishes under the action of underwater blasting shock wave. The research achievement can provide a theoretical basis for ecological protection of the fishes in the waterway regulation project of the upper reaches of the Yangtze River.

Abstract:
The crimped flame arrester is a common disaster prevention and control device, most of the researches about it focus on the higher-pressure working conditions instead of the pressure lower than 0.1 MPa when it applies in special areas or environments. The quenching characteristics of different combustible gas-air mixtures passing through crimped ribbon flame arrester at different initial pressures were investigated, so that replenish the low-pressure protection test and understand the factors affecting the performance of flame arrester deeply. The experiments carried out at different initial pressure were in the DN80 circular pipe, and the crimped ribbon plate slit channel whose cross section is approximately equilateral triangle is 38 mm long and 0.8 mm high. The experimental gases are premixed propane-air with volume fraction of 4.2% and premixed ethylene-air with different concentrations which were distributed according to the partial pressure method. The ignition voltage is 10 kV. In this paper, the activity, concentration and initial pressure of combustible gas will affect the stability of flame velocity, propagation mode and quenching difficulty. The results shows that there are three modes of flame propagation: direct quenching, quenching after passing through the flame retardant unit, and quenching failure. They can explain as the flame not pass the slits, flame pass slits but extinguish before reaching the pipe end, and flame keeps spreading until pipe end. Also, the velocity oscillation occurs in the pipeline on the unprotected side, and the velocity rises incredibly when the quenching failure flame passes through the protected side. The formula of deflagration flame quenching velocity of premixed propane-air in closed pipe was based on the heat transfer effect and verified by the quenching experiment of premixed gas with concentration of 4.2%. The maximum initial pressure is defined as the limit pressure that quenching would fail at initial pressure higher than it. It is proposed to use the limit pressure to characterize the degree of quenching difficult. It is worth remarking that quenching is the most difficult at stoichiometric concentration where the limit pressure is the smallest, and the limit pressure will remain constant within a certain concentration range.
Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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Abstract:
To meet the requirements of a tandem penetrating warhead for high penetration depth and large perforation, a jetting projectile charge (JPC) was designed. The damage test of a large-scale reinforced concrete wall was carried out to analyze the impact of standoff distance on the damaging effect. By constructing a large air domain covering the whole reinforced concrete wall for the transmission of explosion shock wave and JPC, the coupling damage of JPC high-speed penetration and explosion shock wave to the reinforced concrete wall was considered. The damage evolution, strain rate and other parameters of the Karagozian & Case (K&C) model were modified, based on which a numerical model was established to simulate the whole process of the combined damage of JPC and explosion shock wave to the reinforced concrete wall. The reliability of the numerical model was fully verified by comparing the simulation and test results from the failure mode, crater depth and crater diameter of the reinforced concrete wall. On this basis, the combined damage effect of JPC and explosion shock wave on the reinforced concrete wall was further studied, and the influence of wall thickness on the damaging effect was analyzed. The results show that JPC can penetrate the reinforced concrete wall with a thickness of 80 cm (6.67 times of charge diameter) at the standoff distance of 1.67 times and 2.50 times of charge diameter, and form cylindrical holes with a diameter of more than 6 cm (0.50 times of charge diameter). The multi-load damage characteristic of shaped charge determines the damage result of the reinforced concrete wall, and the explosion shock wave can intensify the damage range of the front crater and back crater of the reinforced concrete wall. The wall thickness has no significant effect on the diameter and depth of the crater on the front of the wall and the diameter of the internal penetration hole. With the increase of the wall thickness, the crater diameter on the back gradually decreases and the crater depth on the back gradually increases.
Abstract:
The expanding ring experimental technology mainly refers to the explosion expanding ring and the electromagnetic expanding ring experimental technology. During the experiment, the loading strain rate of the expansion ring decreases rapidly with the expansion of the ring after reached the peak value, which creates great inconvenience to the study of tension fragmentation of strain-rate sensitive solids. In this paper, a constant strain-rate loading technology is developed on the basis of the liquid-driving expanding ring experimental technology. Since it is not possible to apply sudden loading to the expansion ring during the experiment, it is assumed that the strain rate of the expansion ring during the expansion process is divided into linear growth stage and stable stage of the strain rate. By reasonably controlling the loading velocity and loading time of the liquid, an approximate expression of the liquid-driving loading curve required to realize the constant strain-rate expansion of the metal ring is deduced theoretically. The tension fragmentation process of the 1060-O aluminum ring under liquid-driving loading is simulated by the fluid-solid coupling numerical simulation. Under the liquid-driving loading curve, the hoop strain rate of the expanding ring fluctuates within a maximum of 20% in the stable stage of the strain rate. Before occurring of the significant necking of the expansion ring, the circumferential velocity of the expansion ring is basically zero, indicating that the expansion ring is under uniform tensile loading and there is no stress wave propagation in the circumferential direction. When the expansion ring is significantly necked, an obvious sudden change in the circumferential velocity will take place, indicateing that a Mott wave from the fracture site propagates to the corresponding position. The influence of the loading curve on the strain rate during the fracture process is further studied. Then an expanding ring experiment was carried out on the 1060-O aluminum ring on the liquid-driving expanding ring experimental device to verify the feasibility of the constant strain rate loading technology.
Abstract:
Studying the microstructure evolution of metals subject to shock waves is significant for understanding the structural deformation and failure mechanism of such a pipe under a very high rate of loading. The microstructure evolution and phase transformation characteristics of the material under the action of shock wave are discussed through the microscopic analysis of the cross-section of explosive recovered fragments of 20 steel cylindrical shell driven by explosive expansion. The finite element method also was used to simulate the explosion experiment of 20 steel cylindrical shell under the condition of PETN charge and to analyze the cylindrical shell’s thermodynamic characteristics during the expansion fracture process. The results show that the α-grans near the cylinder’s inner surface contain numerous slip lines, distributed in parallel. The FEM simulation indicates that these regions meet the αε phase transition thermo-dynamic condition. Furthermore, Electron Back Scattered Diffraction analysis of the microstructure of the regions with parallel slips line demonstrates the formation of a strongly fragmented. And there are {332}<113> twins and {112}<111> twins. At the same time, the ε phase structure of the hexagonal close-packed lattice (HCP) exists in the fragmented structure area of the parallel slip line. However, there was no residual ε phase structure in the original structure of the sample and the area except for the sample wall thickness (inner 0~ 3 mm) after the explosion. Analysis deems in which the αεα transformation occurred. The change of material properties caused by phase transformation may affect the cylindrical shell's internal stress and strain state and the fracture process. Considering the impact of the dynamic phase transition of metal materials on the deformation and failure of structures under shock waves, it is significant to accurately simulate the deformation and failure of such cylindrical shells, and it is necessary to further study the influence of phase transformation.
Abstract:
To explore the flexible measurement technology of low-intensity shock wave, the sensitivity calibration experiment was performed on PVDF (polyvinylidene fluoride) filmed pressure gauges by using a shock tube. The measurement reliability of flexible PVDF pressure gauge for low intensity shock wave was evaluated. To improve the measurement stability and sensitivity, the filmed pressure gauge was modified based on the microstructure design and obtained a flexible gauge with high force-electric sensitivity, which was more suitable for low-intensity shock wave measurement. It was found that the effective output charge caused by the out-of-plane shock wave and the signal-noise ratio were too low when the pressure gauge was in an individual piezoelectric mode that was mostly used in high intensity pressure measurement. The measurement results were significantly influenced by the nonlinear force-electric response of the piezoelectric membrane, the deformation and vibration of the structural surface, and the packaging factors inside the gauge. The effects of these factor sled to unstable piezoelectric sensitivity and large discrepancy among different gauges when the gauges were used under low intensity pressure. By using the micro-structure design with circumferential fixed constraint on the filmed gauge, the low-intensity out-of-plane shock can be transformed into a high-amplitude in-plane tensile stress field in the PVDF filmed gauge, causing a coupling piezoelectric working mode. The produced coupling piezoelectric effect by the micro-structure can greatly improve the nominal sensitivity coefficient of the gauge and reduce the individual difference. The nominal sensitivity of the developed flexible gauge is about 900-1350 pC/N within the 0.2-0.7 MPa pressure range, which is about 40 times higher than that in the individual piezoelectric working mode. In addition, the relative measurement error can be controlled within ± 13% under the coupling piezoelectric mode. The proposed flexible measurement method of low-intensity shock wave can provide effective design technique for the development of high-sensitive flexible devices which are suitable for shock wave monitoring of personnel equipment.
Abstract:
The paper is aimed to determine the distance between blast holes (a) and the distance between boreholes and the empty holes (L) in the straight-hole cutting with empty holes. Firstly, by considering the crack mainly being fractured during the quasi-static expansion of explosion gas and the effect of empty hole, the calculation formula of the crack length is derived; and then, the calculation formulas of the distance between boreholes and the distance between blast holes and the empty hole are determined. Moreover, the formula of the length of the crack zone around the empty hole in the straight-hole cutting with large empty holes is obtained, and the criterion of the radial crack at the blasting side of the empty hole is established based on the effect of stress concentration around empty hole. Secondly, by considering two different design ideas, the blasting parameters and cut blasting effect are compared and analyzed for the blasting in both limestone (hard rock) and mudstone (soft rock),while the reliability of the theoretical analysis is verified by engineering practice. The results show that the rock breaking mechanism of straight-hole cut blasting with empty hole is different under the two design ideas. Namely, if a is taken as the main factor, then the coalescence of cracks between adjacent boreholes is the key factor to the formation of the cavity, whilst if L is taken as the main factor, the bore holes and empty holes are preferentially penetrated to form the cavity based on the empty hole effect. In addition, the contributions of stress wave (dynamic action) and detonation gas (static action) to the crack length in both hard rock and soft rock are about 4:1 and 9:1, respectively. Considering the empty hole effect, the flake fracture zone in soft rock is larger than that in hard rock, to which more attention should be paid in the design of blasting parameters. Whereas, the critical length of radial crack initiated from the empty hole is less than the sum of the blasting crack length from cutting hole and the radius of empty hole, so that the radial cracks initiated from the empty hole will not be generated, which can be ignored in the blasting parameter design. The results indicate that the two different design ideas have great influence on cutting blasting parameters and blasting effect, and the calculation model of blasting crack length based on the driven of detonation gas can provide a good reference for the design of blasting parameters.
Abstract:
The crimped flame arrester is a common disaster prevention and control device. Most of the research focuses on the higher-pressure working conditions instead of the pressure lower than 0.1 MPa when it applies in special areas or environments. This paper explores the quenching characteristics of different combustible gas-air mixtures passing through crimped ribbon flame arresters at different initial pressures to replenish the low-pressure protection test and understand the factors affecting the performance of the flame arrester deeply. The experiments were carried out in the DN80 circular pipe. And the crimped ribbon plate slit channel with a cross-section of an approximately equilateral triangle is 38 mm long and 0.8 mm high. The experimental gases are premixed propane-air with a volume fraction of 4.2% and premixed ethylene-air with different concentrations obtained according to the partial pressure method. The ignition voltage is 10 kV. It is found that the activity, concentration, and initial pressure of combustible gas will affect the stability of flame velocity, propagation mode, and quenching difficulty. The results show that there are three modes of flame propagation: direct quenching, quenching after passing through the flame retardant unit, and quenching failure. They can be explained as the flame not passing through the slits, the flame passing through the slits but being extinguished before reaching the pipe end, and the flame keeps spreading until the pipe end. Also, the velocity oscillation occurs on the unprotected side of the pipeline, and the velocity rises incredibly when the quenching failed flame passes through the protected side. The formula of deflagration flame quenching velocity of premixed propane-air in a closed pipe was established based on the heat transfer effect and verified by the quenching experiment of premixed gas with a volume fraction of 4.2%. The maximum initial pressure is defined as the limit pressure that quenching would fail at initial pressure higher than it. It is proposed to use the limit pressure to characterize the degree of quenching difficulty. It is worth remarking that quenching is the most difficult at stoichiometric concentration, where the limit pressure is the smallest, and the limit pressure will remain constant within a certain concentration range.
Abstract:
Natural materials such as shells and oysters have attracted extensive attention in the field of material design due to their lightweight and high-strength mechanical properties. However, due to the complex structure of shells, it is very difficult to study their mechanical behavior. In recent years, fractional-order models have been successful in studying the mechanical properties of materials. Compared with the traditional constitutive model, the fractional model can better characterize the relationship between the complex media’s stress or strain and time. Therefore, based on wave propagation theory and using the time-dependent fractional-order model as the material constitutive model, the complex medium is simplified to the uniform medium, and its governing equation is obtained by then. The analytic solution of the governing equation which is a function of space coordinate x and Laplace variable s is obtained by the Laplace transform. It’s hard to obtain the analytical solution of space coordinate x and time t directly through the inverse Laplace transform, so the numerical inverse Laplace transform is used to obtain the numerical solution of the governing equation in the time domain. The sensitivity of wave attenuation to parameters in the fractional model is analyzed. The 'inertial' properties, which are different from the elastic and viscous properties of materials, are also discussed by analyzing the attenuation characteristics of stress waves when the order α is respectively 0, 1.0, and 2.0. Then, based on the analytical solution of the governing equation and a variety of experimental test signals, a fitting formula to obtain the parameters of the fractional model is given. Oyster material with layered structure is taken as the research object. To obtain the local dynamic mechanical properties of oyster samples, the CO2 pulse laser was used to carry out the impact loading of the small sample due to the high variability of the density distribution of oyster samples, and the two-point laser interferometer velocimetry system (VISAR) was used to measure the surface particle velocity. The particle velocity time history curve of the oyster sample with different densities and thicknesses was obtained. Combined with the above fitting formula, the parameters of the Abel model and Maxwell fractional differential model of oyster samples were obtained by fixed and unfixed the values of fractional order α, and the model parameters reflected the fine microstructure characteristics of oyster samples. The results showed that the higher the density of the oyster sample was, the higher the proportion of pearl layer with brick and mud structure in fine and micro, the greater the velocity attenuation, and the greater the viscosity of the oyster sample. This is because the laser wavelength emitted by the CO2 laser pulse is similar to the size of the gap between brick and mortar structures in the pearl layer of the oyster sample, so the laser has a large scattering when it impacts the pearl layer of the oyster sample. This study has a good reference significance for the study of the dynamic properties of meso-isomeric and macro-continuous complex media.
Abstract:
According to the Π principle, a similarity law was proposed between the prototype and the scaled-down models of the steel frame under a far-field explosion load. Based on the explosion experiments of steel frame substructures, a numerical model of the substructure was established by AUTODYN to verify the reliability, accuracy, and computational efficiency of the fluid-structure interaction method in the structural explosion response analysis and the analytical blast boundary method by comparing the numerical simulation results with the experiments of the steel frame under the far-field explosion load. The results show that the analytical blast boundary method can reasonably simulate the dynamic response of the steel frame under far-field explosion loads with high computational efficiency. Finally, the dynamic response and damage of a two-story three-span steel frame structure under a far-field explosion load were analyzed by the analytical blast boundary method using different scaling ratios. The results show that when the two-story three-span steel frame is fully scaled according to the geometric similarity ratio, the dynamic displacement responses of the prototype and the scaled-down models of the steel frame under the far-field explosion load are similar. And the damage effects of the prototype and the scaled-down models based on the assessment index of interlayer displacement angle are similar.
Abstract:
To investigate the influence of the initial droplet diameter on the flow field of gas-liquid two-phase rotating detonation engine, an Eulerian-Lagrangian model of unsteady two-phase detonation is established based on the assumption of an initially uniform droplet diameter and considering atomization and evaporation processes. Non-premixed two-dimensional numerical simulations of detonation for liquid kerosene and high temperature air mixture are conducted. The results show that a single stable rotating detonation wave is formed in the initial droplet diameter range of 1–70 μm. For the global equivalent ratio of 1, the air area before the detonation wave front is larger than the vapor area of kerosene droplets, resulting in inhomogeneous mixing before the wave front. Both oil-rich and oil-poor areas form before the wave front. Due to the speed difference between two phases of the gas and droplets, the air is separated to form a low-temperature strip. When the initial diameter of kerosene droplets is small, the mixing process of reactants is mainly affected by evaporation and the detonation wave propagates stably. When the initial droplet diameter is reduced to 1 μm, evaporation occurs at the entrance, and the rotating detonation flow field shows the characteristics of gas phase propagation, and the structure of the detonation wave is smooth. When the initial diameter of kerosene droplets is relatively large, the mixing process of reactants before the wave front is mainly affected by droplet break-up. For the same fuel mass flow rate with different initial droplet diameters, the maximum residence time of kerosene droplets accounts for more than 80% of the detonation wave propagation time and the detonation velocity increases with the increased ratio of gaseous part of the fuel. The velocity of the detonation wave increases first and then decreases with the increased initial droplet diameter in the range of 10–70 μm.
Abstract:
The blast resistance of sacrificial cladding has been extensively studied in the field of blast protection. As a polymer material with a cellular structure, non-water reactive foaming polyurethane also has the potential to act as a sacrificial cladding due to its good mechanical properties. In order to study the blast damage mitigation effect of polymer sacrificial cladding on reinforced concrete structures, a contact explosion test on the reinforced concrete slab with polymer sacrificial cladding was carried out, while an ordinary reinforced concrete slab was set as the control group, and the effect of polymer sacrificial cladding on the damage characteristics of the reinforced concrete slab was compared and analyzed. In addition, the SPH-FEM (Coupled smooth particle hydrodynamics and finite element method) coupling model of the field explosion test was established by using AUTODYN software, and the reliability of the coupling model was verified by comparing with the test results. On this basis, the effects of explosive charge, the density, and the thickness of polymer sacrificial cladding on the damage features and energy absorption characteristics of reinforced concrete slabs with polymer sacrificial cladding were investigated through parametric sensitivity analysis. The results show that the polymer sacrificial cladding can effectively disperse the blast loads and mitigate the impact of the blast loads on the reinforced concrete slab with good protective performance under contact explosions. The polymer sacrificial cladding can maintain a high level of energy absorption even with the explosive charge increased within limits. Increasing the density and thickness of the cladding is beneficial to enhance the energy absorption ability of the polymer sacrificial cladding, while the change in thickness will cause a change in the damage mode of the protected reinforced concrete slab. The research results are helpful in providing a relevant reference for the further research and application of the new non-water reactive foaming polyurethane in the field of blast protection of engineering structures.
Abstract:
Based on the Navier-Stokes equations for compressible multicomponent, the interaction of a planar shock wave (Ma= 1.23) with an annular SF6 cylinder whose inner and outer radii were set as 8 mm and 17.5 mm respectively was numerically studied. The simulation was conducted based on the finite volume method. For capturing the complex shock and vortex structures as well as the interfaces, the adaptive mesh refinement method, level set method, and fifth-order weighted essentially non-oscillatory scheme were used for the simulation. The adaptive mesh refinement method dynamically refines the uniform Cartesian grids around the multiple moving shocks and accelerated interfaces. The level set method tracked the interface, while the fifth-order weighted essentially non-oscillatory scheme captured discontinuities such as shock waves and contact surfaces. Time advancement was achieved with the third-order strong-stability-preserving Runge-Kutta method. Compared with the previous experimental results, numerical results revealed the complex evolution of shock wave structures generated in the process of four shock transmissions in the annular cylinder. It is found that the transition from free precursor refraction to free precursor von Neumann refraction occurs when the transmitted shock wave passes through the inner cylinder. In addition, the complex shock structures that developed between the inner and outer downstream interfaces cause the pressure gradient direction to reverse several times on the inner downstream interface, which eventually leads to three reversals of vorticity on the inner downstream interface. In the later stage, the “jet” structure formed on the inner cylinder would impact the downstream interfaces, and finally induces the interfaces to generate a pair of primary vortices, a pair of secondary vortices and a reverse "jet". Quantitative analyses of the variation of the length, width, displacement, the circulation and mixing rate of the annular cylinder were conducted. The results demonstrate that the presence of the inner cylinder attenuates the influence on the height and length of the annular cylinder during the process of small vortexes merging into the large vortexes in the early stage, and increases the mixing rate of the heavy gas and the ambient gas.
Abstract:
To study the effect mechanism of magnetic fields on methane explosion, an experiment was carried out by detonating the premixed gas of methane with the volume fraction of 9.5% and air as the rest constituent in a magnetic fields. Effect patterns of magnetic fields on methane explosion characteristics emerged based on the explosion pressure measured by pressure sensors and flame propagation velocity measured by detonation velocity meter. The gas after explosion was quantitatively sampled by gas sampler, and the volume fraction of reactants and products was detected by flue gas analyzer and gas chromatograph. Thus, the effect patterns of magnetic fields on the volume fraction of methane explosion products and reactants was obtained. The experimental results show that in the magnetic fields, the maximum explosion pressure of methane is decreased by 27.33%, and the explosion pressure rise rate is decreased by 40.96%. Along the flame propagation direction, the magnetic fields first promote and then suppress the flame propagation velocity of methane explosion, and the suppression effect is stronger than the promotion effect. Under the magnetic fields, the average flame propagation velocity of methane explosion is decreased by 16.39%. The volume fraction of reactants and products show obvious differences. The residue of methane and oxygen increased by 28.81% and 66.98%, respectively. The production of CO and CO2 decreased by 20% and 12.90%, respectively. Combined with sensitivity analysis, the methane explosion chain reaction process is simulated by the Chemkin-Pro software to derive the key radical and radical reactions in the methane explosion process. The ·H, ·O, ·OH, ·CH3, ·CH2O are the key free radicals of methane explosion. Through theoretical calculation, the forces of different free radicals under the action of magnetic fields are analyzed. Combined with the reaction paths analysis, the effect mechanism of magnetic fields on methane explosion was explored. Due to the high magnetic susceptibility of ·O, it is attracted to areas with dense magnetic induction line. The collision probability of ·O with other free radicals is reduced, thereby reducing the rate of the ·HCO→CO→CO2 chain reaction, resulting in a decrease in the production of CO and CO2, which ultimately leads to a decrease in methane explosion intensity.
Abstract:
Adiabatic shear is a common form of deformation and failure of materials under high-speed impact loading. It generally exists in high-speed deformation processes such as high-speed impact, stamping forming, projectile penetration, high-speed cutting, and explosive crushing. A TA2 pure titanium plate with a total deformation of 70% was obtained by multi-pass large strain cold rolling on a two-high mill. By heating cold rolled TA2 pure titanium plates at 500 ℃ and annealing at varying holding times, titanium plates with different recrystallization structures were produced. Based on a hat-shaped specimen and a limit-ring deformation control approach, dynamic impact freezing experiments were carried out on the specimens with different recrystallized structures by using a split Hopkinson pressure bar. The microstructure changes of the specimens before and after impact were characterized by using an optical microscope and a scanning electron microscope. The effects of recrystallized structures on adiabatic shear behaviors of TA2 pure titanium were studied, showing that with the increase of annealing holding time, the proportion of recrystallized grains increases gradually, and the grain distribution changes from dispersion to local aggregation. Under the same strain and strain rate, adiabatic shear bands were observed in all specimens. The specimens with high proportion of recrystallized grains are more likely to induce crack nucleation and propagation in adiabatic shear bands. The changes of recrystallization structures and geometric necessary dislocations before and after deformation were compared. Combined with the analysis of the overall temperature rise in the shear area, the recrystallized grain as the material softening zone can induce the formation of shear band. The adiabatic temperature rise effect mainly occurs in the later stage of the development of shear band, which promotes the secondary recrystallization of materials in the shear band, improves the toughness of materials in the shear band and delays the formation of shear cracks.
Abstract:
The main challenge of numerical simulation of intense explosion is how to accurately determine the equation of state for the explosive products. The traditional equations of state are mostly empirical or semi-empirical formulas, which can just deal with ordinary explosions, but the treatment of intense explosions is of great limitation. The parameters of intense explosive products span an extremely wide range, which often exceeds the scope of empirical formula. Neural network has an excellent nonlinear fitting function and can realize the function of the equation of state. At the same time, there are a lot of state parameters of material in the sesame library, and the material parameters suitable for intense explosive products were selected as training datas of neural network. The tabulated datas of intensive explosive products samples were pretreated to make them better used in neural networks, then the datas was adopted as training set to train the BP neural network and a one-dimensional spherical numerical code embedded with neural network equation of state was used to calculate the blast wave parameters of the explosion of fission device. In the process of neural network construction, the structure of neural network was optimized by enumeration experiment, and the structure of multi-layer neural network with a simple structure and good precision was obtained. In the process of numerical calculation, the code called the embedded neural network equations of state module, calculated the pressure of the explosive product through the density and the specific internal energy, and the flow field parameters of the whole explosive blast wave were finally obtained. The numerical results show that the calculated peak overpressure, arrival time and positive pressure duration coincide with the standard values, which proves the feasibility of the application of the neural network equation of state in the intense blast wave calculations. The results are of great significance to the numerical simulation of intense explosion.
Abstract:
One of the fundamental scientific problems of dynamic fracture of ductile metals is spallation of low melting point metals. The classical spallation and micro-spallation of single crystal (SC) and nanocrystal (NC) tin were carried out using the non-equilibrium molecular dynamics (NEMD) at shock pressures of 13.5-61.0 GPa. In order to achieve the spallation in the SC and NC models, the piston-target method was utilized. Specifically, the rigid piston was assigned an initial velocity, then the piston impacted the target to generate stress wave, and the stress waveform was controlled by adjusting the loading time after the length of the model along the shock direction was determined. The simulation results showed that: during the loading stage, the shock wave velocity has no influence on the waveform evolution of the SC Sn model, but it does have an effect on the waveform evolution of the NC Sn model, in which the front width of the stress wave in classical spallation of NC Sn model is mainly affected by grain boundary sliding. The void nucleation sites in classical spallation and micro-spallation are found at high potential energies in the SC model. In the NC model, for the classic spallation, voids mostly nucleate at grain boundaries (including the triple junctions of the grain boundaries) and grow along grain boundaries, resulting in intergranular fractures; for the micro-spallation, voids nucleate at the grain boundary and inside the grain, resulting in intergranular fracture, intragranular fracture, and transgranular fracture. The void volume fraction increases exponentially, and the variation law of void volume fraction of SC and NC Sn is the same under the same impact velocity. The two turning points of the void volume fraction curve in classical spallation represent the transition from nucleation to growth and the catastrophic transition from damage to fracture.
Abstract:
A medium strain rate compression experimental system based on a progressive cam was developed to realize multiple medium strain rate loading. The developed experimental system uses the servo motor to drive the energy storage flywheel to rotate at a certain speed, and when the clutch is started, the energy storage flywheel can drive the loading cam to rotate. The loading cam pushes the loading guide bar and the input bar to compress the sample. When the loading cam rotates one circle, a single medium strain rate compression is completed. At the same time, when the first stage compression is about to end, the stepper motor rapidly pushes the energy storage flywheel close to the loading cam for the next compression, and the cycles repeat to achieve multiple medium strain rate compression. The load and deformation of the material during compression were measured by strain gauges and a velocity interferometer system for any reflector (VISAR), respectively. The strain gauges were affixed to the input bar and the support bar, respectively. The strain signals of the bars during compression were recorded by the strain gauges and the forces exerted on the sample were obtained based on these strain signals. Two fiber optic probes of the VISAR system were used to measure the velocities of the input bar and the support bar during compression. Based on the two velocity curves measured, the velocity difference curve between the two ends of the sample was obtained, and then the deformation of the sample was gained by integrating the velocity difference. The stress-strain curves were obtained from the load- and deformation-time curves. Taking the paper honeycomb sample as an example, the reliability of the developed medium strain rate experimental system was discussed based on the high-speed images. The dynamic compressive mechanical properties of the paper honeycomb samples with the thickness of 10 mm and the diameter of 14.5 mm at the strain rate of 3.5 s−1 were studied. The stress-strain curves and deformation processes of the paper honeycomb samples during single compression and double compression were obtained. The experimental system could realize multistage progressive medium strain rate loading. The peak strength and plateau stress of the paper honeycomb samples at medium strain rates well connect the dynamic compression results at high strain rates with the quasi-static compression results at low strain rates. The failure modes of the samples are mainly out-of-plane buckling and in-plane shear after quasi-elastic deformation.
Abstract:
Zr-based bulk metallic glasses are novel class of functional materials that comprehensively use chemical energy and kinetic energy to improve the damage effect of warhead. To investigate the mechanism of shock fragmentation reaction of Zr-based bulk metallic glass fragments, quasi-sealed venting chamber was used to measure the released energy of Zr62.5Nb3Cu14.5Ni14Al6 bulk metallic glass fragments under impact conditions. The fragments were driven by a 14.5 mm ballistic gun, with various levels of velocity, to impact the sealed chamber covered by 0.5 mm thick steel plates. High-speed camera was used to record the shock-fragmentation-reaction process through an observational window. The pressure in the chamber was measured by two pressure sensors installed in different positions on the inner wall of the chamber. The particle size of the fragment debris was measured by laser diffraction method and weighting method. And the debris with different particle sizes was analyzed by X-ray diffraction. According to one dimensional shock wave theory, the impact temperature of Zr-based bulk metallic glass was derived. Combined with the impact temperature, the fragment debris distribution model and metal particle ignition model, the shock-fragmentation-reaction theoretical model was developed to quickly calculate the extent of reaction of Zr-based bulk metallic glass fragments. The experiments results show that the reaction depth of material under impact loading increases with the increase of impact velocity. The distribution of debris conforms to the piecewise power law, and the size distribution of debris was fitted. The main chemical reaction induced by material impacting is the combustion of Zr and O2 in the air, and the main reaction product is ZrO2. Theoretical analysis results show that the shock-fragmentation-reaction theoretical model based on impact heating, debris distribution and debris combustion can explain the reaction law of Zr-based bulk metallic glass under impact loading well. And the theoretical calculation is in good agreement with the experimental results.
Abstract:
In order to study the propagation law and load characteristics of shock wave at the corner due to internal blast in closed cabin, a typical cabin explosion test was carried out using a scaled model. The explosion test obtains the overpressure load of shock wave in one-sided, two-sided corner and three-sided corner. The EULER-FCT algorithm in AUTODYN software is used to simulate the explosion test in the cabin, and the shock wave propagation law and load characteristics at three characteristic positions are studied. The results show that the overpressure time history curve of the wall reflected shock wave far from the corner is a single-peak structure, and the reflected shock wave propagates in a spherical shape. Within a certain range from the two-sided corner, the shock wave overpressure curve is a double-peak structure. The shock wave overpressure time history curve at the edge of the two-sided corner is a single-peak structure. And the corner convergent shock wave propagates in an ellipsoid shape. The peak overpressure and specific impulse of the two-sided corner convergent shock wave are about 2.5 times and 2.09 times more than the wall reflected shock wave at the same position. Within a certain range from the three-sided corner, the shock wave overpressure curve is a multi-peak structure. The shock wave overpressure time history curve at the three-sided corner is a single-peak structure. And the corner convergent shock wave propagates in a spherical shape. The converging ability of the three-sided corner to the shock wave is stronger than that of the two-sided corner. The peak overpressure and specific impulse of the converging shock wave in the three-sided corner are about 9.6 times and 5.8 times that of the wall reflected shock wave at the same position. Under certain assumptions, according to dimensional analysis and numerical simulation of typical compartments under different TNT charge internal explosion conditions, the empirical calculation formula of corner convergent reflected shock wave load at the first impact is obtained.
Abstract:
A detonation experimental system was established to explore the characteristics of underwater detonation gas jets from the detonation tubes with different types of nozzles. The effects of different types of nozzles on underwater bubble shapes and pressure characteristics during detonation were experimentally studied. The digital particle image velocimetry was used to visualize the bubble pulsation pictures captured by a high-speed camera, and the bubble velocity fields in the different nozzle cases were obtained. Two dynamic pressure sensors were installed at the end of the detonation tube to confirm whether the stable detonation wave was formed, and to observe the transmission and reflection characteristics of the detonation wave on the gas-liquid two-phase interface, respectively. An underwater explosion sensor was installed at a certain distance from the nozzle to measure the underwater pressure wave. The results show that the bubble pulsation process in the divergent nozzle case is basically the same as that in the case of the straight nozzle, but the divergent nozzle improves the gas jet velocity and increases the bubble volume of the first bubble pulsation. The combined effect of the convergent nozzle and its reflected shock wave reduces the injection speed of the detonation gas. Because of the continuity of the gas jet, the bubble pulsation process in the convergent nozzle case is obviously different. The maximum bubble volume in the convergent nozzle case is smaller, but the attenuation of the second bubble pulsation duration is smaller than that of the first pulsation duration. The divergent nozzle increases the gas velocity and kinetic energy, which enhances the bubble pulsation intensity, the bubble pulsation pressure and transmitted shock wave pressure in the divergent nozzle case are much higher than those in the straight nozzle case. The bubble pulsation pressure and the transmitted shock wave pressure in the convergent nozzle case are both low, but the continuity of the convergent nozzle gas jet retards the attenuation speed of the bubble pulsation pressure. Compared with the straight nozzle, the bubble pulsation time in the divergent nozzle case is longer, the bubble pulsation pressure and transmitted shock wave pressure are higher. The duration of the bubble pulsation in the convergent nozzle case is shorter, and the convergent nozzle can obviously inhibit the transmitted shock wave pressure and the bubble pulsation pressure.
Abstract:
The effects of different diminished ambient pressure, temperature and altitude from sea level on blast wave parameters (overpressure, impulse and wave front trajectory) were investigated by employing the dimensional analysis theory and the AUTODYN software. Meanwhile, the relationship equations between blast wave parameters with diminished pressure and temperature were established, which were verified by numerical simulations and experimental data. Results indicate that the equations can evaluate the blast wave parameters at diminished temperature and pressure effectively. It is noted that the blast wave overpressure and far-field (scaled distance Z>0.2 m/kg1/3) impulse decrease, but the propagation velocity increase, as the ambient pressure decreases. The blast wave impulse increases, and the propagation velocity decreases, but has little effect on the overpressure, as the ambient temperature decreases. It is shown that when the altitude increases by1000 m (the range of 0~9000 m above sea level), the overpressure and far-field impulse of blast wave decrease in average by about 3.9% and 3.2%. In addition, the blast wave propagation velocity in near-field increases, but the far-field decreases with the altitude increase. The influence of diminished pressure on blast wave overpressure and impulse is greater than diminished temperature at high altitude. The blast wave propagation velocity depends on diminished pressure in near-field, but on diminished temperature in far-field.
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2022, 42(12).  
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2022, 42(12): 1-2.  
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Abstract:
Invited Article & General Review
Abstract:
The pulse wave constitutive relation determines propagation characteristics of pulse wave. How to determine it through experimental studies, and how to obtain it from the existing literature data through these methods, is one of the cores of the current research. Three feasible approaches were explored: (1) inverse analysis of the relationship C(p) (non-invasive method), (2) direct measurement of pulse wave p-V relationship (invasive method), and (3) Lagrange inverse analysis of a series of measured pulse wave (non-invasive method). By using the above methods and according to the existing literature data, it is found that the exponential p(V) constitutive relation can be deduced from the Rogers-Huang simplified formula of C(p) relation. The logarithmic p(V) constitutive relation can be deduced from the MK-Hughes equation. Pulse wave propagation characteristics vary significantly with nonlinear constitutive parameters. According to the viewpoint of body constitution classification in traditional Chinese medicine (TCM), the corresponding constitutive relation of pulse wave also has different types in principle, depending on people. In this sense, the Lagrange inverse analysis of pulse wave has a broad development prospect, but it puts forward higher requirements on the correct selection of measurement points and improving the sensitivity and accuracy of measurement.
Explosion Physics
Abstract:
In order to study the mechanism and the predictors of blast lung injuries, a finite element model including the human body and the explosion flow field was developed. The fluid-structure coupling algorithm of LS-DYNA was used to simulate the blast effect on the thorax. The developed model was validated using victims’ lung injury data in an explosion accident. A total of 39 simulation experiments were carried out. By changing the explosion equivalent and stand-off distance between the thorax and the explosive, the thorax was subjected to blast loads of different magnitudes, and the lung injuries ranged from no injury to extensive injuries. Base on the developed model, the pressure distribution in the explosion flow field, the dynamic response of the thorax and the stress distribution in the lung were investigated to clarify the mechanical mechanism of blast lung injuries. The thorax injuries and response of the human body model were analyzed, and the predictors of blast lung injuries were proposed. The results show that when subjected to the blast load, the anterior chest wall gains speed almost instantly and impacts the thoracic organs with a high velocity, causing the propagation of stress waves in the lung. Subsequently the anterior chest wall continuously compresses the thoracic organs and the ribs under inertia, which causes the thoracic deflection. The stress wave is the main cause of blast lung injuries, and the thoracic deflection is less likely to cause lung injuries. The damaged lung tissues are mainly in the area close to the anterior chest wall and heart. The peak sternum velocity and peak sternum acceleration have direct effects on the stress wave in the lung, and can be used as the predictors of blast lung injuries. The thoracic deflection and viscous criterion cannot reflect the damage to the lung caused by stress wave, and are not suitable for evaluating the blast lung injuries.
Impact Dynamics
Abstract:
In this paper, a finite element model of the granular slug launcher was constructed. Using the discrete element-finite element coupling method, the dynamic response and mechanism of mitigation and energy absorption of sandwich beams with reentrant honeycomb core of negative Poisson’s ratio subject to high velocity granular slugs were investigated. Effects of the load impulse, impact angle, core strengths and friction between the granular slug and face sheets on dynamic response of sandwich beams were analyzed. The results demonstrated that the active deformation mode of sandwich beam subject to the normal impact of the granular slug is combined local denting and overall bending. The deformation mode of the sandwich in-plane core is local denting mode due to the bending of cell walls, whilst the sandwich out-plane core is local folding mode due to buckling of the cell walls. Compared to the same areal density of the sandwich beam with the in-plane design of the soft core, the deflections of the sandwich beam with the out-of-plane design of the hard core are smaller but both its initial peak and level of impact force are higher and its response time is shorter. The mid-span maximum deflections of front and rear face sheets of the sandwich beam increase with the impact loading approximately log-linearly. Compared to the normal impact, the deformation mode of the sandwich beam subject to the oblique impact is asymmetrical and the local denting area reduced. The mid-span maximum deflections of the front and rear face sheets, the initial peak of impact force and the proportions of kinetic energy and momentum transferred to the sandwich beams subject to velocity granular slug with different impact angles decrease with the increase of the impact angles, while the friction between the granular slug and the face sheets has little effect on dynamic response of sandwich beams.
Abstract:
In order to study the damage of concrete structures which have relatively strict requirements on the formation and propagation of cracks, such as dam, pier and nuclear power plant containment, suffered by impact loads, numerical studies were conducted on the mechanical response of (reinforced) concrete slabs under two types of explosion loadings (contact explosion and closed explosion) by a three-dimensional meso-mechanical model together with a comprehensive computational dynamic constitutive model for concrete material, followed by a parametric discussion about the interfering factors of final crack morphologies in concrete targets. To generate the three-dimensional meso-mechanical model, regular hexahedral meshes were firstly applied to whole concrete specimens/structures and all the elements were assigned as mortar matrix, then the assemblies of elements as aggregate were randomly selected and the outer surfaces of each aggregate element assemblies were covered with shell elements as interfacial transition zone layers. The three-dimensional meso-mechanical model, in which taking the influence of internal meso-structures of concrete (e.g. volume fraction, size and gradation of coarse aggregate) and mechanical properties of three phase materials into consideration, succeeds in accurately predicting the crack patterns and crater sizes in the concrete slabs subjected to the two types of explosion loadings. It is shown that the numerical results are in good agreement with the experimental observations in terms of crater shapes and sizes in the contact explosion, as well as the number of main cracks in the closed explosion when compared with the predictions by the macroscopic homogeneous models. Parametric studies performed for further study on the influence factors of the explosion results indicate that both the global mesh size of the model and the relative mesh size of each component in the model produce effects on the accuracy of the numerical results, the balance between the computational accuracy and efficiency can be achieved by setting a similar mesh size for concrete material with air grids. In addition, the influence of the aggregate size can not be neglected in the response and failure of the concrete slabs subjected to explosion loadings. The three-dimensional meso-mechanical model plays an important role in understanding the meso-mechanism and influencing factors of the response and failure of the concrete structures subjected to impact loadings, which is of great theoretical and practical significance for engineering design and safety assessment.
Abstract:
Chloroform was used to bond a polycarbonate (PC) plate and a polymethylmethacrylate (PMMA) plate to fabricate a model with a heterogeneous cemented interface. A cylinder blasthole was set in the PC plate with a certain angle to the interface. Base on the locations between the interface and the explosive initiation points, two kinds of initiation methods were used in the experiment. The one is the top initiation method, in which the initiation point is settled far away from the interface; and the other is the bottom initiation method, in which the initiation point is close to the interface. The digital image correlation (DIC) method was used to study the evolution of the strain field during the passage of the blast waves in the medium with the heterogeneous interface. The results show that the propagation pattern of the blast stress wave varies significantly after it passes through the interface. In the top initiation, a stress concentration zone is formed on the interface under blast loadings, and induce a crack initiate at the interface. The transverse tensile wave is the main reason for the cracking of the interface. Besides, it can be found that the initiation methods have different contributions to both the magnitude and the locations of the tensile/compressive strain in both the transverse and longitudinal directions. Moreover, in the bottom area of the borehole, the influence of the initiation method on the time-related characteristics of the strain field mainly has two aspects, namely, the duration time and the strain magnitude. And it is found that the transverse/longitudinal strain is of "short duration, high magnitude" variation characteristic for the top initiation. In terms of the strain magnitude, the influence of the initiation method on the transverse strain is much greater than it on the longitudinal strain. In addition, the initiation method can significantly influence the attenuation characteristics of the strain field, which is more obvious for the longitudinal strain field. In terms of the attenuation rate, the magnitude blast stress waves attenuated faster in the PC plate, whereas the blast stress waves attenuated slowly when it passed through the interface and propagated in the PMMA plate regardless of the initiation method.
Abstract:
Based on the Kong-Fang concrete material model and the multi-material arbitrary Lagrangian Eulerian (MMALE) algorithm available in LS-DYNA, the attenuation of stress wave in concrete subjected to explosion was numerically studied. On the basis of comparative analysis of different material models, numerical algorithms and selection of appropriate mesh size, the proposed numerical algorithm and material models along with the corresponding parameters were firstly validated by comparing the numerically simulated spherical charge detonated in a concrete target with the corresponding test data in terms of peak stress and stress-time history. Then the attenuation of stress wave subjected to spherical charge detonated in concrete was numerically investigated, in which the radial and circumferential stress-time histories at different scaled distances were analyzed in detail to reveal the mechanism of stress wave attenuation. The numerical results were fitted to develop an empirical formula for the peak stress of the free-field compression wave in concrete at the close zone with the aid of dimensional analysis. Besides, the applicability of the developed empirical formula was also discussed. The influence of charge buried depth on peak stress in concrete at different distances was also numerically studied to develop a quantitative relationship between charge buried depth, distance and the so-called coupling factor. Numerical results demonstrate that the Kong-Fang concrete material model can be used to simulate the attenuation of explosion stress wave in concrete with good accuracy. The influence of the charge buried depth and the distance from charge the center on the coupling factor of peak stress can be quantified by defining the mass coefficient and coupling constant. The empirical formula for peak stress of compression wave in concrete at the close zone is appropriate for varied charge buried depth, distance and concrete strength. The present numerical results are useful for blast-resistant design and can provide a reliable reference for estimating the damage degree of concrete caused by explosion.
Abstract:
By means of a 30-mm-caliber ballistic gun platform, a series of experiments were carried out on 2A12 aluminum targets subjected to normal penetration by three kinds of 30CrMnSi2A steel projectiles with different elliptical cross-section shapes in the striking velocity range from 200 m/s to 600 m/s. The residual velocities of the projectiles and the failure modes of the targets were experimentally obtained. Based on the experimental results, the corresponding numerical models were established and verified. And the influences of the major-to-minor axis length ratios of the projectile cross-sections on the failure modes and response characteristics of the targets were systematically analyzed. The results show as follows. The maximum cross-sectional areas of the projectiles are the main factor affecting the residual velocities of the projectiles, while the major-to-minor axis length ratios of the projectile cross-sections have little effect on the residual velocities. Therefore, in engineering applications, the engineering model for the circular cross-section projectile penetrating a target can be directly used to calculate the residual velocity of the elliptical cross-section projectile with the same maximum cross-sectional area. In addition, under normal penetration of the circular cross-section projectiles, the sizes, shapes and distribution of the petals induced at the back faces of the targets are uniform. However, under normal penetration of the elliptical cross-section projectiles, as the major-to-minor axis length ratios of the projectile cross-sections increase, the numbers of the petals induced at the back faces of the targets increase and the petal sizes decrease, and the petal numbers and the uplifted height in the minor axis direction are greater than those in the major axis direction. The radial displacement, radial stress and tangential stress of the targets under the normal penetration of the elliptical cross-section projectiles are obviously different from those of the targets under the normal penetration of the circular cross-section projectiles. Under normal penetrations of the circular cross-section projectiles, the above response characteristics of the targets change basically the same along the circumferential directions and the targets are under simple compression states with the tangential stress of zero. But, under normal penetrations of the elliptical cross-section projectiles, the stress states of different points of the targets are closely related to the major-to-minor axis length ratios and the circumferential angles of the projectiles, and the targets are subjected to the coupling effects of the compression and shear stresses.
Abstract:
In order to solve the problems of structural damage and ballistic runaway caused by huge impact loads suffered by air-drop vehicles and rocket-assisted vehicles during high-speed water-entry, a slotted wrapping buffer head cap was proposed to guarantee the structural safety of the vehicles during water entry. Firstly, the structural composition and detailed parameters of the head cap were given, and a numerical model for the high-speed water-entry of the vehicles was established based on the arbitrary Lagrangian-Eulerian (ALE) algorithm. The Lagrangian viewpoint was used to solve the small deformation of the vehicle and the head cap, and the Eulerian viewpoint was used to capture the large deformation of the free surface such as water and air, thereby overcoming the problems that the Eulerian mesh was not accurate enough to solve the structural deformation and the numerical oscillation caused by mesh distortion in solving large deformation problems by the Lagrangian mesh. On this basis, the evolution processes of the cavity and flow field around the vehicle entering the water with the head cap at different angles were studied by numerical simulation, and the interaction process between the head cap and the water was given. Furthermore, the distribution of effective stress of the buffer was analyzed when it entering the water vertically and obliquely. Finally, the load reduction performances of the head cap when the vehicle entered the water at different velocities and angles were investigated. The results show that the cavities obtained by the simulation are basically consistent with the experimental images, and the change trends of impact acceleration are basically consistent with the experimental results. The relative error of the axial peak acceleration between the numerical simulation and experiment is 6.72%, and the relative error of the radial peak acceleration is 7.52%. The ratio of axial load reduction is 22.17% when the vehicle enters the water vertically with a head cap at 300 m/s. At the same time, the ratio of axial load reduction is 31.83% and the ratio of radial load reduction is 66.80% when the vehicle with a head cap enters the water at 100 m/s and 60°. So this research has a certain guiding role in the design of new load-reduction structure.
Experimental Techniques & Numerical Methods
Abstract:
One-dimensional cylindrical load was imposed on the middle part and half height of the metal cylinders which have the initial height of 160 mm, the wall thickness of 4 mm and the external diameter of 48 mm, by the way of an electric exploding wire initiating explosives, and then drove the nylon lining to expand the metal cylinder. At the same time, a validity criterion of the one-dimensional cylindrical load was proposed based on the load or radial velocity monitoring on the outside surface of the cylinder along its axis and circumference. Compared with the load of sliding detonation, the one-dimensional cylindrical load has the advantages of simple stress state and easy analysis as a problem on a simplified two-dimensional axial symmetrical structure, and can provide an explicit analysis on the stress components related to the fracture of the cylinder. Based on the radial velocities of the test points distributed at the outside surface of the cylinder, a method was proposed to diagnose the initial fracture over the periphery of the cylinder. The principle of the proposed diagnosis method is that the fracture of the cylinder under homogeneous load can result in the bifurcation (or change of the evolution trend) in the uniform velocity-curve cluster. And the initial fracture time and position will be the same as the bifurcating time of the velocity curves and the position of bifurcated velocity curve, respectively, when the bifurcation angle of the velocity curves exceeds the normal scope corresponding to structure strength of the tested cylinder. Compared with the high-speed framing photography which can obtain the exact fracture information over part of the periphery of the cylinder, the distributed velocity monitoring can obtain the exact initial fracture information over the whole periphery of the cylinder. The initial fracture parameters of the 304 steel and 45 steel cylinders under one-dimensional dynamic expanding load were obtained by using the established loading and diagnosis technologies for expanding cylinder experiment with linear initiation explosives. These parameters include the fracture strain and the average strain rate. The fracture strain or ductility of the 45 steel cylinder is lower than that of the 304 steel cylinder.
Abstract:
A two-stage light gas gun is a common hypervelocity launcher. Over the years, most researchers adopted simplified one-dimensional models and rarely used three-dimensional finite element models. This paper used the coupled Eulerian-Lagrangian algorithm to calculate the gas-driven hydrodynamic field in a 14-mm-caliber two-stage light gas gun. The two-stage light gas gun was decoupled into two three-dimensional numerical models according to whether the diaphragm was broken. A three-factor four-level orthogonal test was carried out to get the material friction coefficient and the broken diaphragm pressure, which were difficult to measure in experiments. The ordinary least square method was used to calculate the orthogonal test data. The friction coefficient between the piston and the pump tube was 0.82, the friction coefficient between the projectile and the launch tube was 0.30, and the broken diaphragm pressure was 11.73 MPa. The orthogonal test showed that the friction coefficient and the broken diaphragm pressure significantly influenced the calculation results. The friction could not be ignored in calculating the launch process of the two-stage light gas gun. So keeping the gun body clean was necessary to improve the projectile velocity. The numerical model for the two-stage light gas gun was established based on the method mentioned above, which completely reproduced the launch process of the gas gun, and visually represented the change of the flow field. The velocities of the projectile were numerically obtained by the established model, which were highly consistent with the experimental results. In addition, the verification condition was selected to analyze the change of the flow field, and the pressure nephograms at the critical moments were given. It should be noted that the velocity range of the projectile was 3-5 km/s. The method is fully applicable for the projectile velocity below 3 km/s and is generalizable for the higher projectile velocity. The gas gun simplification method, grading idea and key parameter confirmation method can be extended to other two/multi-stage light-gas guns, such as solid propellant driven and detonation driven.
Applied Explosion Mechanics
Abstract:
Pipelines with a gasketed bell and spigot joint are more vulnerable to external load damage, leading to pipeline failure. To ensure the safe operation of adjacent high-density polyethylene (HDPE) bellows during blasting excavation, control of the influence of blasting vibration load on the pipeline is the main focus. The vibration velocity and dynamic strain response data of the pipeline were collected from the field test of a full-scale embedded single-segment HDPE bellow. The HDPE bellow models without socket contact and with an elastic sealing ring were established using the LS-DYNA numerical simulation software. The reliability of the model parameters of the HDPE bellows without a joint was verified by the field test data, and the response laws and failure mechanisms of the structural displacement, vibration velocity, and effective stress of the HDPE bellows with a gasketed bell and spigot joint were compared and analyzed. The safe vibration velocity of the pipe was determined using the pipeline response law and the allowable rotation angle of the interface in conjunction with the current specification. The research results show that the resultant vibration velocity, resultant displacement, and effective stress of the bellow with a gasketed bell and spigot joint are greater than those of the bellow without a joint. At the same cross-section, the resultant vibration velocity and effective stress on the explosion side of the bellow with a gasketed bell and spigot joint are higher, and the maximum resultant displacement occurs on the back of the explosion side of the cross-section. Along the axis direction of the pipeline, the resultant displacement and the resultant vibration velocity of the pipeline decrease continuously from the center to both ends of the pipeline, and the resultant displacement of the pipeline with a gasketed bell and spigot joint is larger. The safe vibration velocity of the pipeline with a gasketed bell and spigot joint under such working conditions is 24.77 cm/s, according to the allowable rotation angle of the interface.
Abstract:
Semi-armor-piercing warhead is likely to penetrate into the inner space of warship to induce severe damage. Published research indicated that the corner part of ship cabin tended to fail first. In present study, the novel design of corner structure aims to improve the capability of explosion-proof of ship cabin. Motivated by this idea, six kinds of typical corner connection structures were designed using the concept of weakening converged shock wave, improving the structure stress and strain state, coordinating deformation and transforming failure modes. The LS-DYNA software was employed to investigate the dynamic response of cabin structure subjected internal blast loading. Lagrange shell element and solid element based on multi-material ALE algorithm are used to simulate steel structure and air region, respectively. The interaction between shock wave and structure was fulfilled using fluid-structure interaction algorithm. The accuracy of the numerical model proposed in present paper was validated by comparing the published experimental results. Main attention of present study focuses on the effects of corner connection structure on the maximum deflection, corner pressure and deformation/failure mode of cabin structure. It attempts to explore the failure mechanisms of cabin structure. Simulation results confirm that the corner position of cabin structure is susceptive to fail under internal blast loading. Compared with the original structure without corner connection, the existence of corner connection structure can obviously reduce the plastic deformation of cabin structure. To be specific, the corner connection in the flat-plate form could reduce the maximum deflection by up to 31.9% relative to the original structure. In addition, the application of the corner connection in the arc shape could decrease the equivalent plastic strain by about 60%. Moreover, the existence of corner connection structure could ameliorate the position of high plastic strain and the failure modes of cabin structure. In present study, the corner connections in flat-plate form, concave form and arc shape could effectively avoid the failure behavior of cabin corner.
Abstract:
Study on propagation characteristics of detonation in bifurcated tubes is of great significance to the safety protection of gas explosion in pipelines and engineering application. The propagation states of detonation vary with the geometrical structure when passing through the bifurcated tee. Based on the detonation circular test tube, the stoichiometric hydrogen-air mixture gas with 29.5% H2 in the volume fraction under different initial pressures was ignited by a 10-kV double high-voltage electrode to be detonated before entering the 30°, 45° and 90° bifurcation tees, respectively. The propagation characteristics of the detonation in the bifurcated tubes were analyzed based on the propagation velocity and cellular structure evolution characteristics obtained from the feedback signals of flame sensors and smoke-foils records. The results show that the H2/air detonation will decay when it passes through a bifurcated tee which is affected by rarefaction wave, but it is only a local phenomenon. The detonation re-initiation is gradually completed from regular reflection to Mach reflection after collision of incident shock wave and wall. In the straight branch tube, the detonation decay is mainly affected by the inlet area of the collateral branch tube. With the increase of the bifurcation angle, the inlet area decreases, and the detonation decay and re-initiation distance decrease as well. In the collateral branch tube, the detonation decay is affected by both the inlet area of the collateral branch tube and the gradual expansion of the section. When the bifurcated angle exceeds the critical value, the inlet area becomes the main influence factor. In addition, it is proved that increasing the experimental initial pressure of premixed gas can significantly improve the detonation stability and weaken the influence of bifurcation geometry. The mechanism of detonation decay and re-initiation in the bifurcated tubes is clarified by this study, which enriches the study of detonation diffraction and contributes to provide a scientific reference for engineering application and taking proper measures of explosion safety protection of gas pipelines as well.
Abstract:
Explosion venting and inerting are two commonly used explosion protective measures in hydrogen-based industries, both of them are effective in reducing the maximum explosion overpressure when used alone. However, the coupling effects of venting and inerting on hydrogen deflagrations have not been well understood. To this end, experiments were carried out in a 1 m high top-vented vessel with a cross-section area of 0.3 m×0.3 m to investigate the effects of nitrogen volume fraction (φ) in the range of 0 to 50% by volume on vented hydrogen-air explosions with a fixed equivalence ratio. The premixed hydrogen-nitrogen-air mixtures obtained according to Dolton’s law of partial pressure were ignited in the center of the vented container by an electric spark with an energy of about 500 mJ. A 0.75-m long transparent window was installed in the center of the vented container, through which the flame images in the container were recorded by a high-speed camera at 2 000 frames per second. The pressure-time histories within and outside the vented container were measured by four piezoresistive pressure sensors with a measuring range of 0–150 kPa. The experimental results reveal that φ significantly affects the vented deflagration of hydrogen-air mixtures. The pressure peak owing to the external explosion dominates the internal pressure-time histories when φ≤40% and that resulting from the rupture of vent cover becomes dominant for higher values of φ. Under the current experimental conditions, Helmholtz-type oscillations with a frequency decreasing with φ are always observed, and acoustic oscillations appear in the tests only for φ=25%, 30%. The maximum internal explosion overpressures (pmax) near the vent, at the center of the vessel, and near the bottom of the vessel decrease with increasing φ. Moreover, the highest overall pmax is obtained always near the bottom of the vessel. However, the difference of pmax between the three measuring points is negligible when φ is larger than 40%. The maximum external explosion overpressure decreases with increasing φ. In addition, significant effects of the external explosion on the internal pressure-time histories are observed in all tests, regardless of its explosion overpressure.

Founded in 1981    monthly

Sponsored byChinese Society of Theoretical and Applied Mechanics
Institude of Fluid Physics, CAEP

Editor-in-ChiefCangli Liu

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