• ISSN 1001-1455  CN 51-1148/O3
  • EI、Scopus、CA、JST收录
  • 力学类中文核心期刊
  • 中国科技核心期刊、CSCD统计源期刊
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Abstract:
Hydrogen plays a key role in the global clean energy transition, but its flammability and high explosion hazard also make hydrogen safety a research hotspot. Focusing on the latest research achievements in the field of hydrogen explosion suppression by scholars at home and abroad, this paper comprehensively reviews different types of explosion suppression materials and mechanisms. Firstly, it introduces the research progress of gas, liquid, solid, and multiphase composite explosion suppression materials, and compares and analyzes the explosion suppression effects, key parameters, and their variation rules. Secondly, it discusses the physical, chemical, and physicochemical processes by which explosion suppression materials affect hydrogen explosions, to reveal the explosion suppression mechanisms of various materials. Finally, it looks forward to the future development trend of hydrogen explosion suppression materials, emphasizing the exploration of high-efficiency explosion suppression materials and the deepening of mechanism research, as well as the many challenges faced in practical applications. This provides a reference and inspiration for the research and development of new hydrogen explosion suppression materials.
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Richtmyer-Meshkov (RM) instabilities are observed in various fields, including inertial confinement fusion, supernova explosions, and supersonic combustion engines. While considerable research has been conducted on the single-mode RM instability induced by low-Mach number shock waves, there is a notable gap in studies on the RM instability of a single-mode interface under high-Mach number shock waves. Additionally, the influence of thermo-chemical non-equilibrium effects resulting from high-Mach number shock waves remains unknown. In this study, a two-dimensional code for high-temperature non-equilibrium gas, based on the finite volume method with unstructured adaptive grids, was employed to simulate the single-mode RM instability caused by high-Mach number shock waves in air. In the numerical solution process, a splitting method was employed to separately solve the convective and source terms. The convective term was solved using the MUSCL-HANCOCK method for second-order space-time reconstruction and the HLL scheme for calculating numerical fluxes. The source term was solved using a single-step implicit time format with A-stability. Two scenarios were considered: light/heavy interface and heavy/light interface, with shock Mach numbers ranging from 6 to 9 and 9 to 11, respectively. The research compared the evolution of flow fields under three gas models: frozen gas, thermal non-equilibrium gas, and thermo-chemical non-equilibrium gas. This study gave the disturbance growth and the growth rate of each gas model and compared the numerical results with linear and nonlinear theories. The influence of the initial shock Mach number and the initial disturbance scale on RM instability was analyzed. Furthermore, the distribution of vorticity fields and the evolution of circulation were discussed. The findings reveal significant differences in thermo-chemical non-equilibrium flow compared to frozen flow, particularly in the transmission and reflection waves, as well as the interface velocity. Thermo-chemical non-equilibrium flow exhibits a decreased peak amplitude growth rate, weakened fluctuations in the interface growth rate, and a slowed-down growth of interface instability compared to frozen flow. Comparative analysis with multiple theoretical models indicates that the ZS model is more suitable than other models for describing single-mode interface RM instability under high-Mach number shock waves. The study of vorticity reveals two main regions with strong vorticity generation: one near the interface and the other behind the transmitted shock wave. This is notably different from RM instability induced by low-Mach number shock, where vorticity is primarily generated at the interface. Additionally, the investigation into circulation demonstrates that the amplitude of vortices in thermo-chemical non-equilibrium flow is smaller than in frozen flow, aligning with the conclusion that disturbances grow more slowly in thermo-chemical non-equilibrium flow compared to frozen flow. This study contributes valuable insights into RM instability under high-Mach number shock waves, expanding the understanding within the RM instability research community.
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Cellular projectiles are widely used in the impact tests of protective structures, but the actual loads of cellular projectiles acting on the tested sandwich structures are still unclear. In this paper, the dynamic response process of a uniform/graded cellular projectile impacting a foam sandwich beam is studied through theoretical analysis, numerical simulation, and impact tests. The foam sandwich beam is equivalent to a monolithic beam to simplify the analysis. Based on the shock wave model of the cellular projectile and the equivalent response model of the foam sandwich beam, a coupling analysis model of the cellular projectile impacting the foam sandwich beam is developed, and its governing equations are presented. Meso-finite element simulations of a uniform/graded cellular projectile impacting a foam sandwich beam are carried out, and impact tests are performed on the test platform of cellular projectiles. It is found that the coupling analysis model can accurately predict the process of a cellular projectile impacting a foam sandwich beam and the impact pressure of the cellular projectile. Subjected by cellular projectiles with the same initial momentum but different density distribution or initial velocity, foam sandwich beams with the same configuration present different mechanical response processes, which demonstrates that the impact of cellular projectiles cannot be simply equivalent to impulse loading, and the coupling effect between the projectile and the sandwich beam cannot be ignored. Compared with uniform cellular projectiles, the impact pressure waveform of the graded cellular projectile is sharper and shows stronger nonlinearity during its attenuation. This study clarifies the loading effect of cellular projectiles on foam sandwich beams and lays a theoretical foundation for the optimal design of cellular projectiles simulating blast loads.
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Propellers serve as pivotal components within ship propulsion systems, directly influencing a vessel's performance through their stability and efficiency. Current research on the resilience of propulsion shafts often simplifies propellers to homogenous discs, neglecting their structural intricacies. This approach fails to accurately capture the transient damage features of propellers under the effects of underwater explosion. Therefore, this paper takes into consideration the propeller's structural characteristics. By initially employing wet modal analysis, the study determines that solid modeling outperforms shell modeling. It investigates the response and damage characteristics of propeller surfaces under the influence of far-field shockwaves while considering the propeller's structural attributes. The paper also analyzes the transient damage characteristics of propellers in conjunction with the hydrodynamic cavitation state generated during high-speed propeller rotation. The research findings demonstrate that at attack angles of 0 degrees and 90 degrees, surface loads on the propeller due to shockwave incidence are higher, but they exhibit an upper limit that correlates with the propeller's structural features. When accounting for the hydrodynamic cavitation state, stress levels on the blades remain consistently uniform. The primary plastic damage zone on the blades is near the root, showcasing both local and complete plastic deformation modes. This paper delves into the damage and cavitation characteristics of propellers under far-field explosions, and its results offer valuable insights for protecting propulsion shafts and propellers against shock impacts.
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Coral concrete is a material with severely asymmetric tensile and compressive strengths. Therefore, studying the dynamic tensile mechanical properties of coral concrete is of great significance for island reef protective engineering. To investigate the dynamic tensile mechanical properties of coral sand cement mortar reinforced with carbon fiber(CF) and stainless steel fiber(SSF) under impact loading,
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Once an explosion accident occurs on a civil aviation aircraft, it will cause fatal damage to the aircraft structure. In order to provide a research basis for the structural design and engineering application of airborne anti-explosion vessel, the directional explosion venting characteristics of anti-explosion vessel with shear pin were studied. The structure system is mainly composed of cylindrical vessel, venting cover, shear pin and aluminum alloy panel. Firstly, the numerical model of anti-explosion vessel under implosion was established with LS-DYNA. The critical diameter of shear pin was obtained in the explosion tests and the reliability of the model was verified. Then, the propagation of shock wave and distribution of blast loading in the anti-explosion vessel were elucidated by analyzing the distribution of explosion flow field and changes in shock wave pressure. Meanwhile, the motion law of venting cover during the process of explosion venting was studied by varying the TNT charge mass and shear pin diameter. Finally, a functional relationship between the charge weight and shear pin diameter was established under different venting cover masses, to investigate the critical fracture issue of the shear pin. The results show that the critical diameter of the shear pin is determined to be 22mm through 100g TNT internal explosion tests. Following the TNT explosion, the shock wave propagates reciprocally in the vessel. At approximately 3.8ms, the venting cover is ejected from the vessel, while the residual pressure at the bottom of the vessel is approximately 0.5MPa by 5ms.
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In order to solve the bottleneck problems such as the high cost of charge safety and reliability test and the difficulty of strong overload environment test, the overload environment of the charge when the projectile penetrates the steel plate was simulated by using AUTODYN finite element numerical simulation software, aiming at the equivalent simulation of the overload environmental force of the internal charge when the projectile penetrates the steel plate. Based on the parameters of waveform, pressure peak and pulse width obtained from the simulation, a charge loading simulation experimental device composed of initiation system, loading system, auxiliary system and pressure test system was designed, and the charge overload environmental force equivalent simulation experiment was carried out. To a certain extent, the equivalence of the charge loading state when the experimental system simulated the projectile penetrating the steel target at the speed of 500~1200m/s was verified, which broke through the requirement that the loading pressure was greater than 1GPa and the pulse width was greater than 100μs. The results indicate that the overload pulse received by the projectile penetrating the steel plate charge is a sine wave monopulse. The waveform adjuster can not only regulate the generated waveform, but also have a significant impact on the attenuation of pressure values. As the thickness of the waveform adjuster increases, the pressure loaded on the surface of the test drug gradually decreases, and the pulse width significantly increases. As the thickness of the flyer increases, the driving speed obtained by the flyer gradually decreases, and the pressure loaded on the surface of the test drug significantly decreases, with no significant change in pulse width. The comparison between the pulse characteristic values formed by the loading simulation test device and the numerical simulation results of the projectile penetrating the steel target shows that the maximum error of the overpressure peak is 5.71%, and the maximum error of the first peak pulse width is 14.8%, both lower than 15%. This verifies the equivalence of the loading state of the propellant when the test system simulates the projectile penetrating the steel target.
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In order to investigate the variation law of the blasting characteristics of the gas-powder two-phase mixed system, the blasting experiments with different static operating pressure (Pst) at the blasting outlet were carried out in the self-built stainless steel flame acceleration pipeline, and the variation law of Pst on the two-phase blasting pressure, flame propagation velocity and blasting flame morphology was emphatically studied. Pst is determined by the blasting hole blocking ratio (θ) and the number of blasting film layers (n). The increase of θ and n together increased Pst. The increase of Pst strengthened the constraint of gas powder and reaction products flowing out of the pipe, increased the viscosity effect of the fluid in the pipe, promoted the reaction of gas powder in the pipe, and reduced the degree of "secondary explosion" of unfired gas outside the pipe. For the pressure time interval curve analysis, Pst increased from 2.97kPa to 14.64kPa, and the pressure time interval curve showed a "double peak" structure with a "keep" platform. The first pressure peak increased from 5.48kPa to 10.20kPa, the "keep" time extended from 6ms to 25ms, and the second pressure peak decreased from 23.03kPa to 9.71kPa. When Pst is 16.08kPa and 24.12kPa, the pressure before bursting film is superimposed and reflected for many times, resulting in the time-history curve of bursting film pressure showing a special oscillating and rising "three-peak" structure. In the analysis of flame propagation velocity, the increase of Pst decreased the average flame propagation velocity from 161.33m/s to 67.99m/s. When n=2, the increase of θ makes the flame structure change from cluster to jet. When θ=88.9%, the blasting flame shown a typical jet shape. The increase of θ and n made the flame brightness gradually decrease, the length of flame luminescence zone decreased, the time interval from breaking film to flame emergence and the flame duration increased.
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In order to study the explosion process of carbon-iron nanomaterials synthesized by gaseous detonation, the effects of different molar ratios of hydrogen-oxygen (2:1, 3:1, 4:1) on the peak value time-history curve of detonation parameters (detonation velocity, detonation temperature, detonation pressure) and the morphology of carbon-iron nanomaterials were studied by combination of hydrogen-oxygen experiments and numerical simulations. The explosion experiments used hydrogen and oxygen with a purity of 99.999% in a closed detonation tube. The precursor was ferrocene with a purity of 99%. A high-speed camera was used to observe in the middle of the tube. After the experiments, the samples were collected and characterized by transmission electron microscopy. The numerical simulation used ICEM software for modeling and meshing and then used FLUENT software to verify the rationality of the mesh size, and then performed simulation calculations after confirming the optimal mesh size. The results that hydrogen-oxygen explosion inside a detonation tube involves two processes: the propagation of explosion/detonation waves and the attenuation of combustion waves, and the hydrogen-oxygen molar ratio has a significant impact on the peak time history curves of detonation velocity, detonation temperature, and detonation pressure. With the increase of the molar ratio of hydrogen to oxygen, the detonation velocity, detonation temperature, detonation pressure and attenuation rate of the explosion/detonation wave all decrease. The molar ratio of hydrogen to oxygen affects the morphology growth of carbon-iron nanomaterials by influencing the propagation and attenuation of explosion/detonation waves. At zero oxygen ballance, the sample consists of carbon-coated iron nanoparticles. As the hydrogen-oxygen molar ratio increases, the number of carbon nanotubes in the sample gradually increases. Adjusting the molar ratio of hydrogen to oxygen can achieve control over the propagation and attenuation process of explosions/detonation waves, and also achieve the goal of controlling the preparation of carbon iron nanomaterials with specific morphologies through gaseous detonation.
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There is a lack of reliable calculation theory for the transmission and reflection pressure of shock wave at the water-soil interface. Using the mass conservation equation, momentum conservation equation, and the equations of state of water and soil, the Hugoniot relationship and the p-u curve of the propagation of shock wave in water and soil medium are derived, and then the transmission and reflection pressures of the shock wave at the water-soil interface can be analyzed theoretically. Two-dimensional numerical models of the free field in water and water-soil layered medium field are established, in which the water and soil parameters are consistent with those in the three-phase medium saturated soil model used in the theoretical derivation. The calculation results show that the theoretical and numerical solutions of the water-soil interface transmission and reflection pressures are highly consistent. Using 80 g TNT explosives, from the water-soil interface 0.1—0.9 m (proportional burst distance of 0.232—2.089 m/kg1/3) explosion, the theoretical and numerical solutions of the transmission and reflection pressure error is less than 7%, according to the analytical solution of the reflection pressure and the ratio of the incident pressure in the water, the coefficient of the reflection pressure is in the range of 1.6—1.8; from the water-soil interface 0.5 m, the saturated soil containing pressure of the water and soil interface, the reflection pressure coefficient of the water and the water interface, the reflection pressure coefficient of the water and the water interface. At 0.5 m from the water-soil interface, the gas content of the saturated soil varies in the range of 0-10%, and the transmission and reflection pressures are 63.8—70.0 MPa, and the reflection pressure coefficients are in the range of 1.55—1.70 at this time. Derived from the shock wave in the water-soil interface transmission, reflection pressure calculation method, the physical meaning of clear, high precision calculations, can be carried out for the underwater explosion on the submerged soil damage assessment of engineering structures in the soil to provide a theoretical basis.
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To enhance the service safety of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessel under low temperature and dynamic loads, the mode I dynamic fracture toughness of nodular cast iron was experimentally investigated at ambient and cryogenic temperatures (20℃, -40℃, -60℃ and -80℃) using an improved split Hopkinson pressure bar technique. The ductile-brittle transition behavior of the material was specially investigated. The crack initiation time of the specimen was determined by the strain gauge method. The dynamic stress intensity factor (DSIF) at the crack tip and the mode I dynamic fracture toughness (DFT) of the material were determined by the experimental-numerical method. The results show that under the same impact velocity, the DFT and fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. Through quantitative analysis of the microscopic fracture morphologies, it is revealed that there is a failure mechanism transition at different temperatures. As the temperature decreases, the number of dimples on the fracture surface decreases, while the river patterns as well as cleavage steps increase, which indicates that the ductility of the material is weakened but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
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In order to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. X-ray diffraction test is used to analyze the changes of the mineral composition of the granite before and after filling with water. The Hopkinson device is used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact damage were selected for electron microscope scanning test to analyze the fracture failure characteristics. Fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact damage and the scanning image of the fracture under electron microscope, and the influence of the image magnification selected during electron microscope scanning on the fractal dimension was discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportion of hornblende, albite, microcline and quartz in the saturated granite decreases, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases, while the fragmentation degree and the fractal dimension of block gradually increase, and the influence of initial damage on the fractal dimension of block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning image increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering reference for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
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To investigate the anti-external-blast performance of underground utility tunnel structures, field explosion tests were conducted to study the dynamic response characteristics and failure modes of cast-in-place and precast segmental utility tunnel structures subjected to the ground surface explosion. Via field explosion tests including 11 cases, the failure characteristics and dynamic responses of cast-in-place and precast segmental utility tunnels were observed under explosion with different scaled distances. And the anti-blast performance of cast-in-place and precast segmental utility tunnels was compared and analyzed. The research results indicate that both the roofs of the cast-in-place and precast segmental utility tunnel ultimately exhibit bending and shear failure, when subjected to ground surface explosion. The anti-blast performance of the cast-in-place utility tunnel is better than that of the precast segmental utility tunnel. The initiation position has a significant impact on the blast responses of the precast segmental utility tunnel, and it is unfavorable when the initiation position is above the center of the segment. Under a small-scale ground surface explosion, the damaged area of the cast-in-place utility tunnel is larger than that of the precast segmental utility tunnel. The damage of the precast segmental utility tunnel is concentrated in the section or connection joint located near the explosion center, and there is a significant residual slip between segments.
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To investigate the velocity distribution characteristics of elliptical section warhead (ECSW) fragments under different detonation modes, a numerical simulation model was established for five ECSWs with different shape ratios. Numerical simulations were conducted to investigate the velocity distribution and energy output characteristics of fragments from ECSW under five different detonation modes: central single-point initiation, dual-point initiation at the midpoint of the short (or long) axis, four-point initiation at the midpoint of the major and minor axes, as well as surface-initiated detonation. The research findings indicate that in the radial direction, the maximum radial velocity of fragments from the warhead exhibits a consistent logarithmic growth pattern across different detonation modes. It increases from the major axis to the minor axis direction. Furthermore, with an increase in the shape ratio, the difference in fragment velocities between the major and minor axis directions gradually decreases. However, the maximum velocity profiles of fragments from elliptical section warheads exhibit distinct differences in average velocities under different detonation modes. Specifically, surface-initiated detonation yields the highest average radial velocity, while single-point initiation results in the lowest. As the number of initiation points increases, the overall average fragment velocity on the maximum velocity profile gradually rises. In the axial direction, the influence of rarefaction waves causes the maximum fragment velocities at different azimuthal angles to occur near the 1/4 position from the non-initiating end. Initiating points along the minor axis enhance the fragment velocity in the major axis direction near the initiating end compared to initiating points along the major axis. However, there are no significant variations in the axial velocity distribution of fragments in the minor axis direction. Furthermore, the different detonation modes have negligible effects on the energy output characteristics of elliptical section charges. Approximately 27% of the charge energy is converted into shell kinetic energy, while 50% of the energy is dissipated through shell fracture deformation and air shock wave propagation.
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The dynamic tensile spallation damage caused by shock wave reflection on the free surface of target is one of the typical damage modes of materials. The initial microstructure of materials, the strength and strain rate of impact loading, temperature and other factors directly affect the spallation damage evolution process in materials.The change of free surface velocity c of target indirectly reflects the evolution process of spall damage in materials. For the research of physical model of spallation damage, there are few literatures about using suitable spallation damage model to simulate the free surface velocity profile of target under different impact loading waveforms. The relationship between loading waveforms and free surface velocity profile and the evolution process of spallation damage is mainly discussed by means of experiments. Considering that the shear viscosity coefficient and the hardening coefficient are the basic parameters of the material, the calculation method of the initial damage parameters of the damage model is given by analyzing the relationship between the spall strength, the loading strain rate and the initial damage paramer of the damagr model. The initial damage parameter of the damage model is effectively associated with the loading strain rate, and the program automatic calculation of the intial damage parameter under different loading strain ratea is realized. On this basis, not only the free surface velocity profiles of spallation tests of aluminum materials loaded by square wave, triangular wave and Taylor wave can be well simulated, the calculated spall strengths and spall plate thicknesses are also consisten with the tests results. In addition, the relationship between the distribution of initial damage, spall strength and loading strain rate at different positions in the target is further anayzed. So, compared with the existing damage model, the new method not only further improves the existing damage model, but also improves the validity of the calculation results. At the same time, it also provides ideas for improving other spall damage models.
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Based on the background of the further requirements for lightweight, explosion and impact resistance, and vibration reduction and noise reduction in the development of honeycomb structure in engineering science, a liquid metal honeycomb sandwich structure was proposed, and the preparation, impact experiments, and numerical simulation research of the liquid metal honeycomb sandwich structure were carried out. A preparation method for the liquid-filled metallic honeycomb sandwich structure was developed to meet the requirements of effective sealing of the internal liquid, adjustable liquid filling content, and controllable filling position within the structure. The first level light gas gun was used to launch foam bullets to simulate the explosion shock wave load, and the dynamic response of the structure under different impact velocities was obtained. At the same time, the commercial finite element software Abaqus/Explicit was used to carry out numerical simulation of the impact response of foam bullets in the metal honeycomb sandwich structure using the smooth particle hydrodynamics method, and further discussed the impact speed of foam bullets, the liquid content in the cell on the impact resistance and post-impact vibration characteristics of the structure. The results indicate that the liquid-filled structure exhibits superior impact resistance and post-impact vibration performance compared to the unfilled structure. Moreover, with an increase in the liquid content, the displacement response of the liquid-filled structure shows a monotonic decrease, while the damping ratio demonstrates an increasing trend. When the core is fully filled with liquid, the structure achieves optimal impact resistance performance, with a decrease in peak displacement of approximately 13.66% compared to the unfilled structure, and an increase in damping ratio by approximately 1.6 times. The aforementioned research establishes the foundation for the extensive application of liquid-filled metallic honeycomb composite structures in the field of impact protection.
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In order to obtain the physical and mechanical properties of NiTi alloys with different initial phase transition temperatures under high strain rates, the responses of NiTi alloys with different initial phase transition temperatures were systematically studied under quasi-static compression and tension at strain rate 10−3 s−1, quasi-isentropic compression at strain rate 105 s−1, and shock compression at strain rate 107 s−1. Dog-bone specimens and cylindrical rod specimens were used in the quasi-static tension and compression experiments, respectively. A series of quasi-isentropic compression and planar shock wave compression experiments were performed by using the pulsed power generator CQ-4, which can deliver pulsed currents with peak values of 3–4 MA and a rise time of 470–600 ns to short circuit loads. Velocities were measured by a photonic Doppler velocimetry (PDV) system with accuracies of 1%. The quasi-static loading stress-strain curves showed twice modulus changes for both the initial martensitic and initial austenitic NiTi alloys. The modulus changes were caused by crystal reorientation and plastic deformation of the martensitic NiTi alloy. In experiments of the initial austenitic phase, the modulus changes were caused by martensitic phase transition and plastic deformation after phase change. The Lagrangian sound speed increased continuously with the particle velocity for the initial martensitic NiTi alloy under quasi-isentropic loading. However, there are discontinuities in the sound speed curves for the initial austenite phase. The sound speed decreases intermittently from the transverse wave speed to the longitudinal wave speed and then increases linearly with the particle velocity. In shock experiments of initial martensitic NiTi alloy, a double-wave structure appeared at the free surface velocity of about 34 and 100 m/s for the initial sample temperature of 302 and 402 K, respectively. The austenite-martensite phase transition occurred during sample heating of the initial martensitic NiTi alloy. The inflection points on the velocity curve were caused by plastic yielding of martensitic and austenitic phases separately. For the initial austenite NiTi alloy, an obvious elastic-plastic transformation of austenite NiTi alloy was observed at a free surface velocity of approximately 260 m/s. The elastic limit of austenitic NiTi alloy increased from about 2 GPa to about 4 GPa with the increase of strain rate from about 105 s−1 to 107 s−1. The elastic limit decreased to 1.7 GPa at a strain rate of 107 s−1 with the initial sample temperature of 402 K. The results show that the elastic limit of NiTi alloy is greatly affected by temperature and strain rate.
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By exploring the effect of mass parameter on the vibration displacement of beam members under air blast loading, an effective method was proposed to reduce the vibration displacement of beam members by increasing mass. An equivalent single degree of freedom (SDOF) system was used to analyze vibration displacement for beam members. The displacement formulas with mass parameter for flexible and rigid beam members in each stage under air blast loading were respectively established. These stages included elastic forced vibration, elastic free vibration, plastic forced vibration, plastic free vibration, and rebound vibration. Rectangular and circular sections were selected as typical cross sections of beam members, and 13 typical calculation cases with mass parameters ranging from 1.00 to 1.20 were designed. The vibration displacement-time history curves, maximum elastic displacement, maximum elastic-plastic displacement, and residual deformation were calculated and analyzed. Taking the data with a mass parameter value of 1.0 as the reference value, the displacement reduction rate of other calculation cases relative to the reference value could be obtained. The difference between the types of beam members for displacement reduction rate was further analyzed. The results are as follows. For flexible and rigid beam members subjected to air blast loading, increasing the cross-sectional area and considering only the mass parameter will result in a smaller reduction in vibration displacement. Therefore, the displacement should be analyzed according to the coupling effect of the mass parameter and additional stiffness parameter. For beam members with rectangular cross-sections, the reduction ranges of maximum elastic displacement, maximum elastic-plastic displacement, and residual deformation calculated from the coupled effect of mass parameter and stiffness parameter are about 4.75, 3.28, and 2.96 times that of mass parameter alone. For beams with circular cross-section, the data are 3.75, 2.56, and 2.32 times. These conclusions apply to both flexible beam members and rigid beam members, and there is no significant difference.
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Compared to traditional alloys, the new multi-component alloy exhibits an excellent "cocktail effect". This effect allows for the collaborative control of structure and performance, making it highly suitable for application in the demanding service environment of the aviation industry. To expedite the adoption of multi-principal component alloys in the aviation industry, experimental conditions simulating high temperature and high strain rate coupling environments encountered by aero engines are employed. Using the CoCrFeNiMn multi-principal element alloy as the research object, dynamic impact tests were conducted at different temperatures (298, 673, 873, 1073, 1273 K) by using a split Hopkinson pressure bar with an impact velocity of 20 m/s. Dynamic stress-strain curves at five temperatures were obtained, and the results indicate that the stress-strain curve at 1273 K has higher strain hardening ability compared to 873 K and 1073 K. When the temperature increases to 1273 K, the material's yield strength can still reach 200 MPa, demonstrating good high-temperature performance. The grain size, dislocation density, and microstructure types of the samples before and after deformation were discussed by electron backscatter diffraction tests. The experiment result reveals that an increase in dynamic plastic strain at 1273 K leads to grain coarsening phenomenon, with higher substructure breeding ability observed at the grain boundary. In addition, the change in adiabatic temperature rise and ambient temperature during dynamic plastic deformation is quantified. It is also highlighted that the current dynamic constitutive relationship is inadequate in predicting the dynamic stress-strain relationship of the CoCrFeNiMn multi-principal component alloy across a wide temperature range. Finally, an exponentially phenomenological dynamic constitutive equation is established by decoupling the temperature effect between the initial yield and the plastic flow stage. This constitutive equation allows for the accurate prediction of the yield strength and plastic flow behavior of multi-component alloys under impact loads across a wide temperature range.
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The diffusion behavior of shear instability control under dynamic load is the inducement for the development of local large deformation and the deterioration of macroscopic mechanical properties of rock. Firstly, the energy function of the unstable interface is established; and then based on the generalized variational principle, the interface disturbance analysis is carried out, while the first and second-order variances of the function are taken into consideration. Thus the governing equation of dynamic instability of the interface under shear load is established. Based on the discriminant equation, the influence of shear force and dynamic effect on the angle of the unstable interface is obtained. The results show that the angle of the shear deformation zone increases to a certain extent with the increase of external shear force. With the increase of the local dynamic coefficient, that is, the increase of the local inertial force, the shear band angle decreases obviously. By solving the diffusion equation with the edge displacement, the analytical expression of displacement is obtained, showing that the displacement increases gradually with the increase of loading time. To verify the reliability of the theoretical model and further study the deformation behavior of interface instability and its influence on wave propagation, the evolution of the fine and microscopic morphology of the contact surface during dynamic shear was described by combining with the SHPB rod-beam experiment technique, and an evaluation method for the influence of the evolution of surface contact parameters on mechanical parameters during interface instability is proposed. The numerical analysis model is established, and its result shows that interface instability is the leading condition of local shear failure slip. With the increase of interface thickness and shear force, the local displacement increases. The interfacial shear diffusion behavior greatly reduces the amplitude and changes the frequency of the transmitted wave. This study provides a good theoretical reference for the study of localization deformation and dynamic strength of rocks.
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In order to examine the influence of loads on the penetration behavior of the armor-piercing rod in a steel target, two sets of experiments were performed where both loaded and unloaded rods were used to penetrate 603 armored steel plates. Structural failures of the plates were observed under both loaded and unloaded conditions. Subsequently, numerical simulation methods were employed to analyze the penetration characteristics of both loaded and unloaded armor-piercing rods under various conditions, including incident angles of 45° and 60°, and impact velocities ranging from 1300 to 1600 m/s. An analysis was conducted to evaluate the effects of loads, incident angles, impact velocities, and load centroid positions on both the penetration depth and deflection angle of the rods. The research findings indicate that the inclusion of loads substantially enhances the oblique penetration depth of the armor-piercing rod while simultaneously reducing the ballistic deflection angle, thereby effectively improving the overall penetration efficiency. Conversely, in the case of positive penetration, the energy consumption caused by the load striking the target plate’s surface impedes the armor-piercing rod’s ability to penetrate. It is noteworthy that under an impact velocity of 1400 m/s and an incident angle of 60°, the inclusion of loads results in a decrease in the critical jump velocity of the armor-piercing rod. Moreover, observations revealed that as the distance between the centroid of the armor-piercing rod and its head surpasses half of the rod’s length, there is an increase in penetration depth accompanied by a corresponding decrease in the deflection angle. Specifically, it has been found that an increased distance between the centroid of the armor-piercing rod and its head leads to an improvement in penetration effectiveness. These findings highlight the substantial impact of load position on the penetration effectiveness and offer valuable insights for future design optimization. The research outcomes offer essential support and guidance for the design of high-speed kinetic energy missiles, thereby facilitating the enhancement of their penetration capabilities.
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The theoretical study of the attenuation law of underwater blast shock waves was of great significance for the prediction of the underwater blast power of the combatant. According to the pressure-impulse function when the material was subjected to shock loading, the pressure-time interval curve equation applicable to the shock loading of the underwater explosion was derived. Through the underwater explosion experimental method to measure the pressure time course curve of different amounts of drugs and different distances. Used MATLAB software to curve fit the experimental data, the underwater explosion shock wave attenuation section of the fitted curve. The experimental data were curve-fitted using Cole theoretical equations, Орленко theoretical equations, and the new model equations, respectively, and the fitting resolvability coefficients (R2) of the three equations were obtained. The impulse and energy parameters of the shock waves of the fitted curves were calculated and compared with the results of the general Cole and Орленко theories to verify the accuracy of the fitted curves. The correlation between the pressure decay curves obtained by the new method and the experimental values is closer than that of the exponential and inverse ratio segmental expressions of Cole and Орленко, and the coefficient of determination of the accuracy of the fit is more than 0.988. In calculating the values of the specific impulse and the specific energy of underwater explosive shock waves, the new model has a better accuracy of the calculations. The error between the new model and the experimental values in calculating the specific impulse does not exceed 4%, which is 5-10% higher than the error between the theoretical and experimental values of ОРЛЕНКО. The error of the specific shock wave energy from the experimental value does not exceed 1 percent, and the accuracy of the calculation is comparable to that of the general theory.
Abstract:
In order to explore the underwater anti-explosion mechanism of different corrugated steel-concrete slab composite structures, the damage process of concrete slab under underwater contact explosion was simulated by smoothed particle hydrodynamics and finite element method (FEM-SPH), and the validity of the numerical method was verified by comparing with the experimental results. The FEM-SPH method was used to explore the damage process and failure mode of the wall panel under different protection schemes, to reveal the underwater explosion-proof mechanism, and to construct the prediction curve of the damage grade of the wall panel. The results show that the simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under different protection schemes, the damage range of the wall panel with 12 mm thick corrugated steel composite structure (T-12), 75o angle corrugated steel composite structure (A-75) and 70 mm corrugated steel composite structure (WH-70) is 83%, 81.6% and 82.5% lower than that of the unreinforced wall panel, respectively. In the composite structure, the explosion shock wave propagates to the corrugated steel in the form of incident wave and then propagates in the structure in the form of transmitted wave and reflected wave. When the transmitted wave reaches the lower surface of the corrugated steel, part of the shock wave will continue to propagate to the wall panel, while the remaining shock wave is reflected to form reflected longitudinal wave and reflected transverse wave, which further attenuates the transmitted shock wave acting on the wall panel to achieve the effect of wave clipping and energy absorption. The prediction curve can directly evaluate the influence of explosive amount and wave height change of corrugated steel in composite structure on the damage grade of wall panel.
Abstract:
The precise control of explosive energy to form an effective radial fracture network in shale is the key of shale gas dynamic extraction. In order to elucidate the damage and fracture mechanisms of shale under directional fracture-controlled blasting and establish a quantifiable relationship for shale damage and destruction under various blasting conditions, explosive tests were conducted on cubic shale specimens with four different fracture angles. The evolution of surface strain fields on the shale specimens was monitored using digital image correlation (DIC) technology. Additionally, the fractal dimensions of surface cracks on the shale specimens at different fracture angles were computed based on the box-counting theory. A programmed analysis of post-blast fragment size distribution was carried out using Matlab software, resulting in the development of a fully automated particle size analysis program with visual delineation of particle sizes. The experimental results demonstrate a negative power-law relationship between crack density and scaled distance within different scaled distances. The angle between the fracture direction and the weak plane of the bedding significantly influences the location of micro-damaged areas. Particularly, when the weak plane of the bedding is parallel to the fracture direction, damaged areas tend to concentrate along the weak plane, affecting the macrocrack propagation path and favoring the formation of a single crack. Energy dissipation at the weak planes of the bedding is identified as a crucial factor leading to suboptimal fracturing effects in shale blasting. When the fracture direction aligns with the weak plane of the bedding, a higher proportion of large fragments is observed in the post-blast specimens. The average fractal dimension of fragment size distribution is the lowest among all groups, measuring only 0.7843. Conversely, when the fracture direction is perpendicular to the weak plane of the bedding, the distribution of post-blast fragment sizes becomes more uniform. The average fractal dimension of fragment size distribution increases to 2.5233, indicating relatively better blasting fragmentation results in such scenarios.
Abstract:
Understanding the role of temperature rise in dynamic shear is of great significant, as it helps us to predict accurately the dynamic failure of materials and structures. In order to obtain the temperature rise and the distribution of temperature in the shear zone of TC11 titanium alloy, dynamic shear tests were conducted on the “flat-hat” shaped specimens of TC11 titanium alloy by using a split Hopkinson pressure bar. Based the high-speed infrared InSb detecting technology, the evolution of temperature rise in the shear zone with time was obtained. Theoretical analysis of the distribution of temperature rise in the shear zone with time and space is carried out by solving the one dimensional thermal conduction equation. The initiation and propagation of shear band and the relative distribution of temperature fields in the shear zone are obtained by FEM simulation analysis. It was found from the experimental results that the TC11 titanium alloy behaves brittlely under dynamic shearing. The fracture morphologies demonstrate that significant temperature rise occurs during dynamic shearing. The temperature rise test results demonstrate that the maximal temperature rise in the shear zone achieved 430 ℃. Furthermore, the loading rate plays insignificant effect on the temperature rise in the shear zone. The temperature rise in the shear zone is highly localized, the significant temperature rise distributes several micro-meters around the center of the shear zone, and the significant temperature rise maintains several tens of micro-seconds. The results of the theoretical analysis and FEM simulation demonstrate that the maximal temperature rise can achieve 751 ℃, and the distribution laws of the temperature are consistent with the experimental results. It is found from the experimental and FEM simulation results that the maximum temperature rise occurs at the time of failing of material, indicating that the temperature rise in the shear zone results from the highly localized shear deformation.
Abstract:
In response to the problems of the lack of corresponding empirical formulas and the poor timeliness of simulation for the explosive shock tube, and to quickly obtain the peak pressure of the shock tube used in explosions, a four-layer back propagation (BP) neural network was established to predict the peak pressure in the experimental section of the shock tube. After verifying the grid independence, numerical simulation was used to calculate the peak pressure of the test section of the shock tube, and the simulation data were compared with the experimental data of the shock tube explosion, and the average relative error is 2.49%. After proving the accuracy of the numerical simulation values, the 195 sets of peak pressure obtained from the numerical simulation in the shock tube test section were used as the output layer, and the TNT dosage in the shock tube driving section, aspect ratio of the charge column, and explosion proportional distance were used as the input layer for BP neural network training. To speed up the neural network iterations and increase the prediction accuracy, Adam's algorithm was used as an optimization algorithm for neural network error gradient descent. The results show that the predicted results obtained through the trained neural network are basically consistent with the simulated values, and the average relative error between the predicted results and the numerical values is 3.26%. In contrast to the evaluation metrics obtained using multiple regression analysis (mean absolute error (MAE) of 480 and coefficient of determination (R2) of 0.58), the four-layer BP neural network obtains a MAE of 25.4 and an R2 of 0.99 for the validation set. The BP neural network model can reflect the mapping relationship between the peak pressure of the shock tube explosion and the influencing factors, and improve several times compared with the time required for numerical simulation, so it has the value of practical engineering applications.
Abstract:
The wave propagation and pressure distribution during the interaction between long duration blast waves and structures are important foundations for the large scale explosion protection design and safety assessment. In order to understand the interaction mechanism between long duration blast waves and cylindrical shells, as well as the distribution law of the surface load on the cylindrical shells under their action, the overpressure histories on the cylindrical structure surface were obtained through the 150ms long duration blast wave shock tube experiment, and the shock wave evolution and the pressure load distribution were investigated numerically using the large eddy simulation and hybrid WENO-TCD (weighted essentially non-oscillatory-tuned centered difference) method. The results show that the overpressure load of the calculation results is in good agreement with the experimental results, and the overpressure load on the cylindrical shell appears a clear angle and height correlation. The pressure on the back shell is higher than that on the side surface or even comparable to the blast on the facing surface, which exhibit different pressure attenuation modes from the traditional short duration blast wave propagation. The sudden expansion on the side surface is the main reason for the initial oscillation of pressure, and has a lower pressure than that at the windward and leeward sides. On the other hand, a series of diffracted shock waves collides and reflects on the symmetry plane of the shell leeward, as well as the stationary and superimposed effects of the series of decelerating shock waves near the 135° phase, which are the main mechanisms that cause the overall increase of the pressure load on the cylindrical shell. In addition, the formation and evolution of wake vortex structures on the leeward side due to the boundary effects is a key factor leading to differences in the load distribution along the height direction. The above analysis methods and related results lay the foundation for the subsequent study of load distribution models for typical structural components under long duration blast waves.
Abstract:
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact loading, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. The impact velocities in the SHPB tests were about 6.8, 7.8, 8.8, 9.8 and 10.8 m/s, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a baseline of comparison), 0.10%, 0.20%, 0.30% and 0.40%, respectively. Then, based on the test results, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic enhancement factor show linear positive correlations with impact velocity. When the loading level remains the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with the impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes was 0.30%, the impact toughness of concrete achieved a relative maximum, being about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation performance.
Abstract:
To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were experimentally studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which is based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images is derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g/m3, both the explosion overpressure (∆pmax) and the explosion pressure rise rate ((dp/dt)max) reached the maximum, ∆pmax=0.799 MPa and (dp/dt)max=52.438 MPa/s, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders all increase with the increase of mass ratios (I), while the trend of maximum pressure rise time is opposite. The variation rules of the maximum explosion overpressure and maximum average temperature are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of the maximum explosion pressure rise rate and the combustion rate are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, so metal powders should be appropriately selected as energetic additives according to the damage performance index in the formulation design of FAE.
Abstract:
The reflected and transmitted waves in split Hopkinson pressure bar (SHPB) tests provide crucial information for obtaining the stress-strain relationship of materials. Accurately analyzing the formation process and influencing mechanisms of the reflected and incident waves is a key prerequisite for precise experimental design and accurate data processing. In this paper, the propagation and evolution of one-dimensional elastic-plastic waves in the loading stages of the SHPB test are presented particularly for a sandwich bar system consisting of the incident wave, specimen, and transmitted bar. Based on the theory of elastic-plastic incremental waves and numerical simulation calculations, the propagation of elastic-plastic waves in the specimen, the transmission and reflection of elastic-plastic waves at the two interfaces, and the interaction of the resulting series of transmitted and reflected waves are quantitatively investigated. The research findings are as follows. Firstly, although the design principle of the SHPB apparatus is based on linear elastic wave theory, the elastic-plastic waves, especially the stress waves, have a major influence on the transmission and reflection at the elastic-plastic interface, while the transmission and propagation of purely elastic waves have a relatively minor effect. Secondly, when the loading interval of the incident wave has a certain width, the multiple transmission and reflection of elastic waves at the two interfaces in bar 2 attenuate the reflected wave while further strengthening the transmitted wave. This attenuation causes the peak of the reflected wave for the half-sine wave to occur earlier than at 0.5 nondimensional time. Thirdly, in contrary to the preliminary laws of elastic wave transmission and reflection at interfaces in traditional SHPB analysis, variations in the Young’s modulus and density of the specimen material have little effect on the waveform and peak intensity of the transmitted wave, regardless of whether the incident wave is rectangular, trapezoidal, or half-sine. This investigationprovides a scientific basis for the refined design of SHPB experiments and precise analysis of data.
Abstract:
To study the dynamic mechanical properties of deep marble, the micro parameters of deep marble were calibrated based on the coupling method of discrete element (particle flow code, PFC) and finite difference (fast Lagrangian analysis of continua, FLAC). Then, the dynamic stress equilibrium condition and uniformity assumption in the impact simulation of three-dimensional split Hopkinson pressure bar (SHPB) test were numerically validated. Finally, an in-depth analysis was conducted on the stress-strain response, fracture characteristics, and energy evolution mechanism of marble under true triaxial stress environment. It has found that the numerical results of the true triaxial SHPB test based on the PFC-FLAC coupling theory satisfy the assumption of stress uniformity, and the simulated stress-strain curves are highly consistent with the measured ones. Peak stress and peak strain decrease with the increase of pre-pressure in the impact direction (axial pressure hereafter) . At the same axial pressure, the peak stress gradually drops down with the increase of incident stress; When the incident stress is fixed, the axial pressure weakens the peak stress of the specimen, while the confining pressure perpendicular to the impact direction (lateral pressure hereafter) increases the compressive strength. During the loading process, the outbreak period of acoustic emission events generally occurs in the post-peak stage, and during this stage, a relatively obvious macroscopic fracture zone is formed within the specimen. Under true triaxial dynamic compression, the failure specimens are mainly characterized by tensile cracks, accounting for over 80% of the total number of cracks. The specimen undergoes energy changes from loading to failure. At the peak stress point, the strain energy storage reaches its limit, which is then transformed into an energy form dominated by dissipated energy and supplemented by particle kinetic energy. The relevant conclusions have important guiding significance for the study of the dynamic characteristics of deep marble and the long-term stability evaluation of deep rock engineering.
Abstract:
In order to study the energy release characteristics of composite charge in confined space, a type of coaxial composite charge was designed with the inner layer of thermobaric explosive and the outer layer of mixed fuel of different components. And the mixed fuel was mainly composed of Al/PTFE active material or boron-based fuel. Al/PTFE active material can undergo a detonation-like reaction and provide energy for the shock wave, but its reaction products are all solid. The lack of gaseous medium is not conducive to shock wave propagation. However, boron-based fuel can decompose to produce gas under detonation loading, which can make up for the shortcomings of Al/PTFE active material. The mixed fuel formulations were designed and the content of boron-based fuel in different formulations was determined. The internal explosion test of composite charge was carried out by using sealed explosion device. The shock wave overpressure on the device wall and the quasi-static pressure were obtained, which can be used to evaluate the implosion power of the composite charges. The effects of boron-fuel content, secondary ignition energy and reactant concentration on the post-combustion reaction and energy release characteristics of the composite charges were investigated by using the method of implosion power evaluation. The experimental results show that the quasi-static pressure of the composite charge with the same mass but different boron-based fuel content increases first and then decreases with the increase of boron-based fuel content, and the optimal volume fraction of boron-based fuel decomposition products participating in the secondary reaction is about 1.0%. For the composite charge, because the oxygen content in the confined space is limited, when the concentration of substances involved in the secondary reaction reaches a certain threshold, the quasi-static pressure cannot be effectively improved by increasing the ignition energy or the reactant concentration, and the energy utilization rate is not improved.
Abstract:
To investigate the effects of the inlet equivalence ratio distribution on the performance of a rotating detonation combustor (RDC), the radial or circumferential function model of equivalence ratio at the entrance of the RDC was established. The distribution function of component mass fraction in radial or circumferential direction was obtained by substituting the function model of equivalence ratio into the function of component mass fraction and equivalence ratio. The distribution function of entry boundary components was constructed by the user-defined function tool in the Fluent code. A three-dimensional transient Euler equation was employed to simulate the propagation process and flow field characteristics of detonation waves in a C10H22/air RDC, and the characteristics parameters of the detonation waves and RDC were compared under different equivalence-ratio distributions. The results show that the uneven distribution of the inlet equivalence ratio will affect the characteristics of the detonation waves. When the equivalence ratio ranges from 0.4 to 1.6 and is not uniformly distributed along the radial direction, the height of the detonation wave decreases with the increase of equivalence ratio at the midline of the inlet surface. When the equivalence ratio ranges from 0.4 to 1.6 and the distribution is non-uniform in the circumferential direction, the height of the detonation wave is almost not affected with the increase of the number of changing periods. The uneven distribution of equivalence ratio will weaken the pressure-gain effect and temperature rise effect of the RDC, and the influence of the uneven distribution of equivalence ratio along the radial direction is more obvious than that along the circumferential direction. In the RDC, the induction and reactant region of detonation wave is not strictly behind the leading shock wave, but is located at the oblique rear of the leading shock wave, and under the influence of curvature, the leading shock wave propagates along the circumference of the middle diameter cylinder near the outer wall of the RDC.
Abstract:
In order to study the load distribution and dynamic response of tunnel structures under underwater explosion, a 1/10 scaled tunnel model was designed and manufactured, and underwater explosion tests were conducted for three times.The pressure, impulse, and displacement of the tunnel model were studied. The results show that the shock wave produces a significant water surface truncation effect in the shallow water area, which reduces the impulse near the water surface. The experimental value of the peak pressure of the free field shock wave is in good agreement with the theoretical value, and the error is within 20%. The peak pressure on the front surface of the circular cross-section tunnel is about 1.626-1.716 times that of the free field, the peak pressure on the top surface is about 55.4%-65.2% of the free field, and the peak pressure on the back surface is about 25.5%-31.3% of the free field. The impulse time history curve under the action of underwater explosion shows a clear step shape, and each bubble pulsation is accompanied by a corresponding increase in impulse.The displacement analysis shows that the underwater explosion causes the vibration of the tunnel structure. The vibration process can be divided into three stages: the rapid deformation of the tunnel structure, the large amplitude vibration of the tunnel structure, and the tremor of the tunnel structure. The maximum displacement of the tunnel structure occurs during the large amplitude vibration of the tunnel structure.
Abstract:
In order to study the pressure parameters of HMX-based aluminized pressed explosives at the ignition moment of slow cook-off, slow cook-off test were designed at 0.1 and 1℃/min heating rates, and an internal multi-point temperature measurements were taken inside explosives. On this foundation, based on the universal cook-off model of explosives, combining the multi-step decomposition reaction mechanism of HMX-based explosives with the reaction of aluminum powder, and considering the phase transition process in the decomposition of HMX-based explosives, a slow cook-off calculation model for pressure-department reaction rate of HMX-based aluminized pressed explosives was established. This study wrote the calculation model as a user defined function and imported it into Ansys Fluent to perform calculations. Slow cook-off tests were conducted on large aspect ratio (5:1) HMX-based aluminized pressed explosive charges with 4 mm shell thickness at heating rates of 0.1℃/min and 1℃/min and compared with simulation results. And then, the numerical simulations of the temperature field and internal pressure changes were performed before ignition of the cook-off bomb at heating rates of 0.055, 0.1, 0.2, 0.3, 0.5, and 1℃/min. It was found that at the heating rate of 0.1℃/min, after the test reaction, the end cover was ejected, the shell was axially cracked, and there was no powder left, which was judged to be a deflagration reaction; at the heating rate of 1℃/min, the shell was slightly deformed, with some powder left, and it was judged that a combustion reaction had occurred. The numerical calculations show that as the heat stimulus increases, the ignition temperature of the explosive tends to increase logarithmically, while the extent of reaction and internal pressure of the cook-off bomb tend to decrease exponentially. Before the HMX phase transition, the internal pressure inside the cook-off bomb grows slowly, after the HMX phase transition rapidly increasing, and finally it rises sharply near the ignition moment.
Abstract:
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young’s modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young’s modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young’s modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young’s modulus. However, the accuracy of Young’s modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young’s modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
Abstract:
Studying the strength, deformation and damage mechanism of freeze-thaw treated rock mass under the action of cyclic dynamic disturbance was of important significance for reducing engineering disasters and improving rock breaking efficiency in cold regions. The cyclic impact tests of freeze-thaw treated red sandstone under two kinds of impact pressure were carried out to investigate the effects of cyclic impact number and freeze-thaw number on stress wave propagation, dynamic stress-strain curve, peak stress, and peak strain. In addition, the calculation method of cumulative damage factor, which can comprehensive consider the effects of cyclic impact and freeze-thaw, is proposed based on the Lemaitre strain equivalence principle. Finally, the microstructure characteristics of red sandstone after freeze-thaw and cyclic impact are analyzed in detail. Results show that red sandstone specimens treated with different freeze-thaw number show tensile failure mode under cyclic impact load. The cyclic impact number that red sandstone specimen can withstand is negatively correlated with freeze-thaw cycle number, and red sandstone specimen after 75 freeze-thaw cycles treatments reaches the failure state after the first impact loading. Moreover, the cyclic impact number mainly affects the jump point, abscissa corresponding to peak point and amplitude of transmitted waves, and the amplitude of reflected waves. While the freeze-thaw number shows a great effect on the jump point, abscissa corresponding to peak point, and amplitude of transmitted waves during the first impact process. The cumulative damage factor of red sandstone specimen exhibits a good negative correlation with the dynamic peak stress. After the combination effects of freeze-thaw and cyclic impact, the cracks inside red sandstone spread along the grain boundary and connect with the pores to form a complex network.
Abstract:
Compared to the reflection and transmission analysis process during the incident wave loading phase, the incident wave plateau phase lasts longer, and the elastic-plastic propagation and evolution behavior are much more complex. The effects of elastic-plastic wave interactions within the specimen during this phase are very pronounced. Using the elastic-plastic incremental wave theory, combined with numerical simulation, the calculations of elastic-plastic wave’s interactions inside the specimens under rectangular incident wave action and its elastic-plastic transmission and reflection behavior at the two interfaces are carried out. The attenuation characteristics of the reflected waves in the sandwich rod system are investigated. The results show that under strong incident wave action, the specimen internally forms a curve-shaped elastic-plastic interface due to the interactions of elastic-plastic waves. This causes the transmission end to reach the yield state significantly earlier. This elastic-plastic interface propagates towards the reflection end at a speed greater than the elastic sound speed. The attenuation of the reflected wave during the plastic phase is the sum of the increase in generalized wave impedance due to the increase in the specimen's cross-sectional area and the increase in the number of back-and-forth plastic waves caused by compression. Calculations also show that although the change of the specimen density significantly affects its wave speed and wave impedance, the sum of the attenuations caused by these two factors is close to zero. Hence, the effect of density changes on the transmission and reflection wave plateau phase can be ignored. An increase in the plastic modulus causes the reflection wave plateau to attenuate faster, but the effect of the specimen's diameter is not monotonous. When it increases from 4mm to 10mm, the reflection wave attenuation speed increases, but when it further increases to 12mm, the attenuation amount decreases. This study has certain reference value for in-depth analysis of split Hopkinson pressure bar test for the transmission waveforms as well as for the detailed test design and data processing.
Abstract:
Integrated with a high-speed oblique water entry test of a large caliber conical nose projectile, the deflection behavior of the projectile obliquely entering water was studied based on the arbitrary Lagrange-Euler (ALE) fluid-structure coupling method. Firstly, based on the experiment of projectile impacting on inclined water tank at high speed, the finite element model was established to simulate the corresponding response characteristics, and the rationality of the numerical model and related method was verified. Secondly, the variation of contact force mode as well as load characteristics of the projectile in the condition of water entry at 500 m/s was analyzed, and the corresponding mechanism was discussed. In addition, the influence of water entry angle on the deflection behavior of projectile was also investigated. Related analysis demonstrated that the projectile will deflect upward due to the effect of pitch moment, and the deflection velocity increases first and then decreases gradually during the entry process. The variation trend of deflection degree is different within different entry angle range: When the entry angle is less than 15°, the projectile usually jumps out of the water; When the entry angle locates in the range of 30°–60°, the deflection trend of projectile is almost the same, i.e., the projectile rotates from the initial tilted state to the horizontal state and further the vertical state, and finally it moves downward with its nose opposite the initial water entry direction; When the entry angle increases to 75°, the projectile cannot continue to rotate to a vertical state after it rotates to a horizontal, instead it moves downward in a tilted state with its nose facing upward. Under different water entry angles, the axial force exerted on the projectile is negative, and it makes the projectile velocity decreases continuously; comparatively, the transverse force is positive, and the peak value decreases with increasing the water entry angle. Moreover, the penetration depth of the projectile increases with the increase of entry angle, and it almost shows an exponential relationship.
Abstract:
The solid rocket motor is the only power source of the system in the rocket sled test, the traditional monorail rocket sled generally consists of the rocket motor, the motor mounting components, the reinforced longitudinal beam and the slippers, in which only the test object and the motor charge are effective mass, while the rest of the structures are additional mass, so reducing the additional mass can improve the thrust-to-weight ratio of the rocket sled system. In response to the problem of excessive mass added to the components of the conventional monorail rocket sled system, an integrated rocket sled and motor structure consisting of motor and slippers is proposed. The three-dimensional Euler-Bernoulli beam unit is used to discretize the rocket sled system and obtain the optimal distribution position of the slippers, then it is found that the vibration is minimized when the middle slipper is located between the front slipper and the back slipper. Three options for connecting the slipper to the motor housing are designed: in the first option the slipper is wrapped and connected to the motor housing by serrated welds; in the second one the motor housing is stacked directly on the slipper body; and in the third one the motor housing is connected to the slipper by supported transition plates. A comparative analysis of the on-rail safety of the latter two options is performed using the sled-rail coupling dynamics method, which indicates that the mechanical environment of the integrated rocket sled is better when the sled slippers and the motor housing are connected by the supported plates as transition structures, and the additional mass of the system is reduced by 73% compared to that of the traditional monorail sled. Finally, the validation test of the integrated motor with sled validation test was implemented and the collected data were analyzed, showing that: the integrated motor with sled proposed in this paper is reasonable and feasible, and the motor vibration level is comparable to that of the traditional rocket sled.
Abstract:
A kind of microporous modified coal gangue (MCG) with rough surface and large specific surface area was obtained by roasting, acid-alkali excitation and physical grinding of industrial solid waste coal gangue (CG) as raw material. Using MCG as matrix, a new flame retardant sodium alginate (SA) was combined with MCG by mechanochemical technology (MCT) to prepare an efficient, environmentally friendly and economical modified coal gangue-sodium alginate (MCG-SA) powder explosion suppressor. The three powders were characterized by thermogravimetric analysis, SEM analysis and XRD analysis to determine their thermal decomposition characteristics, micro-morphology and crystal phase composition. Through the SEM analysis, it can be clearly observed that the powder is irregularly stacked with particles, has many micro-pore cracks, rough surface, and weakened agglomeration effect. The XRD analysis shows that there are characteristic peaks of SA and MCG in the composite powder, which proves that the combination of the two is successful. It is not difficult to see from the thermogravimetric analysis that the composite powder has both the thermogravimetric characteristics of MCG and SA, and the mass loss of thermal decomposition is as high as 67.02%, which has excellent heat absorption performance. On the basis of the self-built test platform, the effects of MCG, SA and their composite powders on the explosion pressure and flame propagation speed of methane-air premixed gas under different compounding ratios and adding masses were investigated. The results show that MCG, SA and MCG-SA powders have good anti-explosion effect, and the anti-explosion ability of composite powders is better than that of single powders. Among them, the composite powder with mass of 250 mg and SA mass fraction of 50% has the most significant synergistic inhibition effect on 9.5% methane/air explosion, and the maximum explosion pressure and maximum flame propagation velocity are reduced by 36.72% and 68.93%, respectively. The arrival time of the maximum explosion pressure and the maximum flame propagation speed is extended by 243.36% and 171.33%, respectively. The mechanism of explosion suppression of composite powder is mainly reflected in barrier effect, heat absorption, adsorption and consumption of free radicals. This research has certain research significance and reference value in the field of industrial environmental protection and gas explosion protection.
Abstract:
Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, Expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
Abstract:
In order to improve the blast resistance performance of engineering structures to ensure the safety of important targets and reduce the adverse effects of high cement content on the environment of cement-based ultra-high performance concrete, a new type of composite slab based on geopolymer ultra-high performance concrete(G-UHPC) is proposed. Three G-UHPC composite slabs were prepared with G-UHPC, steel wire mesh and energy absorbing foam materials, and one ordinary concrete slab was prepared with C40 concrete. In order to verify the blast resistance performance of the new G-UHPC composite slab, the explosion test was carried out in the field. The diameter and depth of the crater and spalling of each specimen under the 0.4 kg TNT contact explosion were analyzed, and the blast resistance performance and failure mode were discussed. The effects of G-UHPC, steel wire mesh and energy absorbing foam materials on the blast resistance performance of concrete slabs were discussed. Based on the explosion test results, a refined finite element model was established using LS-DYNA finite element analysis software and numerical simulation analysis was conducted. The effectiveness of the numerical model was verified by comparing the experimental results with the simulation analysis results. On this basis, the model is used to further analyze the impact of G-UHPC and steel wire mesh on the blast resistance performance of concrete slabs, and the failure process of composite slabs is analyzed by simulating the propagation of explosive waves in energy absorbing foam reinforced G-UHPC composite slabs, revealing the failure mechanism of G-UHPC composite slabs. In order to further study the blast resistance performance of G-UHPC composite slab, the parameter analysis was carried out. Based on the damage morphology of G-UHPC composite plate, the mid-span displacement of the plate bottom and the energy absorption of the energy absorbing layer, the influence of the energy absorbing foam material layout on the blast resistance performance of G-UHPC composite slab was discussed. The research results indicate that replacing ordinary concrete with G-UHPC can effectively improve the blast resistance of concrete slab, and steel wire mesh can reduce the degree of blast pits and peeling damage of concrete slabs. The blast resistance design of composite slab must consider the compressibility of energy absorbing foam material and its matching with the wave impedance of G-UHPC, so as to have a favorable impact on the blast resistance performance of composite slab. The high compressibility and low shear strength of energy absorbing foam are the main reasons for punching failure of concrete slab. The increase of the number of polyurethane foam plates will lead to the reduction of the blast resistance performance of the concrete slab, which is specifically reflected in the increase of the depth of the explosion pit and the increase of the displacement of the bottom span of the slab.
Abstract:
Aircraft fuel tanks, marine liquid tanks, oil liquid storage tanks, and other types of liquid filled structures may be threatened by blast waves, projectile penetration, and other impact loads during the engineering practice. The dynamic response of the liquid filled structure under impact load may be affected by various factors such as the characteristics of the load, the configuration of the structure, and the way of liquid filling. Accordingly, the protection mechanism of the liquid filled structure against various types of shock loads involves the fluid-solid interaction of multiphase media, wave propagation in different media, cavitation of liquid media, dynamic mechanical properties of the structure, and several other scientific issues. In this paper, the dynamic response and protection mechanism of the liquid filled structure under different impact loads are reviewed, the typical forms of the liquid filled structure in the engineering field are summarized, and the dynamic response processes, damage modes, load dissipation processes, energy conversion, and absorption processes of various types of the liquid filled structure under the loads of blast shock wave, projectile penetration and their combined effects are analyzed. Furthermore, the impact dynamic response characteristics of the liquid filled structure under the action of blast shock wave loading, projectile penetration loading, and the combined loads of blast shock wave and high-speed fragmentation group are summarized. The protection mechanisms of the liquid filled structure against various types of impact loads are summarized from the perspectives of attenuating and dissipating loads, and transferring and converting energy. In the end, the research on anti-impact characteristics of the liquid filled structure prospects from the perspectives of dynamic response and protection characteristics of the multi-cell liquid filled structure, mechanisms for destruction of the liquid filled structure by combined loads, efficient numerical computation methods, and dynamic response and protection mechanism of the liquid filled structure made of new materials.
Abstract:
To study the thermal relaxation behavior of the graded medium satisfied the power law, the one-dimensional hyperbolic non-Fourier heat conduction equation of the graded material which satisfied the power law was derived from the Cattaneo-Vernotte linear hyperbolic heat transfer equation with the thermal relaxation coefficient and graded exponent induced. The equation was first treated dimensionless. Based on the Laplace transformation, the new heat conduction equation was found to conform to the general form of the Bessel equation called the Lommel equation in the frequency domain, and the Bessel series solution of the temperature field in the frequency domain was obtained. With the asymptotic expansion of the Bessel series, the simplified expression of the temperature field in the frequency domain containing trigonometric function was obtained. The inverse Laplace transformation of the temperature field in the frequency domain was employed to get the first analytical solution of the temperature field in the time domain. Besides the first analytical solution, the new heat conduction equation in the frequency domain was simplified to the Euler equation, and the second kind of analytical solution was obtained by the pole residue method. The second analytical solution exhibits similar fluctuation attenuation and diffusion features, and both the waveform and response time are sensitive to the relaxation time coefficient. However, the second kind of analytical solution differs from the first kind of solution in terms of waveform elements which are highly related to the graded structure. The accuracy of the analytical result is verified by numerical calculation. Taking Mo-ZrC graded composite as an example, the thermal relaxation behavior of graded material satisfied power law under the first kind of temperature boundary and temperature pulse loading are discussed in detail. The temperature field shows both fluctuation attenuation and conduction characteristics. With the increase of the thermal relaxation coefficient, the response time and temperature wave amplitude increase, the unit waveform develops from a trapezoidal wave to a rectangular wave, and the oscillation approaching to the boundary shows an obvious bias.
Abstract:
A high-pressure-gas-driving blast wave simulation shock tube, commonly composed of driving section, throat section and expansion section, is an ideal platform for explosion damage effect research of long positive shock pressure duration time in the laboratory, as the ability of generating simulated shock wave with similar characteristics to real explosion wave. One of the core problems in the design of blast simulation shock tubes, is the control method of the simulated wave attenuation process by modifying the variable section structure and the driving section shape of the shock tube. In this article, a numerical calculation model of one-dimensional flow in the shock tube is established based on the explosion simulation shock tube in the laboratory, a similarity evaluation method of simulated shock wave and standard explosion wave in a shock tube based on determination coefficient is proposed referring to the statistical theory. Then, based on the flow characteristics of the variable section shock tube, the influence of the shape of the driving section on the shock wave attenuation history is studied. The results show that, it is feasible to acquire simulated wave with approximate exponential attenuation history of real blast wave, by using variable cross-section driving tube, of which the section diameter decreases with the growth of distance to the throat, optimizing the variable cross-section structure due to the determination coefficient, and controlling the motion property of expansion and compression wave in the shock tube.
Abstract:
Aiming at the problem that the traditional single-phase explosion suppression medium is not effective, it is proposed that the gas-solid two-phase medium cooperates with different explosion suppression principles to achieve efficient and rapid suppression of gas explosion. The method of using NaHCO3 powder and CO2 gas to synergistically suppress gas explosion was studied. The standard 20 L spherical explosion test device was selected, and the configuration optimization of reactants, transition states and products in the microscopic reaction mechanism of methane explosion was carried out by DFT (density funchtion theory). On this basis, the subsequent calculation was carried out. The results show that the single-phase medium with a volume fraction of 16% CO2 and 0.35 g/L NaHCO3 has an excellent effect on suppressing gas explosion, but the presence of 0.1 g/L powder will increase the maximum boosting rate by 17.9%. Compared with single-phase CO2 and single-phase NaHCO3 powder, the gas-solid two-phase medium explosion suppression phase reduces the maximum explosion pressure. When 8% volume fraction CO2 is used in conjunction with 0.125 g/L powder, the maximum explosion pressure of gas explosion is reduced by 72.42%, and the maximum pressure rise rate is reduced to 2.345 MPa/s. The suppression effect is optimal; however, when 4% volume fraction CO2 cooperates with 0.05 g/L powder, the maximum explosion pressure rise rate increases by 93.68%, and the reaction shows a certain intensification phenomenon. The quantum chemical calculation shows that in the process of gas-solid two-phase medium synergistic inhibition of gas explosion, the decomposition of NaHCO3 powder will absorb the heat in the reaction system, and its decomposition products will preferentially react with OH· and H· in the mixed system, hindering the generation of O·, inhibiting the chain process in the CH2O stage, and then inhibiting the transfer process of chain reaction. The CO2 produced by the decomposition of NaHCO3 powder and the CO2 in the mixed system dilute the volume fraction of methane in the mixed system, reduce the probability of collision between methane and oxygen molecules, and effectively inhibit the reaction process.
Abstract:
Ammunition warheads are typically cylindrical charges that detonated at moving stage. To accurately calculating the blast wave power field and the blast loadings acting on the structure of cylindrical charges air moving explosion, the peak overpressure and maximal impulse of the incident and reflected blast waves of the cylindrical charges air moving explosion were numerically simulated. Firstly, a three-stage finite element analysis method for cylindrical charges air moving explosion was proposed based on the AUTODYN finite element analysis program, and the reliability of the method was verified by comparing the simulated and test data of existing charges air static and moving explosion tests. Then, on the basis of considering factors such as charge moving velocity, length to diameter ratio, scaled distance, azimuth angle, and rigid reflection, numerical simulations were conducted for 200 sets of scenarios of the cylindrical charges air moving explosion. The distribution characteristics of the moving explosion blast wave field, incident and reflected blast wave loadings were quantitatively analyzed. The results indicate that the blast wave field of moving explosion is moved forward compared to the static explosion, and the wavefront strength is enhanced in the direction of charge movement and weakened in the opposite direction. The effect is positively correlated with the charge moving velocity, while changing the length to diameter ratio is less affected the blast wave field. Furthermore, for the typical scenarios of cylindrical charges air moving explosion in free field and reflected field where cylindrical charges were perpendicular to the target surface air moving explosion, the calculation models for the peak overpressure and maximal impulse of the incident and reflected blast waves of cylindrical charges air moving explosion were proposed. Finally, through carrying out numerical simulations of 40 sets of scenarios for the moving explosions of two simplified cylindrical TNT charges of prototype warheads, and comparing data of calculation models and simulations, the applicability of the proposed calculation model was validated. The results indicate that the calculation model is good at evaluating the blast wave loading of cylindrical charges air moving explosion, which can also provide a certain reference for predicting the moving explosive power of warheads.
Abstract:
In the experiment conducted using a custom-built 5L dust explosion flame propagation apparatus, the focus was on studying the characteristics of the flame propagation of magnesium hydride (MgH2) dust explosions within a semi-enclosed space.The results of the experiment showed that as the concentration of MgH2 dust increased,the time required for the MgH2 dust explosion flame to transition from ignition to stable propagation decreased initially,but then increased as the dust concentration further increased.Similarly, the width of the preheating zone followed the same pattern.Initially, it decreased with increasing dust concentration,but once the concentration reached a certain threshold,it started to increase.Beyond that,the flame brightness, smoothness of the flame front, and flame propagation speed showed similar trends.They initially increased as the MgH2 dust concentration increased,suggesting enhanced combustion activity.However, as the concentration further increased,these characteristics started to decline,indicating a diminishing combustion efficiency.The best combustion state was observed at a dust concentration of 800 g/m3.The instantaneous speed of the MgH2 dust explosion flame propagation exhibited a fluctuating pattern across different concentrations.The fluctuation amplitude initially decreased as the dust concentration increased, suggesting a more stable flame propagation.However,beyond a certain concentration, the fluctuation amplitude began to increase again.It is worth noting that the change in instantaneous propagation speed variation displayed different trends as the concentration varied.The exact behaviors were found to be dependent on the particular concentration level.Finally,analysis of the X-ray diffraction (XRD) test results of the MgH2 explosion products revealed a complex reaction mechanism.The MgH2 dust explosion primarily involved the combustion reaction of MgH2 but also included multiple overall reactions such as the decomposition of MgH2 and Mg(OH)2,as well as the oxidation of Mg and H2.The final product of the explosion reaction was identified to be MgO.
Abstract:
A visual square tube water mist suppression system was independently designed in order to study the inhibition effect of water mist on RDX dust explosion. The system is composed of closed explosion chamber, powder spraying system, ignition system, high-speed photography system, water mist generation system, data acquisition system and time control system. The automatic control of powder injection and ignition is carried out by the time control system. Various experimental conditions such as different nozzle types, nozzle diameters, and atomization pressures were selected. The effect of water mist on RDX dust explosion characteristics was evaluated by comparing the changes in flame propagation dynamics, explosion pressure, and explosion temperature of RDX dust explosion. The results show that the explosion pressure, and temperature of RDX dust clouds increase with the increase of explosive mass. The inhibition effect of water mist on RDX dust explosions varies with different types of nozzles at the same atomization pressure. The water mist sprayed by centrifugal nozzle has the best explosion inhibition effect, and the spiral nozzle has the worst explosion inhibition effect. As the atomization pressure increases, the explosion inhibition effect of water mist enhances. The water mist sprayed by centrifugal nozzle with diameter of 1.5 mm shows the optimal explosion inhibition effect among the five centrifugal nozzles with diameters of 0.8, 1.2, 1.5, 2.0, and 2.4 mm used in the experiment. The explosion pressure and temperature attenuation of water mist on RDX dust explosion increased with the increase of spray pressure. The explosion pressure of RDX dust is only 0.1184 MPa at an atomization pressure of 4 MPa. the peak pressure is reduced by 74.0% compared to the situation without water mist where the explosion pressure of RDX dust is 0.4561 MPa. The explosion temperature is 234 ℃, which is 69.8% lower than the explosion temperature of RDX dust without water mist (774 ℃).
Abstract:
In order to explore the effect of the aspect ratio of rectangular tube on the propagation of the spinning detonation under the limiting detonation propagating conditions, the structure of the three-dimensional gas-phase spinning detonation wave and its propagation modes in rectangular cross-section tubes are numerically investigated based on Euler equations with a 5th-order WENO finite difference scheme and the two-step global reaction model. A linear stability theory of planar detonation wave based on the normal mode method is firstly adopted to examine the chemical reaction parameters for numerical simulations and then several cases with different aspect ratios in cross-section of rectangular tube are investigated to study the structure and propagation mode of three-dimensional gaseous spinning detonation waves. By recording motions of triple lines, flow-field distributions and high-pressure imprint of detonation wave under different sizes of tube cross-section, the effect of cross-sectional geometry on the stable propagation of gaseous detonation under the limiting detonation propagating condition is revealed. The results show that the spinning detonation propagation can be maintained within a certain range of small tube cross-section size, through the movements of horizontal and vertical triple lines and an oblique triple line that is produced by interaction between both horizontal and vertical triple lines. For a square tube with 1 of aspect ratio in cross-section, the high-pressure imprint of spinning detonation on the wall forms the helical strip pattern. With the increase of the aspect ratio of the cross-section size of the tube, the pattern of a high-pressure imprint formed by the spinning detonation on the channel wall varies from the strip structure to a dotted distribution structure, the trajectory of the oblique triple line on the wave front gradually develops from the circular motion in a single direction to a complex trajectory with varying direction. When the aspect ratio is further increased, there is a tendency for the three-dimensional spinning detonation wave to eventually degenerate into a two-dimensional single-head detonation wave structure.
Abstract:
Different initiation methods directly determined the stress wave propagation and explosion energy transmission law caused by drilling and blasting, thus affected the effect of rock fragmentations. In this paper, the collision mechanism of stress wave and rock fragmentation characteristics induced by blasting with different initiation methods were studied. Based on the theory of frontal and oblique collision of stress waves, the interaction mechanism of stress waves between holes was studied to prove stress enhancement effect caused by wave collision under the staggered initiation mode. By using the RHT model for rock and JWL state equation for explosive in the ANSYS/LS-DYNA software, the magnitude of stress waves between holes and the rock fragmentation characteristics were simulated under staggered, bottom and top initiation modes. Finally, combined with on-site experiments, the interaction of stress waves and the characteristics of fragmentation distribution for blasting of rock mass containing gravel under different initiation modes were compared and analysed. Results show that under the staggered initiation mode, a frontal collision of stress wave happens at the midpoint between two holes, and the pressure after collision is 2.4 times that of the stable propagation of the stress wave; An oblique collision occurs between 0° and 44°, and the ratio of collision pressure to the stable pressure ranges from 4.1 to 2.3; Mach reflection occurs between 44° and 90°, and the ratio of collision pressure to the stable pressure ranges from 3.5 to 1. The rates of rock fragmentations with the size less than 250mm under staggered and bottom initiation modes are 25.5% and 20.9%, respectively. And the rates of rock fragmentations with the size larger than 750mm under staggered and bottom initiation modes are 9.2% and 17.5%, respectively. The stress enhancement effect caused by wave collision under the staggered initiation mode can significantly improve the blasting fragmentation of rock mass containing gravel.
Abstract:
The liquid in partially filled tanks is prone to slosh under external excitation, and the additional forces and moments generated by liquid sloshing can have adverse effects on tank trucks. In order to avoid significant sloshing of the liquid in the tank when the tank truck brakes, several types of baffles were proposed, and the influence of baffles and their geometric parameters on the liquid sloshing inside the tank truck was studied. Firstly, a numerical model of liquid sloshing based on the Finite Volume Method was established. Secondly, a series of liquid sloshing experiments were conducted. The effectiveness of the numerical model was verified by comparing the free surface waveforms obtained from the experiments at different times with those obtained from numerical simulations under the same conditions. Finally, the validated numerical model was used to analyze the influence of the geometric parameters of the baffle on the liquid sloshing response parameters under different liquid-filling conditions. The research results indicate that the perforated baffle can not only effectively suppress the peak of the sloshing response parameters in the tank but also significantly shorten the time for liquid sloshing to reach stability. The position and number of baffle orifices have little effect on the peak longitudinal force caused by liquid sloshing during vehicle braking, while the peak pitch moment is more significantly affected by the geometric parameters of the baffle. By studying liquid sloshing in the tank at different filling heights, it is found that the decrease rate of the peak value of the sloshing response parameter will first decrease and then increase with the increase of the filling height. When the peak value of pitch moment reaches its maximum value, the baffle has the worst suppression effect on liquid sloshing in a partially filled tank.
Abstract:
Underwater explosions can cause serious damage to ships and other structures in the water, seriously endangering the vitality and combat capability of ships. Ships in the combat process by torpedoes or mines and other underwater weapons attack, the explosion produced by the breach continued multi-directional into the water, the ship unsinkability has a greater impact. In order to explore the underwater explosion damage distribution characteristics, carried out a real-scale near-field underwater explosion ship test, analyzed the test obtained along the direction of the ship's length of the acceleration as well as strain measurement point data, the use of acoustic-solid coupling method to calculate the shock wave and bubble jet load under the joint action of the whole ship structure of the damage, get the whole ship plastically deformed area of the depth of the depression is 85 cm, The depth of the plastic deformation area of the whole ship is 85 cm, the width of the “L” type breach is 30 cm, and the area of the breach is 0.2 m2. Comparing and analysing the experimental and simulation data, the error in the size of the computed breach is less than 20%, and the position of the breach matches well, which verifies the accuracy of the model. The model was used to carry out simulation calculations under different blast distances, analyse the structural damage distribution in the calculation results, put forward the distributed damage pattern of the barge under the action of near-field underwater explosion load, and make it clear that in addition to the overall fracture of the structure of the ship, there is also a wide distribution of small cracks in the bulkheads, the outboard side of the plate and other parts of the ship's structural damage, when the impact factor decreases from 5.84 to 1.91, the size of the bilge breach decreases, the size of the breach decreases, the location of the breach is a good match, and the accuracy of the model is verified. Bilge breach size decreases, the number of cracks in the cabin increases, which indicates that the larger the burst distance, the greater the scope of the underwater explosive load on the ship, the bubble pulsating load will make the barge appear “whiplash movement” will appear as a whole fracture of the barge to form a fatal damage to the overall structure of the impact factor of 1.91-2.87, the bilge breach for the The bilge breakage is scattered small breakage. Research results in the port side, bulkhead and bilge connection for the weak parts, small cracks are distributed more, in the ship design process can focus on strengthening the protection. This paper provides a design reference for the damage and protection of ships under the action of underwater explosive loads.
Abstract:
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
Abstract:
Typical sandstones distributed in cold regions were chosen as the research object to study the impact mechanical properties of frozen rock mass and provide reasonable unit explosive consumption for frozen rock mass in blasting excavation engineering in cold regions. Sandstone specimens with different moisture contents were prepared by the controlled mass method. Comprehensive research methods of indoor split Hopkinson pressure bar (SHPB) test and theoretical analysis are used to study the impact mechanical properties and blasting fragmentation energy dissipation characteristics of frozen sandstones. The results are as follows. (1) The dynamic compressive strength and dynamic elastic modulus of frozen sandstone are overall improved compared to the room temperature state, while the peak strain is generally decreased. Comparing the dynamic and static load test results of the mechanical properties of sandstone, the difference between the compressive strength of sandstones with the same physical parameters under dynamic and static loads is small, and the dynamic elastic modulus is significantly higher than the static elastic modulus. (2) The energy dissipation of room-temperature and frozen sandstone specimens decreases gradually with the increase of moisture content, and the energy dissipation of frozen sandstone is higher than that at room temperature. Under the moisture content of 0, 0.25ω, 0.50ω, 0.75ω, and 1.00ω, the energy dissipation of frozen sandstone increased by 21.6%, 64.9%, 80.3%, 78.2%, and 83.3%, respectively compared with the room temperature state. (3) The unit explosive consumption of frozen sandstone with the same moisture content is higher than that at room temperature, with moisture contents of 0, 0.25ω, 0.50ω, 0.75ω and 1.00ω, the unit explosive consumption of sandstone in the frozen state is 20.4%, 61.3%, 60.0%, 55.6% and 66.7% higher than that in room temperature state. (4) By fitting the unit explosive consumption values of sandstone at room temperature and frozen state, a correction model for the unit consumption of sandstone blasting in different states is obtained, which can provide correction suggestions for the unit explosive consumption for sandstone blasting engineering in cold regions.
Abstract:
Hydrogen energy is an important component of the future national energy system. Mixing hydrogen with natural gas to form enriched hydrogen fuel can provide support for the transition towards renewable and green energy in the energy structure. However, it also brings more severe safety challenges. In order to systematically understand the current application status of enriched hydrogen methane fuel and its safe utilization, literature research was conducted to review and discuss the combustion characteristics and explosion suppression research of enriched hydrogen methane from several aspects, including propagation characteristics of deflagration flames, explosion characteristic parameters, deflagration mechanism, and explosion suppression materials. The research direction in recent years was also analyzed and summarized. The results showed that with an increase in the hydrogen addition ratio, parameters such as inherent flame instability, flame propagation speed, and explosion intensity were enhanced to varying degrees, while the suppression effect of explosion suppressants was continuously weakened. Currently, there is a lack of research on the explosion characteristics of enriched hydrogen methane under the coupling of multiple factors, and the co-suppression mechanism of explosion suppressants has not been clearly revealed. Based on this, the urgent directions and future research focus for the safe development of enriched hydrogen methane fuel are proposed, which can provide theoretical basis for the large-scale development of the enriched hydrogen natural gas industry.
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2024, 44(4).  
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2024, 44(4): 1-2.  
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Abstract:
On the Cove
Abstract:
The fiber back plate in ceramic/fiber composite armor cannot provide sufficient support for the ceramic panel due to its low stiffness, which weakens the erosion effect of the ceramic panel on the projectile. In order to enhance the overall structural stiffness of composite armor, a metal sandwich layer material was added to the ceramic/fiber composite armor. The ballistic performance of the sandwich composite armor against 12.7-mm incendiary projectiles was studied through experiments and numerical simulations. The experimental results indicate that the core of the penetrator exhibits a brittle fracture failure mode, while composite armor exhibits multiple failure modes, including petal-shaped expansion of the sandwich layer, delamination and protrusion deformation of the UHMWPE (ultra-high molecular weight polyethylene) laminate. A three-dimensional numerical model was established to analyze the evolution of the entire ballistic response, and the accuracy of the simulation was verified through experimental results. The simulation results indicate that the armor of the 12.7-mm penetrator will cause damage to the ceramic, which will erode the pointed oval head of the projectile core, making the core head blunt and weakening the penetration ability of the projectile core into the UHMWPE backing plate. Most of the kinetic energy of the residual projectile is absorbed by the UHMWPE layer, and the failure mode of the UHMWPE laminate will change from shear failure to tensile failure as the number of layers increases. In addition, as a sandwich layer, the porous TC4 board can provide support for the ceramic panel, increase the energy absorption of the ceramic panel and erosion of the projectile, and the 12-mm-pore-size TC4 sandwich layer can provide greater stiffness support, increase the energy absorption efficiency of the overall composite structure by 10%.
Impact Dynamics
Abstract:
To investigate the failure mechanism of tantalum capacitors under shock loads, shock experiments were conducted on tantalum capacitors using shock waves generated by underwater explosions with an electronic detonator. Five groups of experiments with different shock intensities were designed by varying the distance between the capacitor and the electronic detonator. The transient voltage characteristics of tantalum capacitors under different intensity shock loads were studied. The voltage variations of tantalum capacitors were explained based on the changes in internal leakage current and external charging current, and the failure modes of tantalum capacitors were analyzed. Scanning electron microscopy was utilized to observe the microstructure of damaged areas in tantalum capacitors and the micro-failure mechanisms of tantalum capacitors under shock loads were discussed. The results indicate that tantalum capacitors experience short-circuit failures after shocks, with a significant decrease in voltage initially, followed by a slow rise and self-recovery. As the shock wave overpressure increases, the probability of tantalum capacitor failure increases, with a critical overpressure threshold of approximately 32 MPa. Different types of voltage variations correspond to different failure modes, including instant self-recovery after breakdown, slow self-recovery after breakdown, and repetitive breakdown with self-recovery. Different types of voltage variations exhibit significant differences in the peak values of initial leakage currents, with the first type ranging from 2.5 A to 5 A, the second type ranging from 1 A to 2 A, and the third type ranging from 8 A to 9 A. Moreover, larger peak values of leakage currents result in narrower peak widths. The micro-failure mechanisms of tantalum capacitors under shock loads include the propagation of microcracks within the oxide film leading to excessive local electric field strength and breakdown, impurities and surrounding crystalline oxide film protruding to form conductive channels in the region of thinner oxide film, and the formation of through-cracks followed by gas ionization leading to breakdown.
Abstract:
Cuttlefish bone is a biomineralized shell produced inside the cuttlefish that enables deep and shallow floating by adjusting the gas-liquid ratio. As a typical porous material with high specific stiffness, its light-weight and high rigidity make it well adapted to the deep-sea environment. Consequently, cuttlebone is often mimicked to design biomimetic porous materials with high porosity and high stiffness mechanical properties. However, the mechanical behavior of cuttlebone under dynamic loading is still unclear, which is extremely unfavorable for the dynamic design of cuttlebone. This study delves into an extensive exploration of cuttlebone's mechanical behavior under compressions with different loading strain rates using Instron material testing machine and split Hopkinson pressure bar experimental device. Under quasi-static loading conditions, the compressive stress-strain curves of cuttlebone were obtained and exhibited three typical stages, namely linear elastic stage, long plateau stage and densification stage. The specific energy absorption of cuttlebone calculated from the stress-strain curve is illustrated, showing that cuttlebone has a better energy absorption capability compared with other common bionic structures and porous materials. Under dynamic loading scenarios by using split Hopkinson pressure bar, the dynamic stress strain curves of cuttlebone were obtained at loading strain rates of approximate 400−530 s−1. Both the dynamic initial crushing stress and the plateau stress of cuttlebone exhibited a pronounced escalation with increasing loading strain rates, indicating that the cuttlebone structure is strongly sensitive to the loading strain rate. Furthermore, the mechanical attributes of cuttlebone with respect to different growth directions during quasi-static compression tests were investigated. As the growth direction increased, a discernible decline in both stiffness and energy absorption performance within the cuttlebone structure was observed, thus revealing the anisotropy of the compression behavior of cuttlefish bone. These insights not only deepen the understanding of cuttlebone's mechanical behavior but also offer valuable knowledge that can inform biomimetic and bioinspired engineering designs for a range of applications.
Abstract:
As a novel folded structure, the truncated square pyramid (TSP) structure exhibits excellent impact resistance and energy absorption performance. It also has the merit of simple and modulated fabrication of its unit cell. To further verify the performance of TSP sandwich panels under local impact load, impact tests are carried out in this work by using an air cannon testing system. The unit cells are firstly prepared by multi-stage mold-pressing and then modular arranged to form single and multi-layer sandwich panels. The impact protection performance and energy absorption properties of the back-supported cladding cases and unsupported sandwich structures are investigated under different impact scenarios. Their impact resistance performances are evaluated by measuring and comparing the displacement time histories of the single-layer sandwich structures and their deformation modes after impact. For the back-supported cladding cases, a measuring system with five load cells is placed behind the back plate of the cladding and is rigidly supported to record the time history and distribution of the transmitted force of the claddings under impact. Their impact mitigation performances are evaluated by analyzing the recorded force-time histories under various loading scenarios. It is found that the maximum displacement and residual displacement of the back plate increase with the increase of impact velocity for the unsupported cases. For the rigidly supported claddings, the double-layered cladding shows significantly improved energy absorption and impact mitigation performance than the single-layered one. It shows a better utilization of the core, which leads to a reduced initial peak transmitted force. In addition, it is found that the impact position has a significant effect on the dynamic response of the claddings as it changes the peak transmitted force and its occurrence time because of the change in deformation modes. The research results provide a reference for the engineering design and application of TSP sandwich structures.
Abstract:
In order to study the dynamic behaviors and energy dissipation characteristics of marble under cyclic impact loading, a split Hopkinson pressure bar system was first adopted to determine the five representative incident velocities of striking projectile through the trial impact method. Based on this, constant amplitude cyclic impact tests of the marble samples were performed, and stress uniformity of the samples was examined. Then, a systematic analysis is conducted on the test data from the aspects of strain rate time history curve, stress-strain relationship, impact times and energy dissipation properties. Finally, a damage variable is defined based on the energy evolution, and the associated mechanism between energy dissipation and damage development of the rock samples is further explored. The results show that the time-history curves of the strain rate of the samples exhibit a plateau segment with a constant rate of change at low projectile velocities, and the stress-strain curve has a certain rebound at the post-peak stage. The peak stress of the rock samples decreases with the increase of the number of cycles, while the peak strain, average strain rate and cumulative absorption specific energy take on the opposite trend, and their change rates all show a sudden increase phenomenon before sample’s break or fracture. The peak stress has a linear relationship with the average strain rate, while the variation of sample elastic modulus with average strain rate generally follows an exponential decay law. There is a positive linear correlation between the dissipated specific energy and the average strain rate of the marble samples. The damage variable defined based on energy dissipation analysis can better characterize the break or fracture process of the marble samples under dynamic loading. The research results of this study have certain reference value for revealing the evolution mechanism of rock internal damage under cyclic load disturbance.
Abstract:
The existing specifications and studies mainly focus on the scenarios that the spherical charges are ignited at the central point and explosion is in free air, while the studies of the blast loadings of cylindrical charges air explosion, especially the reflected overpressure acting on the structure, are relatively limited. The blast loading calculation formula for spherical charge cannot be applied for cylindrical charge as attributed to the parametric influences such as scaled distance, length-to-diameter ratio, ignition method, azimuth angle, incident angle and relative location of reflected plane. To explore the incident and reflected blast loadings of cylindrical charges air explosion, firstly, three shots of explosion test of the single-end ignited cylindrical TNT charge were conducted. The corresponding numerical simulations are conducted based on the finite element program AUTODYN, and the applicability of the adopted finite element analysis method is verified by comparing with the experimental incident and reflected overpressure-time histories of spherical and cylindrical charges air explosion of tests, as well as the peak incident overpressure-scaled distance relationship of unified facilities criteria (UFC) 3-340-02 of spherical charges air explosion. Furthermore, the numerical simulations of more than 1000 sets of cylindrical charges air explosion scenarios considering the scaled distance, length-to-diameter ratio, ignition method, azimuth angle and rigid reflection are carried out based on validated finite element analysis method. The distribution characteristics of peak overpressure, maximal impulse of the incident blast wave and the corresponding shape factors are examined and discussed. The judging criteria and determination methods for the critical scaled distance of peak overpressure and maximal impulse are proposed by using data fitting, and the variation law of the reflected peak overpressure and the rigid reflection coefficient are revealed. Finally, a calculation method for the incident and reflected blast loadings of cylindrical charges air explosion is proposed and experimentally verified by 360 sets data. The method can rapidly predict the blast loadings on building structures, and provide reference for evaluating the ammunition damage efficiency, analyzing structural dynamic response and failure, as well as for the corresponding blast-resistant design.
Abstract:
To investigate the effect of the steel ratio on the impact resistance of glass fiber reinforced polymer (GFRP) tube concrete-encased steel composite members, 15 numerical models of composite members were established. The whole impact process, the dynamic response and the stress distribution of each composite member at different characteristic moments during the low-velocity impact were analyzed. The bending moment contributions at typical cross sections and the energy dissipation under different impact moments were explored. Meanwhile, the corresponding failure mode was determined, based on the maximum principal plastic strain distribution of concrete, tensile and compression damage of GFRP tube matrix, and equivalent plastic strain distribution of steel. Additionally, the effect of the steel ratio on the impact performance of members with different slenderness ratios was investigated by analyzing the time history curves of the impact force, displacement, energy transformation and energy consumption. The results show that the impact load-bearing capacity of GFRP tube concrete-encased steel members is improved by 7% to 134% and the lateral displacement is reduced by 13% to 68% compared with the GFRP tube concrete members. Furthermore, it can be observed that the failure mode of the members is mainly bending, and the concrete is crushed in the impact region. The bending stiffness has a significant influence on the impact performance of the member under lateral impact loading. The impact force of the member increases with the increase in the steel ratio, whereas the impact force of the member decreases with the increase in the slenderness ratio. Moreover, narrow flange steel with a higher moment of inertia is more favorable for the impact resistance of the member when the difference in steel ratio is 1.5%. The energy consumption of the encased steel is a major contributor to the total energy consumption of the member when the slenderness ratio is greater than or equal to 20. The GFRP tube plays a dual role in bearing the impact force and confining the concrete in a circumferential direction at the oscillation stage during the impact process.
Abstract:
To investigate the feasibility and characteristics of high-velocity formed projectile formation driven by electromagnetic loading, exploratory experiments of projectile formation by electromagnetically driven the linear liner were conducted using the pulsed power generator CQ-7. Photon Doppler velocimeter (PDV) was employed to measure the velocity of the electromagnetic-driven projectiles and validate their penetration into aluminum targets. A physical model and numerical simulation method for electromagnetic-driven projectile formation were established using fluid dynamics software and corresponding electromagnetic simulation modules. The changes in current density and magnetic pressure during the electromagnetic loading stage were studied and the dynamic processes of projectile formation and penetration into aluminum targets were simulated. The numerical simulation method was verified through the comparison between numerical results and experimental data. Based on this, the influences of liner configuration and loading energy on the projectile formation parameters of equal wall thickness hemispherical liner were explored. The results indicate that the outer curvature radius has a minor impact on the head velocity of the projectile, while the head velocity significantly increases with decreasing wall thickness and increasing loading energy. The aspect ratio of the projectile gradually increases with decreasing outer curvature radius and wall thickness, as well as increasing loading energy. The conversion between quasi-spherical and long rod-shaped projectile modes can be achieved by changing the structural parameters, and for the same structural parameter, the conversion between two modes can be achieved by controlling the loading energy. Finally, the feasibility of obtaining high-velocity and high-mass-formed projectiles using electromagnetic-driven technology was predicted using numerical simulation methods, and it can be figured out from the results that a projectile with a higher velocity and larger mass can be formed by increasing the loading energy and the sizes of the shaped liner, effectively breaking through the velocity limit of a traditional penetrator driven by explosive detonation.
Abstract:
In order to compare and analyze the characteristic and mechanism of damaging on 45 steel target plate penetrated by the WF/Zr-MG and 93W rod, a penetration experiment under hypervelocity impact was carried out. The analysis of penetration was performed at both macro and micro levels, in which the macroscopic quantitative characterization quantity was studied by equivalent diameter of reamer, and the microscopic morphology, phase transition and hardness characteristics of the target plate were obtained by scanning electron microscopy, optical microscope, X-ray diffraction and microhardness tester.The experimental results indicate that the WF/Zr-MG rod completely penetrated the target plate, while the 93W rod remained in the target plate. The armor-piercing capacity of WF/Zr-MG rod is higher than that of 93W rod with equivalent reaming diameter of 16.7 mm and 18.4 mm respectively, and the former is 10.18% lower than the latter. From the microscopic perspective, the aspect ratios of the fine grain layer after penetrated by the WF/Zr-MG rod and the 93W rod are 4.5 and 7.3, respectively. In addition, the width of the high-hardness layer are 10.2 mm and 8.9 mm, with Vickers hardness HV peaks at 249 and 287, respectively. The wider high-hardness layer observed in the former case can be attributed to the continuous burning of the Zr-based amorphous alloy during the penetration process, resulting in a larger temperature affected zone and consequently a greater area of hardness enhancement. On the other hand, in the latter case, the strength of the target plate during penetration is significantly higher due to the buckling and backflow of the WF/Zr-MG rod, while the 93W alloy core exhibits a "mushroom head" phenomenon. This reduces extrusion deformation on the target plate, thereby weakening the effect of grain elongation, reducing the increase in hardness peak value, and minimizing energy loss per unit length of the target plate. Ultimately, it enhances the armor-piercing capability of the WF/Zr-MG rod.
Applied Explosion Mechanics
Abstract:
Decoupled charge structure is widely used in contour blasting for rock excavation engineering, and its efficacy in rock breaking is tied intricately to both the decoupling ratio and the transfer features of explosion energy. In this study, the analysis delves into the damage degree and failure patterns of cubic red sandstone samples through two groups of lab-scale blasting tests utilizing various charging modes. To precisely quantify the features of rock fragmentation size distribution (FSD) induced by blasting load, a three-parameter generalized extreme value (GEV) function was introduced. In addition, a three-dimensional finite element model was developed in ANSYS software. The numerical model was calibrated based on the tested results of sample R1 by comparing the fracture networks and FSD curves. This validated model was then deployed to model the rock fracture behavior under decoupled charge blasting, and the evolution of blasting cracks and explosion pressure inside the rock sample was reproduced. Moreover, the effects of axial and radial decoupled ratios and the choice of coupling medium on the rock fragmentation and fracture patterns were discussed. The results showed that the three-parameter GEV function can better characterize the rock fragmentation features resulting from blasting. Notably, the average size of the fragment decreases linearly with the decrease of the decoupling ratio, and the degree of fragmentation tends to be uniform. By comparing the energy distribution and damage levels of rock when using different coupling mediums, it was found that water as the coupling medium exhibits the highest efficiency in energy transfer, followed by wet sand and dry sand, and air has the lowest energy transfer efficiency. Furthermore, the theoretical stress transmission coefficient calculated by the equivalent wave impedance method can well reflect the rock fragmentation features and serve as a valuable reference for rock blasting in decoupled charge.
Abstract:
In recent years, with the rapid development of technology and equipment in the fields of aerospace, defense, and military industries, multilayer lightweight metal composite materials have attracted widespread attention to face complex service environments and reduce equipment weight. Titanium, aluminum, magnesium, and other lightweight metals and their alloys have advantages such as high specific strength, high specific elastic modulus, high damping and shock absorption, high electrostatic shielding, and high machinability, making them the most promising lightweight metal materials for application. In this study, the explosive welding experiments of TA2/AZ31B/2024Al multilayer light metal plate were carried out using a parallel explosive-welding process. Using scanning electron microscopy, electron backscatter diffraction, split Hopkinson pressure bar, and three-dimensional contour scanning, the interfacial microstructure characteristics, material phase changes, dynamic mechanical properties, and impact fracture characteristics of multilayer explosive welded composite plates were studied systematically. The results indicate that the four joining interfaces of the multilayer lightweight metal composite plate after welding present unique waveform structure characteristics of explosive welding, and there are no obvious defects at the joining interfaces. The overall welding quality is good. The grain refinement occurs at the joining interfaces and forms the fine grain region. The grain structure in the 1060Al transition layer exhibits typical elongated layered grain characteristics due to strong plastic deformation, and deformation texture and recrystallization texture characteristics appear at all four joining interfaces. The maximum dynamic compressive strength of the sample along the X-direction is 605 MPa, and the three-dimensional morphology of the fracture interface presents unique structural features similar to the water ripples. The maximum dynamic compressive strength of the sample along the Z-direction is 390 MPa, and the three-dimensional morphology of the fracture interface presents fibrous ductile fracture characteristics. Due to the different wave impedance of the metals, the delamination failure occurs in the X-direction sample, which is caused by the shear stress between the Al/Mg joining interfaces. Since the strength of 1060Al is lower than that of other metals, the Z-direction sample is first destroyed from the 1060Al layer, and slip shear fracture occurs along the 45° direction.
Abstract:
In order to find a new, clean and efficient inhibitor of PE dust explosion, the Mg-Al hydrotalcite was used to inhibit PE dust explosion by using standard 20 L spherical explosion test system and minimum ignition temperature test system of dust cloud. The inhibition properties of Mg-Al hydrotalcite for PE dust explosion are analyzed from the aspects of explosion overpressure and minimum ignition temperature, and are compared with aluminum hydroxide and magnesium hydroxide. The results showed that the inhibition effect of Mg-Al hydrotalcite on explosion overpressure and minimum ignition temperature of polyethylene dust is superior to that of aluminum hydroxide and magnesium hydroxide. In terms of explosion overpressure, when the inhibition ratio is 2, Mg-Al hydrotalcite can completely inhibit the explosion of polyethylene dust, while the inhibition ratios required for aluminum hydroxide and magnesium hydroxide to achieve complete explosion suppression of polyethylene are 4 and 5 respectively. With the increase of inhibition ratio, the maximum explosion pressure rise rate of polyethylene dust decreased. The inhibition effect of Mg-Al hydrotalcite on the explosion pressure rise rate of polyethylene dust is also better than that of aluminum hydroxide and magnesium hydroxide. In terms of minimum ignition temperature, when the inhibition ratio was 1, Mg-Al hydrotalcite increased the minimum ignition temperature of polyethylene dust to 710 ℃, which was 290 ℃ higher than that of pure polyethylene dust. Under the same conditions, aluminum hydroxide and magnesium hydroxide can increase the minimum ignition temperature of polyethylene dust by 260 ℃ and 250 ℃ respectively. Therefore, the inhibition effect of Mg-Al hydrotalcite on the minimum ignition temperature of polyethylene is also greater than that of aluminum hydroxide and magnesium hydroxide. In addition, the inhibition mechanism of Mg-Al hydrotalcite on polyethylene dust explosion was analyzed based on its pyrolysis characteristics and infrared spectra.The physical effect is mainly realized by absorbing heat from the reaction system and diluting the oxygen concentration. The chemical action is mainly achieved by the pyrolysis products carbon dioxide and water participating in and blocking the polyethylene explosion chain reaction.
Abstract:
In order to further reveal the characteristic of metal mesh to inhibit the flame propagation of hydrogen-methane premixed mixture, hydrogen and methane mixed gas with hydrogen mixing ratio of 0%, 10%, 20% and 30% were selected to conduct the experimental investigation of the effect of hydrogen mixing ratio inhibiting the fire processing through wire mesh with varied size in an explosion pipeline with an inner diameter of 60 mm and a total visible length of 1024 mm. Firstly, the flame propagation process was recorded by a high-speed camera, and the effect of hydrogen mixing ratio on fire resistance of wire mesh with different mesh numbers and the change of flame morphology were analyzed. Secondly, the average velocity of flame front movement was calculated according to the interval of 50 mm, and the flame propagation velocity within the visible area of the pipeline was analyzed. The interaction law between the metal wire mesh and the flame was mainly characterized by the flame propagation velocity on both sides of the metal wire mesh. The results show that with the increase of hydrogen content, the difficulty of flame retardancy of metal wire mesh increases, and the flame retardancy effect of metal wire mesh can transition from success to failure, and the impact on flame propagation may shift from inhibition to promotion. When the wire mesh fails to resist the fire, the wire mesh will cause the flame to fold and cause the flame to accelerate, but the first appearance of the tulip flame is delayed. With the increase of hydrogen mixing ratio, the acceleration phenomenon of flame passing through the wire mesh is more obvious. Increasing the mesh number of wire mesh can improve the fire resistance of wire mesh to hydrogen-methane premixed flame. The larger the mesh number, the stronger the fire resistance. More than 60 mesh wire mesh can effectively quench hydrogen and methane premixed flame.