• 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
Display Method:
Abstract:
In the complex battlefield environment, soldiers will not only face the impact damage of bullets and fragments, but also be subjected to the combined effect of shock wave and bullets caused by explosion. In order to enhance the performance of the existing protective equipment, this paper designs a composite protective structure of the human chest composed of polyurea, Kevlar and foam. LS-DYNA was used to numerically simulate the mechanical response of the chest composite protective structure under the impact of blast wave and fragments, and the influence of the layout type and thickness of protective structure on the chest protection was analyzed. The results show that under the action of single explosion shock wave, the different arrangement types of protective structure have little influence on the anti-explosion effect, and the polyurea-Kevlar-foam arrangement structure has better anti-explosion effect, which is 2.42% lower than the peak value of Kevlar-polyurea-foam structure with the largest transmission pressure peak value; Under the combined action of explosion shock wave and fragments, the protective effect of polyurea-Kevlar-foam arrangement structure is better, and the peak value of polyurea-Kevlar-foam structure is 18.49% lower than that of polyurea-Kevlar-polyurea-foam structure with the largest transmission pressure peak value; Increasing the thickness of the structure appropriately can reduce the damage to the human chest caused by the combined action of explosion shock wave and fragments, but increasing the thickness further will have limited gains in the protective performance.
Abstract:
Under irradiation conditions, a large number of micro-defects such as helium bubbles are produced in some materials, and the size and number density of helium bubbles increase with the increase of irradiation years. The variation of helium bubble distribution not only affects the physical and mechanical properties of the material itself, but also directly affects the distribution characteristics of fracture particle size in the later stage of spallation damage evolution. The evolution process of spallation damage in ductile materials generally includes nucleation, growth and confluence of pores. However, due to the inhibition of existing pores on new nucleation pores, when the initial number density of pores reaches a certain critical value, the calculation of spallation damage can not consider the influence of new nucleation. Based on the characteristics of early damage evolution, a formula for calculating this critical value is given, and based on this formula, the calculation method of spallation damage of plutonium materials irradiated by helium bubbles is further discussed. Then, in order to solve the problem of the difference between the initial damage parameters of the damage model and the real initial damage of the material, we give a method to determine the damage parameters in the VG (Void Growth) model. Finally, this problem is analyzed qualitatively by using the experimental results of spallation of conventional aluminum materials containing helium bubbles. The analysis results show that, for the calculation of spallation damage of irradiated materials containing helium bubbles, when the helium bubble size changes little and the helium bubble concentration is lower than the critical helium bubble concentration given in this paper, it is necessary to consider the comprehensive influence of initial helium bubbles and new holes; On the contrary, a simple spallation damage model can be adopted, and the nucleation of holes does not need to be calculated.
Abstract:
At present, the excavation of foundation pits in construction projects have increasing requirements for the flatness of the foundation surface with the damage of reserved rock formations. Based on the analysis of brittle fracture model of rock , an new method is proposed in this paper that to use multi-point shaped charge jet impact on rock at the same time,for cracking guidance and propagation from the perspective of increasing the energy conversion efficiency of explosive energy. In order to the fracture surface energy of rock materials, and realize rock directional splitting. One of the multi-point shaped charge that can be used for rock splitting was designed, and the directional splitting mechanism of brittle rock-like materials under the impact of shaped charge jet was studied by numerical calculation method, and the impact splitting effect of metal rods of different shapes on rocks was calculated and compared. The formation of the shaped charge jet and the fracture process of rock penetration were analyzed using numerical simulation calculation, and the optimal shaped charge structure and blasting height for splitting were obtained. In the experiment, two shaped charges were used to successfully split the rock according to the design direction, the peak rock surface stress obtained from the test were approximately 0.5-0.8MPa which proved the comprehensive cutting effect of prefabricated cracks and multi-point impact splitting of rocks. The results show that the blasting height at 25mm can form a wedge metal rod with a length diameter ratio of about 1:3, and produce a better directional splitting effect after multi-point impact of the rock with prefabricated cracks, which reduces the non-effective energy dissipation of explosives, and provided a new method for the directional blasting and splitting of rocks to achieve precise boundary control in the construction of mass rock excavation.
Abstract:
Ultra High Performance Concrete (UHPC) is a new type of protective material with both ultra-high strength and ultra-high toughness can be adopted as an ideal material in the impact resistant design of structures. In this paper, the impact resistance of 160MPa UHPC was investigated experimentally by conducting the high-speed projectile penetration tests which launched by the 30mm-diameter, smooth-bore powder gun at the striking velocities 216 m/s and 350 m/s. The test results show that with the increase of projectile velocity, the penetration depth and crater diameter increase obviously. The MAT_RHT is implemented into finite element package LS-DYNA for UHPC. In order to verify the accuracy of the material model, split Hopkinson pressure bar (SHPB) testing results are used to validate 3D finite element material model. With the validated numerical model of UHPC, Numerical studies are conducted to simulate the projectile penetration process into UHPC targets with the assistance of a computer program LS-DYNA. The numerical results in terms of the depth of penetration and crater diameter are compared with the experimental results. In addition, parametric studies are conducted to investigate effects of UHPC compressive strength, projectile mass, projectile striking velocity, projectile diameter and projectile caliber-radius-head (CRH) ratio on the depth of penetration of UHPC targets. Moreover, an empirical formula to predict the depth of penetration is derived according to the simulated data.
Abstract:
Damage elements such as high-speed shaped charge projectile and strong discontinuous shock wave are generated during the process of the shaped charge associated with the underwater explosion. The theory of the action time sequence of the shaped charge projectile and the shock wave should be improved because their action time is close. Therefore, it is of great significance to investigate the action time sequence of different loads and their damage into ship structures. First, the basic form of acceleration and velocity equations are deduced in the formation process of the shaped charge projectile, based on contact explosion theory and Newton's second law. Subsequently, based on the Eulerian control equations, numerical models of air and water explosions of shaped charges are established. The evolution of pressure at the interaction of the charge and the liner is obtained. The acceleration and velocity equations of the shaped charge projectile are given quantitatively in this manuscript as a result. Besides, the obtained theoretical formulation can be utilized to solve the problem of the action time sequence of the shaped charge projectile and direct shock wave. In order to verify the reliability of this theoretical formulation, the case that the air cavity length is five times of the charge radius is conducted. The numerical results are in general agreement with those of the theoretical derivation. The results show that when the length of the air cavity is five times of the charge radius and the stand-off distance is larger than three times of the charge radius, the shock wave precedes the shaped charge projectile. The basic form of theoretical formulas is presented for the acceleration and velocity of the shaped charge projectile. Besides, the idea of solving the action time sequence problem of these two loads, which provides a theoretical basis for analyzing the action time sequence of underwater explosives.
Abstract:
Accurate predictions of the penetration depth and critical perforation thickness of earth penetration weapons into concrete materials are key issues in the field of protective engineering. However, the widely-used formulas have limited predictive accuracy for penetration depth when earth penetration weapons have a large diameter and a high aspect ratio, and are lack of theoretical basis for critical perforation thickness. To resolve the two issues above, the engineering calculation models of rigid projectile penetrating and perforating into concrete targets are investigated in this paper on the basis of 145 sets of penetration data and 32 sets perforation data. Firstly, based on the resistance analysis of rigid projectile penetrating into concrete target, a two-stage resistance model is proposed, and then a practical calculation model of penetration depth with the consideration of scaling effect is proposed. The reliability of the proposed model is verified by comparing with 15 sets of penetration data with large diameter and high aspect ratio and the predictions by widely-used ACE formula and NDRC formula. The results show that the average errors of the proposed formula, ACE formula and NDRC formula are 5.5 %, 15.7 % and 24.9 % respectively. Secondly, based on the assumption that the scabbing is caused by the tensile failure of concrete, a formula for the scabbing height is derived based on the force equilibrium. Then the formulas for the critical perforation thickness, ballistic limit and residual velocity are deduced, which are validated by the relevant experimental data. The proposed calculation models can provide reliable reference for engineering design.
Abstract:

To investigate the sympathetic detonation (SD) response and protection method of shell explosive in the packaging box, the sympathetic detonation experiment of JHL-2 (RDX/Al/binder = 65.5/30/4.5) explosive charges in the packaging box was carried out. The response of the acceptor charges was characterized by the residual of explosive and the breakage of the shell. A calculation model for the sympathetic detonation of shell explosives in packaging box was established, and the numerical simulation of the sympathetic detonation experiment was carried out by using the nonlinear finite element method. The calculation model was verified to be reliable according to the test results. The result of the simulation study show that the main cause for SD of charges in packaging box is the impact of high-speed fragments. According to the experiment result, simulation result and the fragmentation impact initiation criteria of explosive charge, the anti-sympathetic detonation design was implemented for the packaging box. The anti-sympathetic detonation design considering weight and price is as follows: 20 mm wooden partition was set in the adjacent explosive charge, and 2 mm aluminum partition was set at the bottom of the packaging box. A new sympathetic detonation experiment was performed with anti-sympathetic detonation modifications on the packaging box included. The results show that under the unprotected condition, two acceptor charges in the same packaging box with the donor charge and one acceptor charge in the packaging box below the donor charge detonated, and one acceptor charge in the lower packaging box didn’t react; when 20 mm wooden partition was set between adjacent charges and a 2 mm aluminum plate was set at the bottom of the packaging box, only one of the acceptor charges adjacent to the donor charge had a reaction from deflagration to explosion level, and the other three acceptor charges did not react. The research result proves that the installation of partitions inside the packaging box can effectively reduce the possibility of sympathetic detonation, so as to avoid the disastrous consequences caused by sympathetic detonation.

Abstract:
In order to investigate the anti-explosion performance and post-blast reinforcement and repair performance of precast concrete (PC) columns under close-in explosion, the explosion test of full-scale PC column and axial compression test of repaired blast-induced damage PC column were conducted. The PC columns with the two widely used assembly connections, half grout sleeve connection and slurry anchor lap connection, were selected to investigate the effect of connection type on blast resistance and to compare the damage and dynamic response with the reinforced concrete (RC) column of the same specification. The explosion test results show that PC columns show a local damage failure mode. The concrete spall and oblique cracks occur near the explosion center appear and penetrating cracks appear at the interface of the assembly position. The damage of the anchor slurry lapped PC column is more severe than the grouting sleeve PC column. The PC columns of the two assembly forms have comparable dynamic response and damage characteristics as the RC column in general, but the assembly interface weakens the integrity and shear resistance of the PC column because of its discontinuity. It is the typical weak position of the PC column and should be noticed in design and protection. The axial compression test results show that the axial bearing capacity of the PC column repaired by concrete replacement exceeds 20.8 % and 30.6 % compared to the undamaged RC column test value and the calculated value of the same specification respectively. The exceeding proportion of the PC column repaired by concrete replacement and wrapping continuous fiber reinforced polymer (CFRP) sheet is 38.3% and 49.6% respectively. The results show that it is feasible to reinforce and repair the damaged PC column using the concrete replacement or combining concrete replacement with the wrapping CFRP sheet method, which can meet the requirements of axial bearing capacity.
Abstract:
The loading technology of cosine distributed load by chemical explosion is the main method for evaluating the dynamic response of space structures under the irradiation of high-altitude nuclear explosions with soft X-rays. In order to meet the design requirements of complex configuration, high synchronicity and low specific impulse load in the structural assessment of new space vehicles, a loading method of discretely distributed sheet explosives synchronously detonated by a Mild Detonating Fuse (MDF) network was proposed. In terms of experimental research, the cross-shaped sheet explosive made by stacking explosive strips with a cross-sectional size of 0.33 mm × 0.5 mm can be directly detonated by a MDF with a diameter of 0.5 mm. Compared with strip distribution, the space uniformity of cross distribution was improved by 76.7%. A high-speed camera was used to record the shock wave luminescence during the detonation process. The results showed that the detonation rate of the 21-point MDF detonation network reached 100%, and the detonation
Abstract:
To study the explosion characteristics of the elliptical cross-section penetrator, the static explosion experiment was designed and carried out. The penetrator with a mass of 255 kg was erected on a wooden cartridge, the centroid height was 2 m from the ground, and the test fuse was used to detonate the penetrator explosive. The aerial drone was used to record the whole explosion process in real time, the sector effecting steel plates were arranged in the major and minor axis directions to obtain the number and perforation rate of fragments, and the shock wave overpressure at the distance of 7 m, 10 m, and 12 m from the penetrator axis was measured. The macroscopic scene and the characteristics of fireball, fragment, and shock wave overpressure after explosion were analyzed in detail. Results show that the evolution morphology of the fireball and the fragment distribution area are symmetrically distributed with respect to the major axis and minor axis. The evolution of fireball can be divided into rapid growth stage, high temperature stability stage and free diffusion stage. The fireball size reached its maximum at 41.7 ms after explosion, and the maximum size in the minor axis and major axis directions was 21.86 m and 19.29 m, respectively. Additionally, the fireball size in the major axis direction had obvious secondary expansion. The fragments in the minor axis were small in size, large in number, and strong in perforation, while the fragments in the major axis had the opposite characteristics. The overpressure peak value, impulse, and velocity of shock wave decrease with the increase of propagation distance. Based on the experimental results, it can be concluded that the non-axisymmetric structure and non-uniform wall thickness of the elliptical cross-section penetrator have a great influence on the explosion characteristics, which is the morphology of the non-axisymmetric distribution of the fireball and fragments.
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Abstract:
Explosion tests on the ground surface was carried out in calcareous sand and silica sand. The propagation laws of the blast wave of two kinds of sands were studied, including peak pressure, elastic wave and plastic wave velocity, rising time of pressure and cater. The result show that cater produced by surface explosion in calcareous sand has smaller size than in silica sand, and the diameter and depth of cater are positively correlated with the explosive charge. The elastic velocity in calcareous sand is 236m/s to 300m/s, and in silica sand is 218m/s to 337m/s, and the elastic wave and plastic wave velocity increase with the increase of the explosive charge. As the scale distance increases from 0.329m/kg1/3 to 1.154 m/kg1/3, the rising time of the blast wave pressure in calcareous sand increases from 0.17ms to 0.81ms. In silica sand, pressure rises in a short time, and the range is 0.07ms to 0.09ms, which is much less than in calcareous sand. The attenuation coefficient of calcareous sand with low moisture content is 2.86, and 2.79 for silica sand. This study can provide a reference for the study of dynamic mechanical properties of calcareous sand.
Abstract:
FRP-concrete-steel double skin tubular columns (FRP-DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them infilled the concrete. This type of members has been applied in bridge piers, and the impact resistance is an important index for its utilization. Therefore, based on the previous test, the finite element analysis (FEA) models considering the coupling of axial and impact loads were established using ABAQUS software and verified by comparing the simulation and test results. In the model, the static implicit and dynamic explicit analysis were coupled by using “Restart” and “Import” commands. In addition, the strain rate effect of the steel and concrete were considered. Firstly, the mechanism of impact resistance under coupling axial and impact loads was analyzed. Then, the influence of thickness and fiber orientations of FRP, axial-load ratio, impact velocity, hollow ratio, diameter thickness ratio of steel tube and material strengths on the impact resistance were investigated. Finally, the formula used to predict the dynamic increase factor (δDIF) of the plateau impact force under coupling axial and impact loads was suggested. Results indicate that the deformation pattern of FRP-DSTCs mainly presents flexural deformation, and the plastic deformation of concrete is the main energy dissipation mechanism of such members. The outer FRP can significantly improve the lateral impact resistance of the specimen, and increasing the number of FRP layers leads to enhanced impact resistance. Additionally, the axial load has an obvious effect on the impact resistance, and the effect is negative when the axial load ratio exceeds 0.7. The diameter thickness ratio of steel tube presents marginal effects on the impact resistance. The proposed formula that considers the hollow ratio, strengths of concrete and inner steel tube, thickness of FRP, axial load ratio and impact velocity can reasonably predict the impact bearing capacity of FRP-DSTCs.
Abstract:
This study carried out dynamic split tests with strain rate in 1.72~7.42 s-1 for UHPFRC discs with fibre volume fraction in 0~3% by a split Hopkinson pressure bar. The surface crack propagation process was captured by a high speed camera and the images were analyzed by digital image correlation (DIC) for strain evolution. Micro X-ray computed tomography (μXCT) scanning of specimens before and after tests was also conducted and the 3D images with a voxel resolution of 56.7 μm were processed to obtain statistical data of pores and fibres and investigate failure mechanisms. The results show that: (i) the addition of 1~3% steel fibres increased the static and dynamic splitting strength by 84~131% and 47~87%, respectively. The dynamic increase factor (ratio of dynamic to static strength) was 1.07~1.72; (ii) DIC strain images showed that the fibres led to more dispersed cracks, slower crack propagation, higher energy consumption and higher ductility; (iii) The μXCT image analysis showed that the fibre volume fraction was 1.04~2.47%, consistent with the designed proportion. The porosity was 0.98~1.71%. More fibres reduced the porosity and the number of pores, but increased their average volume and equivalent diameter. The increase of crack-bridging fibres reduced the volume and width of main cracks and increased the surface roughness and the relative surface area of cracks, resulting in increased strength, energy dissipation, toughness and ductility of specimens. The research data are useful for improvement of dynamic design guidelines and optimization for UHPFRC materials and structures.
Abstract:
Abstract: In the numerical simulation study of Ultra-High Performance Concrete(Ultra-High Performance Concrete, UHPC), reasonable determination of its constitutive model parameters is the basis of improving the calculation accuracy and design reliability. This paper determined the parameters of HJC constitutive model of UHPC based on uniaxial compression test, SHPB test and existing tri-axial compression test and so on. In the process of parameters determination, the parameters of HJC constitutive model were divided into five categories. The yield surface parameters were determined by the static failure surface equation. The parameters of state equation were determined by P-μ relation. Damage parameters were determined according to relevant literature. The basic physical parameters were determined according to the test and so on. LS_DYNA was used to simulate the explosion test of the one-way slab. Firstly, the finite element model of the one-way slab was established. The HJC constitutive model was used for UHPC, and the linear reinforcement model was used for reinforcement material. The reinforcement and UHPC were connected by common joints. The air and explosive models were established, and the fluid-solid coupling method was used for calculation. By comparing the simulation results with the damage degree and the maximum deflection of the one-way slab in the test, the effectiveness of the determined parameters was verified. In order to further understand the anti-blast mechanism of UHPC members, the determined parameters were used to conduct numerical simulation research on the one-way slab explosion condition, and the influence of reinforcement and size effect on the explosion result was analyzed. Results show that during the explosion process, the maximum mid-span deflection of the one-way slab can be reduced by increasing the longitudinal reinforcement ratio, and the length of oblique cracks on the side of the one-way slab can be reduced by properly encrypted stirrups. UHPC one-way slab has obvious size effect, and the variation of thickness and length has the greatest influence on the explosion result.
Abstract:

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

Abstract:
Under the threat of terrorism attacks and military strikes, building columns of the perimeter frames are likely to suffer near-field near-ground explosion. To rapidly assess the dynamic responses and failure modes of the building columns under such blast scenarios, in this paper numerical simulation method is employed to investigate the distribution pattern of the shock waves on the front face of building columns under near-field near-ground blast scenarios, and a corresponding simplified blast load model is proposed. To this end, firstly, the existing experimental data of overpressure and impulse are selected to validate the numerical model for blast load. Then, a typical numerical model under near-field near-ground blast scenarios is established to study the effects of the scaled distance and scaled height of the spherical charges on the characteristic values of the shock waves acting at the building columns. Finally, formulae for the maximum reflected impulse and the representative value of the positive overpressure duration are derived based on regression analysis, and the blast load at each location of the column front face is represented by an equivalent triangular load model. The results indicate that when the scaled height of the charge is less than 0.3 m/kg1/3, the distribution of the maximum reflected impulse along the column length can be represented as a trilinear model and a bilinear model for the scaled distance of 0.4 m/kg1/3-0.6 m/kg1/3 and 0.6 m/kg1/3-1.4 m/kg1/3, respectively. Moreover, under a given scaled distance and a scaled height, with increasing the charge weight, the peak reflected overpressure remains constant but the maximum reflected impulse is proportional to the cubic root of the charge weight at the locations with the identical scaled height of the column.
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Abstract:
Based on high-speed photography technology, the oblique water-entry experiments of high-speed projectile under multiple conditions are carried out. During the experiment, five experiments were conducted for each condition, and the same phenomenon appeared in the experiment. A self-programing is utilized to capture the image’s pixels and extract the experimental data for the experimental photographs. By analyzing the formation, development, and collapse processes of the oblique water-entry cavity of high-speed projectile, the evolution characteristics of projectile cavitation during tail-slapping are concluded. In addition, by comparing and analyzing the variations of the cavity size, and the velocity and acceleration of projectiles with different initial velocities of the water-entry of the projectile, the influence of the initial velocities of the water-entry of the projectile on cavitation evolution characteristics and water-entry motion traits is summarized. The results show that after the tail-slapping of the projectile, part of the projectile tail penetrates through the original cavity and gets wet, and a new tail-slapping cavity is generated backward from the projectile tail. The tail-slapping cavity fits closely with the original cavity. At the end of the tail-slapping, the location of the tail-slapping cavity under the water is basically unchanged. The tail-slapping cavity is pulled away from the surface of the original cavity of the projectile and collapses, while the original cavity at the same depth accelerates and collapses under the influence of the jet generated by the tail-slapping. With the increase of the initial velocities of the water-entry of the projectile, the size of the tail-slapping cavity and the length of the original gradually increase, and so does the maximum wet area of the tail. With the increase of the number of tail-slapping, the velocity attenuation amplitude and the energy loss of the projectile in each tail-slapping increase, and the capacity of the speed storage of the projectile decreases.
Abstract:
The failure law of shallow-buried reinforced concrete straight wall arch structure in soil under secondary explosion of conventional weapons was studied by explosion test and numerical simulation. Test structure adopts scale model based on similarity principle. Three groups of six shots were set up in the test. LS-DYNA is used to simulate the three groups of working conditions. By comparing the pressure of the measuring point in the soil, the speed of the structural measuring point, the structural deflection and other data, it is found that the simulation results are basically consistent with the experimental results. After comparing the numerical simulation results with the test, the numerical simulation conditions of the secondary explosion are expanded. When the comparison verifies that the numerical simulation is consistent with the experimental results, the secondary explosion conditions under the action of conventional weapons are simulated to study the dynamic response of structures under repeated impacts. Through calculation, it is found that when the proportional distance is set between 0.6 m/kg3 - 0.4 m/kg3, the damage of the structure is mainly caused by the overall damage. Combined with the macroscopic description of structural damage and the maximum deflection span ratio, the damage grade of the structure under the overall effect is divided. By discussing the initial damage of the structure and the failure law of reinforced concrete straight wall arch structure under different explosion sequences, the following conclusions are obtained: When the structure is damaged by explosion, such as cracking and bending, some concrete is out of work due to cracking or entering plasticity, resulting in the change of stiffness of the structure. The final damage degree of the structure is affected by the strike sequence, and the effect of initial explosion on the final damage of structure is greater than that of secondary explosion.
Abstract:
With the development of the times, the demand for explosion-proof and impact resistant materials in the military and aerospace fields is increasing. As a traditional energy absorption and shock absorption protective material, polyurethane needs higher dynamic mechanical properties. One way to effectively improve the impact resistance of polyurethane materials is to add ceramic balls as reinforcing phase to polyurethane matrix. At present, the main research on ceramic ball reinforced materials is focused on the nano and micron size, and most of them are static mechanical properties and anti penetration properties. In order to study the effect of millimeter ceramic balls on the impact resistance of polyurethane composites under explosion load, the dynamic response of multi-size Al2O3 ceramic balls reinforced polyurethane matrix composites under small equivalent explosion load is simulated based on the ALE algorithm of LS-DYNA, and the deflection, velocity, acceleration The effects of appropriate explosion equivalent and ceramic ball size on the properties of composites were explored by absorbing energy and other parameters, and the correctness of numerical simulation was verified by using henrych's empirical formula of explosion overpressure in free field. The conclusions are as follows: the deflection of the center point of the back wave surface of the composite plate is smaller than that of the surrounding point within a certain time, and the velocity also shows the same trend; The acceleration of ceramic ball and polyurethane always keep the opposite direction, and the existence of ceramic ball reduces the amplitude of overall acceleration oscillation; With the increase of explosion equivalent, the deflection / velocity of the composite increased steadily and the energy absorption efficiency of polyurethane increased continuously; At the same area density, the smaller the ceramic ball size is, the stronger the deformation resistance of the composite plate is, the lower the sensitivity to the change of impact load is, and the overall acceleration fluctuation range becomes larger.
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Abstract:
A three-dimensional finite element (FE) model was developed to quantify the effect of attack angle on the penetration resistance of aramid laminates having varying thickness against flat-nosed projectile. The model was created through a macroscopic approach, which did not take into account the internal microscopic structure of the laminate and macroscopically equated each laminate as a homogeneous orthotropic anisotropic material. The validity of FE simulation results was compared with existing experimental data, with good agreement achieved in terms of residual velocities of the project and damage patterns of the aramid laminates. The validated FE model was subsequently employed to simulate the ballistic responses of 4 mm, 8 mm, and 16 mm target plates in the range of 0° ~ 30° attack angle. The residual velocity of the projectile, energy absorption rate of target, ballistic limit, and perforation energy threshold were calculated to characterize the ballistic performance of aramid laminates. By comparing the damage patterns of the aramid laminates and the contact forces applied to the project under different conditions, the mechanical mechanism by which the attack angle affected the ballistic performance of the aramid laminate at different impact velocities and different target thicknesses was explained. Within the studied working conditions, obtained results revealed that: the attack angle affects significantly the ballistic performance of aramid laminates, depending upon projectile impact velocity and target thickness; the ballistic limit and perforation energy threshold decrease with increasing attack angle, and the degree of such decrease is reduced as target thickness is increased; the residual velocity of projectile increases with increasing attack angle when the impact velocity is close to the ballistic limit and decreases with increasing attack angle when the velocity is well above the ballistic limit; the influencing mechanism of attack angle on ballistic
Abstract:
Polymer material has the characteristics of fast forming and good expansion performance. Its composite structure with gravel and reinforcement has obvious advantages in foundation treatment and urban road void removal and reinforcement. In this paper, polymer gravel slab and reinforced polymer slab were designed and manufactured, and experimental research under contact explosion impact was carried out. The damage characteristics of the two kinds of slabs were studied through the damage size and the measured shock wave data. Based on ANSYS / AUTODYN nonlinear explicit finite element program, the damage mode and damage diameter of reinforced polymer slab were studied, and compared with the test results to verify the accuracy and applicability of the established finite element model. The sensitivity of reinforced polymer slab to explosive quantity and slab thickness was analyzed parametrically, and the prediction formula of failure diameter of the top surface and bottom surface of reinforced polymer slab was put forward by using the multi-parameter regression analysis method. The results show that under the action of air contact explosion, the damage mode of polymer gravel slab is mainly local collapse and perforation at the contact part. Under the impact load of contact explosion, there are punching and cutting explosion pits on the top surface of the slab, tensile failure and collapse area on the bottom surface, and a through failure hole is formed in the center of the slab, in addition to some damage cracks; Under the action of air contact explosion, reinforced polymer slab mainly occurs crater damage on the top surface, spalling damage on the bottom surface and central punching perforation damage. The reinforced polymer slab has a good attenuation effect on the explosion shock wave. The diffuse reflection effect of the closed bubble in the polymer structure on the shock wave can absorb more energy to alleviate the explosion shock wave, which further shows that the polymer has the potential to be applied to the field of anti-explosion shock protection.
Abstract:
To study the ignition behavior of micro-mesoscopic hot spots in the matrix of pressed PBXs under GPa, 10μs-level slow-front ramp wave loading, a ramp wave loading device driven by non-shock initiation reaction of heavily constrained pressed PBX explosive was designed. The burning rate model of laminar combustion and the self-compiled two-dimensional axisymmetric finite difference program were used to analyze the characteristics of the pressure wave output by the device, the influence of the crushing degree of the donor explosive during the combustion process and the structural parameters of the device (the thickness of the case and the partition) on the output pressure wave were discussed. The calculation results show that the combustion specific surface area formed by the crushing of the donor explosive is the key factor affecting the pressure evolution of the non-shock initiation reaction. With larger combustion specific surface area comes greater ramp wave pressure. The ramp wave pressure can reach above GPa, and the corresponding rising front of the pressure wave can be reduced from tens of milliseconds to several milliseconds. The thickness of the case of the donor explosive, that is, the strength of constraint, has a significant effect on the pressure during non-impact initiation reaction. As the thickness of the interlayer increases, the output ramp wave pressure decays approximately exponentially. According to the calculation results, the structure design of the device was completed, and the ramp wave loading experiment was carried out on the tested PBX. The pressure at the incident interface of the tested explosive measured by PVDF is 1.6GPa, and the front of ramp wave is 25μs, which preliminarily proved the feasibility of realizing GPa, 10μs-level ramp wave pressure output by using the non-shock initiation reaction of heavily constrained pressed PBX explosives.
Abstract:
On the premise of good crushing effect, reducing the rock mass vibration above the bottom of the upward fan-shaped deep hole by reducing the peak pressure of the shock wave at the bottom of the hole is an effective measure to reduce the vibration and protect the superstructure. In order to determine the reasonable length of the air column at the bottom of the hole, the variation law of the length of the air column on the impact pressure of the hole wall when the air at the bottom of the hole is not coupled is studied by combining the theoretical research with the field model blasting dynamic test. Based on the theories of one-dimensional unsteady hydrodynamics and theoretical detonation physics, The action process and propagation law of shock wave in the blast hole after the explosion of bottom air interval charge column under the condition of cylindrical charge are discussed in stages. Considering the reflection and transmission of shock wave at the interface of different media, the parameters of shock wave front propagating in different directions and the initial shock pressure and action time acting on the hole wall in each stage are analyzed, Thus, the calculation formula and variation curve of pressure acting on the hole wall in each stage are obtained. In order to verify the above laws, six groups of 12 cylinder thick wall concrete models with different sizes were designed and made, and the bottom air interval blasting model tests were carried out. The air column lengths were 200mm, 400mm, 600mm, 800mm, 1000mm and 1200mm respectively. During the blasting process, the blast ultra high-speed multi-channel dynamic strain testing system was used to monitor the hole wall impact pressure, analyze the monitoring data and verify with the theoretical results, Finally, the variation curve of axial decoupling coefficient and hole wall impact pressure with time under the condition of uncoupled charge in air interval at the bottom of blast hole is obtained; Based on the dynamic compressive strength of rock, the reasonable length range of bottom axial air interval suitable for soft, medium and hard rocks is determined. In order to verify the rationality of the conclusion, the field industrial test is carried out, the charging blasting is carried out by using the air interval at the hole bottom, and the observation and photo analysis of the roof forming and blasting pile size after blasting are carried out. The research results show that the existence of air interval significantly increases the action time of impact pressure, The peak value of impact pressure decreases obviously; When k = 1.5 and the length of air column is 200mm, the attenuation ratio of peak pressure at the hole bottom is 73.4%; when k = 4 and the length of air column is 1.2m, the attenuation ratio of peak pressure at the hole bottom reaches 96.7%. When the air compartment is greater than 60cm, the area with low pressure value appears at the bottom of the blast hole. The reasonable bottom air interval length can not only ensure good blasting fragmentation, but also reduce blasting vibration by reducing the peak pressure at the hole bottom, so as to protect the stope roof and other protected objects.
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In order to obtain the material constitutive model parameters of polymethyl methacrylate (PMMA) in the numerical simulation of explosive cutting, and to avoid the multiple tests required by the traditional method of obtaining the material constitutive model parameters, a neural network-based inversion method of the Johnson Holmquist Ceramics (JH-2) constitutive model parameters of PMMA was established. Firstly, a 2.5-mm-wide linear shaped charge was used to cut 14 mm PMMA flat plate, and the results of the explosive cutting test were analyzed to classify and quantify the damage of PMMA flat plate into three kinds of damage data: penetration depth, impact fracture thickness and spallation damage thickness. Based on the empirical parameters of the JH-2 constitutive model obtained from the explosive cutting experiments and existing studies, the adjustment interval of the constitutive model parameters was determined. LS-DYNA was used to simulate the process of cutting 14 mm PMMA flat plate with 2.5 mm wide linear shaped charge and to collect a flat plate damage data set containing the three kinds of damage data. A neural network model between the parameters of the PMMA flat plate constitutive model and the damage data was developed, and the model was trained using the plate damage data set. The inversion of the JH-2 constitutive model parameters of the PMMA flat plate was performed by the trained neural network model. In order to verify the reliability of the parameters obtained by the inversion method, a 4.2 mm wide linear shaped charge cutting 19 mm PMMA flat plate experiments and finite element numerical simulation were conducted, and the fracture characteristics and damage data of the PMMA flat plate in the calculation results were less different from the experiment results, indicating that the JH-2 constitutive model parameters obtained by the inversion can be better applied to PMMA flat plate explosive cutting numerical simulation. The parameter inversion method can obtain more accurate material constitutive model parameters with less experiments and tests than the traditional material parameter acquisition method.
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The physical mechanism of electrically exploding wires has caused much attention recently; fruitful experimental results have been reported by domestic researchers. Modeling and studying of the electrical metal wire explosion problems can help to understand the basic physics of Z pinches and other related magnetically driven plasma problems, and to evaluate the parameters of the state equation and electrical conductivity. A zero-dimensional (0D) dynamical model of the underwater electrical wire explosion is developed, in which the single wire is modeled as a plasma cylinder undergoing self-similar radial motion with uniform density, temperature and pressure, while its velocity varies linearly with radius. The kinetic equation and internal energy equation are derived from the hydrodynamic equations and used as the basic governing equations. To close the 0D model, other parameters are supplemented, with the real gas quotidian equation of state (QEOS) model for pressure and internal energy, the modified Lee-More electrical conductivity model for resistivity, and an external circuit model for the current density. The boundary conditions are constructed from the shock Hugoniot relations in water, the pressure at the wire boundary is assumed to be equal to the water pressure behind the shock. The calculations are carried out from a cold start of wires with density and temperature in laboratory status. Results of the 0D model are validated by comparing with the results from simulations of one-dimensional (1D) magneto-hydrodynamic (MHD) model and experiments. Examples of electrical explosion of copper wires in water are taken in the applications, the rise time of the short-circuit current pulse is 5μs and the wires vary from 50μm to 200μm in diameter. Results from the 0D-dynamical model agree well with the MHD simulation results and experimental data, typical discharging modes are achieved by varying the parameters of the wires. The 0D model can be used for parameters optimizing and data analysis in similar experiments.
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The dynamic response and failure of sandwich beams with gradient metal foam core subjected to high-velocity impact are studied experimentally. The impact resistance of five sandwich beams with different density gradient arrangements but the same surface density composed of three aluminum foams with different densities is analyzed. All the sandwich beams are simply-clamped. Combined with the quasi-static three-point bending tests, the impact resistance of the gradient sandwich beams is evaluated in terms of dynamic deformation and failure modes by considering the effects of core density gradient and impulsive intensity. The results show that the density gradient effect significantly influences the dynamic response and failure mode. The initial failure mode plays an important role in the structural response and the predominant energy absorption mechanism. Since the impact condition can not produce the local compression of the medium-density core, the initial failure mode of the uniform and negative gradient sandwich structures is the overall bending deformation, while the local core compression is the initial failure mode of the other structures with weak cores located in the first two layers. When the impulsive intensity is low, the gradient sandwich beam has superior impact resistance to the uniform counterpart. With increasing intensity, once a critical intensity is exceeded, the gradient sandwich beam shows low bending resistance to the uniform counterpart. Therefore, the optimal design of the core density gradient can efficiently improve the impact resistance of the sandwich beams under the high-velocity impact, which is a valuable reference for engineering applications.
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Dynamic triaxial cyclic impact experiments on the coal rock samples with the bedding angles of 0°, 30°, 45°, 60°, and 90°, respectively, were conducted using a 50-mm split Hopkinson pressure bar (SHPB) system to study the dynamic mechanical behaviors of the coal rock with characteristic bedding under complex ground conditions. A 3D profile scanner was utilized to quantify the fracture interface roughness and to investigate the bedding effect on the dynamic fracture process of the coal rock. The bedding angle effect and confining pressure effect on the dynamic properties of the coal rock were explored by combining dynamic parameters such as compressive strength, elastic modulus, energy distribution evolution with the fracture surface roughness variation. The research shows that when confining pressure is applied, the stress-strain curve of the coal rock has an elastic aftereffect. The dynamic compressive strength and failure strain of the bedding coal rock with confining pressure are respectively 3.9-4.2 and 2.59-3.05 times higher than those without confining pressure. As the bedding angle increases, the dynamic compressive strength, elastic modulus, and energy transmitted ratio of the coal rock display the U-shaped distribution, which decreases first and then increases, reaching the minimum at the bedding angle of 45°. Meanwhile, the energy absorbed ratio and fracture surface roughness show the ∩-shaped distribution, first increasing and then decreasing, and the damage variable shows the N-shaped distribution, reaching the maximum at the bedding angle of 45°. The failure of the coal rock with 45° bedding is the most serious, which is more prone to intergranular and spalling fractures. However, the 90° bedding coal rock is more likely to absorb energy and to form transgranular fractures, resulting in a large number of mesoscopic fractures. Variation of the damage characteristics of the coal rocks with bedding angle can be summarized as a tensile damage (0°)-shear damage (30°, 45°, 60°)-splitting damage (90°) evolution process. The relevant characteristic results obtained from the experiments can provide a theoretical support for the safe and efficient exploitation of coalbed methane resources in the complex environment under practical working conditions.
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In order to study the anti-penetration performance of concrete-filled steel tubular (CFST) with honeycomb structure, six experiments on anti-penetration of CFST with honeycomb structure were conducted by using 125 mm smooth bore gun. The failure pattern and penetration depth of target under different working conditions were measured, and the typical failure modes of CFST with honeycomb structure were analyzed. The difference of failure pattern of target under different ratio of target and projectile size were compared, while the influences of impact point and steel tube wall thickness on the anti-penetration performance of CFST with honeycomb structure were explored. Uniaxial compression tests on 7 groups of hexagonal concrete-filled steel tubular column with different wall thicknesses and 3 groups of hexagonal concrete column were carried out. The enhancement effect of the hexagonal steel tube on the strength and ductility of the core concrete under different wall thicknesses were studied, and the relationship between the strength enhancement coefficient of the core concrete and the hoop coefficient is obtained by data fitting. By refining the empirical formula for calculating the penetration depth of ordinary concrete, the formula for calculating the maximum penetration depth of CFST with honeycomb structure is given. The results show that the wall thickness is an important factor that affects penetration depth; that is, the greater the wall thickness, the smaller the penetration depth. The location of impact point has a great influence on the failure pattern of the target surface, but the influence of the location of impact point on the penetration depth is complex. The existence of steel tube can effectively increase the strength and ductility of core concrete. The refined penetration depth formula can predict the maximum penetration depth of the projectile to the CFST with honeycomb structure.
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To describe the dynamic mechanical properties of frozen sandy soil under active confining pressure, a dynamic damage constitutive model, which could consider the effect of active confining pressure on the dynamic strength and deformation characteristics of frozen sandy soil, was established by connecting a plastic body to the nonlinear Zhu-Wang-Tang model. The effects of damage parameters on the characteristics of stress-strain curves, yield point, peak stress, and peak strain were analyzed. In addition, the model parameters were determined based on the dynamic test data of frozen sandy soil. The applicability and accuracy of the established model were verified by comparing the model with the test data and analyzing its prediction errors under different test conditions. The results show that the damage parameters have no significant effect on the elastic stage and yield point of the dynamic stress-strain curves. However, it significantly affects the plastic and failure stages. The stress-strain curves predicted by the established constitutive model are in good agreement with the test results. The model is appropriate in predicting the characteristics including large portion of the plastic stage and obvious yield point caused by active confining pressure. Moreover, the model can also describe the enhancement effect of confining pressure on the dynamic compressive strength of frozen sandy soil. The predictions of the model on the peak stress and yield stress are better than those on the peak strain and yield strain under different negative temperatures and active confining pressures.
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To investigate the standoff distance of underwater explosions on the damage to gravity dams and to explore whether there is an “optimal standoff distance,” a numerical model of a fully-coupled explosive-water-air-gravity dam was established. The numerical model was validated by comparing it with centrifuge test results. The results demonstrated that the employed numerical model could predict the dam failures and the effect of bubble pulse well. Then, a numerical scheme including 60 numerical calculations was designed. In these calculations, the water depth is 600 mm, the explosive mass is 2.2 g, and the geometrical scaling factor of the gravity dam model is 1/80. The detonation depth ranges from 50 to 250 mm with five detonation depths. Each detonation depth corresponds to 12 standoff distances ranging from 10 to 200 mm, with the scaled standoff distance ranging from 0.077 to 1.54 m/kg1/3. The damage degrees to the gravity dam under underwater explosions with different standoff distances are compared. Quantitative comparisons of dam average damage, element erosion rate, stress, and strain are also presented. The results show that for the overall structural failure of the gravity dam, such as the structural bending-induced tensile failure, there is an “optimal standoff distance” for the damage effects of underwater explosions on gravity dams, that is, with the increase of standoff distance, the damage degree of gravity dam increases first and then decreases. The quantitative results also indicate that with the increase of standoff distance, the average damage of the damaged area in the dam upstream face, the element erosion rate, the average value of the maximum tensile stress of the dam heel, and the average value of the maximum tensile strain of the dam heel all increase first and then decrease, and reach their maximum values around a standoff distance of 40 mm. With identical water depth, explosive mass, and geometrical model of gravity dam, the “optimal standoff distances” for the damage effects of near-surface underwater explosions at five different detonation depths on the gravity dam are all near 40 mm. It suggests that for near-surface underwater explosions, the detonation depth owns limited influence on the “optimal standoff distance.”
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It is a developing trend of protection engineering to use high resistance materials such as ultra-high performance concrete to construct bullet-shielding structures. The phenomenon of projectile body rebound was found in the test of projectile body penetrating ultra-high performance concrete. Projectile rebound effect is very important in the study of engineering protection, weapon damage and warhead design. In order to study the rebound velocity of projectile body after penetration and its influencing factors, the stress of projectile body from penetration to rebound was analyzed. Based on the expression of penetration resistance given by cavity expansion theory, a one-dimensional elastic bar potential energy model was established from the perspective of the accumulation of deformation energy by penetration resistance, and a one-dimensional stress wave model was established from the perspective of stress wave generated by penetration resistance. The analytical solutions of the rebound velocity were derived from the two models respectively, and the physical quantities affecting the rebound velocity were analyzed. Through numerical simulation, the rebound phenomenon of the projectile body after penetrating the ultra-high performance concrete is reproduced, and the numerical results of the rebound velocity agree well with the two analytical solutions. Through numerical calculation of the same penetration model with different material parameters, the relationship between the rebound velocity and the material parameters in the analytical solution is verified, and the reliability of the theoretical model is proved. The results show that the projectile body accumulates deformation potential energy due to penetration resistance, and the projectile body bounces back due to the release of deformation potential energy after penetration. The initial rebound velocity is independent of the target velocity, proportional to the target material, yield strength and warhead shape coefficient, and inversely proportional to the elastic modulus and density of the projectile body. The results can preliminarily predict the rebound velocity and provide a reference for the design of ultra-high performance concrete protective structure and warhead.
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In order to understand the effect of initial void ratio on the thermal phase transformation and ignition response characteristics of HMX based PBX-3 in slow cook-off condition, it has been designed and conducted a series of experiments of confined PBX-3 with initial void ratio of 1.0%, 4.2% and 13.8% during slow cook-off test. For each test, the PBX-3 sample composed of two cylindrical pieces of explosive, 25mm in diameter and 10mm in height for each, were stacked. The temperature was monitored by the five small size Type K thermocouples, 0.25mm in width and 0.15 mm in thickness for each, among which four were arranged at the different positions in the interior of the PBX-3 and one was positioned on the surface of the shell. The experimental apparatus was positioned in a slow cook-off chamber with a transparent glass cover. The slow cook-off setup was heated to 150℃ within 30 minutes, followed by a 45-minute soak at 150°C, and then heated at 0.25℃/min until thermal explosion occurred. During the process, the temperature of different location inside of explosive and surface of shell were acquired. The process of HMX phase transition, the mechanism of the effect of initial void ratio on HMX phase transition and the effect of HMX phase transition process on the thermal explosion temperature were analyzed in detail. The result shows that the smaller the initial void ratio is, the greater the thermal stress the PBX-3 is subjected to when it is heated to the HMX phase transition temperature, which delays the transformation process of β-HMX into δ-HMX during slow cook-off. Due to the higher thermal sensitivity of δ-HMX, the slower the phase transition process of HMX in the slow cook-off is, the slower the heat accumulation resulted from the δ-HMX exothermic decomposition reaction, and the higher the confined shell temperature at the time of thermal explosion.
Abstract:
The complex terminal ballistic parameters of the warhead will affect the circumferential propagation law of the near ground explosive wave and the damage degree to the target. Studying the propagation law of the near ground explosive wave of the cylindrical charge has important engineering significance to accurately evaluate the damage efficiency. By using AUTODYN-3D software, the near ground explosion of cylindrical charge with different terminal ballistic parameters is simulated and calculated, and the data of shock wave pressure in the front, back and side directions produced by the near ground explosion of cylindrical charge are obtained by modeling in two directions respectively. Thus, the influences of four parameters, namely, the velocity of the battle group, the impact angle, the height of the explosion center and the ratio of the length to diameter of the charge, on the propagation of the shock wave produced by the near ground explosion of the cylindrical charge are studied. The evolution process of the shock wave, the peak pressure and the height of the Mach stem are analyzed. The results show that the height of the explosion center is the main factor affecting the height of the shock wave Mach stem during static explosion, and the impact angle and the length-to-diameter ratio of the charge are the main factors affecting the difference in the height direction of the Mach stem. During dynamic explosion, the height of circumferential Mach stem can be increased, especially in the front; in addition, the peak value of forward shock wave increases linearly with the increase of dynamic detonation velocity. The results of orthogonal optimization show that the dynamic detonation velocity has the largest range to the front peak pressure of the cylindrical charge among the four variables; the impact angle has the largest range to the rear peak pressure; and the height of explosion center has the greatest influence on the height of Mach stem. By studying the circumferential propagation law of the shock wave produced by near ground dynamic explosion of the cylindrical charge, the results show that reasonable adjustment of the charge parameters and the front of the near ground explosion can be used for reference to achieve the maximum damage or reduce the hyper-pressure damage in a certain direction.
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To study the distribution of the impact energy of the coupled ground of underground explosion, the key is to obtain the experimental parameters of the volume of the crater compression zone under the coupling effect between the clay medium and explosion energy. To reveal the relationship between the distribution of the blast coupling ground impact energy in clay and the compression volume of the crater, 10.5 gTNT explosive spheres were used as the blast source, and blast tests under variable burial depth were conducted in a \begin{document}$\varnothing$\end{document}1500 mm×1490 mm layered blast test apparatus. The real volume of the crater under different burial depths was recorded by using three-dimensional scanning equipment, and the pressure data under different distances from the blast center were measured by earth pressure sensors to obtain the blast wave propagation law. Meanwhile, the law of energy distribution of coupled ground impact was theoretically revealed, which is proportional to the volume of medium damage. Three conversion relations of coupling coefficient were given, and the coupling coefficient curve of clay was drawn using the Boltzmann function. The experimental results show that in the range of −0.056 m/kg1/3h ≤ 0.37 m/kg1/3, as the burial depth of the charge ratio increases, the attenuation coefficient increases, and the peak pressure of the blast core distance in the same design ratio also increases, and the share of the explosion impact coupling medium also increases with the increase of the charging ratio burial depth. This indicates that the increase of the charging proportion burial depth intensifies the effects of the explosion. This finding implies that the change in burial depth has a negligible impact on the energy of the explosion impact coupling medium. The critical depth of ground shock effect of compacted clay is about 0.55 m/kg1/3, which is slightly larger than the radius of underground closed explosion cavity. The experimental value of visible diameter is in good agreement with the corresponding ConWep predicted value. The macroscopic failure critical depth is about 1.46 m/kg1/3. Combined with the test results, the variation law of the energy distribution of explosion coupling ground impact in clay with the buried depth of the charge ratio is given, and the calculation method of the equivalent closed equivalent of underground explosion is established. This provides a load basis for underground engineering blast resistance research and structural design.
Abstract:
In order to control and prevent the safety risks caused by volatile gases during the storage and transportation of crude oil, the explosion limit of the ternary flammable gas mixture composed of volatile light hydrocarbons including CH4, C3H8 and C2H4 in crude oil was experimentally investigated in the 20 L spherical explosive device. The experiment was carried out at 20 °C and 0.1 MPa, and the method of partial pressure was used to distribute the gases. Taking the rise of pressure over 5 % as the criterion for explosion, each group of the experiments was repeated three times. Methods for predicting the explosion limit of the ternary flammable gas mixture based on Le Chatelier’s law and the model of one-dimensional laminar premixed flame in Chemkin were proposed, and the reliability of the two methods was verified by the experiment. The results show that the explosion limit of the ternary flammable gas mixture is always within the explosion limit of these three pure components, which tends to approach the explosion limit of a certain pure component with its increase. The influence of the three pure components on the upper explosion limit is more pronounced than on the lower explosion limit, and the effect of C2H4 on the upper explosion limit is particularly obvious than the other two pure components. Both methods of prediction are highly consistent with the experimental regularity. The prediction of the lower explosion limit by Le Chatelier’s law is relatively accurate. However, the deviation of the upper explosion limit increases with the raise of C2H4 due to its special characteristics of combustion, and the deviation decreases significantly after correction of Le Chatelier’s law; Although the prediction of the lower explosion limit in Chemkin, which predicts the lower explosion limit by calculating the laminar burning velocity near the lower explosion limit has a certain deviation, it’s within the allowable range of experimental deviations. Therefore, it can be used as a new method to predict the lower explosion limit of the ternary flammable gas mixtures, but the model of one-dimensional laminar premixed flame is not suitable for the prediction on the upper explosion limit.
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The calculation process of the break caused by the underwater close-range non-contact explosion of the ship is complex, involving many factors such as the hull frame, weapon charge, explosion distance and orientation, etc. the empirical formula is usually used in engineering practice. Based on the assumption that the ship is attacked by a "directional" warhead, the damage surface is approximately perpendicular to the damage axis, and the explosion process instantaneously meets the basic condition of approximate "energy conservation", the calculation method is given according to the assumption that the initial kinetic energy of the explosion shock wave and the plastic deformation energy of the structure in the explosion action area are equally transmitted. Considering the effect of the equivalent thickness of the hull shell plate attached with stiffeners on the resistance to shock wave damage, and using the basic principle that the ultimate strain of the hull plate under the action of explosion shock wave exceeds the dynamic ultimate strain of the plate, resulting in the cracking of the shell plate, the calculation flow of "two-step iterative method" is designed, and a simple and easy-to-use iterative calculation table is given. 768 sets of data are calculated for the damage of hull shell plates with typical thickness of 6 mm and 8 mm under the action of four typical charge equivalent shock waves, with a length of 5-20 m, an explosion distance within 11 M. By introducing the plane fitting equation, the applicability criterion of the calculation method is given by judging the similarity analysis of the section plane, and the applicable range of the calculation parameters is discussed to ensure that the "two-step iteration method" can objectively reflect the actual damage effect of the underwater short-range non-contact explosion. Combined with the calculation results of empirical formulas and the measured data of damaged ships, the method is verified. The practice shows that the "two-step iterative method" is easy for engineering practice and has good accuracy.
Abstract:
With the rapid development of air transportation, the safe usability of aviation fuel is extremely important. However, during the storage, transportation and use of aviation fuel, it is very easy to form steam because of its good fluidity and volatility. In case of leakage, it will quickly form a flammable mixture with the air in the cabin, and combustion and explosion accidents may occur in case of fire source, while the combustion and explosion parameters of aviation fuel may vary in different compartment structures. In order to understand and grasp the hazard of aviation fuel combustion and explosion in different structural cabins, a numerical simulation study of aviation fuel vapor combustion and explosion in various structural aviation fuel cabins is conducted by using CFD. The results show that when the premixed deflagration of aviation fuel vapor occurs in the closed aviation fuel cabin, the pressure changes are more uniform, the flame surface is spherical diffusion, and the combustion reaction mainly occurs on the flame surface. Under the conditions of this numerical simulation, the maximum combustion and explosion pressure of aviation fuel in the closed compartment without partition and the closed compartment with incomplete partition are 0.76 MPa and 0.74 MPa, respectively; that is, the special structures such as incomplete partition in the compartment have no significant effect on the maximum pressure generated by aviation fuel combustion and explosion. The existence of special structures such as diaphragms makes the air flow vortex in the cabin, increases the fuel consumption rate, and increases the propagation speed and pressure rise rate of the flame surface. The change of temperature distribution is highly consistent with the propagation process of the flame surface, while the combustion reaction mainly occurs on the flame surface. The mass fraction of fuel in the cabin is determined by the flame surface.
Abstract:
In order to investigate the combustion characteristics of a new aluminum-containing solid propellant, the ignition and combustion process of the propellant at elevated pressure for simulating the solid propellant rocket engine were systematically studied by using a variable power fiber-laser and optical diagnostic techniques. The near-infrared fiber laser was employed to ignite the propellant slices placed in a high-pressure optical tank which was designed and manufactured for simulating solid propellant rocket engine conditions. The successive images of the laser-ignition and combustion process were captured by a high-speed camera while the optical emission spectroscopy was recorded with fiber-based spectrometers. Therewith, the regression rate, the ignition delay, and agglomerate particle size of the propellant were determined from the quantitative measurement and analysis of the former, likewise, the combustion temperatures were deduced by the latter. Accordingly, the maximum combustion temperature, the magnitude of the ignition delay, and rules of regression rate were mastered, as well as their dependence on laser power and ambient pressure. Firstly, the analysis of emission spectra shows that the maximum combustion temperature of this propellant should be higher than 3 300 K which grows with pressure. It reveals that the fundamental mechanisms of the propellant receding rate and ignition delay are affected by the ambient pressure from the perspective of chemical reaction dynamics. Meantime, the exponential decay law of ignition delay is determined while its formation mechanism is explored, based on the real-time monitoring of the propellant burning surface with high spatial and temporal resolution. Furthermore, it was also found that the regression rate of this propellant increases rapidly at low pressure, but appears to be saturated gradually when the ambient pressure exceeds 4 MPa. Whereafter, it is confirmed that the receding rate rules strictly follow the Summerfield burning rate equation. Finally, through the quantitative analysis of the luminous area of agglomerates in the combustion process, the effects of the agglomerate particle size in the propellant product by environmental parameters are concluded.
Abstract:
Safety separation distance is one of the key concerns in the engineering construction and the study of hazards warehouses. In order to reduce the safety separation distance, a novel type of hazards warehouse is proposed based on the current codes and structural patterns of existing hazards warehouses. The novel warehouse is mainly composed of a shallow-buried main body, a reinforced concrete (RC) distribution slab and a heaped-up earth cover (HEC). Considering the variations of distribution slab and the strength of the main body, three scaled models of the novel hazards warehouse were built and internal explosion tests were carried out. The overpressure time histories of shock waves generated in the explosion tests were recorded and the distribution of blast debris around the warehouse were counted. According to the testing data and damage criteria of personnel subjected to shock waves, the safety separation distance of the novel hazards warehouse is plotted. Moreover, the effects of the RC distribution slab and the main body strength on shock wave propagation and debris distribution are analyzed. The results show that the novel hazards warehouse can bring about directional venting during internal explosions and effectively restrain the shock waves propagation and debris flying. The safety separation distance of shock waves has significantly directionality. Compared with the ground explosion, the safety separation distance of the novel hazards warehouse can be reduced up to 77% on both sides and the rear. In the rear direction, the safety separation distance of the novel hazards warehouse is only 50% of that of the earth-covered hazards warehouse. As the key component of the novel hazards warehouse, the RC distribution slab can reduce the safety separation distance by 30% in the rear direction. Compared with the corrugated steel main body, the RC main body can reduce the safety separation distance up to 38% in the rear direction.
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The most common hypervelocity propulsion systems are light gas guns. Especially, the ability of two-stage light gas guns is suitable to accelerate projectile at velocities ranging from 2 km/s to 9 km/s. However, velocities higher than 10 km/s are demanded eagerly for ballistic limit equations on on-orbit impacts and meteoroids. In order to enhance the launch performance of the light-gas guns, a concept of using density-gradient gas as the driven gas instead of single helium or hydrogen gas has been proposed. An analytical acceleration model of the projectile in the launch tube with constant cross-sectional area is deduced. The launch process can be divided into three stages. The first stage is the projectile driven by the first shock wave. The second stage is the projectile driven by shock waves reflected on the gas interface. The last stage is the projectile caught up by the rarefaction wave created by the suddenly stop of the piston. The comparison in launch performance between neon-helium density-gradient driven gas and helium driven gas is made, and the influences of parameters of the gradient gas on the launch performance are studied. Results show that the neon-helium density-gradient driven gas can improve the launch velocity by about 0.4−1.4 km/s or lower the maximum base pressure by about 0.2−0.9 GPa. The biggest influential factors for the launch velocity and the maximum base pressure are the density of high density gas and the piston velocity, following by the initial gas pressure and the gaseous polytrophic index. High density gas with both high density and high gaseous polytrophic index would be the prior choice due to the reason that higher gaseous polytrophic index could make the maximum base pressure lower. The launch velocity has little correlation with the ratio of high density gas. However, low ratio of high density gas could lower the maximum base pressure.
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When the projectile passes through the gas-liquid interface, the sudden change of density may cause a violent impact load and do untold damage to it. It seriously affects the working effect of the projectile. In order to reduce the water entry load of projectile, based on Rabbi’s idea of load reduction, a kind of structure of projectile with front body was proposed. The S-ALE (Structured Arbitrary Lagrange-Euler) algorithm and the fluid-structure coupling method with penalty function were used to simulate the shape of the cavitation wall and the projectile motion state, which is coincident by comparing with those of experiments. The validity of the numerical method is verified. Furthermore, the influence of the water entry angle of front body, the dimensionless water entry time interval parameter between main projectile and front body, the size of front body, the initial water entry velocity of main projectile and front body on impact load were researched by numerical simulation. The simulation results show that the front body will impact the main projectile when they both entering water vertically, which increases the impact load due to the collision of them. When the front body enters the water obliquely and the main projectile still enters the water vertically, the collision between main projectile and front body could be avoided and a good load reduction effect is obtained. The maximum load reduction rate is up to 90%. The dimensionless time interval parameter range for obtaining a good load reduction effect is from 0.8 to 0.9. Within this range, variation laws of the water entry load of main projectile with the size of the front body and the initial velocity of entering water were discussed in detail. The effect of load reduction increases with the increase of the size of the front body and the initial water entry velocity.
Abstract:
Accurately evaluating the damage and failure of concrete shield subjected to combination of penetration and explosion of warheads can provide an important reference for the design of protective structures. Firstly, based on the frame of Karagozian & Case (K&C) model, a newly dynamic-damage constitutive model was established. The hydrostatic pressure, Lode angle, strain rate, and damage were all considered in strength surface. The tension and compression damages were described separately with a continued transition. Besides, the contribution of shear deformation and hydrostatic compression were also considered. Then, the combined penetration and explosion test of 105-mm-caliber projectile on the semi-infinite concrete target was conducted. The corresponding numerical simulation was conducted to verify the accuracy of the constitutive model, the parameters, and the finite element analysis approach in describing the dynamic resistance of concrete. Furthermore, by conducting the numerical simulations of the existing prefabricated hole charge explosion test on the finite concrete plane, the accuracy of the established constitutive model, parameters, and finite element analysis approach in describing the damage evolution and cracking behavior of concrete was validated. Finally, the perforation limit and scabbing limit of normal strength concrete subjected to the combination of penetration and explosion of three typical warheads at sound velocity were determined. The results show that, the perforation limits of the SDB, WDU-43/B, and BLU-109/B warheads are 1.4, 3.4, and 3.8 m, respectively. The scabbing limit are 3.6, 6.3, and 8.3 m, respectively. Due to the differences of the explosive mass in warheads, the ratios of perforation limit and scabbing limit under combined penetration and explosion to the depth of penetration are not constant. The corresponding ratio ranges are 1.49−2.13 and 2.90−4.66, respectively.
Abstract:
The microstructure of adiabatic shear band (ASB) is influenced by the specimen geometric shape. High-speed impact tests were performed on specimens of three different shapes of cylinder, hat-shaped, and shear-compression by a split Hopkinson pressure bar, to study the effect of the specimen shape on the formation and microstructure of the adiabatic shear band in the bearing steel. The results show that at the strain rate from 1800 to 3100 s-1, the flow stress remains almost the same with increasing the strain rate in three different shapes of sepcimens, indicating that the material shows low strain rate sensitivity. At high strain rates, the cylindrical specimen exhibits a strong strain hardening, while the hat-shaped specimen and the shear-compression specimen (SCS) show both strain hardening and no strain hardening features at different strain rates, but their flow stresses are not increased due to hardening effect. The fracture surface of the cylindrical specimen presents a large number of dense and tiny elliptical dimples. The number of dimples is greatly reduced on the hat-shaped specimen. The dimple, however, has a width that is twice of that of the cylindrical specimen. There is a distinct shearing path of carbides. In contrast, the SCS has even fewer but much larger dimples, with the width of 1.6 μm, twice of the hat-shaped specimen, and the shearing path of carbides reaches 7 μm. Local melting occurs on both the hat-shaped specimen and SCS, especially the SCS, a massive melting is displayed. A long and narrow ASB is produced in the cylindrical specimen, and only strain-induced grain refinement occurred in the ASB, which belongs to the deformed ASB. Large patch of ASBs is generated in the hat-shaped specimen and SCS. The ASBs consist of equiaxed grains and belong to the transformed ASB as the phase transformation from martensite to austenite occurred. In particular, the equiaxed grains in the ASB of the SCS have very clear grain boundaries, which are typical dynamic recrystallization grains. It can conclude that the shape of the specimen has a great influence on the microscopic morphologies and microstructures of ASB. The cylindrical specimen is in a typical compressive stress state, while the hat-shaped specimen and SCS are in complicated stress dominated by shear. The temperature rise int the ASB of the cylindrical specimen is much lower than the austenite transformation temperature, while it is higher than the melting point of martensite in the hat-shaped specimen and SCS, leading to local melting and microstructural change.
Abstract:
The main challenge of numerical simulation of intense explosion is how to accurately determine the equations of state for the explosive products. The traditional equations of state are mostly empirical or semi-empirical formulas, which can just deal with ordinary explosions, but the treatment of intense explosions is of great limitation. The parameters of intense explosive products span an extremely wide range, which often exceeds the scope of empirical formula. Neural network has an excellent nonlinear fitting function and can realize the function of the equations of state. At the same time, there are a lot of state parameters of material in the sesame library, and the material parameters suitable for intense explosive products were selected as training data of neural network. The tabulated data of intensive explosive product samples were pretreated to make them better used in neural networks, then the data was adopted as training set to train the BP neural network and a one-dimensional spherical numerical code embedded with neural network equation of state was used to calculate the blast wave parameters of the explosion of fission device. In the process of neural network construction, the structure of neural network was optimized by enumeration experiment, and the structure of multi-layer neural network with a simple structure and good precision was obtained. In the process of numerical calculation, the code called the embedded neural network equations of state module, calculated the pressure of the explosive product through the density and the specific internal energy, and the flow field parameters of the whole explosive blast wave were finally obtained. The numerical results show that the calculated peak overpressure, arrival time and positive pressure duration coincide with the standard values, which proves the feasibility of the application of the neural network equation of states in the intense blast wave calculations. The results are of great significance to the numerical simulation of intense explosion.
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2023, 43(3).
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Abstract:
2023, 43(3): 1-2.
Abstract:
2023, 43(3): 031101.   doi: 10.11883/bzycj-2022-0408
Abstract:
Magnetically driven quasi-isentropic compression is one of the important experimental techniques to study high-pressure physics and dynamic behaviors of materials under off Hugoniot states. It is of great significance to carry out quantitative evaluation of experimental uncertainty. By combining with the process analysis of magnetically driven quasi-isentropic compression experiments and two forward data processing methods, an uncertainty quantitative evaluation method was established for such experiments based on the Monte Carlo method (MCM). The uncertainty quantification evaluations of physical quantities such as sound speed, stress, strain, and the parameters of equations of state and constitutive models were realized. Compared with the conventional method such as guide to the expression of uncertainty in measurement (GUM), the MCM uncertainty evaluation is more applicable to the cases in which the probability distribution of the input quantities is non-symmetric and the measurement model is non-linear. In fact, the uncertainty evaluation results obtained by the MCM is reasonable and not the ones under the maximum estimation condition. Employing the law of large numbers, nested cycle setting of the probability density functions (PDF) and nested loop construction of virtual samples makes the uncertainty evaluation results more accurate. By using the established MCM uncertainty evaluation method, the uncertainty evaluations of the experimental results of tantalum and copper samples under magnetically-driven quasi-isentropic compression were quantitatively analyzed firstly. The results are consistent with the data proposed in the literatures, which proves the correctness and reliability of our method. And then, the quantitative evaluation was conducted on magnetically-driven quasi-isentropic compression experiments of NiTi alloy carried out on a CQ-4 device. The results show that the experiments on the CQ-4 device are reliable and precise for high-pressure physics and material dynamics studies. Finally, the error correlation and sensitivity of magnetically-driven quasi-isentropic compression experiments were discussed in depth, and the results show that the measurements of step sample thickness and particle velocity are the main factors affecting the experimental accuracy but have different influence weights. This work has important guiding significance for studying high-pressure physics and dynamic behaviors of materials by using magnetically-driven quasi-isentropic compression experimental technology.
2023, 43(3): 032101.   doi: 10.11883/bzycj-2022-0352
Abstract:
To investigate the influence of multi-factor coupling on the explosion characteristics of methane, an explosive gas test platform with a 1.2 L cylindrical explosive device was designed and established. From the perspective of the maximum explosion pressure, the effects of different equivalence ratios φ (0.6–1.4), initial temperatures T0 (25–200 ℃) and initial pressures p0 (0.1–0.5 MPa) on methane explosion characteristics were comprehensively analyzed. Based on the maximum explosion pressure data by the experiments, a nonlinear regression prediction model among the maximum explosion pressure of methane, equivalence ratio, initial temperature and initial pressure was developed by the 1stOpt software. The results show that: under the coupling effect of the initial temperature and initial pressure, the higher the initial pressure, the more the significant effect of the initial temperature on the maximum explosion pressure. However, with the increasing of the initial temperature, the effect of initial pressure on the maximum explosion pressure is weakened. Under the coupling effect of the initial pressure and equivalence ratio, and within the experimental conditions of the study, when φ<0.9 or φ>1.2, the higher the initial pressure, the more dramatically on the maximum explosion pressure changes. Under the coupling effect of initial temperature and equivalence ratio, and within the experimental conditions of the study, when φ>1.15, the higher the initial temperature, the more significantly the maximum explosion pressure changes. In addition, comparing the prediction results of the 1stOpt prediction model with the experimental results, the relative error is less than 10%. It is indicated that the prediction model can provide high accuracy and good adaptability.
2023, 43(3): 032201.   doi: 10.11883/bzycj-2022-0075
Abstract:
In order to deeply understand the formation mechanism of local cavitation in the near-wall flow field caused by an underwater explosion, the optical images showing the local cavitation effect near the wall were obtained by using a self-developed rotating-mirror framing camera with high frequency and high resolution. Numerical simulations were carried out to present the flow-field pressure of shock wave propagation by giving the location of the cavitation area. The Taylor plane wave theory, an efficient method for describing the formation time of local cavitation, was applied to explain the reason that the cavitation did not form in the experimental case 1 that the explosive center was 120 mm from the wall. And the cavitation dynamics theory was used to analyze the local cavitation effect in the experimental case 2 that the explosive center was 80 mm from the wall, by calculating the motion laws of the cavities with different radii under different external environmental pressures. It is indicated that the existence of the rarefaction waves reflected by the interfaces and the expansion of the cavitation nuclei in the water result in the cavitation effects in the near-wall flow field. The external flow-field pressure hardly affects the initial stage of cavitation bubble expansion, but it exerts great influences on the movement behavior of the cavitation bubbles in the later stage. The cavitation bubbles with different sizes will take on different movement behaviors in the low-pressure environment. The cavitation bubbles with the small size less than 10 μm will expand and collapse rapidly in the low-pressure environment so that they have little effects on the flow field cavitation. While the cavitaion bubbles with the large size more than 10 μm may lose the stability, with the result that they have great influences on the flow-field cavition. The random spatial distribution of different-size cavitation nuclei in water is the main reason that the cavitation zone presents an irregular shape during the evolution progress.
2023, 43(3): 032202.   doi: 10.11883/bzycj-2022-0268
Abstract:
A detonation experimental system was established to explore the characteristics of underwater detonation gas jets from the detonation tubes with different types of nozzles. The effects of different types of nozzles on underwater bubble shapes and pressure characteristics during detonation were experimentally studied. The digital particle image velocimetry was used to visualize the bubble pulsation pictures captured by a high-speed camera, and the bubble velocity fields in the different nozzle cases were obtained. Two dynamic pressure sensors were installed at the end of the detonation tube to confirm whether the stable detonation wave was formed, and to observe the transmission and reflection characteristics of the detonation wave on the gas-liquid two-phase interface, respectively. An underwater explosion sensor was installed at a certain distance from the nozzle to measure the underwater pressure wave. The results show that the bubble pulsation process in the divergent nozzle case is basically the same as that in the case of the straight nozzle, but the divergent nozzle improves the gas jet velocity and increases the bubble volume of the first bubble pulsation. The combined effect of the convergent nozzle and its reflected shock wave reduces the injection speed of the detonation gas. Because of the continuity of the gas jet, the bubble pulsation process in the convergent nozzle case is obviously different. The maximum bubble volume in the convergent nozzle case is smaller, but the attenuation of the second bubble pulsation duration is smaller than that of the first pulsation duration. The divergent nozzle increases the gas velocity and kinetic energy, which enhances the bubble pulsation intensity, the bubble pulsation pressure and transmitted shock wave pressure in the divergent nozzle case are much higher than those in the straight nozzle case. The bubble pulsation pressure and the transmitted shock wave pressure in the convergent nozzle case are both low, but the continuity of the convergent nozzle gas jet retards the attenuation speed of the bubble pulsation pressure. Compared with the straight nozzle, the bubble pulsation time in the divergent nozzle case is longer, the bubble pulsation pressure and transmitted shock wave pressure are higher. The duration of the bubble pulsation in the convergent nozzle case is shorter, and the convergent nozzle can obviously inhibit the transmitted shock wave pressure and the bubble pulsation pressure.
2023, 43(3): 033101.   doi: 10.11883/bzycj-2022-0374
Abstract:
2023, 43(3): 033201.   doi: 10.11883/bzycj-2022-0098
Abstract:
2023, 43(3): 033301.   doi: 10.11883/bzycj-2022-0182
Abstract:
To study the influence mechanism of shaped charge liner on the perforation and damage-induced fracturing effect of shale reservoir by shaped charge penetration, a three-dimensional perforating charge-air-shale model was established. The cone angles of the liner are 50°, 60°, 70°, and 80°. The liner thicknesses are 0.5 mm, 1.0 mm, and 1.5 mm. And the materials of the liner are copper, steel, titanium, and tungsten. The numerical calculation was carried out using the ALE-Lagrangian coupling method in the non-linear program ANSYS/LS-DYNA. The ALE method was used to describe shell, explosive, liner, and air, while the Lagrangian method was used to describe the shale reservoir. A systematic analysis was carried out on the aspects of jet velocity and shape, shale perforation effect, and fracture extension characteristics of shale. The results show that with the decrease of the cone angle of the liner, the jet velocity and penetration depth increase, and the pestle velocity and perforation diameter decrease. In a certain range, with the decreasing liner thickness, the jet velocity, penetration depth, and perforation inclination increase, and the mass of the pestle decrease. The liner material significantly influences the jet velocity, pestle structure, and shale perforation effect. Among them, the penetration depth of perforating charge with a tungsten liner is the largest, but the perforation diameter is the smallest, the penetration depth of perforating charge with a titanium liner is the smallest, but the perforation inclination is the largest, and the penetration depth of perforating charge with a copper liner is slightly larger than that with a steel liner, but the perforation diameter is slightly smaller. Because the detonation pressure has an obvious difference before and after the detonation wave transmitted to the end of the explosive, which affects the jet velocity and penetration depth, the charge with a shell has a greater jet velocity and penetration depth than the charge without a shell. By comparing the fracture extension characteristics of shale in different groups, it is found that the fracture extension of shale mainly occurs in the stage of re-reaming of a pestle on shale. It is concluded that the material and structure of the liner have a significant influence on the shaped charge jet and its penetration effect, which then affects the damage-induced fracture formation and extension in shale. The fracture extension of the shale can be promoted by reducing the initial perforation diameter of penetration, increasing the diameter of the pestle, and increasing the speed of the pestle.
2023, 43(3): 033302.   doi: 10.11883/bzycj-2022-0029
Abstract:
To investigate the dynamical responses and failure behaviors of prefabricated reinforced-concrete (RC) box-girder flyovers caused by collision of over-height vehicles, a recent actual engineering accident is taken as an example to carry out refined numerical analysis by the finite element method, and a double mass-parallel spring (DM-PS) simplified vehicle model is proposed to effectively simulate the eccentric collision between the over-height vehicle and bridge superstructures. The effectiveness of the proposed DM-PS model is fully assessed through comparison with two widely-employed vehicle models, i.e., a full-scale (FS) model and a simple rigid (SR) model. The comparisons display that the failure characteristics of the collision area can be obtained by using the FS model, which is basically consistent with the photos of the accident scene; the SR model overestimates the local damage of the structure and underestimates the overall structural deformation; while the DM-PS model has high accuracy for predicting the structural failure. Therefore, the proposed DM-PS model can provide a simple and effective analysis tool for the protection design of bridge structures subjected to over-height vehicle collision. On this basis, a detailed parameter analysis of the structural behaviors is carried out by the DM-PS model, and the effects of vehicle collision velocity, mass, position, and structural form are investigated in depth. It is shown that the structural sensitivity of the impact dynamic behavior to the collision velocity of the vehicle is significantly greater than that of the collision mass of the vehicle; the deformation and failure modes of mid-span collision and side-span collision are quite different, and the damage of side-span collision to one side base is more serious; the box plate and reinforced plate in the box girder can effectively improve the structural impact resistance. Numerical results and conclusions can provide a reference for the crashworthiness design of bridges. The critical information of the finite element analysis process is presented in detail.
2023, 43(3): 033303.   doi: 10.11883/bzycj-2022-0115
Abstract:
The formation process of the Yilan crater was numerically studied based on the iSALE-2D simulation code. The Euler algorithm was used to carry out the numerical simulation, and eight groups of working conditions were simulated. According to the scaling law, it was determined that the projectile diameter range was 90 to 120 m, and the projectile velocity was 12 and 15 km/s. Simulation results under the corresponding working conditions within 150 s of impact were obtained, including the crater diameter, depth, and crater profile curve. The optimal impact conditions of the Yilan crater were studied, and the formation and distribution of the molten layer during the cratering process were statistically analyzed. Combined with the point source cratering similarity law model, the relationship of cratering radius under the strength mechanism was obtained by fitting. The research results show that, according to the comparison between the simulated data and actual exploration data, a granite asteroid with a diameter of 120 m and an impact velocity of 12 km/s vertically hits the surface, forming a crater with a shape similar to the Yilan crater. The crater has a final diameter of 1 840 m and a crater edge depth of 263 m, which is in good agreement with the exploration data of the Yilan crater. Three stages of crater formation were reproduced: contact and compression, excavation, and modification. The distribution of the impact melting layer of the target plate material during the crater formation under the simulated conditions were revealed. The material melted completely when the peak pressure exceeds 56 GPa during the impact process, and this process was completed within 20 ms. Most melts was distributed at the bottom of the crater in layers and stacks, and a small amount of melts was deposited discretely on the surface of the target plate. The mass of the completely melted material is about 24 times the projectile mass. The relative error between the simulation results and the fitted crater radius relational results under the conditions with 120 m diameter and 12 km/s impact velocity is 10.3%.
2023, 43(3): 034101.   doi: 10.11883/bzycj-2022-0344
Abstract:
2023, 43(3): 034201.   doi: 10.11883/bzycj-2022-0390
Abstract:
Gun barrel erosion is primarily caused by the intense heat and mass transfer between the propellant gas and the tube during firing. To investigate the erosion characteristics of a 155 mm barrel in a high-temperature, high-pressure, and high-velocity gas, an unsteady CFD fluid-solid interaction heat transfer model is developed with improved accuracy of temperature calculation. The eroding process is separated into two stages relevant to its temperature dependence. Thermochemical erosion occurs when the temperature is between the austenite phase-transition temperature and the melting point of cementite. When the temperature is above the melting point, melting becomes the dominant factor influencing erosion, so this is the melting erosion stage. Therefore, a piecewise model is developed. The numerical results of the calculation are as follows. The wall temperature rises rapidly and then falls gradually. In addition, the temperature decreases with the increase of axial distance in general. At the beginning of rifling, the wall temperature is the highest, and the erosion consists of melting and thermochemical erosion. In most of the rifling areas, only thermochemical erosion occurs. The amount of erosion is reduced continuously with the increase of axial distance. The most severe erosion happens near the beginning of rifling, where 5.06 μm (288 K) of erosion is found after one shot. The method is valid through the comparison with test results. Concurrently, the effect of different operating conditions on the erosion characteristics of the tube is investigated. The erosion distribution properties are found to be similar at different ambient temperatures and firing times. The erosion is the most severe near the beginning of rifling and decreases monotonically along the axis, although the peak value and range of erosion are different. Continuous firing and the increase of the external environment temperature will aggravate erosion. As a result, erosion has a strong positive correlation with initial wall temperature, and the temperature rise will accelerate the tube’s deterioration; therefore, rapid cooling of the barrel will effectively extend the service life of the artillery.
2023, 43(3): 034202.   doi: 10.11883/bzycj-2022-0110
Abstract:
Under impact, aluminum foam undergoes significant plastic deformation, and the kinetic energy of the impactor is dissipated in the process, thereby protecting the structure from damage. The failure modes of aluminum foam sandwich structures under impact are complex, involving plastic deformation, panel failure, and cracking of the bonding interface. Traditional numerical simulation methods are difficult to solve these discontinuous problems. Peridynamics is a non-local numerical method that describes the mechanical behavior of materials by solving spatial integral equations. It has unique advantages in solving crack propagation, material failure, progressive damage of composite materials, and multi-scale problems. Although the basic bond-based peridynamic theory cannot describe plasticity, the ordinary state-based peridynamic method decouples distortion and dilation and can easily simulate the plastic deformation of materials. Therefore, based on ordinary state-based peridynamics, the Mises yield criterion and the linear isotropic hardening model were introduced to study the factors affecting the impact resistance of aluminum foam sandwich structures. Two-dimensional mesoscopic models of aluminum foam sandwich structure were established by the Monte-Carlo method and impact was simulated using the peridynamic method. The influence of the porosity of aluminum foam on the impact resistance and damage mode of the sandwich structure was analyzed. The results show that the good plastic deformation ability of aluminum foam sandwich structure is the main factor for its buffering and protection, and within a certain range, the higher the porosity of aluminum foam core, the better impact resistance of the sandwich structure. When the porosity of aluminum foam increases from 0.4 to 0.7, the kinetic energy absorption rate of aluminum foam to the impactor increases from 90% to 99%. The simulation results are in good agreement with the experimental results, which verifies the accuracy of the simulation results and the effectiveness of the analysis conclusions. The numerical simulation predicts the crack propagation morphology of the plexiglass backplate, and the results show that improving the porosity of aluminum foam can obtain a better protection effect.
2023, 43(3): 034203.   doi: 10.11883/bzycj-2022-0017
Abstract:
To investigate the propagation process of the underwater blasting shock wave in a fish body and its effect on typical swim bladder fishes, a critical safety wave pressure model for typical fishes was established and verified through theoretical analysis and field tests. According to the transverse reflection pattern of one-dimensional elastic compression wave between different media, the relationship between the critical safety wave pressure and the body length of typical swim bladder fishes was established. The length and mechanical properties of the swim bladder and fish body were measured using a vernier caliper, a digital micrometer, and a microcomputer tensile tester. Based on the measured data, the positive correlations of the length, width, wall thickness, and radial critical tensile stress of the swim bladder with the fish body length were determined, and the parameters in the fish critical safety wave pressure model were calibrated. The wave impedance ratio of the water medium and swim bladder wall medium was 0.3–2.0. The width, wall thickness, shape, and radial critical tensile stress coefficients of the swimming bladder were 0.04–0.09, 0.002, 0.6–1.1 and 60, respectively. The underwater blasting shock wave pressure and its effect on the fishes were measured using a blast wave tester, and the damage to the fishes was divided into three types: death, survival with influence, and survival without influence. The fish critical safety wave pressure model was verified by the statistical results of fish damage. The results show that the damage states of fishes with different body lengths at different shock pressures are conformed with the maximum and minimum critical safety wave pressure that the fishes can withstand. The proposed fish critical safety wave pressure model can be used to describe the relationship between the critical safety wave pressure and body length of the swim bladder fishes under the action of the underwater blasting shock waves. The research achievement can provide a theoretical basis for ecological protection of the fishes in the waterway regulation project of the upper reaches of the Yangtze River.
2023, 43(3): 035101.   doi: 10.11883/bzycj-2022-0333