Abstract:In order to study the law of crack initiation， growth and evolution of explosives under weak load. The numerical simulation of crack initiation and evolution of explosives was carried out by using the material model considering the phenomena of tensile and compressive anisotropy with strain rate effect. The numerical results are in good agreement with the test data， and the applicability of the numerical model is verified. The typical characteristic images of crack generation and evolution of explosives were obtained through a series of numerical simulations， and the effects of initial crack size， loading rate and loading position on the crack propagation process of explosives were also analyzed， which can provide reference for the analysis of damage and fracture process as well as the dynamic response of explosives.

Abstract:The new challenge to the existing coating layer process was put forward by the development of solid rocket motor technology. In recent years， thermosetting resin as the matrix was used， combined with continuous automatic coating technology， the popular coating production method of coating layer lies in whether complete molding and excellent performance can be obtained quickly. The flow properties and casting condition of unsaturated polyester （UPR） coating layer were studied. The chemical rheological model of the UPR coating layer during continuous automatic manufacturing is obtained by introducing exponential function based on Kinua-Fontana model. The functional relationship of viscosity versus time and temperature of cured UPR is established. The suitable temperature for casting operation was obtained. The filling volume fraction distribution， flow rate distribution and weld line position of coating layer were predicted by introducing of POLYFLOW simulation software， which the constitutive equations is established on the base of Bird-Carrea power-law equation. The casting process was simulated at the constant rate and pressure， respectively. The results show that the casting temperature is below 35 ℃， the casting pressure is more than 1 MPa， and the inlet flow rate is more than 150 mm³·s^-1 and less than 175 mm³·s^-1 in the coating layer casting process.

Abstract:In order to explore the characteristics of ignition and flame-propagation process of the modular charge， a small metal modular cartridge was designed and the ignition test was carried out. On this basis， the internal ballistic two-dimensional gas-solid two-phase flow model of the test was established， the model was solved by using CE/SE method. The variation characteristics of flow field parameters in the chamber are obtained， and the numerical results are in good agreement with the experimental results. The numerical results reveal the changing process of the pressure distribution of the ignition tube and main charge area during the flame-propagation process， the flow law of the gas phase and the influence of its radial propagation effect on the combustion of the propellant in main charge area； The rupture of the cartridge’s end cap will lead to the formation of a shock wave in free space of the chamber， the reason for the formation of the shock wave are discussed. In addition， the numerical simulation of the gas jet of the vent hole breaking-progress under the hypothetical working condition is carried out， the gas phase flow law and the pressure-boosting law of the main charge area are studied. The comprehensive results show that under the condition of modular charge， the radial effect of the gas phase in the ignition tube is obvious during the entire ignition and flame-propagation process， and the particularity of the charge structure can easily lead to the formation of shock waves.

Abstract:Polymer Bonded Explosive （PBX） is a multiphase composite material composed of pure explosive particles occupying a high volume fraction and a little polymer binder. The interface debonding between particles and binder and the mesostructure play a critical role in the mechanical properties of the material. In this paper， according to the stochastic simulation method combined with the Voronoi method， the representative volume element model of PBXs is established at the mesoscale. When the particles generated by Voronoi method are multi-graded， the particles around the large ones show a strip-scattering shape. The method of mesostructure modeling of PBXs was improved based on Voronoi method. Considering the mesoscopic interface characteristics of PBX-9501， the interface damage evolution between particle and binder under static tension was numerically simulated by using the constitutive relationship of three-stage bonding interface. The results show that the macroscopic mechanical properties of PBX-9501 agree well with the experimental data. The relationship between convergence and the size of representative volume element is discussed. It is concluded that the larger the size of the representative volume element is， the worse the convergence of the interface debonding simulation is.

Abstract:In order to study the thermal decomposition properties of the characteristic groups of 3，4-Dinitrofurazanylfuroxan （DNTF）， differential scanning calorimetry （DSC） and fast scanning Fourier transform infrared spectroscopy （FTIR）were adopted to study the thermal decomposition properties of DNTF in condensed phase. The changes of characteristic groups of DNTF were studied by using FTIR technology at three different heating rates of 2.5， 5.0， 10 ℃·min^-1. The thermal decomposition kinetic parameters of C─NO₂， furazan ring， and furoxan ring of DNTF were calculated by the Coats-Redfern method. The thermal decomposition mechanism of DNTF was inferred based on the thermal decomposition properties of the characteristic group of DNTF. The results show that the thermal decomposition of DNTF is controlled by the three-dimensional diffusion mechanism. The reactivity of groups in DNTF molecule is nitro>furoxan ring>furazan ring. With the increase of heating rate， the reactivity of each group shows an increasing trend. It is speculated that the thermal decomposition process is that C─NO₂ breaks first， and then the C─C bond connecting furuzan and furoxan ring breaks， and finally the N─O bond in furazan ring and furoxan ring breaks. The furoxan ring decomposes faster than furazan ring.

Abstract:The crystallization process of 1，3，5-triamino-2，4，6-trinitrobenzene （TATB） will be affected by dioctyl sulfosuccinate sodium salt （AOT） and the molecular dynamics （MD） method was used to study this crystallization process in this work. The crystal morphologies of TATB crystal in vacuum were predicted by Bravis-Friedel-Donnary-Harker （BFDH） and attachment energy （AE） models. Seven important crystal planes of TATB were determined， which are （0 0 1）， （1 0 -1）， （1 -1 0）， （1 0 0）， （1 -1 1）， （0 1 -1） and （0 1 0）. The interface model for TATB with AOT was established and performed the molecular dynamics simulation. The modified AE model was used to analysis simulation data. After calculation， we found that the crystallization rate of TATB was improved under the influence of AOT solution. After analyzing the molecular structure and the intermolecular interaction of TATB， it is considered that because of the special plane structure， the intermolecular interaction between （0 0 1） plane and AOT is weak and the attachment energy （119.832 kJ·mol^-1） of （0 0 1） plane is low. So， the growth rate of （0 0 1） plane is relatively slow. The attachment energies of （1 0 -1）， （1 -1 0）， （1 0 0）， （1 -1 1）， （0 1 -1） and （0 1 0） planes are all higher than （0 0 1） and they all grow faster than （0 0 1）. Therefore， in the experimental process， a leaf-like TATB structure formed first. With the reaction time was further， the （0 0 1） plane gradually grows， the leaves become longer.

Abstract:To investigate the influence of the loading density of main propellant charge on the propagation characteristics of ignition charge gas in the granular propellant bed， the test platform for ignition and propagation of a large-diameter dense propellant bed was established， and the flame sequence diagram and the pressure changes of partial pressure gauges were recorded in tests. The porous medium model was used to simulate the granular propellant bed in the charge chamber， and the ignition and propagation model corresponding to the test device was established to numerically simulate the flow process of ignition charge gas in the granular propellant bed. The simulation results were compared with the test results to verify the reliability of the model， and then the propagation characteristics of temperature and pressure fields of gas in the propellant bed with different loading densities were calculated. The results show that the calculated results are in good agreement with the experimental flame propagation sequence process and the experimental pressure histories， which verifies the reliability of the model. Under the condition of any porosity， the axial displacement of flame front develops rapidly and the axial velocity decreases from 25-30 m·s^-1 to 10 m·s^-1 during 0-10 ms， ， and the axial velocity decreases to 2-3 m·s^-1 during 10-40 ms. Similarly， under the condition of any porosity， the development of radial displacement of flame front is concentrated during 2.2-3 ms， and the radial velocity decreases to 20-22 m·s^-1 at 3 ms. However， the radial velocity at the initial time is large for large porosity. When the porosity increases from 0.3 to 0.5， the pressure difference at different positions in the chamber decreases 16.7% from 0.24 MPa to 0.20 MPa， and the uniformity and instantaneity of ignition are improved. With the increase of porosity， the axial and radial resistances of the flame front in propagation process decrease， the axial expansion displacement of the flame front and the initial velocity of flame propagation in the axial and radial directions increase， but the final velocity tends to be the same. The smaller the pressure in the chamber， the smaller the pressure difference in the chamber.

Abstract:In order to study the damage of polymer bonded explosive（PBX） under dynamic shock loads， the constitutive curve of the mechanical damage of PBX under different strain rates was obtained by using the Split-Hopkinson pressure bar（SHPB） test device. And the constitutive parameters in the Z-W-T constitutive model with damage variables were fitted in sections. Then， based on the fitting results， the finite element theory， elastoplastic mechanics and ABAQUS/VUMAT， the subroutine of PBX containing damage is completed， and is verified by the finite element simulation. The model is used for finite element engineering examples. Results show that the verification results of finite element samples are in good agreement with the experimental results， and the correlation degree of the results is higher than 0.95.The stress cloud diagram and damage variable cloud diagram for fragment penetration example reflect the change and possible damage location of PBX under shock loads.The evolution process of damage cloud diagram reflects the correlation between damage evolution and strain rate effect of PBX.

Abstract:Laminated composite charge is composed of two or more different charges by way of superposition， in which the safety and power performance can be regulated through the design of charge structure. To study the sympathetic detonation safety of laminated composite charge， typical composite charges which contain both the high energy charge and insensitive charge were selected as research objects. The effect of different charges structure on critical sympathetic detonation distance was explored through numerical simulation and sympathetic detonation tests. Results showed that， compared to simple high energy charge， the sympathetic detonation of composite charge decreases 53.3%（from 7.5 mm decreases to 3.5 mm）， while energy decreases 22.9%. The thickness of insensitive charge must reach a certain threshold（3 mm） in order to reduce the critical sympathetic detonation distance obviously. As the content of insensitive charge increases， the critical sympathetic detonation distance is closer to insensitive charge.

Abstract:To investigate the influence of temperature-induced phase transition of polytetrafluoroethylene （PTFE） on the fracture toughness of Al-PTFE reactive material， the quasi-static tensile test and fracture toughness test were performed， and the normalization data reduction technique with single specimen in ASTM E1820 was applied for analyzing the elastic-plastic fracture toughness of Al-PTFE by J-integral method. Combined with the microstructures analysis of the fracture surface， the effect of temperature on the fracture toughness of Al-PTFE was revealed. The results show that the strength of Al-PTFE reactive material decreases with the increase of temperature， while the fracture toughness increases. Moreover， the yield strength and fracture toughness of this material change obviously after crossing the phase transition temperature. The crack propagation pattern changes from brittle fracture to ductile fracture. Furthermore， when PTFE is in phase Ⅱ， less PTFE fibrils can be formed by stretching. However， increasing temperature can lead to the transform of the crystal phase for PTFE to phase Ⅳ and Ⅰ. Besides， the stable formed PTFE fibrils can effectively dissipate the external energy in the form of local plastic deformation. The crack tip is passivated by winding bridging， so as to prevent the crack propagation and improve the fracture toughness of this material.

Abstract:Slow cook-off test is one of the key tests of low vulnerability assessment for solid rocket motor. In order to study the influence of the charge size of HTPB composite propellant on the slow cook-off characteristics， slow cook-off tests and numerical simulation were carried out to compare and analyze the ignition growth laws of solid rocket motor under slow cook-off tests， with charge dimensions of Φ100 mm × 200 mm， Φ160 mm × 400 mm and Φ522 mm × 887 mm. Their corresponding ignition temperatures， ignition positions and response levels were determined. Results show that the ignition temperature of specimens of Ф100 mm×200 mm， Ф160 mm×400 mm and Ф522 mm×887 mm of solid rocket motors are 244 ℃， 172 ℃ and 155 ℃， respectively. Taking test data as inputs， the calculated ignition temperature is 250， 269， 154℃， and their corresponding calculation errors and response levelsare 2.88%， 1.17%， 0.64%， and explosion， explosion and deflagration. The calculated cloud diagram shows that the ignition position of medium and small test pieces is located in the center of charge cylinders， and the ignition position of full-scale solid motor is in the center of meat thickness of solid propellant front-end， which is a ring shape area.

Abstract:Composite solid propellant contains more solid particles， so it is difficult to accurately simulate the extrusion process of the propellant in twin-screw extruder with traditional finite element analysis method. Whereas， the coupling of discrete element method （DEM） and computational fluid dynamics （CFD） is an effective method for simulation the production process of composite solid propellant， but it is very difficult to implement. In this paper， based on the calibrated contact model parameters， the simulation of solid particles in solid propellant with aluminum powder and ammonium perchlorate as main components in twin-screw extrusion process was realized with DEM， and then the DEM-CFD coupling calculation of the solid propellant solid particles and the liquid phase was realized. The results show that the transportation of solid propellant particles in twin-screw calculated by DEM is consistent with the experimental law. Comparing the results between DEM-CFD coupled simulation and DEM for solid particles， it can be seen that the fluidity of materials was significantly improved by adding the liquid phase The filling rate of materials in the screw conveying section increases from 20% to 40%， and the average conveying speed of solid particles increases by 150%， but the stress of screw does not change much.

Abstract:In order to clarify the influence mechanism of H₂O and H₂O₂ molecules on the thermal stability of energetic cocrystals， molecular dynamics （MD） simulation method was employed to analyze the diffusion behavior and thermal decomposition mechanism of solvent molecules in α-CL-20 and CL-20/H₂O₂ （orthogonal/monoclinic）. The results show that both H₂O and H₂O₂ will diffuse out of the cell as the temperature rises， among which H₂O molecules diffuse faster； when the temperature is lower than 500 K， the monoclinic CL-20/H₂O₂ lattice framework has the ability to hinder the diffusion of H₂O₂ molecules. When the temperature rises above 500 K， this hindering effect no longer exists. In the process of thermal decomposition， α-CL-20 releases energy the slowest， and the decomposition of CL-20 also proceeds the slowest； when the temperature is lower than 1500 K， the solvent exhibits a certain stabilizing effect on the thermal decomposition of energetic components， but this effect disappears as the temperature rises. In addition， the presence of solvents can increase the lattice energy significantly.

Abstract:In order to ensure the safety of the incineration process， the incinerator must be able to withstand the impact of accidental explosion when the waste energetic materials are incinerated. The dynamic coefficient method and the method proposed by Atomic Weapons Establishment （AWE Method） were used to design the shell of vertical incinerator for waste energetic materials. Then， three-dimensional numerical simulation of the shell stress of the designed incinerator under detonation of energetic materials was carried out using AUTODYN software. The influence of exhaust gas outlet， outlet position and detonation position of energetic materials on the anti-explosion performance of the incinerator was analyzed. Numerical simulation results show that the existence of the outlet destroys the continuity of the shell， therefore， the stress concentration occurs near the outlet， and the maximal stress appears at the upper edge of the outlet. Besides， as the diameter of the outlet increases， as the center of the outlet is closer to the shell cover， and as the detonation position of energetic materials is closer to the outlet， the stress concentration at the upper edge of the outlet becomes more serious. When the energetic material is close to the incinerator shell， the explosion will cause plastic deformation of the shell. Hence， when the diameter of outlet is determined， some measures can be taken to ensure the safety of the incineration process， such as keeping the outlet away from the seal plate， setting a stiffening ring at the outlet and keeping a certain distance between energetic materials and the shell.

Abstract:In order to extract the effect characteristic parameters （smoke screen width， smoke screen height， smoke screen coverage area， masking time） and motion characteristic parameters （vertical and horizontal diffusion speed） from measured infrared smoke screens and， the layout of the test site for field measurement of infrared smoke screens was designed. The infrared thermal imager was used to collect the video data of the explosion and diffusion process of the infrared smoke bomb in 112 secs， and the five-frame difference method was used to segment and extract the infrared smoke screen from the video sequence of the infrared thermal imager， then the effect characteristic parameter area and motion characteristic parameter area of the infrared smoke screen were obtained. According to the geometric relationship of the site layout， the test results have been corrected for wind direction. The pixel points of the infrared smoke screen image were used as the basic unit that the actual smoke screen height and width values represented by each pixel in each frame of the video sequence were solved， and then the effect characteristic parameters and motion characteristic parameters of the infrared smoke screen were obtained. It was verified by the analysis of actually measured infrared smoke screen videos that this method can quickly extract the characteristic parameters of infrared smoke screen. At the moment of explosion， the width， height， and area of the smoke screen rapidly increase to 4.7 m， 5.2 m， and 24.2 m²， respectively， and the front diffusion speeds along the wind direction reached 126 m∙s^-1 horizontally and 146.3 m∙s^-1 vertically.， It has highly practical application value for the research on infrared smoke screens， including the correction of diffusion simulation equation， the combat effectiveness evaluation， and on the combat operation.

Abstract:In order to investigate the mechanical response process of porous propellant under impact loading and the effect of geometric parameter changes on the mechanical properties of the particles， ANSYS/LS-DYNA was used to establish the numerical models of seven-hole and nineteen-hole propellants to simulate the force of the particles under impact loading. Then， the models of single-hole propellant， seven-hole and nineteen-hole propellants with aspect ratios of 1∶1 and 2∶1， and lace-shaped seven-hole and nineteen-hole propellants were established to study the influence of the number of holes， aspect ratios and shape on propellant stress. The results show that the particles rebound after being compressed， the stress on the surface in contact with the drop hammer increased gradually from the center to the boundary， and the middle of the particles expanded. The increase of the number of holes will change the continuity of the stress distribution on the end surface due to the stress concentration at the hole. Compared with the single-hole propellant， the duration under stress and the maximum compressive displacement of the seven-hole propellant are increased by 3.39% and 3.76%， respectively， whereas the duration under stress and the maximum compressive displacement of the nineteen-hole propellant are increased by 10.17% and 15.05%， respectively. When the number of holes remains constant and the aspect ratio increases from 1∶1 to 2∶1， the peak stress decreases and the peak compressive displacement increases. The lace-shaped particles were more prone to cause stress concentration in the concave of lace than the cylindrical ones. The study of the stress response process of the propellant and its influencing factors provides fundamental data to study the mechanical properties of the propellant.

Abstract:In order to analyze the mechanism of shock sensitivity of CL-20/HMX cocrystal close to that of HMX， ReaxFF molecular dynamics simulation was used to investigate the mechanical-thermal structural changes and subsequent initial chemical reactions in CL-20/HMX cocrystals with or without voids. The structural deformation and subsequent chemical reaction process are effectively analyzed by using the momentum mirror model combined with shock-front absorbing boundary condition. When shocks subjected to CL-20， HMX， and CL-20/HMX， it is found that the decomposition speed of CL-20 is faster than that of HMX， while CL-20/HMX"s decomposition speed is very close to HMX"s. Besides， the decomposition speed of CL-20/HMX ［100］ shocks is faster than ［111］ shocks. This phenomenon is related to alternative arrangement of CL-20 and HMX molecular layers and the relative slip amount. When CL-20/HMX with 20 nm diameter void is shocked along the ［100］ direction at particle velocity of 2 km·s^-1， hydrodynamic jet collapse does not occur instead of viscoplastic pore collapse. It largely promotes the rapid decomposition of CL-20 and HMX molecules in the high temperature and high pressure conditions formed by pore collapse and the viscoplastic deformation of crystal structure. A new hot spot formation from the void collapse further enhances the shock loading process.

Abstract:To predict the resistance to penetration of the ultrahigh molecular weight polyethylene laminate（UHMWPEL） accurately， a three-dimensional finite element simulating method of composite structures laminate based on the ABAQUS/Explicit solver platform was developed. A user-defined subroutine VUMAT was proposed to define material behavior by dividing the laminate into two parts with orthotropic lamina and cohesive interface. The lamina and cohesive interface utilized the Hashin criterion and the quadratic stress criterion as the damage initiation criterion separately， while both of them adopted the bilinear constitutive model and the damage evolution method derived from fracture toughness. The residual velocities and damage states of UHMWPEL with thickness of 10 mm and 20 mm penetrated by wedge-shaped steel fragment simulation projectile（FSP） with different initial impact velocities were simulated. The results show that， compared with the existing experiments， the prediction errors of ballistic limits of 10 mm and 20 mm UHMWPEL are 0.6% and 11.3%， respectively， and those of all residual velocities of FSP are less than 14.2%. During the damage and failure process of UHMWPEL， punching failure and local bulging occur in the first stage， followed by large-scale bulging， large-area delamination and fiber tensile failure. This two-stage characterization is similar to that observed in existing experiments， which verifies the reliability of the proposed simulating method.

Abstract:In order to improve the ballistic stability of penetrating projectile obliquely penetrating multi-layer concrete target， the structure design of head grooved projectile and pointed oval projectile is proposed. Numerical simulation was carried out based on LS-DYNA software， and two projectiles penetrating 10-layer concrete target were tested. Research shows that in the process of penetrating single-layer concrete thin target， the attitude deflection angle of projectile increases with the increase of initial attack angle， and the attitude deflection of grooved projectile is relatively small compared with that of sharp oval projectile. Compared with the test results of penetrating 10-layer concrete target， grooved projectiles can significantly reduce the deflection attitude of projectiles relative to Ogive-nosed projectiles， which has good ballistic stability and provides reference for the design of projectile with ballistic stability of penetrating multiple targets.

Abstract:To study the initiation process under jet impact and obtain the critical initiation threshold of explosives with different thicknesses， experiments of jet formation with Φ40 mm shaped charge were performed and captured by the high-speed video. The 43-mm thick TNT explosives were covered by 50SiMnVB cover plates with different thicknesses in experiments. The critical initiation threshold， the response under different stimulus intensities and the expansion velocity of reaction products were obtained. The numerical simulation of finite-thickness explosive under jet impact was carried out by using numerical simulation software. The propagation process of bow wave in explosive under jet impact and the relationship between critical initiation threshold and the thickness of finite-thickness explosive were analysed. The simulation results were compared and verified by the experimental data. The results show that the critical initiation threshold of TNT with a thickness of 43 mm is 37 mm³·μs^-2， and the expansion rate of reaction products varies by at least one order of magnitude between different responses. When the jet impacts on a finite-thickness explosive， a certain distance is required for a bow shock wave evolving into a detonation wave. The higher the tip velocity of the residual jet is， the shorter the distance is required for the evolution of bow shock wave to detonation wave. Therefore， the decrease of explosive thickness will lead to the increase of critical initiation threshold of finite-thickness explosive， and the logarithm of critical initiation threshold is approximately linear with the logarithm of explosive thickness.

Abstract:To study the jet formation and penetration characteristics of the shaped charge with elliptical cross-section， and the influence of the ratio of long axis to short axis at a fixed short axis， DOP （Depth of Penetration） tests at stand-off 80 mm were carried out for shaped charges with elliptical cross-section. The short axis diameter of elliptical cross-section is 56 mm and the ratio of long axis to short axis are 1， 1.5 and 2， respectively. By using ANSYS/LS-DYNA software to construct related finite element models， the jet formation and penetration process are simulated numerically. The results showed that except for the jet head， the rest of jet was cohesionless at the late stage of stretching. The non-condensed part of jet consists of two fluids with lateral velocity symmetrically distributed over the section of long axis. The non-condensation of jet will significantly reduce the penetration ability of the shaped charge with elliptical cross-section. For the shaped charge with a short axis diameter of 56 mm， the penetration depth decreased by 68.3% from 150 mm to 47.5 mm when the ratio of long axis to short axis changed from 1 to 1.5， while no significant change of penetration ability occurred while the ratio of long axis to short axis changed from 1.5 to 2.

Abstract:To study the stability of a cast polymer-bonded explosive （PBX） during penetration， projectiles with the PBX-1 charge was launched by a 155mm gun to penetrate concrete targets. The penetration depths at different velocities were obtained， and the critical penetration velocity for maintaining the charge stability was about 490 m·s^-1. Based on the viscoelastic statistical crack （Visco-SCRAM） model， the experiments for testing penetration stability were modelled by a fluid-solid coupling method with large deformation. Thermal-mechanical responses of the charge during penetration were obtained and reasons for the unexpected ignition of the charge were analyzed. The numerical results and experimental data are in a good agreement. The results show that no obvious deformation or damage is observed for the projectile shell， while the cast PBX charge undergoes large deformation and part of charge seeps out from the end gap. During the penetration process， the charge collides with the bottom of charge chamber at high speed and forms a local high-pressure zone. The maximum pressure exceeds 500 MPa when the charge tail is impacted. The tail of the charge is deformed and damaged severely， which may lead to a highly localized temperature and even ignition.

Abstract:The dynamic characteristics of unreacted solid explosive PBX-59 under ramp wave compression were studied with a magnetic driven loading experimental technique， and the dynamic response of PBX-59 under a peak pressure up to 18.5 GPa was obtained. The p-V relationship， the acoustic velocity-particle velocity relationship and other dynamic parameters of PBX-59 were obtained by the iterative Lagrange data processing method modified by impedance matching under the ramp wave compression. Combined with the dyamic parameters and isentropic equation of state derived from experimental data， the experimental results were hydrodynamically simulated. The numerical calculation agree well with the experimental results， which verifies the validity of the experimental technology， data processing method， and physical model.