The ceramic/fiber composite ballistic plates are widely used in personal protection equipment. Studying the performance of ballistic plate subjected to multi-impacts is of great significance for reducing the number of casualties in the battlefield.This paper investigates the Al₂O₃/UHMWPE composite ballistic plate,focusing on numerical simulations conducted for various bullet impact points.The reliability of the simulated results is validated by comparing with the experimental results.The relationship between the energy absorption and damage characteristics of the ballistic plate is derived from the ceramic and fiber damage results,and the penetration probability of the next impact is effectively calculated.The results indicate that the damage patterns of ballistic plates are roughly the same and the impact resistance of ceramic layer at the joint decreases.when the impact point of the first bullet is located at the center of a ceramic plate,within the gap between two plates,or at the gap of quadrilateral jointing.Specifically,when the impact point of the first bullet is located at the center of ceramic plate,the subsequent bullets tend to penetrate through the gap between adjacent plates.As the proximity between successive impacts decreases,the energy absorption by the ceramic layer diminishes while the energy absorbed by the fiber layer increases.When two impact points are located parallelly and diagonally apart,the middle ceramic plate does not suffer macroscopic damage due to the joint structure.When the first impact point is in the center of the ceramic plate,the penetration probability of the second impact is 1.04%.When the first impact point is in the center of the ceramic plate,and the second impact point is in the horizontal adjacent center,the four corners of the gap,or the diagonal adjacent center,the penetration probability of the third impact on the ballistic plate is 5.45%,7.35%,and 5.05%,respectively.This method can be used to quickly evaluate the resistance of damaged equipment to multiple penetrations.

In order to study the performance of explosives after the impact detonation of different shaped charges on targets in water,three kinds of shaped charge structures,i.e.,explosively formed projectile (EFP),jetting projectile charge (JPC) and shaped charge jet(JET),are selected for underwater penetration and underwater impact detonation tests.The measured velocities of different shaped charge penetrators before entering water,before hitting a target and after penetrating into a target,the penetration effect on the arc target plate and the impact detonation effect on B explosive behind the target are obtained through the tests.The impact detonation mechanism of different shaped charges in water and the variation law of impact detonation coefficient k at different water medium lengths are compared and analyzed.The results show that the impact detonation performances of EFP,JET and JPC after impacting a target in water decrease nonlinearly with the increase in the length of water medium,and the performance of JPC is better than those of JET and EFP.The critical impact detonation coefficient of explosive B is 18.22mm³/s² after EFP,JET and JPC penetrate the metal target plate with a thickness of 2cm and a length of 0-100cm water medium and a water medium with a length ranging from 0 to 100cm.

The thickness equivalence of composite radome under the far-field explosion loads is studied by taking the fiber-reinforced polymer (FRP) laminate as the research object.A serial artificial neural network (S-ANN) model based on the principle of deflection equivalence is proposed to predict the thickness equivalence relationship between glass fiber radomes with different performances.A finite element model for the dynamic response of FRP laminates under explosive loads is established.The maximum deflection of FRP laminates under the conditions of different detonation distances,laminate thicknesses,densities,and longitudinal elastic moduli is obtained by conducting batch calculations on this finite element model.Based on this,a S-ANN thickness equivalence model is established.The proposed model achieves the thickness equivalence for different types of FRP materials under far-field explosion loads.In addition,the frequency response characteristics of the glass fiber equivalent radome are analyzed using the \overline{A}\overline{B}\overline{C}\overline{D} transmission matrix and a numerical simulation method.The research results show that the longitudinal elastic modulus has the greatest influence on the explosion resistance and equivalent thickness of glass fiber radome under far-field explosion loads.The equivalent thickness has little influence on the amplitude of the radome’s transmission efficiency,but it changes the resonant frequency of the radome’s transmission efficiency.This study can provide reference for the thickness equivalence research and optimization design of radomes.

In order to study the explosion driving characteristics of shell fragments driven by cylindrical charge with cavity and reveal the mechanism of the influence of shaped charge structure on the initial velocity of shell fragments,the explosion driving process and initial velocity distribution of shell fragments under different cavity cone angles are studied through the numerical simulation.The initial velocity distribution function of shell fragment along the axial direction is fitted by analyzing the rarefaction wave propagation path,velocity loss coefficient and fragment acceleration process.The relative error between the calculated and simulated results is less than 15%.The results show that the earlier generation of rarefaction wave and the decrease in cross-section ratio of mass of charge to shell are the main factors contributing to the decrease in the initial velocity of fragments.The initial velocity of the fragments near the non-detonation end decreases with the decrease in the cone angle of cavity and the increase in the cone top height of cavity.The rarefaction wave reflected from the non-detonation end is an approximately planar wave and is at a certain angle to the cavity surface.The instant when rarefaction wave reaches shell is linearly and positively correlated with the axial position of the shell.The cross-section ratio of mass of charge to shell has a quadratic function relationship with k,where k is the ratio of the distance from the cross section to the non-initiating end to the height of cavity cone top.The velocity loss coefficient decays exponentially with the decrease in k.The research can provide a useful reference for the overall structural design,material selection and structural optimization of anti-armour and anti-personnel composite warheads and the deformable fragment warhead with cavity charge structure.

Studying underwater explosions near warships is crucial for hull structure design,explosion impact damage prediction,and personnel safety.To this end,an improved six-equation compressible multiphase flow model based on the diffuse interface method is proposed to resolve thermodynamic state prediction deviation under shock waves and support anti-shock mechanism research and numerical method optimization.The model is improved via a hybrid energy correction equation and a more accurate gas equation of state.A numerical algorithm on an unstructured grid system is constructed,adopting the second-order MUSCL-Hancock scheme (with least-squares reconstruction and Barth-Jespersen limiter) and two-phase HLLC Riemann solver to solve homogeneous hyperbolic equations,and Newton-Raphson iteration for instantaneous pressure relaxation equation.Results show that after total energy equation correction,the model’s simulation of shock wave velocity and interface is highly consistent with the Euler equation’s exact solution,resolving near-interface numerical oscillation.Compared with experimental data,the improved model has a 1.13% relative error and 0.33% higher accuracy; more accurate SG-EOS parameters are obtained by fitting the shock Hugoniot curve.It also clearly shows underwater explosion phenomena:shock wave propagation,bubble expansion-contraction,and bubble collapse water jet.However,it has deficiencies in bubble interface clarity and jet precision,mainly limited by numerical scheme dissipation under extreme gradients.In conclusion,the improved model effectively enhances the accuracy of simulating underwater explosions near naval vessels,supports in-depth warship anti-shock mechanism research,and lays a solid foundation for future numerical method optimization.

Explosion-induced seismic waves have become the main factors inducing secondary disasters such as building collapse and infrastructure damage due to their long wavelength,strong amplitude and fast propagation speed.Based on two kinds of typical explosion-proof equipment,the static explosion tests with different TNT dosages are carried out to study the propagation and attenuation law of explosion-induced seismic waves under three different protection conditions of free-air blast (FAB),steel explosion-proof (SEP) and flexible explosion-proof (FEP).The vibration velocity time-domain responses and main vibration frequency characteristics of SEP and FEP equipment are analyzed.The three-axis peak vibration velocity vector and attenuation models under the protection of SEP and FEP equipment are constructed,and the damage level of building is divided accordingly,which is subdivided into three criteria of safety,slight damage and serious damage.It is found that the vector sum of triaxial peak vibration velocities increases with the increase of TNT charge,and decreases with the increase of detonation distance.The triaxial dominant frequency shows no obvious change rule when the detonation distance or TNT charge increases.Compared with FAB,both SEP and FEP show significant protection performance against the triaxial peak vibration velocity of explosion-induced seismic waves.The research results can provide reference for the structural design of related explosion-proof equipment and the evaluation of explosion-induced seismic wave protection effectiveness.

To develop the electrically-heated composites that have both anti-icing/de-icing functionality and meet load-bearing performance requirements,three types of electrically-heated fabrics containing nickel-chromium alloy wires with parallel spacings of 6.67mm,4.00mm and 2.86mm and their reinforced composites are designed and fabricated based on the tailored fiber placement process.The lowest surface temperature of the composites reaches 87.2℃ within three minutes at 25W.The low-velocity impact properties,electro-thermal properties and compression properties of the composites subjected to 7J impact load are tested and analyzed using a drop weight impact tester,an infrared thermal imager,and a universal testing machine.The results indicate that the impact energy absorption of composite with a the nickel-chromium alloy wire electrically-heated layer is increased by at least 23.6%.The surface temperature of the damaged areas in the electrically-heated composites can still reach above 72.4℃ after impact,and the retention rates of post-impact compressive modulus and compressive strength are 88.73% and 94.97%,respectively.Compared to glass fiber/epoxy composites,the decrease in the parallel spacing of nickel-chromium alloy wires results in a more pronounced delamination phenomenon in the electrically-heated layer under post-impact compressive load.These findings provide practical guidance for the design of electrically-heated composites for aircraft anti-icing/de-icing applications,ensuring a balance between mechanical performance and functional requirements.

In order to study the mechanochemical response behavior of PTFE/Al/W fluoropolymer-matrix reactive materials under shock loading,the drop-weight impact test of fluoropolymer-matrix reactive materials is carried out,and a weak coupling trans-scale numerical calculation method is proposed.Based on this method,a trans-scale numerical simulation model is established for the drop-weight impact loading reaction process of macro-meso scale fluoropolymer-matrix reactive material.The mechanochemical response behaviors and impact activation mechanisms of macroscopic and mesoscopic structures of sample in the drop-weight impact test are discussed and analyzed through trans-scale numerical simulation.The results show that the content of W has a significant effect on the impact activation reaction of fluoropolymer-matrix reactive materials,and the impact activation threshold of the reactive materials system decreases with the increase of W content.The weak coupling trans-scale numerical simulation analysis model effectively simulates the mechanochemical response process of fluoropolymer-matrix reactive materials.The X-shaped shear band is the dominant mechanism for the breakage and activation of fluoropolymer-matrix reactive materials,and its formation,evolution and distribution are greatly affected by W content.

To explore the explosive shock wave characteristics of typical cylindrical explosives with elliptical cross-section,an experiment on the static explosion of variable-section cylindrical explosives in free field is conducted,and a corresponding numerical simulation model is established.The reliability of the numerically simulated results is verified by comparing with the experimental results.The explosions of cylindrical explosives with different cross-sectional shapes in free field are numerically simulated to investigate the influence of cross-sectional shape on the power characteristics of explosive shock waves.The research results indicate that the explosive shock wave generated by the cylindrical explosives with elliptical cross-section produces a wave system structure similar to that generated by the cylindrical explosives with a circular cross section,but there are differences in the propagation characteristics of shock wave at different azimuth angles.The peak overpressure,maximum impulse,and shock wave velocity in the short-axis direction are all greater than those in the long-axis direction.For elliptical cross-section explosives with different aspect ratios of long axis to short axis,the greater the aspect ratio is,the more significant this difference becomes.An equivalent radius is introduced to fit and obtain a formula for calculating the peak overpressure and the shape factor of peak overpressure,which includes the aspect ratio as a variable,and a deviation between the calculated results and the numerically simulated results is less than 10%.

The staggered layout of urban building complex makes the propagation path of explosion shock wave more complicated,thereby increasing the difficulty of evaluating the damage effect comprehensively and accurately.Numerical simulation methods based on computational fluid dynamics can accurately simulate the blast loading,but the calculated amount is large and the calculation time is long.In order to rapidly predict the blast loading in urban building complex,a fast blast loading prediction method based on neural network is proposed.The influence of the number of training samples on the prediction accuracy and the effect of regional division on the prediction performance of the model are analyzed.In order to meet the data requirements for training the neural network model,the explosion simulation software is used to analyze the mesh sensitivity in a typical dense urban building complex and generate a dataset for 80 sets of explosion scenarios while considering simulation speed and accuracy.In order to determine the appropriate model structure,the fully connected neural networks with different numbers of layers are constructed for comparative experiment and analysis.The effects of the number of training samples,the division of region and the construction of dual models on the prediction accuracy of the model are analyzed through comparative experiments.The results show that the prediction error of the proposed method is less than 10% on 16 sets of test data except the training data,and the inference time only takes 2 seconds.The proposed method has a balanced and good prediction ability for various ranges of peak overpressure,and provides a new approach and perspective for realizing the rapid prediction of blast loading in urban building complex.

In order to clarify the injury mechanism of human head under blunt ballistic impact,a finite element model fitting the characteristics of Chinese 50th percentile male adult heads is constructed by the material parameter optimization,proportional scaling and fluid-structure interaction methods based on the total human model for safety (THUMS) model.LS-DYNA (Livermore software technology corporation's dynamic analyzer) is taken as a simulation platform,and the arbitrary Lagrangian-Eulerian algorithm is used to define the fluid characteristics of cerebrospinal fluid,optimize the elastic-plastic material parameters of skull and brain tissue,and realize the localization of head size and anatomical structure through mesh deformation technology.The biomechanical response of the model is verified by comparing the data of Nahum cadaver experiment and THUMS model for the typical vulnerable parts,such as forehead,parietal wall,occipital and posterior fossa,of human body.The results show that the peak values of intracranial pressure in the vulnerable area of the improved model are 150kPa,75kPa,53kPa and 69kPa,respectively,and the error between the improved model and the experimental data is 4%-10%,and the shape of the dynamic response curve is consistent.The maximum von Mises stress of brain tissue (29.5kPa) and the principal stress of skull (18.7kPa) are close to the threshold of Marjoux and Yoganandan simulation experiment,which verifies that the proposed model could effectively predict the risk of craniocerebral injury.The assessment based on NATO AEP-103 standard indicates that the peak value of the forehead intracranial pressure under typical impact is 511.1kPa,far exceeding the threshold of skull fracture (150kPa),which highlights the optimization needs of existing protective equipment.The proposed model has strong applicability and can provide reference and theoretical support for head injury assessment and safety protection under blunt ballistic impact.

Bottom mines are typically deployed on the seabed and are designed to damage the surface ships and submarines during underwater explosion.The casing of bottom mine is the key factor influencing the energy output structure of charge underwater explosion (UNDEX).Based on the theory of UNDEX,the coupled Euler-Lagrange (CEL) method is used to establish a numerical model of the UNDEX of cased charge near the seabed.The characteristics of shock wave loads generated by the underwater explosion of cased charge are studied and the effects of various factors,such as charge shape,detonation mode,casing configuration,casing thickness ratio,and casing-to-charge mass ratio,on the characteristics of shock wave loads generated by underwater detonation of charges are analyzed.Furthermore,a casing with a variable wall thickness suitable for near seabed conditions is proposed,which significantly enhances the shock wave load.The results show that the constraint characteristics of the casing can cause the slower attenuation in the shock wave due to the underwater explosion of charge with distance.The casing with variable wall thickness has an enhancing effect on the shock wave load due to the underwater explosion of charges.The peak pressure of shock wave at 800 mm significantly increases with the increase of δ,and the growth rate can reach 9.74%.It can provide reference for the design of underwater weapons.

The dynamic impacts generated during the transient shifting process of a planetary integrated transmission system for tracked vehicle have serious effect on the service performance and reliability of transmission system.For a certain planetary integrated transmission system,the torsional dynamics models of gear transmission components,clutches and brakes,etc are established,and a dynamics model of transmission system during the shifting process is constructed.The simulation and bench tests of the shifting process of the integrated transmission system are carried out.The changing trends of the simulated and test results are basically consistent,thus verifying the correctness of the dynamics model.The impact loads of typical components during the shifting process are further studied,and the influence laws of the throttle opening and the characteristics curves of oil charging and discharging,etc.on the dynamic torques of the operating components are revealed.The main conclusions are as follows.The reverse dynamic torque of disengaging operating component and the maximum impact torque of engaging operating component gradually increase with the increase in oil discharging delay.With the extension of oil discharging time,the reverse dynamic torque of disengaging operating component gradually increases,and the maximum impact torque of engaging operating component decreases first and then increases.The faster the oil charging is in the fourth pressure increasing stage,the greater the maximum impact torque of engaging operating component is,and the maximum impact value is 11% higher than the minimum impact value.With the increase in throttle opening,the maximum dynamic torque of operating component gradually increases,and the maximum dynamic torque value is 73.8% higher than the minimum dynamic torque value.

Ultra-high molecular weight polyethylene (UHMWPE) is widely used in the protective field due to its lightweight and exceptional mechanical properties,which can effectively resist projectile impacts.However,the micro-scale anti-penetration mechanism and ballistic impact damage modes of UHMWPE remain to be further investigated. This study focuses on two-dimensional woven and unidirectional (UD) UHMWPE composites,establishing a finite element analysis model for ballistic impacts that considers the microstructural characteristics of fiber-reinforced composites.Numerical simulations of normal and oblique penetration were conducted for composite targets with varying thicknesses and fiber layer counts,and the results were compared with experimental data to verify their reliability.Subsequently,the damage modes and energy absorption characteristics of the composite plates under different impact conditions were investigated.The results indicate that the damage modes of the composite plates are similar across different speeds,with lower speeds resulting in larger deformation areas and less energy absorption,reflecting a tendency for the material to experience extensive plastic deformation rather than localized brittle fracture under low-speed impacts.As the penetration angle decreases,the interaction time between the projectile and the target material significantly increases,enhancing energy transfer and absorption.This study not only delves into the ballistic impact mechanical response of UHMWPE composites,but also clarifies the damage modes and energy absorption mechanisms of the material under different impact conditions,providing a solid theoretical foundation for the design of composite plates with high-efficiency anti-penetration performance.

Solid propellants with crack defects are susceptible to crack propagation under shock wave loading during their service life,significantly affecting their structural integrity.The dynamic mechanical response and defect-induced damage evolution of hydroxyl-terminated polybutadiene (HTPB) propellants under varying shock wave intensities are investigated using a shock tube apparatus,and the schlieren imaging and 3D digital image correlation (3D-DIC) techniques.Shock wave loading experiments are conducted on both defect-free and crack-defected propellant specimens within a pressure range of 0.3 to 0.9MPa,and the dynamic deformation and damage evolution processes of propellant specimens are captured in the experiments.The results indicate that the deformation of the defect-free specimen exhibits a parabolic profile,and The deformation of the sample increases with the increase in impact pressure.The specimens with different crack depths show different degrees of crack growth under 0.9 MPa impact pressure,and the multiple impacts will result in superimposed damage.The critical failure crack depth ratio is 50%-75%.Residual specimen analysis reveales that the matrix cracking,particle debonding,and particle fracture are the primary failure mechanisms.These findings provide valuable insights for assessing the structural integrity of solid rocket motors under ignition shock condition.

In order to investigate the effect of polyurea coating on the protective performance of blast-resistant structure,a multi-layer blast-resistant structure reinforced with polyurea is proposed,and the protective characteristics of blast-resistant structure under the actions of shock wave and fragments are analyzed.The overpressure fitting formula of explosive is calculated and obtained,and out-of-plane displacement of blast-resistant structure is measured using a laser 3D scanner.Experimental results of overpressure and displacement are in good agreement with simulated results.Research results show that the position of polyurea coating has great effects on the protective ability of blast-resistant structure.The protective effect of coating located on blast-facing side of sandwich steel plate is better than those of coating located on the back-blast sides of face plate and sandwich steel plate.It can effectively reduce the penetration rate and impact number of fragments,weaken the energy of the combined load ultimately acting on the back plate,and reduce the vibration amplitude and acceleration at the center of back plate.This study can provide a reference for the design of multi-layer blast-resistant structure.

Coral sand is widely used in military protection projects of islands because of its convenience and well anti-explosion buffering performance.It is necessary to obtain the shock Hugoniot data of coral sand before investigating the high-pressure shock equation of state.A shock wave test system for multi-medium is designed based on continuous pressure-conducted electrical resistance probe.The test system can be used to determine the detonation wave and shock wave time history curves of explosives,standard material and tested material in a explosion test.Then the shock Hugoniot curve of the material under test could be calculated based on the impedance matching principle.A feasibility test is carried out using water as the test material to verify the reliability of the method.Finally,the shock Hugoniot curve,represented by shock wave pressure P and particle velocity U_p, of coral sand is determined using the proposed method,which is compared with the Hugoniot data of quartz sand.The experimental results show that the shock Hugoniot curve of test material can be conveniently and reliably determined based on the continuous testing system of multi-medium shock waves and the impedance matching principle.The exploration work provides a supplement to the experimental research on the shock equation of state for large-scale heterogeneous materials.

To investigate the effects of different machine oil-diesel ratios on the explosive properties of site-mixed emulsified explosives, the viscosity and particle size distribution of emulsion matrices with varying oil-diesel ratios by using digital viscometry, laser particle size analysis, and optical microscopy were examined, the internal phase structure of explosive samples was observed. The density of matrices and explosive specimens were measured through PVC tube simulations of borehole charging configurations. Detonation velocity and brisance were respectively determined by using a detonation velocity tester and lead cylinder compression method. The results reveal that as the oil-diesel ratio in explosive formulations increased from 0:5.5 to 5.5:0, the matrix viscosity rose from 1.5×10⁵mPa·s to 3.7×10⁵mPa·s. Concurrently, the sensitized bubble concentration increased while the bubble size decreased, demonstrating improved uniformity. The dispersed phase droplet size distribution narrowed significantly with distribution width decreased from 86.19μm to 6.33μm, the mean particle size reduced from 13.85μm to 2.78μm, and dispersion index declined from 6.23 to 2.27, indicating enhanced homogeneity. At 0.3% sensitizer content, the explosive density increased progressively from 0.95g/cm³ to 1.10g/cm³. Corresponding improvements in detonation performance were observed: the detonation velocity increased by 24.08% from 3155m/s to 3915m/s showing consistency with theoretical predictions from the B-W method, and the brisance increased by 34.48% from 9.05mm to 12.17mm.With increasing the sensitizer concentrations(0.3%,0.5%,0.7%), the bubble density increased and the explosive density reduced. Distinct performance trends emerged based on oil-diesel ratios: formulations with ratios ≤3:2.5 exhibited initial enhancement followed by decline in detonation parameters, while those with ratios ≥4:1.5 demonstrated progressive reduction in explosive performance characteristics.

Hypersonic warheads usually induce serious aerodynamic heating during flying,and the warhead charge also bears a harsh thermal environment because of the structural heating which may affect its thermal safety.The finite volume method and the two-way fluid-structure interaction method are used to simulate the aerodynamic heating and structural heat transfer processes of hypersonic warheads.The temperature field distribution of pneumatic heating of hypersonic warhead and the thermal-ignition response of charge at different speeds and angles of attack are analyzed based on the chemical reaction kinetics model of explosive.The results reveale that the highest temperature occurs at the head of the warhead under aerodynamic heating and structural heating transferduring the hypersonic flight of warhead,and then it decreases backwards and inward.The temperature distribution is asymmetrical at different angles of attack,the temperature on the windward side increases with the increase in the angle of attack,and the temperature on the leeward side decreases with the increase of the angle of attack.After introducing the chemical reaction kinetics model,the ignition of the charge appears on its head at 35.4s and 574K.the faster the warhead’s speed is,the more severe the aerodynamic heating it experiences is,and the shorter the ignition time of charge is.A thermal protection structure is designed,which can effectively increase the temperatures of warhead’s shell and charge by 79.12% and 71.45% during its 100s flight process as well as ensure that the internal charge does not ignite.This study is of great significance in addressing the thermal safety issues of hypersonic warhead charges.

To address the issues of the lack of structural synergy between ceramic plates in existing spliced ceramic bulletproof plates and the poor dissipation of impact energy,a biomimetic topological interlocking ceramic splicing scheme based on the exoskeletal structure of phloeodes diabolicus is designed.The numerical simulation research is made on the protective performance of the designed bulletproof plates under the impact of bullets. A non-standard bulletproof ceramic plate with a phloeodes diabolicus exoskeletal structure is designed based on the microstructure of biological materials and the principle of topological interlocking in engineering structures.The accuracy of the simulation model is verified through 3D-DIC testing,and the penetrations of 5.8mm DBP 10 rifle bullets into square,hexagonal and biomimetic topological interlocking ceramic spliced bulletproof plates are simulated.The results show that the biomimetic topological interlocking ceramic blocks can effectively enable the surrounding ceramics to dissipate the impact energy,The back bulge height of the biomimetic topological interlocking ceramic bulletproof insert after being penetrated is reduced by approximately 8% compared to that of the hexagonal ceramic bulletproof insert.An individual soldier protective insert plate based on the biomimetic topological interlocking ceramic configuration is designed,and the numerical simulations are conducted on the blunt trauma effects of M80 rifle bullet penetrating the human torso of the protected individual soldier.The results indicate that the blunt trauma energy is primarily borne by the muscles and thoracic ribs,and the peak stress on thoracic ribs reaches 30.7MPa,which potentially leads to bone fractures.The maximum stress in the heart is 930.2kPa,and the maximum stress in the lungs is 777.5kPa,potentially causing myocardial injury and lung soft tissue contusion.

Aiming at the dynamic fragmentation characteristics of reactive material and its effect on the impact energy release behavior,two types of reactive materials,Al/Ti and Al/Ti/W,are selected as the research subjects.Dynamic fragment soft-recovery test is conducted to obtain the fragment size distribution characteristics of reactive material at different impact velocities.Additionally,the impact-induced energy release test is performed to analyze the impact pressure characteristics and reaction processes of Al/Ti and Al/Ti/W.Based on these investigations,a calculation method for impact pressure,which considers material fragmentation characteristics and the critical size of the reaction,is proposed.The results indicate that the fragmentation characteristics of reactive material are crucial in influencing its impact energy release behavior.The cumulative size distribution of fine fragments formed after the impact fragmentations of both Al/Ti and Al/Ti/W materials can be described using a Logistic distribution function.The impact reaction process of reactive material in a reaction chamber can be divided into primary and secondary reaction stages.The calculation error of the proposed calculation method is less than 15% when calculating the quasi-static pressure during the primary reaction stage.

The dynamic response and energy dissipation mechanism of foam aluminum sandwich panel under underwater impulsive load are analyzed to provide a scientific basis for the protection design of ships and marine engineering structures.The consistency between the test and simulated results is verified through the underwater explosion equivalent impact test and simulation.The influences of structural parameters,such as core layer mass ratio,panel thickness,foam aluminum density and impact load on the impact resistance of sandwich panels are quantified.Multi-objective optimization of sandwich panel structure is carried out using neural network and genetic algorithm.The results show that the foam aluminum sandwich panels subjected to underwater impact loading exhibit the deformation patterns such as local collapse and boundary shear.When the mass of sandwich panel is constant,there exists an optimal core layer mass ratio and an optimal wet panel thickness,which increase with the increase of dimensionless impulse.As the thickness of wet panel and the density of core layer decrease,the energy absorption efficiency of the compression deformation of core layer increases.The optimized sandwich panel has significantly reduced deformation and mass.

Exploding foil initiators (EFIs) represents a promising initiation technology for meeting the high requirements of miniaturized and integrated weapon systems for initiation capability.To conduct an in-depth research on the initiation and detonation output characteristics of small-sized charges in the exploding foil initiator system,a synchronous test system for observing the electrical explosion-driven flyer characteristics of metal bridge foils and a particle velocity measurement system for measuring the velocity of particle at the explosive-window interface for flyer-impact-initiated small-sized explosive detonation are built.The velocity and morphological characteristics of flyers and the initiation and detonation reaction behaviors of small-sized Ultrafine Hexanitrostilbene (HNS-IV) explosive under flyer impact were investigated.The results show that the flyer velocity is positively correlated with the initiation voltage.When the initiation voltage ranges from 900V to 1500V, the flyer velocity exiting the accelerator chamber is measured at 2000m/s to 4200m/s.HNS-IV-based explosives demonstrates a short growth distance of detonation under high-intensity impact.For instance,a stable detonation is achieved within just 2.14mm under the action of a 3455m/s flyer.The further analysis of detonation wave structure indicates that HNS-IV has a fast detonation reaction rate,with a reaction time of less than 27 ns and a reaction zone width of only 0.13mm.Under the condition of a 3mm-diameter charge,the main detonation reaction of HNS-IV explosives remaines largely unaffected,but the energy decays rapidly in the late stage of reaction.The detonation reaction rate model is first calibrated with the experimental results,and then the effect of charge size on the energy output is studied through simulation.The results show that the increase in charge thickness is more effective in enhancing the energy output at the end of charge than the increase in charge diameter.

In order to obtain the damage characteristics of the double-layer shell structure under the underwater explosion of the shelled charge, the damage test of the double-layer shell structure under the underwater explosion was carried out with a small explosive tank device, and the influence of the hollow medium at the back cavity of the inner plate, the filling medium between the inner and outer plates, the explosion position and distance and other factors on the damage characteristics of the double-layer shell were analyzed, and the damage mode of the double-layer shell structure under the underwater explosion of the shelled charge was obtained. The results show that under the contact explosion of the underwater shell charge, there are three kinds of damage modes: the overall plastic deformation of the double-layer shell, the tearing of the inner and outer plates in the shape of “mouth”, “grid” and “cross”, and the local bending or fracture deformation of the inner and outer plates and ribs. Under the same underwater contact explosion conditions, when the explosion position is at the intersection of the transverse and longitudinal ribs of the double-layer shell, the damage range caused to the inner and outer plates is larger, and the filling of the water medium between the double-layer shells greatly reduces the impact effect on the inner shell and improves the impact resistance of the inner plate of the double-layer shell.

In order to carry out comparative analysis on the implosion power under atmospheric and vacuum conditions, the implosion experiments were applied for JO-8 explosive in a vacuum explosion tank and the implosion power under different conditions was analyzed. The results show that the peak reflected pressure in the forward direction of explosion product propagation is 1.12 times the value in the side direction in vacuum and the peak quasi-static pressure in the forward direction of explosion products propagation is 1.67 times the value in the side direction. The deformation of the effect target in the forward direction of propagation is greater than that in the side direction, proving that the propagation of explosion products has distinct directionality in vacuum. The peak reflected pressure and peak quasi-static pressure under atmosphere are 1.12 and 1.67 times the values in vacuum respectively. Simultaneously, the deformation of the effect target is greater than that in vacuum, showing that stronger damage power is produced under atmospheric pressure because of the lack of air medium in vacuum.

In order to research the explosion characteristics of HMX-based aluminized explosives with different charge structures in confined space, experiments on the confined explosion of samples with composite charge structures and uniform charge structures were carried out. A closed explosion experimental device with temperature and pressure measurement was established. The explosion pressure and temperature of the sample with composite charge structure were compared with the same sample having the uniform charge structure. The result shows that the peak pressure and quasi-static pressure of the explosion shock wave of the sample with composite charge structure are 12.7% and 8.0% higher than those with the uniform charge structure, respectively. The explosion energy release in confined space can be improved through the composite charge structure, which consists of the outer layer with high detonation velocity explosive and the inner layer with high aluminum/oxygen ratio explosive. The peak explosion temperature of composite charge structure is 621℃, which decreses by 124℃ compared with the uniform charge structure of 745℃, but the samples with composite charge structure can maintain a high temperature around 600℃ in confined space for a long period.

In order to study the ignition and explosion properties of micro-nano self-assembled and physically mixed aluminum powder materials, the ignition sensitivity, flame propagation characteristics and explosion parameters of the materials were studied through a 1.2L Hartmann tube and a 20L ball explosion test system. The results show that compared with Al-T4 micron aluminum powder, nano-aluminum powder can significantly reduce the ignition energy of aluminum powder materials.And the ignition sensitivity of the self-assembly process is further increased compared with that of aluminum powder materials with physical mixed process. In terms of the flame propagation speed, the high reaction rate of a small amount of nano-aluminum powder can accelerate the reaction of micron aluminum powder, and the self-assembled aluminum powder is easy to ignite and the heat transfer is more efficient due to the overall synergistic effect of micro-nano aluminum powder. In the 20L ball explosion test system, the maximum explosion pressure and explosion index of self-assembled and physical mixed aluminum powder with 5% mass fraction of nano content are 0.72MPa, 0.75MPa, 43.21MPa·m/s and 31.49MPa·m/s at 500g/m³. The maximum explosion pressure and explosion index of self-assembled and physical mixed aluminum powder with 10% mass fraction are 0.84 and 0.68MPa at 1000g/m³. The explosion pressure and explosion index of 5% mass fraction of nano aluminum powder increase first and then decrease with increasing the concentration, and the explosion pressure and explosion index of aluminum powder with 10% mass fraction increase with the increase of concentration. The explosion power of the composite system isnot only related to the activity, but also has a certain relationship with the calorific value of the powder.

The effects of altitudes and the decoupled conditions of low pressure and temperature on the blast wave parameters of moving charge were investigated by employing the AUTODYN software. Additionally, a theoretical calculation model was developed to predict peak overpressure of the moving charge under low pressure and temperature. The model was validated subsequently through experimental data and numerical simulations. The results indicate that the model can assess the blast wave peak overpressure of moving charge at low temperature, pressure and coupled high-altitude environment effectively. The peak overpressure of the blast wave generated by the moving charge decreased by an average of 35.6%, the action range increased by 62.0% for altitude increased from 0 to 10000m. With the ambient temperature decreased, the peak overpressure of the blast wave increased by an average of 0.43%, the action range decreases by 11.9%; and with the ambient pressure decreased, the peak overpressure of the blast wave decreased by an average of 36.4%, the action range increased by 83.5%. The increase coefficient of blast wave overpressure resulting from the moving charge at various altitudes closely resembles that of low pressure. In high-altitude settings, the action range and overpressure of the blast wave from the moving charges explosion are predominantly influenced by pressure, whereas the effect of temperature is comparatively marginal.

Aiming at the structural damage caused by the water-entry impact of trans-media vehicle, an auxetic hood load-shedding method is proposed to make use of the special tensile expansion effect of auxetic structure, so that the hood can absorb more impact energy. The arbitrary Lagrangian-Eulerian algorithm is used to analyze the influence law of the auxetic hood on the load-shedding characteristics of the vehicle, and the numerical method is verified by experimental data. The results show that, compared with the traditional load-shedding cowl, the auxetic hood effectively reduces the impact load of the structure entering into water on the basis of structural lightweight, and the peak acceleration can be reduced by 75%, 70% and 68% at the water-entry speeds of 20m/s, 35m/s and 50m/s, which is a good load-shedding cushioning effect. And the load-shedding characteristics of auxetic structure differ greatly under the different parameters of the cell angle, the wall thickness and the length of the sides. The load-shedding characteristics of auxetic hood reaches the optimal effect with cell angle of 20°, cell wall thickness of 0.5mm and cell side length of 1.6 times.

In order to study the impact energy release and crushing behavior of N b₁Zr₂Ti₁W₂ high entropy alloy, the test method of dynamic energy release testing during the bullet-target interaction was provided by ballistic gun and quasi-closed reaction tank. The impact energy release process and dynamic crushing law were analyzed, and the cumulative mass distribution model of fragments was established. The impact induced energy release characteristics of N b₁Zr₂Ti₁W₂ high entropy alloy were studied.The results show that N b₁Zr₂Ti₁W₂ produces “explosion-like” energy release effect under high-speed impact load, which releases a large amount of chemical energy mainly due to the oxidation reaction of Zr element. The 5.07g alloy material can produce 0.176MPa overpressure in the 32.7L quasi-closed vessel at the speed of 1631m/s. The distribution of fragments follows the power law, and the size of fragments is closely related to the energy release.

The improved Hartmann tube device was used for ignition experiments to investigate the flame propagation process and thermal radiation characteristics of MgH₂ dust explosion. A high-speed camera, thermal radiometers, and the infrared thermal imager synchronous control system were used to record the flame propagation, heat radiation flux change, and temperature change process of MgH₂ dust, respectively. The results show that after ignition, the MgH₂ flame continues to expand to form a continuous combustion area and when it reaches the maximum, it begins to decay, and a discrete flame appears. When the mass concentration is 150—1000g/m³, the maximum propagation height and the maximum propagation velocity of the flame front reach 1138mm and 45m/s, respectively, at 750g/m³. In addition, the maximum heat radiation flux of No.3 above the fireball reaches 31.7kW/m², which is much higher than those of No.1 and No.2 on both sides. The temperature is highest in the flame center and gradually decreases around it. The high-temperature zone is concentrated in the upper part of the flame.

Aiming at the expansion fracture mechanism of projectile steel shell under implosion loading, the smooth particle fluid dynamics method(smoothed particle hydrodynamics, SPH)was used to simulate the expansion fracture process and crack distribution law of 40CrMnSiB steel cylindrical shell with several wall thicknesses under implosion loading. The comparative experimental study was carried out by using the explosive water well recovery technology, and the crack formation mechanism was analyzed by combining the macroscopic morphology and microstructure of the cylindrical shell fracture fragments. The results show that the fracture mode of 40CrMnSiB steel cylindrical shell gradually changes from pure shear to tension-shear mixing with the increase of wall thickness. When the wall thickness of the cylindrical shell increases from 4mm to 17mm, the proportion of tension cracks gradually increases from 0 to 4/5, and the circumferential density of the cylindrical shell cracks and the total number of fragments formed decrease by 54.54% and 67.06%, respectively. With the increase of the wall thickness of the metal cylindrical shell, the mass distribution of the final fragments gradually disperses. By analyzing the microstructure of the recovered fragments, it is found that the fracture of the cylindrical shell is actually the result of the interaction and competition between the shear cracks generated on the inner surface of the shell and the tension cracks generated on the outer surface, and there is a phenomenon of mutual shielding between the cracks.

To deeply understand the impact initiation,impact ignition,detonation process,and detonation product states of energetic materials under extreme conditions, the decomposition reaction processes of α-, β-, γ-and ε-CL-20 crystals under shock loading were studied using self-consistent charge density functional-based tight-binding(SCC-DFTB)in combination with multiscale shock technique. The influence of water molecules on the decomposition of α-CL-20 was also studied because α-CL-20 generally exists in the form of hydrate. The results show that γ-CL-20 has the largest compression ratio among these four CL-20 crystals at the same shock velocity. When the shock velocity is 8 km/s, γ-CL-20 completely decomposes, while the other three crystals do not completely decompose until the shock velocity reaches 9km/s. Moreover, the addition of water molecules can significantly increase the activity of CL-20 molecules, and accelerate the decomposition of solid phase α-CL-20. In addition, the initial decomposition path of CL-20 under shock loading is not significantly affected by the crystal forms, but is mainly affected by the shock velocity. When the shock velocity is lower than 8km/s, the decomposition reaction is triggered by the dissociation of N—NO₂ bond. However, when the shock velocity is higher than 9 km/s, the N—NO₂ bond is inhibited by high pressure. The H in the C—H bond may preferentially form a five-membered ring with the adjacent NO₂, and further produces NO and OH.

Due to the issue of high parallel deviation in the explosion heat test results of the composite solid propellants, using the thermostatic calorimeter, carry out the accurate test research of composite propellant explosion heat from the three aspects of clarifying the definition of explosion heat, standardizing experimental conditions and improving experimental devices. The results show that the measured values of the combustion heat release of the propellant using its own oxidizing agent tends to increase significantly with the reduction of propellant particle size and the increase of the sample amount. Therefore, the single quality of the propellant explosion heat test sample should be less than 0.14g, and the quality of the propellant sample should be more than the quality of the sample used to measure stable maximum heat release. The pressure measuring element is installed on the oxygen bomb of the calorimeter to realize the whole test record of the pressure in the oxygen bomb during the calorimetry process, and the pressure detection before ignition guarantees the effectiveness of displacing air in oxygen bomb. The maximum pressure in the oxygen bomb provides a basis for eliminating the outliers of inadequate combustion. Combined with the final pressure and the oxygen bomb volume in the experiment, the test of constant pressure explosion heat is realized.

To investigate the enhancement effects of free hydrogen produced by metal hydrides on the damage performance of fuel air explosive(FAE), A 20L spherical liquid explosion test system and the colorimetric temperature measurement technology were used to study the effects of different matrix liquid fuels and metal additives on the shock wave and thermal damage performance of FAE. The results show that epoxypropane(PO)has the best explosion performances of the three liquid matrix fuels commonly used in FAE. When titanium hydride(TiH₂)powders are added to PO, the explosion overpressure, maximum pressure rise rate and maximum average temperature of the mixed fuels increase first and then decrease with the increase of TiH₂ powders content, reaching the maximum values when the mass fraction of TiH₂ powders was 35%, namely, 1.21MPa, 68.73MPa/s and 2398K, respectively. Compare to Ti-PO mixed fuels, the TiH₂-PO mixed fuels has more continuous combustion flame and more excellent explosion performances at the same mass concentration. The research results indicate that as a potential high-energy additives, TiH₂ could be effectively applied to FAE to improve its explosion characteristics and enhance the shock wave as well as the thermal damage performances.

In order to evaluate the damage effect of block charges with different masses on the surface of concrete pier body,the damage characteristics of the concrete pier under the action of contact explosion were studied by numerical simulation,and the damage effect of the concrete pier body was evaluated by the equal damage curve,and the characteristics of the damage area of the top surface,side and side edge of the pier body under the action of contact explosion were obtained,and then the influence of charge quality and placement position on the damage effect of pier body was revealed. By establishing the calculation model of vulnerable volume,the variation curves of the remaining volume of concrete pier body with the charge mass under the action of contact explosion on the top surface,side and side edge were obtained. On this basis,the block charge with different masses was compared in 8 different positions on the concrete pier body during contact explosion,and the number of large fragments and the maximum fragment volume after the explosion were studied. The result shows that the shape of the damage area on the top surface and side of the concrete pier is approximately circular,and its center coincides with the center of the top surface. The shape of the damage area on the side edge is approximately elliptical. When the charge explodes in contact with the top surface,side and side edges,the damage effect at the center position is the best. When the charge mass is 1-3 kg,the damage effect of the explosive exploding at the geometric center of the top surface of concrete pier is the best. When the charge mass is greater than 3 kg,the damage effect of the explosion at the side geometric center is the best.

To study the influence of thickness on dynamic response and energy-absorption characteristics of foamed concrete(FC)under explosion-load impact,the numerical calculation of anti-explosion of FC under 0.8 m/kg^1/3 ratio-detonation-distance and 0-30 mm thickness was carried out by using finite element software. Subsequently,the anti-explosion tests of FC with thickness of 0 mm,10 mm,20 mm and 30 mm,were carried out to verify the accuracy of the numerical calculation. Through numerical calculation,the damage form and energy-dissipation mechanism of FC under the impact of explosion-load were studied,and the ability of FC to absorb explosion-wave energy was quantitatively analyzed,and the law of the energy absorption characteristics of FC and the deformation response of aluminum alloy plate on the back influenced by the change of thickness of FC was obtained,and the corresponding engineering-calculation-model was derived. The results show that,the size of the FC crushing zone gradually shrinks with the increase of thickness. The FC crushing-zone only accounts for 2.9% of the overall volume when the thickness is 30 mm. FC can effectively absorb and dissipate the energy of explosion wave,and its energy-absorption capacity increases with the increase of thickness. The foam concrete with thickness of 5-30 mm can absorb 42.8%-91.9% of explosion wave energy respectively. The displacement response of aluminum alloy backplane steadily shrinks as FC thickness increases. While the thickness of FC is 30 mm,the displacement response of the center of the aluminum alloy backplane drops to 3.2 mm,which is only 12.6% of that without FC.

In order to study the explosion shock wave propagation law of triacetone triperoxide(TATP)in the air, Raman spectrometer, Fourier transform infrared spectrometer(FTIR)and gas chromatography-mass spectrometry(GC-MS)were used to inspect the structure of homemade TATP. Then the parameters of the explosion shock wave of TATP in the air were tested by the shockwave test system. The variation of peak overpressure, positive pressure duration, specific impulse and shock wave velocity with proportional distance was analyzed. The empirical formulas of peak overpressure, positive pressure duration and impulse of TATP were fitted, and the TNT equivalent of TATP was calculated. The results show that the peak overpressure and specific impulse of TATP decrease with the proportional distance, and the attenuation amplitude also decreases with the proportional distance. The measured average values are 0.87 times and 0.73 times that of TNT, and the TNT equivalent of TATP is 75.39%; The positive pressure duration is affected by both the charge mass and the charge distance. The greater the charge mass and the distance, the longer the positive pressure duration. The average rising rates of the positive pressure duration of TATP and TNT with the proportional distance are 0.066 and 0.100, respectively. In the near field, the positive pressure duration of TATP is longer than that of TNT, and when the proportional distance is greater than 3.646m/kg^1/3, its positive pressure duration gradually decreases smaller than that of TNT. It shows that the explosion shock wave parameters of TATP in the air follow the explosion similarity law, and the empirical formulas obtained by fitting is suitable for the evaluation and theoretical calculation of TATP explosion power.

To investigate the bubble pulsation and water jet characteristics under the gas-liquid-solid multiphase coupling effect of underwater explosions near the seabed, the Euler method was employed to establish a numerical model of underwater explosions near the seabed under different substrate/water depth conditions. The full physical process of underwater explosions near the seabed under muddy substrate conditions was simulated and compared with experimental results, which showed good agreement, verifying the effectiveness of the algorithm in solving the problem of underwater explosion bubbles near the seabed. Based on this, the influence of seabed substrate and water depth on the bubble morphology, radius, period, and water jet of underwater explosions near the seabed was discussed. The results show that under the premise that the bubbles can be split, the harder the substrate, the faster the bubbles split, and the deeper the water depth, the slower the bubbles split. The harder the substrate and the deeper the water depth, the smaller the maximum radius and period of the bubble, the larger the proportion of the bubble in the total bubble volume at the moment of splitting, and the smaller the peak velocity of the two water jets generated by splitting. During the evolution of the downward water jet, a reverse water jet will form. The harder the substrate, the greater the peak velocity of the reverse water jet. In all calculated cases, the depth parameter(H_ref)is in the range of 250—750, and the peak value of the reverse water jet velocity is positively correlated with the H_ref, and the H_ref is in the range of 750—1000, which is negatively correlated.