High-entropy transition metal diborides have been extensively studied due to their high mechanical and thermodynamic properties. However, the conventional synthesis methods of these materials are inefficient. In this paper, we synthesized six types of high-entropy transition metal diborides based on VB₂, NbB₂, and TaB₂ by high-temperature and high-pressure solid-state reactions at 5.5 GPa and 2300 °C. The high pressure promoted the efficiency of solid-state reaction and facilitated the synthesis of high-entropy transition metal diborides. The X-ray diffraction and energy dispersive X-ray spectroscopy results have been confirmed that the six types of high-entropy transition metal diborides possessed pure phase compositions without oxide impurities or second phases, and exhibited uniform elemental distribution without elemental segregation. These results demonstrate that the synthesis of high-entropy transition metal diborides by using high-temperature and high-pressure solid-state reaction method is effectiveness and practicality.

In this study, a flash-heating device was designed and assembled to achieve instantaneous discharge heating of samples under high pressure in the DS 6×14 MN domestic hinged six-anvil large chamber press. By combining large chamber static high pressure and instantaneous discharge heating technologies, the melting state of crystals has been determined by the nucleation and growth characteristics during solidification. The melting behavior of h-BN powder crystal under high pressure was studied by instantaneous discharge heating treatment. Using scanning electron microscopy (SEM), the microstructures of samples obtained by high-pressure instantaneous discharge heating treatment was analyzed in order to assess the melting state of h-BN crystals. It was determined that the melting points of h-BN under 3.4 and 4.3 GPa are (4251±150) K and (4531±200) K, respectively. These results are beneficial for exploring the applications of h-BN and revising the existed temperature-pressure phase diagram of boron nitride.

Dynamic mechanical behaviors of high entropy alloys (HEAs) or medium-entropy alloys (MEAs) have attracted significant attention due to their exceptional strength-toughness balance and promising potential applications in extreme conditions. This work investigates the effects of peak shock stress and pulse duration on the spall damage of the NbTiZr MEA under dynamic shock loading. Peak shock stresses, pulse durations and spall strengths are determined by analyzing free surface velocity profiles, with postmortem microstructural analysis to reveal the underlying deformation and failure mechanisms. The measured spall strength of NbTiZr MEA ranges from 3.77 GPa to 4.80 GPa, showing minimal dependence on the peak shock stress but high sensitivity to the pulse duration. Furthermore, the damage morphologies are significantly influenced by pulse durations. The damage is recognized as a quasi-cleavage fracture mode. No phase transition or deformation twins are observed within the recovered NbTiZr alloy.

G54 steel is a new type of ultra-high strength steel independently developed in China, which has strong potential application value. In order to study the dynamic high-pressure performance of the material and provide data support for its application and popularization, the flyer symmetric impact experiments of G54 steel were conducted by using artillery as loading means. The experimental flyer velocities ranged from 600 m/s to 1400 m/s. By measuring the velocity-time history of particles on the back surface of G54 steel samples, the typical impact transformation and spallation signals were obtained. By analyzing particle velocities, material density and sound velocity measurements, the Hugoniot elastic limit, spallation strength, shock wave velocity-particle velocity (D-u) relationship and impact transformation point of G54 steel under impact pressure of 13–23 GPa were obtained. The metallographic analysis results of the recovered sample show that the damage mechanism of the spallation surface changes from ductile fracture dominated by micropore polymerization to ductile fracture dominated by adiabatic shear with the increase of flyer velocity.

In order to further reveal the acoustic emission characteristics and crack propagation law of soft and hard interbedded rock with different bedding plane dip angles under uniaxial compression, the soft and hard interbedded rock-like samples were prepared by rock-like materials. Based on the RMT-150B rock mechanics test system equipped with DS-5 acoustic emission monitoring system, uniaxial compression experiments were carried out on soft and hard interbedded rock-like samples with different bedding plane dip angles (0°, 30°, 45°, 60°, and 90°). Accordingly, the influences of bedding plane dip angle on acoustic emission characteristics, damage evolution and crack propagation of rock samples were analyzed. The results show that the acoustic emission activity of the sample presents obvious stage characteristics, and its distribution characteristics are obviously different under different bedding plane dip angles. The acoustic emission characteristic parameters show obvious bedding effect, and the cumulative ringing count and cumulative energy of acoustic emission decrease first and then increase with the increase of bedding plane dip angle. The sudden appearance or increase in the proportion of low frequency-ultra high amplitude signals can be used as a precursor information for the failure of soft-hard interbedded rock samples. The failure of low-angle (0° and 30°) samples is the steady expansion of large-scale cracks. The failure of medium-angle (45° and 60°) samples is the sudden instability expansion of large-scale cracks. The failure of high-angle (90°) samples is the sudden instability expansion of small-scale cracks. The dip angle of 60° is the most unfavorable angle for sample failure. The damage accumulation process of the specimens also has obvious stage characteristics. Before the peak stress, the damage accumulation of the specimens is mainly concentrated in the high rate damage stage, and the medium angle (45° and 60°) bedding surfaces accelerate the damage accumulation process of the specimens. The influence of different bedding plane dip angles on the evolution of tensile-shear cracks in soft-hard interbedded rock-like samples is obviously different. The horizontal bedding plane promotes the generation of tensile-shear cracks, and the gradual increase of bedding plane inclination angle promotes the development of tensile-shear cracks in rock-like samples. Under the joint action of bedding plane and rock matrix, with the gradual increase of bedding plane dip angle, the proportion of shear cracks in rock-like samples increases first and then decreases, and the number of shear cracks is at a high level. The research results have certain reference value for the stability evaluation of surrounding rock structure in underground engineering.

After the outer shell of the double-shell submarine is damaged by the near-field underwater explosion shock wave, the subsequent bubble pulsation and jet load will continue to cause serious damage to the inner shell of the submarine. Therefore, it is of great significance to study the characteristics of bubble pulsation and bubble load near the hole. Based on the double-shell submarine structure damaged by the shock wave, a double-layer cylindrical structure model with a prefabricated circular hole is made. Using an electric spark device as the bubble generator, the interaction experiments between bubbles and double-layer cylindrical structure with a hole under different explosion distance parameters (the ratio of explosion distance to the maximum diameter of bubbles) and different hole parameters (the ratio of hole diameter to the maximum diameter of bubbles) are carried out. A high-speed camera is used to capture the bubble pulsation and jet formation process near the double-layer cylindrical structure. The particle image velocimetry technology is used to test the velocity of the explosion flow field to obtain the jet velocity after the bubble collapse. At the same time, a pressure sensor is used to measure the pressure load on the inner cylindrical shell wall. The experimental results show that the detonation distance parameters determine the form of pressure load on the inner wall, whether effective jet is generated after the bubble collapse, and the jet velocity. When the detonation distance parameters are within a certain range, the hole parameters will affect the bubble pulsation and the direction of the water jet generated after the bubble collapse.

Oxides are prone to occur in welded joints by using of conventional welding methods due to high specific oxidation activity of magnesium and aluminum alloys, which leads to a decrease in the bonding performance of the composite plates. In order to improve the bonding strength of Mg-Al composite plates, Mg-AZ31B/Al-6061 composite plates were manufactured by vacuum explosive welding method, and compared with fabricating the same composite plates in air environment. The microstructure, elements distribution and mechanical properties of the interface were analyzed by optical microscope, scanning electron microscope, energy spectrometer and universal testing machine. The results show that the interfacial morphology of composites welded in vacuum environment is largely different from that in air environment due to the difference of gas shock pressure. The vacuum environment effectively inhibited the oxidation of magnesium and aluminum, and no metal oxides were detected in the melting zone. In addition, it was observed that the shear strength and tensile strength of the samples increased significantly under vacuum explosive welding. Therefore, vacuum explosive welding plays an important role in improving the performance of Mg/Al composite plates, and can be used as an high-performance metal welding method.

Compared with the traditional integrated structures, modularized cellular structures can meet the assembly requirements more flexibly. The deformation modes and energy absorption were studied to provide new ideas for the application of cellular structures in engineering, the regular hexagon with positive Poisson’s ratio effect and the re-entrant hexagon with negative Poisson’s ratio effect were selected as the infill units of the modularized cellular structures in this paper, and eight kinds of structures were designed for quasi-static compression experiments. The experimental results were in good agreement with the simulation results. The cellular structures with different infill approaches had different deformation modes under the compression experiments, in which the regular hexagon infill units showed obvious shear failure bands, and the alternate infill approaches can maintain the original units shape. The peak force of the two-layer infill cellular structures were greater than the three-layer infill structures, and the specific absorption energy were greater than the corresponding three-layer infill structures. The total absorption energy, average compression force and specific absorption energy of the hexagon infill structures were always the smallest among the four infill approaches, while the total absorption energy and average compression force of the re-entrant hexagon infill structures were always the largest and the specific absorption energy was kept at a stable and high level.

To study the influence of slit width on the dynamic propagation behavior of blast cracks, the digital laser dynamic caustic line experimental system and fractal theory were used to study the propagation laws of blast cracks at six different crack widths. The results show that the length of burst cracks in the cut direction is greater than that in the non-cut direction. With the increase of the slit width, the propagation length of burst crack increases first and then decreases. When the slit width increases to 0.4 mm, the main crack propagation length is the largest, and when the slit width continues to increase, the main crack propagation length decreases. When the slit width is 0.2 and 0.4 mm, the fractal dimension is larger than that of other slit widths, the expansion length of the main crack is longer than that of other widths, and the directional fracture effect of the specimen is better. With the increase of the slit width, the stress intensity factor and velocity peak value of the main crack propagation of the slot shows a trend of first decreasing rapidly, then increasing to the secondary peak, and finally oscillating and decreasing. When the crack width is 0.2 and 0.4 mm, the peak value of the stress intensity factor and the expansion velocity of the main crack are larger than those of other crack widths. The research results provide a certain basis for the selection of slit parameters in actual blasting engineering.

Inspired by the brick and mortar structure of multi-scale and multi-hierarchy, a nacre-like Voronoi brick and mortar structure was created. Afterwards, the dynamic response of nacre-like Voronoi brick and mortar structure under explosive load was explored by combining 3D printing, explosion experiments, and numerical simulations. The influence of the Voronoi unit cell size and the thickness of the intralaminar soft material on the damage mode as well as the energy absorption of the structure was analyzed. Under the spherical emulsion explosive charge of 40 g, the radial cracks appeared on the front face of the nacre-like Voronoi brick and mortar structure and then spread around, while small pieces of fragments fell off the back panel. A finite element model was built and showed good agreement with the experimental results. The damage modes of nacre-like Voronoi brick and mortar structures under different explosive charges include plastic deformation, cracks occurred on the front and back face, small pieces of material falling off, damage of whole structure accompanied with shear failure at the gripper end. The horizontal normal stress of the stiff material is much larger than the vertical normal stress. Meanwhile, the shear strain in the interlaminar soft material is much larger than that in the intralaminar soft material. The specific energy absorption is 1.8−2.3 times larger in the interlaminar soft material than that in the stiff material. With the increase of the Voronoi unit cell size, the specific energy absorption of the interlaminar soft material increases by 45.6%. As the thickness of the intralaminar soft material increases, the specific energy absorption of the intralaminar soft material increases by 31.1%. This study may provide some definite reference for the design of biologically inspired structures.

To study the charge damage evolution process when a high-velocity warhead penetrated a double-layer target, a numerical simulation study was conducted using a cohesive zone model to investigate the penetration of double-layer target. The cohesive zone model was utilized to calculate the occurrence and evolution of PBX damage, as well as to analyze the relationship between the penetration velocity and damage evolution. The quantification of damage was conducted by means of the damage ratio. Furthermore, a micro-damage finite element model for PBX was established to examine the microscopic damage mechanisms during penetration into a double-layer target. The results show that when the projectile penetrates the target plate vertically, the extent of damage of the charge increases with the increase of penetration velocity. From a microscopic perspective, it was observed that cyclic tensile and compressive loads induced the formation of vertical cracks perpendicular to the loading direction. The primary mechanism of damage in PBX charge penetration into double-layer target is interface debonding. Additionally, the microcracks destabilize, propagate, and converge into a continuous main crack.

To investigate the influence of the crack angle on the strength and energy evolution of granite-concrete composite specimens under uniaxial compression, a numerical simulation study was conducted using the two-dimensional particle flow code (PFC^2D) based on the micro-parameters calibrated through laboratory tests. The research results indicate that the strength and deformation characteristics of granite-concrete are affected by crack angles, and their strength and deformation parameters gradually increase with the increase of crack angle. During the uniaxial compression process, the internal energy of the specimens transforms into macroscopic crack propagation, and the final failure modes are mainly tensile fractures and shear fractures. The total energy and dissipated energy of the composite specimens increase with the increase of crack angle, and the total strain energy is more than the dissipated energy when the specimens are damaged. Based on the calculation of dissipated energy, a damage constitutive equation was constructed, indicating that when the damage factor reaches 0.8, the specimen is already close to its limit state, resulting in significant energy consumption and a decrease in the strength of the composite specimen.

A bi-directional corrugated sandwich tube structure was proposed, inspired by the front jaw of peacock mantis shrimp. The dynamic responses and energy absorption characteristics of bi-directional corrugated sandwich tubes under inner blast loading were investigated numerically and experimentally. It was found that three typical deformation modes including localized plastic deformation, elliptical plastic large deformation and laceration. The numerical results of the mid-point deflection of the outer tube and the final deformation mode of the structure agree well with the experimental results. Subsequently, the effects of the number of corrugation of the bi-directional corrugated core tube, the inner and outer tube wall thicknesses and TNT dose on its dynamic response and energy absorption characteristics were investigated thoroughly. The results show that the energy absorption ratio of the structure increases first, and then decreases with the increase of the number of corrugation. Increasing the inner tube wall thickness and decreasing the outer tube wall thickness can improve the shock resistance performance. Compared with the inner tube wall thickness of 1.5 mm and an outer tube wall thickness of 2.5 mm, the structure with an inner tube wall thickness of 2.5 mm and an outer tube wall thickness of 1.5 mm can reduce the maximum mid-point deflection (MD) of the outer tube by 67.6% and reduce the mass by 6.0%. As the TNT dose increases, the percentage of energy absorbed by the inner tube decreases gradually, while the percentage of energy absorbed by the core and outer tube increases. Finally, the specific energy absorption (SEA) of the structure and MD of the outer tube were predicted using BP (back propagation) neural network model, PSO-BP (particle swarm optimization-back propagation) neural network model, and RSM (response surface methodology) model to optimize the proposed structure.

Sapphire is often chosen as the observation window in shock wave experiments due to its excellent strength, hardness and optical transparency. A deep understanding of the mechanical and thermodynamic response mechanisms of sapphire under impact loading and the causes of internal damage is crucial for accurately evaluating its performance and stability. In this work, molecular dynamics simulations were performed to explore the mechanical and thermal response of a sapphire single crystal under shock loading along the C-plane. The results indicate that the activated slip system after the impact loading is the rhombic plane slip based on the R-plane {$0 \overline 1 12 $}. When the impact velocity is in the range of 1−3 km/s, no slip occurs; when the impact velocity reaches 4 km/s, slip occurs. When the impact velocity reaches to the range of 5−6 km/s, the sample shows inhomogeneous deformation, mainly composed of irregular stripes. Such results suggest that the activation of the slip system in sapphire depends not only on its lattice structure, but also on the partial shear stress (which needs to reach a critical value). The analysis of the temperature field indicates that there is an intrinsic relation between the local slip and temperature increase, i.e., the formation of intense shear localization is accompanied by the higher temperature.

The quasi-isentropic loading technique based on wave impedance gradient materials is a crucial method for understanding the dynamic response characteristics of materials, which is essential for enhancing material service performance. In this study, Ti-Pt periodically modulated gradient materials were successfully prepared using electron beam evaporation deposition technology. By adjusting the thickness of the two components (Ti and Pt single layers) within the periodic layers, a macroscopic gradient in wave impedance was achieved. The total thickness error between the measured gradient material and the theoretical design was only 1.67%, with an average hardness and elastic modulus of 2.8 and 99.8 GPa, respectively. The interfaces between the internal layers of the material were clear, and no metal alloy phases were detected in the phase analysis. The Ti-Pt periodically modulated gradient material was loaded onto a 5 μm-thickness Al target by a one-stage light gas gun, generating a shock-quasi-isentropic loading waveform within the Al target. Numerical simulation results showed good agreement in the rising trend with the experimental curve. For the 5 μm-thickness Al target, the particle velocity, stress, and strain rate curves exhibit significant fluctuations in the quasi-isentropic stage, with the strain rate curve oscillating continuously between positive and negative values with large amplitudes. Stress contour maps indicate that the loading process of the periodically modulated gradient material involved the chasing, superposition, and integration of multiple wave systems. Simulation shows that when the target thickness is 60 μm, the wave systems complete integration and change into continuous compression wave loading. Based on the simulation result, light gas gun loading experiment for the Al target with a thickness of 60 μm were conducted. The particle velocity and stress curves in the quasi-isentropic stage change into smooth loading waveforms, and the strain rate curve remains overall positive, achieving a good quasi-isentropic loading. This indicates that the periodically modulated gradient material and target thickness need to be designed to match each other. The results of this study provide a guidance for the application of novel periodically modulated gradient structures.

Carbon fiber-reinforced polymer (CFRP) with excellent blast-resistant performances is gradually applied in the anti-shock design of warships. In order to investigate the protective performance of metal/CFRP composite laminates subjected to underwater contact explosion, a fluid-structure coupling numerical model was established based on arbitrary Lagrangian-Eulerian (ALE) method. The deformation and energy absorption characteristics of laminates were analyzed, and the effect of layup types on the blast-resistant performance was compared. The results show that steel-CFRP-steel structure had better blast-resistant performance. On the basis of this structure, the optimal thickness ratio was given as 1.1∶4.0∶1.1.

In the application research of underwater explosion theory and technology, an explosion tank is a very important basic experimental device. The research on the blasting vibration effect and vibration damping of the explosion tank is of guiding significance for the vibration control and the selection of vibration damping materials during the blasting of the cylindrical water tank. In order to explore the impact of explosive vibration caused by the internal charge explosion on the surrounding ground of the cylindrical pool, and to seek effective vibration reduction methods, two kinds of vibration reduction materials, construction gravel and SD-type rubber vibration reduction pad, were selected, and explosion tests were carried out in a small explosive pool under three modes, single charge without vibration reduction, with SD-type rubber vibration reduction pad and with gravel vibration reduction. The collected blasting vibration signals were analyzed by peak particle velocity, EEMD-HHT (ensemble empirical mode decomposition-Hilbert-Huang transform) processing and wavelet packet analysis. The results showed that the vibration signals include the blasting vibration caused by the explosion shock wave and the ground vibration caused by the pool jumping, and the the ground vibration caused by the pool jumping can be effectively identified by Hilbert instantaneous energy analysis. Compared to the single charge without vibration reduction, the vibration velocity and vibration energy under the gravel layer modes are reduced by 53.0% and 43.1%, the vibration velocity and vibration energy for SD-type rubber cushion modes are reduced by 64.9% and 57.4%. The frequency of blasting vibration signal for the three vibration reduction modes is mainly distributed in the range of 10–80 Hz. The energy proportions for the frequency range of 10–40 Hz under the three operating modes are 79%, 69% and 66%, respectively, and the energy proportions for the frequency range of 40–80 Hz are 11%, 29% and 31%, respectively. The gravel and SD-type rubber have the effect of absorbing energy and reducing low-frequency components, and increasing high-frequency components, which can effectively reduce the peak vibration velocity of nearby measurement points. Compared to the effect of the two kinds of vibration absorbing materials, the construction gravel results more uniform energy distribution of the vibration signal frequency band than that of the SD-type rubber.

Sodium-ion batteries (SIBs) have become one of the mainstream research objects of electric vehicle energy storage system due to their advantages of high safety performance and low cost. In the use of electric vehicles, thermal runaway may occur when the battery pack is subjected to compression loading, so it is crucial to study the collision safety characteristics and thermal runaway behaviors of SIBs for their development. In order to reveal the flat plate compression safety characteristics of SIBs, this work focused on 18650-type SIB with a positive electrode of NaNi_1/3Fe_1/3Mn_1/3O₂ and a negative electrode of hard carbon. A test platform for the flat plate compression safety characteristics of the batteries was established to investigate the force-electric-thermal response during the battery compression, the state of charge (SOC) range and the critical speed range for thermal runaway of SIBs were explored, the internal short-circuit process was analyzed, and the secondary usage limit of damaged batteries was determined. The results indicate that thermal runaway occurs at charge states of 80% and 90% for cylindrical SIBs, a critical speed for thermal runaway is between 14 mm/min and 15 mm/min, and the battery compression process conforms to a standard “4-stage” process. The damaged cylindrical SIBs under compression have a secondary usage safety limit.