Hydrogen-rich materials are considered to be the most potential candidates for room-temperature superconductors, yielding a research hotspot in physics, material science and so on. Remarkably, the new covalent hydride H₃S and clathrate like LaH₁₀, exhibit record high superconducting transition temperature (T_c) above 200 K both found theoretically and experimentally, which further promotes the study on the superconductivity of hydrogen-rich compounds. Very recently, the successful experimental discovery of high-temperature superconductivity at 288 K in a carbonaceous sulfur hydride system at high pressure shows the light for achieving room-temperature superconductors. In this paper, we introduce the structures and superconductivities of three typical hydrogen-rich compounds, including HfH₁₀, a "pentagraphenelike" superconductor exhibiting an extraordinarily high T_c of around 213–234 K at 250 GPa, which was recently discovered for the first time in layered structure hydrides.

To study the effects of the sintering pressure on the mechanical properties of TaC with various grain sizes, nano- and micro-sized TaC powders are sintered at high pressure and high temperature (HPHT) to acquire bulk TaC ceramics under different sintering conditions. Different characterization approaches, such as X-ray diffraction (XRD), are used to observe phase, elements distribution, and indentation state. The observations reveal that the TaC phase is stable during the sintering process and there is no impurity infiltration. Three ceramic samples at the various sintering pressures (3.0, 4.0, 5.5 GPa) are measured by the Vickers hardness tester and their microstructures are also analyzed. The results show that as the sintering pressure increases from 3.0 GPa to 5.5 GPa, the Vickers hardness of Micro-5.5-TaC (21.0 GPa) is higher than that of Nano-3.0-TaC (17.5 GPa) and Nano-4.0-TaC (19.2 GPa). In addition, it is found that 3.0 kg is the most accurate load for measuring the Vickers hardness. This study has a guiding significance for sintering structural ceramics and exploring the Vickers hardness of ultra-high temperature ceramics (UHTCs).

Study on the superconducting transition of single crystal Nb₃Sn under high pressure is valuable to understand the mechanism of critical performance degradation in superconducting Nb₃Sn, which is induced by the mechanical deformation. In this paper, on the basis of molecular dynamics simulations, we studied high-pressure induced atomic scale deformation and crystal lattice distortions of single crystal Nb₃Sn. Following this analysis, we established a superconducting transition model of single crystal Nb₃Sn under high pressure. There is a good agreement between model predictions and experimental observations. The results show that the high pressure induces obvious lattice distortions in single crystal Nb₃Sn, the lattice structure, however, remains intact. Pressure-induced change in density of states at the Fermi surface is shown to play a dominate role in superconducting transition in single crystal Nb₃Sn. The results lay a foundation of understanding the high pressure induced superconducting transition of polycrystalline Nb₃Sn. At the same time, they provide some detailed information on understanding the mechanism controlling for strain-induced critical performance degradation in Nb₃Sn.

Magnetized liner inertial fusion (MagLIF) has combined the advantages of the conventional magnetic confinement fusion (MCF) and inertial confinement fusion (ICF), which could reduce the barrier of controlled fusion and has great potential and feasibility for future applications. In this work, a conventional MagLIF configuration is calculated with 27 MA driving current based on one-dimensional simulation code MIST, distributions and evolvement of characteristic parameters (such as density, pressure, temperature and fusion product) are acquired and demonstrated during three stages of MagLIF process, including initialization, implosion and stagnation. The simulation results provide significant data and support for the assessment and analysis of MagLIF process, which would be helpful to understand how MagLIF behaves from preheat through compression into fusion. Comparison of key parameters between MagLIF and traditional ICF also be shown in this work.

Due to the continuous variation of material density in functionally gradient aluminum foams, a feedback load gradually increases within the compression process. Currently, most of the researches have been focused on the longitudinal compression mechanical response. However, considering the possible transverse impact in practical application, we investigated functionally gradient aluminum foams in terms of the axial and transverse compressive mechanical responses based on low-speed impact experiments, and also studied their macro and mesoscopic crushing mechanism via the digital image correlation and numerical simulation technology. The results were shown that: (1) Compared with that under longitudinal compression, the functional gradient aluminum under transverse compression has higher compressive strength and lower platform stress, densification strain and energy absorption. (2) In the aspect of failure deformation mode, the longitudinal compression deformation mode is progressive compression of deformation band, while the deformation band of transverse compression appears randomly at each position of the sample. (3) Under transverse compression, the densification strain and specific energy absorption of the functionally gradient aluminum foam get decreased by the reduction of cellular utilization in the higher porosity zone. (4) The established elastic-plastic hardening-locking (E-PH-L) constitutive model can well capture the longitude compression response of the functionally gradient aluminum foam. This study therefore can provide a reference for the theoretical design of functionally gradient aluminum foam in the protection engineering of explosive impact structures.

In order to reveal the mechanical properties and energy evolution of hard rock under different confining pressures, conventional triaxial compression tests on granite samples under different confining pressures were carried out by the RMT-150B rock mechanics test system. The results showed that the peak stress of the rock sample had a strong linear relationship with the confining pressure. The cohesive force of the granite was 23.548 MPa and the internal friction angle was 57.629° using the Mohr-Coulomb strength criterion. The peak energy, elastic strain energy and dissipation energy of the rock all increased linearly with the increase of confining pressure. According to the linear energy storage law of the rock, a method to determine the rock threshold stress was proposed, the greater the confining pressure, the larger of cracking stress and expansion stress, the larger the energy at the initiation point and the expansion point of the rock sample. When the confining pressure is low, there existed less energy stored in the rock before failure, the energy release rate is low, and the rock sample shows typical splitting failure. Under high confining pressure, the energy gets released rapidly, and the rock sample shows shear failure. Besides, a rock damage evolution model was proposed based on the law of energy evolution, and the law of evolution of damage variable D on the granite was obtained during loading failure under different confining pressures.

In this paper, the dynamic mechanical properties of C45 concrete materials at different temperatures (20, 200, 400 °C) are carried out on split Hopkinson pressure bar (SHPB) equipment with a large diameter of 74 mm. The stress-strain curves of concrete materials at different temperatures and strain rates are obtained through experiments. As the expansion of microcracks inside concrete materials is inhibited by the increase of strain rate, the concrete specimens exhibit strain rate hardening effect. The experimental results show that the concrete material has temperature hardening and strain rate hardening in the temperature range of 20 °C to 400 °C. Through the relevant theoretical derivation, the SHPB experimental data of concrete materials are transformed into the relationship between damage variables and plastic strain. Then the material parameters of the damage evolution equation at different temperatures and different strain rates are determined by relevant experimental data. Finally, the damage evolution equation of concrete materials at high temperatures and high strain rates are applied to the constitutive relation of concrete materials. The prediction results are in good agreement with the experimental data.

In the application environment, the surface of the ultra-high-speed aircraft is violently rubbed with the air to make the temperature extremely high. Compared with ordinary ceramics, ultra-high temperature ceramics possess a higher melting point with good oxidation and ablation resistance performance. Therefore, it is particularly interested to be used as thermal protection materials. In this paper, ZrB₂-20%SiC ultra-high temperature ceramic materials are prepared by using the spark plasma two-step sintering process of ZrB₂ nanopowder and SiC powder at 1700 ℃. The mechanical properties of ZrB₂-20%SiC are studied through nanoindentation experiment and three-point bending experiment. The oxidation behavior of ZrB₂-20%SiC ultra-high temperature ceramics at four different oxidation temperatures of 1000, 1200, 1400 and 1600 ℃ is analyzed in this paper. The results show that the hardness of the ZrB2-20%SiC ultra-high temperature is 18 GPa, and the elastic modulus is 541 GPa with the fracture toughness of 5.7 MPa·m^1/2. When the oxidation temperature is 1600 ℃, the SiC inside the ultra-high temperature ceramic would transform from passive oxidation to active oxidation. As the oxidation temperature increases, the thickness of the ultra-high temperature ceramic oxide layer and the oxidation temperature demonstrate a positive correlation trend.

A helical auxetic yarn (HAY) is a composite yarn which is formed by helically wrapping a high modulus yarn on a low modulus yarn, and it exhibits the so-called negative Poisson’s ratio phenomenon of transverse expansion upon longitudinal stretching. To reveal the mechanisms of HAY’s shock resistance, a study on its dynamic tensile behavior was carried out based on finite element simulation. It was found that there are two stress waves in a shock loaded HAY, one is a fast wave and another is a slow wave which are dominated respectively by the wrap yarn and the core yarn, and between the two wavefronts, both the transverse deformation and the Mises stress change periodically with time and space. The relationships between the wave speeds and loading velocity and friction coefficient are presented and qualitatively discussed based on the concept of effective modulus. The simulation results also show that the internal energy is almost equal to the kinetic energy, and friction has a significant contribution to energy absorption.

The stress state of the target was seldom taken into account in the investigation of the ballistic performance of cement mortar. Based on the self-developed penetration experimental system of concrete under true-triaxial confinement and the experimental results of the anti-bullet performance of cement mortar, the depth and resistance of opening pit under different stress states were discussed in the present paper. The empirical formula of penetration depth and finite element method (FEM) based on HJC model were used to analyze the penetration behaviors of cement mortar results. The results showed that under the lower velocity impact, the UMIST formula and the HJC model were both effective in the prediction of pit depth. At the same time, the stress state had an obvious influence on pit depth. With the increase of the lateral limit, the cement mortar strength increases and the pit depth of the projectile decreases. The acceleration wave in bullet and the wave in the y-axis support rod were calculated by FEM based on HJC model. The results showed that the process of projectile opening pit would be recorded by these two waveforms, and the wave structure in the y-axis support rod would be more significantly. Although the tendency of the simulation results was basically consistent with the experimental waves, there was difference in the stress amplitude to some degree, which also indicated that the calculation method of the pit opening resistance based on HJC model needed to be improved.

The in-plane biaxial impact response of a re-entrant auxetic honeycomb structure is studied by finite element simulation. A re-entrant auxetic honeycomb structure with different regularities is established by using the node perturbation method, and its deformation modes, stress-strain curves and energy dissipation capacity under different impact velocities are compared with the regular honeycomb structure. The results show that the impact velocity is the most important factor affecting the deformation mode of the honeycomb structure. In addition, due to the influence of irregularity, the plateau stage of stress-strain curve is prolonged and the degree of anisotropy of the structure is inhibited under biaxial impact, resulting that the deformation characteristics of the structure change from local compactness to overall compactness. In terms of energy absorption capacity, the irregularity of the structure leads to the lag of the compaction stage, so its plastic energy dissipation is lower than that of the regular model under the same compression degree.

By employing a split Hopkinson pressure bar (SHPB) device, the dynamic crushing experiments of quartz glass beads with diameters of 8.30, 11.68, 15.42 and 17.50 mm, were implemented with impact velocity of 5.6–11.5 m/s. High-speed photographing technology was used to record the crushing process of double glass beads during impact. Combined with the transmitted load-displacement curves and the results of particle size distribution analysis, the failure mechanism of quartz glass under double-particle impact was discussed. Due to the non-uniform load distribution in the double-particle system, the breakage of two glass beads demonstrated a time-varying characteristic, which changed with the increasing impact velocity. Despite of the conventional penetrating oblique crack system, the impact fracture of glass beads was caused by the local Hertz crack expansion and the crack system diffusion at the contact points. The fast infrared temperature measurement revealed two main fracture mechanisms and the existence of critical crushing diffusion resistance. This work has shown to be a significant reference for understanding the dynamic failure mechanism of brittle granular matter.

In this paper, the spallation characteristics of tantalum (Ta) under plate-impact loading are studied through numerical simulation. The feasibility and reliability of the Lagrange and smooth particle hydrodynamics (SPH) methods and several constitutive models (the Johnson-Cook, Steinberg-Cochran-Guinan and Zerilli-Armstrong model) are discussed. Comparison between the simulation results with experimental data, it is found that using the SPH method combined with the Steinberg-Cochran-Guinan constitutive model could produce the best consistency in the strain rate range from 2.31 × 10⁴ s⁻¹ to 5.40 × 10⁴ s⁻¹ for Ta. In addition, by changing the impact velocity and the thickness of the flyer, the free surface velocity curves under different strain rates are obtained, and the spalling characteristics under different strain rates are calculated and discussed. Characteristic parameters of spallation are calculated by using the free surface velocity data. The results have shown that the spalling strength of Ta increases with the strain rate, and is approximately linear in the logarithmic coordinate. Several computation methods of spall strength are considered in this work, and the difference between the results obtained by different methods are within the range of 8%. On the other side of the spectrum, the bounce rate of the free surface velocity increases with increasing strain rate. Finally, the physical meaning of the characteristic parameters in the free surface velocity curve is also discussed.

According to the actual combat background of underwater multiple initiation, the numerical simulation of shock wave load characteristics under the condition of two-point simultaneous initiation is carried out. Based on the self-developed multiphase compressible fluid calculation program, a high precision numerical scheme is used to discretize the fluid control equation. Firstly, the results of free-field underwater explosion calculated by the numerical model are compared with the theoretical results, and the accuracy and reliability of the numerical model are preliminarily verified. And then this numerical model is used to calculate the underwater two-point initiation condition under typical working conditions. The results show that the pressure on the symmetrical plane of the two explosion sources increases by 12% to 16% compared with the peak pressure after the linear superposition of the single explosion source. There is a bimodal phenomenon in the pressure between the vertical sections of the two explosion sources. For the pressure at the measuring point outside the two vertical sections, there is also a double-peak phenomenon, the first peak pressure is equal to the peak value of the linear superposition of the single explosion source, and the second peak pressure is much lower than the peak value of the linear superposition of the single explosion source. The peak pressure can be reduced by as much as 30%. The research results of this paper can provide reference for underwater weapon protection design and threat assessment.

The emission environment can be transformed from water medium to gas medium by water immersion gap-exist launch mode. In order to study the driving impact load of high speed projectile under this condition, the theoretical model of projectile impact load is established. The inlet impact loads of the projectile under different conditions of inlet velocity, head cone angle and inlet attack angle are calculated. The influences of inlet velocity, warhead parameters and inlet angle of attack on driving impact load are analyzed. The research results are of great significance to the prediction of the driving impact load of high-speed underwater projectile and the design of warhead.

Studies on anti-explosion performance of steel-concrete-steel composite structures have been widely conducted in the fields of protection engineering, anti-terrorism and explosion protection. Taking steel-concrete-steel composite plate as an example, the failure mode and dynamic performance of the composite plates under blast loads (the standoff distance is 2.5–7.5 m, TNT explosive quantity is 50–100 kg) are studied by using finite element software ABAQUS. The results showed that the failure mode of the composite plate is closely related with explosive quantity and standoff distance. The larger the explosive quantity and the smaller the standoff distance, the more obvious the damage degree of the composite plate. When the charge is 100 kg and the standoff distance is 2.5 m, the composite plate warps obviously and the plastic hinge appears. The presence of the steel plate could effectively limit the spalling of core concrete. Under the same standoff distances, the larger the explosive amount, the more obvious the deformation of the composite plate, and the greater deflection and peak velocity of the mid span. Under the condition of the same explosive quantity (100 kg), the mid span deflection of the composite plate is 1.53 times at 5.0 m standoff distance than that at 7.5 m standoff distance, and the deflection of mid span of the composite plate is 5.01 times than that at 7.5 m standoff distance.

The damage of shaped charge jet to liquid-filled structure was analyzed by ANSYS/LS_DYNA software.The influence of liner thickness and material parameters on the performance of shaped charge warhead under water is obtained. The thickness of liner between 0.04D_k and 0.06D_k, jetting penetrator charge （JPC） has excellent penetration performance for the liquid-filled defensive structure; When $\delta $ < 0.04D_k, the JPC forming structure is poor, and the decay rate of the kinetic energy in the water is faster.When $\delta $ > 0.06D_k, the initial kinetic energy of the JPC is low, and the effect of the after-target effect is poor; It is also illustrated that among three kinds of linear materials including iron, copper and tantalum: Pure iron JPC has the highest penetration ability; Tantalum JPC has the best water storage kinetic energey performance; Copper JPC has better overall performance.

To assess the effect of cyclic explosion on underground caverns, based on a similarity model test, the finite element software ABAQUS was utilized to analyze the dynamic responses and cumulative damage of underground caverns under cyclic explosion at low levels and a single explosion at high level. The stress wave attenuation characteristics and the cumulative damage evolution laws of the surrounding rock were presented. Besides, the displacement of the vault and the circumferential strain of the cavern wall were compared and analyzed. The results indicate that, with the increase of explosion times, the stress wave attenuation speed of the surrounding rock under cyclic explosion decreases first and then increases. In the single explosion, the peak circumferential strain of the cavern walls changes from tensile strain to compressive strain from the vault to corner. In the cyclic explosion, the peak circumferential strain of the vault changes with the increase of explosion times from compressive strain to tensile strain. Under the same explosion loading in total, the damage of the surrounding rock is greater in the low-level cyclic explosion than that in the high-level single explosion in terms of area and degree. In addition, the cumulative damage of surrounding rock under cyclic explosion presents an irreversible and step-by-step increase, and shows a dramatic nonlinear relationship with explosion times.

In order to study the probability ignition behavior of explosive and the influence of sample thickness on ignition in drop weight test, a three-dimensional numerical simulation of brittle explosive PBX-2 is carried out. The three-dimensional numerical simulation method combining the finite element method and the discrete element method is adopted, and the non-uniformity of explosive material is considered. The ignition probability distribution of explosive under different falling height is obtained. The calculation result of falling height is consistent with the experimental result reported in literature. The influence of sample thickness on the temperature rise process and ignition threshold height of explosive in drop weight test is studied. The estimation formula of pressure peak value and ignition threshold with sample thickness is obtained by fitting, which can provide reference for experimental design.