By using first-principles method based on density functional theory, the crystal structures and the electronic structures of Sc, Ti, V and Zr element doped Cr₂B₃ under zero pressure, and their elastic constants and hardness in the pressure range of 0−150 GPa are calculated. According to the calculation, Cr₂B₃ and its doped compounds all meet the mechanical stability. At zero pressure, the Vicker’s hardness of Cr₂B₃ can be improved by adding Sc, Ti, V and Zr elements, in which the hardness of Ti-doped Cr₂B₃ is increased from 26.3 GPa to 40.2 GPa, increasing by 52.9%, reaching the standard of superhard materials, and the shear moduli of Ti and V doped Cr₂B₃ increase by 14.3% and 16.2%, respectively, and the Young’s moduli of the Ti and V doped Cr₂B₃ increase by 8.2% and 12.0%, respectively. The analysis of electronic structures shows that Sc, Ti, V and Zr can enhance the degree of electronic localization between B and B, thus enhance the covalent bonding strength and increase the hardness of Cr₂B₃. In addition, the elastic constants, the bulk elastic modulus, the shear modulus, the Young’s modulus and the hardness of Cr₂B₃ increase with pressure augmentation, but even so, the hardness is still low, merely 28.3 GPa at 150 GPa, while the hardness of the V element doped Cr₂B₃ is nearly constant (about 37 GPa) in the pressure range of 0−150 GPa. This work provides a theoretical reference for an extending application of Cr₂B₃ in special conditions, such as high pressure.

Geometric structure, electronic structure and optical properties of nitrogen-rich energetic materials (bis 3, 4, 5-triamino-1, 2, 4-triazole)-5, 5′-azotetrazole (G₂ZT) at high pressures are investigated using first-principles based on density functional theory. The calculated results obtained by using vdW-DF2 and PBE-D2 methods show that the crystal structure data fit well with the experimental results, and the error rates are all within 3%. Hirshfeld surface analyses indicate that interactions of the inter-molecular hydrogen bond are weaken with the increasing pressure. G₂ZT crystal possesses a band gap of 2.03 eV at zero pressure, and it is a p-type semiconductor. As the pressure increases, the band gap becomes narrower and the absorption coefficient can approach 3.0×10⁶ cm⁻¹. These results provide a theoretical reference for further analysis of G₂ZT crystal’s characteristics under high pressure.

Ultra-high temperature ceramics have excellent properties, such as high melting point, high thermal conductivity, and anti-oxidative ablation, and thus are important candidates for reusable heat-resistant parts of hypersonic aircraft. In this paper, high-density and ultra-high temperature ceramic ZrB₂-ZrC composites were prepared by high pressure technology. By adjusting the synthesis conditions and the ratio of raw materials, the effects of synthesis pressure and sintering aid ZrC content on the thermal ablation properties of the composites were studied. The results show that the density of ZrB₂-ZrC composite prepared under 3.2 GPa and 950 ℃ is above 95%, and the optimal mass ablation rate of the composite at 1600 ℃ is 17 μg/s. The optimal mass ablation rate at 2000 ℃ is 30 μg/s. Under the synthesis pressure of 2.9 GPa and temperature of 950 ℃, by changing the content of the sintering aid ZrC, the thermal ablation performance of the composites could be affected. When the molar ratio of ZrB₂ to ZrC is 8∶1, the mass ablation rate of the ZrB₂-ZrC composites after ablation at 1600 ℃ has the lowest value (35 μg/s).

In order to understand the deformation and damage behavior of a nickel-based GH4169 superalloy target under the high-temperature and high-speed impact load, a high-temperature loading device of the target was added on the existing ballistic impact gas gun firstly, as well as a synchronous separation mechanism for projectile launching and high-temperature furnace. Then, the method of high-temperature and high-speed ballistic impact test of the GH4169 targets (160 mm×160 mm×2 mm) was verified. The results show that this device can achieve the high-temperature ballistic impact tests with temperatures exceeding 500 ℃ and speeds exceeding 320 m/s. During the ballistic impact test, the difference of temperature between the front and rear of the target was less than 0.1%, the uniformity of temperature inside the target was less than 2.6%. In the ballistic impact tests of GH4169 targets at different temperatures, the global deformation range of the target at 500 ℃ was 29.5% smaller than that at room temperature. The test results show that the impact resistance of GH4169 at 500 ℃ is better than that at room temperature.

Fuze control is one of the key technologies in developing warhead. The signal adhesion of deceleration may lead to wrong response of layer-counting fuze. Based on numerical simulation, the dynamic response of a projectile connected with an accelerometer equipment by pressed fitting is obtained during the projectile perforating multi-layer target. It is indicated that the maximum dynamic gap between the accelerometer equipment and the projectile can reach to 25 μm, which may induce gap collision and increase the signal adhesion of the accelerometer between target layers. The pressed fitting with a proper preload could suppress the gap collision, and then the pressed fitting connection between warhead and accelerometer could be approximated as the ideal rigid connection. With the proper preload, the frequency response of the overload signal obtained by the accelerometer shows a single peak, and the corresponding frequency of the peak is close to the eigen frequency of the stretching out and drawing back in the first order of the projectile. There is a critical minimum preload that makes the pressed fitting connection approximate to the ideal rigid connection. The minimum preload increases with the impact velocity and the target layers quantity. This may be due to the fact that a higher impact velocity and a larger target layers quantity enhance the maximum stress of wave generated in the projectile. This work provides a foundation for the mechanism identification and the control of the deceleration signal adhesion in interlayers. Moreover, it can give a guidance to projectile and accelerometer equipment assembly with pressed connection in engineering applications.

To study the mechanical properties of polyimide, quasi-static and dynamic compression experiments were carried out using the materials testing system (material testing system, MTS) and the split Hopkinson pressure bar (SHPB). The stress-strain curves of the material under different strain rates were obtained. The morphology of the recovered specimens was analyzed, and the characteristics of the polyimide in terms of crack form and size deformation were obtained. A bilinear relationship between the dynamic increase factor of the polyimide and the strain rate was obtained. The bilinear characteristics were described by piecewise fitting model and Cowper-Symonds model. Based on the characteristics of the dynamic mechanical response of the polyimide, its compression deformation mechanism from low to high strain-rates was explained. A phenomenological constitutive model in consideration of the contributions of the $\,\beta $-transition was modified to describe the large elastic-plastic deformation response of the material, in which initial viscoelasticity, yield, strain softening and strain hardening were all included. Then the constitutive model’s parameters were fitted by Bayesian approach. The Bayesian fitting results at different strain rates were in good agreement with the experimental data.

Sandwich panels, consisting of flax fiber-reinforced polymers panels and polyurethane foam cores, were fabricated by the vacuum-assisted resin injection process. After that, water immersion aging experiments, at four temperatures of 25, 40, 55, and 70 ℃, and low-velocity impacts experiment were conducted successively on the sandwich panels. An orthogonal experimental was designed to investigate the effects of hygrothermal aging on moisture absorption rate and the degradation law for impact resistance of sandwich panels at different temperatures. The impact mechanical response history of sandwich panels such as contact force, displacement, and absorbed energy were analyzed, besides, the damage morphology was observed by visual inspection which reveals the impact damage characteristics of sandwich panels after aging. The results revealed that the moisture absorption rate of the sandwich panel gradually increased with the growth of aging temperature and aging time, their impact resistance decreased stepwise. Compared with the aging case at 25 ℃, the maximum contact force of the sandwich panel aged at 70 ℃ for 30 d decreased by 51.6% and the absorbed energy decreased by 56.7% under the impact energy of 12 J.

In this paper, an experimental study on spherical water droplets with diameters of 3.7 and 6.4 mm at hypervelocity impacting typical Whipple protection structure (consisting of a buffer plate and a effect plate) was carried out at room temperature, and the damage characteristics of the double-layer aluminum plate created by different diameter spherical water droplet projectile were obtained. The finite element method-smoothed particle hydrodynamics (FEM-SPH) adaptive method in LS-DYNA software was used to study the damage characteristics of the Whipple protective structure impacted by water droplets with diameters varing in the range of 3−7 mm at different velocities. The influences of water droplet diameter, impact velocity, target plate thickness and other factors on the damage charateristics were analyzed. An empirical formula of dimensionless perforation diameter of water droplet impacting aluminum plate was obtained at hypervelocity in the range of 2−8 km/s. The minimum velocities for different water droplet diameters varing in the range of 3−7 mm required for the Whipple protection structure was obtained.

Concrete is a typical quasi-brittle composite material with tension-compression asymmetry. When the tensile failure is studied by Brazilian splitting test, different loading methods have great impact on the deformation and failure characteristics of concrete. The quasi-static splitting tests of standard disk direct loading, arc loading and flattened disk loading are carried out. Based on the digital image correlation method, the full-field deformation and localized failure characteristics in the process of concrete tensile splitting are studied. The results are as follows. (1) For the direct loading of the standard disk, the stress concentration near the top and bottom of the specimen makes the damage concentration occur preferentially at the end of the specimen, and the high amplitude area in the tensile strain field expands rapidly from the loading end to the center; due to the improvement of stress concentration by the arc loading and flattened disk loading, the strain concentration firstly appears near the center of the specimen and continues to expand from the center to both ends until the crack penetrates the specimen. (2) Arc loading and flattened disk loading meet the central initiation hypothesis of Brazilian splitting experiment; the tensile strength of concrete specimen measured by the flattened disk is about 5 MPa, which is about 31.2% higher than the standard disk due to the greater friction at the loading position and greater central compression tension ratio. (3) Under the three loading methods, the DIC analysis results of the deformation at the center of the specimen are in good agreement with the measurement results of the strain gauge, which verifies the effectiveness of the full-field deformation of the concrete specimen obtained based on the DIC method.

Carbon nanotube (CNT) films have broad application prospects in the fields of artificial muscles, electronic shielding, and impact protection, owing to their excellent mechanical and electrical conductivity properties. However, the latest studies mainly focus on the quasi-static mechanical properties of the CNT films, while the transverse impact mechanical properties and microscopic mechanisms are still under investigated. Herein, the mechanical behavior of CNT films under medium/low-speed penetration is experimentally and numerically investigated. The results show that the critical penetration speed of the single-layer CNT film is about 25 m/s, while the speed of the maximum energy absorption is about 30 m/s, for a 1 mm diameter steel ball impacting the CNT film. In contrast, the critical penetration speed of the double-layer CNT film is about 40 m/s, and the speed of the maximum energy absorption is about 60 m/s. Under the quasi-static condition, the damaged edge of the cavity in the CNT film is thinner and the stretching deformation is more prominent than those in the impact case; the intermediate interface modification by water, oil, and high vacuum grease can improve the impact mechanical properties and energy absorption effect of the double-layer CNT film. Overall, this work can provide a better understanding on the penetration mechanism of CNT films and guide the design of anti-impact structures.

The effects of different inner wall surface roughness of 45 steel cylindrical shell on its shear band behavior were studied based on detonation collapse experiments of thick walled cylinder and finite element numerical simulation. The experimental results show that the surface roughness of the inner wall of the metal cylindrical shell significantly changes the nucleation position and the quantity of the shear bands under external explosion load. When the surface roughness of the inner wall of the cylindrical shell increases, the quantity and length of the shear bands increase, and the propagation speed of some shear bands increases as well. When the average width of the valleys of the inner wall decreases, the interaction between adjacent shear bands enhances with the increase of the nucleation points in the shear band. The finite element simulation and the theoretical analysis show that the maximum shear stress in the cylindrical shell generates on both sides of the valley bottom of the inner wall in the cylindrical shell. The shear stress on the inner surface of the cylindrical shell is enhanced with the increase of surface roughness, or with the decrease of average width of valleys. As the shear stress augments, the nucleation and the propagation of shear bands in the cylindrical shell are promoted, the nucleation quantity of the shear bands increase, the development of the main shear bands accelerate, and the shielding effect of the shear bands enhance.

In this paper, molecular dynamics method is used to study the strain rate dependence of HMX-based polymer bonded explosive (PBX) interface under dynamic tension loading. Our results show that the tension strength and elastic modulus of PBX increase with the increasing of strain rate. The fracture of HMX-F2311 is dependent on the strain rate: the initial strain mainly appears on the binder F2311, a main crack perpendicular to the loading direction is formed at low strain rate, while the failure path distributes on the whole model under high strain rate; the fracture of PBX is due to the debonding of binder. With the increasing of strain rate, the potential energy of HMX-F2311 increases rapidly, and the van der Waals force interaction plays a crucial role in the evolution of potential energy under high strain rate. The simulation reveals the effect of strain rate on the interface microstructure, mechanical behavior and fracture mechanism of the HMX-F2311, providing opinions for the design, preparation and safety of PBX.

The in-plane dynamic mechanical response of the auxetic hexagonal honeycomb under different impact angles, ranging from 0°–10°, and different impact speeds, ranging from 6–100 m/s, is systematically studied based on the corresponding numerical model. A novel formula is adopted for the cross-section to reflect the change of contact area between honeycomb structure and impact plate during oblique impact. The formular can reflect the change of stress from local region to whole model in the impact process well and capture the initial peak stress of honeycomb structure effectively. The results show that the auxetic structure has different deformation modes under oblique impact and axial impact, exhibiting local deformation under low-speed oblique impact, overall deformation under medium-high speed oblique impact, and overall deformation under axial impact. Compared with the regular hexagonal honeycomb structure, the auxetic structure is affected by the negative Poissonʼs ratio effect. Under the same loading condition, the deformation mode of the auxetic honeycomb deforms later than the regular hexagonal honeycomb structure does, exhibiting a delayed mode. In addition, focusing on the energy absorption historical curve, the plateau stress under the two calculation methods of cross-section area is compared and analyzed, which provides a basis for investigating the load-bearing and stability of honeycomb structures under oblique impact.

In order to improve the mechanical response of cylindrical shell under axial impact load, the laminated cellular cylindrical shells were designed, and their mechanical behaviors were studied by changing the laminated way and the number of cell. The deformation mode and energy absorption characteristics of the structure under axial impact load were studied by finite element simulation, and the finite element analysis method is verified by quasi-static compression experiments. The total energy absorption and the peak compression force as well as the average compression force were obtained from compressive force-displacement curves of laminated cellular cylindrical shells. Numerical results show that the energy absorption of cylindrical shell is significantly affected by the lamination ways, while increasing the number of cells have little effect on the energy absorption of cylindrical shell. Two types cellular cylindrical shells with positive and negative Poisson’s ratios of the same mass were compared, the total energy absorption of re-entrant cylindrical shell is 17% higher than that of the hexagonal cylindrical shell on average.

Based on finite element method-smoothed particle hydrodynamics (FEM-SPH) adaptive algorithm of finite element software LS-DYNA, the damage characteristics of a multi-layer protective structure caused by the hypervelocity impact of a kinetic energy block are numerically simulated. Combined with the dimensional analysis method, the effects of the mass and the impact velocity of the kinetic energy block on the perforation characteristics of the multi-layer protective structure are analyzed. The results show that when other parameters remain unchanged and within the range of mass and impact velocity studied in this paper, all kinetic energy blocks can penetrate 17 layers of aluminum alloy plates and form debris clouds behind the target. During the impact process, spallation occurs in the kinetic energy blocks and the aluminum alloy plates. The perforation diameter of the first layer of the aluminum alloy plate increases approximately as a power function with the increase of the mass of the kinetic energy block, and the fitting error is within 5%. The perforation diameter of the second layer of the aluminum alloy plate also increases approximately as another power function with the increase of impact velocity, and the fitting error is less than 10%. The head velocity of the debris cloud increases linearly with the increase of impact velocity. The research results can lay a foundation for analyzing mass and velocity distribution of debris cloud behind target and establishing impact load model.

In order to improve the impact resistance of fiber composite components under hail load, inspired by the unique double-helicoidal structure of coelacanth scales, a numerical model of the double-helicoidal bionic structure made of carbon fiber reinforced composite was established, and the effectiveness of the bionic structure model was verified. The damage characteristics of the bionic-structure and the orthogonal lamination structure under hail load were compared and analyzed, and the influences of the hail impact energy and the hail distribution on the dynamic response of the double-helicoidal bionic structure were studied. The results show that the damage degree of the double-helicoidal bionic structure under the action of hail is better than the orthogonal laminated structure of the same density. When the impact energy reaches 1149.3 J, the orthogonal laminated structure shows an obvious matrix fracture and a fiber breakage, while the double-helicoidal bionic structure only shows a superficial delamination in the impact area with a small fiber fracture. The mechanical response of the bionic structure under hail impact can be divided into three stages. As the impact energy increases, the impact area firstly shows a matrix stretching, and the area near the impact point is delaminated and bulged out-of-plane; then the delamination area expands to the surrounding area, and the displacement of the impact position reaches the maximum under the continuous load of hail; since then, the bionic structure rebounds until it is stable. Both the energy absorption ratio and the contact force of the double-helicoidal bionic structure increase linearly with the increase of the impact energy. Under the same mass hail load, the damage degree of the upper surface gradually decreases with the increase of hail distribution density, and the damage area on the lower surface gradually increases for the bionic structure. The research results lay a foundation for the lightweight design of the coelacanth scales-inspired bionic structure under hail load.

Thin-walled sandwich structures are commonly used in protective structures due to its lightweight performance and excellent energy absorption. In this investigation, axial deformation behaviors as well as the energy absorption are studied for the sinusoidal corrugated cylinder because of its easier manufacturing process and wider engineering application. Based on the quasi-static axial compression experiment, the corresponding numerical simulation is carried out. The experimental result agrees with the numerical one. Hence, the influence of the core thickness A and the number of sine wave cycles N is analyzed on the collapse mode and energy absorption. The results show that the proper A and N not only effectively improves the specific energy absorption but also leads to desired deformation mode. In addition, compared with other parameters of A and N, in case of A=3 mm and N=12, the sandwich cylinder under quasi-static compression exhibits axisymmetric deformation, which shows the best energy absorption property. A=7 mm and N=12 with non-axisymmetric deformation mode has the best specific energy absorption and highest average compression efficiency under impact loading.

In order to study the load characteristics of underwater explosion for an emulsion explosive, underwater explosion experiments of the emulsion explosive were carried out. By changing critical parameters such as explosive charge mass, explosion distance and depth, the typical parameters of underwater explosion shock waves and bubble loads were obtained for different cases. The energy output was analyzed and compared with TNT for the calculation formula of underwater explosion loads, then the TNT equivalence for underwater explosion of the emulsion explosive was attained. The results show that Geers-Hunter formula can predict the general law of load output of underwater explosion for the emulsion explosive, especially with regard to the bubble pulsation period. The bubble oscillation pressure accounts for 10%–20% of the initial shock wave peak pressure, and the bubble energy is about twice the shock wave energy. The oscillation pressure waveform exhibits a trend of slowly rising to the peak, then rapidly falling to zero and keeping a steady state, thus the rising edge of the waveform generally takes longer time than the falling edge. The average TNT equivalence of the emulsion explosive in underwater explosion is about 0.595 as to the same shock wave overpressure, and about 0.646 as to the same bubble pulsation period. This research results can provide important reference for the application of emulsion explosives in underwater explosion.

Perforated armor can effectively reduce weight while meeting anti-penetration performance. Structural lightweight design of perforated armor has practical engineering significance. Considering the influence of uncertain factors, a reliability optimization design of a perforated armor was realized in this research. In the process of the reliability optimization design, the light weight of the perforated armor was taken as the goal of the design, and the anti-penetration performance was taken as the constraint condition. The optimal Latin hypercube design method was used to generate sample points. Based on a development of the commercial software ANSYS, the parametric modeling and the response calculation of the anti-penetration simulation of the perforated armor were realized. The Kriging surrogate model and the expected improvement maximization method were introduced to construct the performance functions. The sequential optimization and the reliability assessment method were applied in the reliability optimization design of the perforated armor. Under the premise of meeting the anti-penetration performance requirements and having a related reliability indicator of 0.9, the weight of the perforated armor after the reliability optimization can be effectively reduced by 11.5%. The research can provide references for the reliability optimization design of other anti-penetration structures.

The distance between explosive roll of surrounding hole is one of the important factors affecting the effect of smooth blasting. Based on the diversion system project of hydropower station in Peru, this paper introduced the blasting design scheme of the project and evaluated the blasting effect. The peripheral hole model under different charge structures was established by ANSYS/LS-DYNA to analyze the blasting effect of the surrounding hole model on rock. At last, the optimal design scheme of surrounding hole is selected for blasting test, so as to improve the over excavation and under-excavation phenomenon of the project. The results show that when the distance is less than 350 mm, the under-excavation will not appear and the over excavation range decreases with the increase of the distance between the surrounding holes. When the distance is more than 400 mm, the under-excavation begins to appear in the blasting effect and increases with the increase of the distance. Through the comparative analysis of the numerical model, it is concluded that the optimal charge spacing of the surrounding hole is 350 mm. The optimal design scheme is adopted for the blasting test. It is obtained that the overbreak range is significantly reduced, and the maximum distance is reduced from 43 cm to 30 cm.