CaF₂ nanocrystals with a size of 11 nm have been investigated using X-ray diffraction technique under high pressure. A phase transition from the fluorite structure to the α-PbCl₂-type structure has been observed at 12 GPa, which is much higher than the value observed in the bulk CaF₂ and slightly lower than the one in smaller-sized CaF₂ nanocrystals. The compressibility of the CaF₂ nanocrystals is discussed, an obviously higher incompressibility than the bulk CaF₂ is observed. The α-PbCl₂-type metastable phase is retained when the pressure is released to ambient conditions. The unique high-pressure behaviors of the 11 nm-sized CaF₂ nanocrystals are attributed to defects and grain size effect. The grain size effect is considered to be the main factor influencing the high-pressure behaviors of the CaF₂ nanocrystals. When the size of the CaF₂ nanocrystals is as small as 11 nm, the higher surface energy leads to the enhancement of the structural stability and the increase of the bulk modulus.

Germanium is a semiconductor with good performances of high carrier mobility and narrow band gap at ambient conditions. Under high pressure, it undergoes serials of polymorphs similar to the case of silicon, and the attractive characteristics in its high pressure phases such as metallization and superconducting transition make it one of the most appealing materials in high pressure research. However, its fundamental phase transition kinetics has been rarely studied. In this work, we present our experimental observations on the phase transition of germanium via a novel designed rapid compression tool and ultrafast time-resolved X-ray diffraction (XRD) acquisition system. The compression rate reaches to tens of TPa/s which is realized by combining gas membrane and piezoceramics compression methods in a symmetrical dynamic diamond anvil cell (dDAC). The time-resolved XRD with high resolution in microseconds is achieved by integrating the high flux pink beam diffraction, an X-ray scintillator to convert diffracted X-rays to visible lights and a high-speed optical camera. It is found that there is a time sequence for diffraction planes disappearing and appearing of dc and $\,\beta $-Sn phases, showing a displacive feature for this phase transition. In addition, the XRD evolution under static compression is also given for comparing with the dynamic compression, the results demonstrate our novel designed rapid compression and ultrafast time-resolved XRD setup shows a great potential for studying the high pressure phase transition kinetics.

Mechanoluminescent materials are widely used in stress sensing, recording and other fields because of their strong luminescence brightness, high force sensitivity, good stability and no need for external bias or ultraviolet irradiation. However, little research has been conducted on dynamic impact response of mechanoluminescent materials. ZnS:Cu powder was prepared by high temperature solid state sintering, and characterized by X-ray diffractometer, Raman spectrometer, scanning electron microscope and X-ray photoelectron spectroscopy. The results show that ZnS:Cu powders have a wurtzite structure, and the average particle size is about 20 μm. The mechanoluminescent film of approximately 50 μm thickness was coated on the target plate by mixing ZnS:Cu powder and sodium silicate. In addition, the plane-plate impact experiments show that the output voltage signal induced by ZnS:Cu mechanoluminescent film has a linear relationship with the impact pressure, which is consistent with the theoretical analysis. Finally, two testing methods based on mechanoluminescent film are proposed. The multi-point impact pressure test method can be used for the distributed measurement of detonation pressure produced by small-scale and large-scale explosive charges, and the shock wave arrival time test method can be used for the measurement of shock wave velocity, shock wavefront shape and other parameters.

On the basis of traditional belt type ultra-high pressure die, a new type of prismatic cavity ultra-high pressure die was studied to obtain higher bearing capacity and larger volume of sample cavity. It is characterized in that the cemented carbide cylinder is discrete and combined, and the inner plane of the cavity body is plane, which provides an effective approach to reduce the circumferential tensile stress. Under the action of pre-tightening force, the cylinder block is extruded each other, which provides the effect of large massive support and lateral support. Additionally, the split angle of prismatic cavity is studied. The simulation results show that the larger the split angle, the smaller the pressure of the cylinder. The prismatic cavity cylinder is subjected to compressive stress in radial, circumferential and axial directions. Therefore, its stress condition is close to hydrostatic pressure state, which can effectively improve the service life of the high pressure die. After further study of the stress distribution of pressure cylinder, it is found that the prismatic radial split cylinder has the best performance in all aspects. Compared with belt type cylinder, experimental results show that split cylinder has higher ultimate bearing capacity, and prismatic radial split cylinder owns higher bearing capacity than tangential split cylinder.

Lattice structure is widely used in lightweight components and pressure-bearing structures due to its light weight, good pressure-bearing performance, and high specific stiffness. In this study, a hollow lattice structure was manufactured by selected laser melting (SLM) technology. A combination of quasi-static compression experiment and finite element numerical simulation was used to study the failure and deformation modes of hollow lattice structures containing hollow micropillars with different sizes during compression deformation. It is shown that there is no obvious collapse and instability for the hollow lattice structure during the compression process. The failure of the node induces the deformation of the micro-pillars in structure, which in turn causes the overall failure. The deformation mode is uniform overall structure. However, when the wall thickness of hollow structure is small, the boundary layer will deform first due to insufficient rigidity. Increasing the size of the hollow tube could increase the rigidity of the structure.

The mechanical strength, molecular structure and thermal properties of Qtech T26 anti-explosion polyurea (T26 polyurea) were studied by wide-angle X-ray diffraction (WXRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and contact explosion experiment of polyurea coated reinforced concrete plate. The blast-resistant properties and protection mechanism of T26 polyurea coated reinforced concrete plate were investigated based on analyses of the macro morphology of reinforced concrete plate with or without coating and the micro morphology of coating. The results show that the tensile strength of T26 polyurea is 25.4 MPa and the elongation at break is 451.9%; the soft and hard segments of the molecular chain are arranged orderly, and the crystallinity of the microcrystalline region is 24.11%; the glass transition temperature of soft segment and hard segment was −44.9 ℃ and 36.5 ℃, respectively. After the explosion experiments, the uncoated reinforced concrete plate had a large pit on the contact blast face. The backburst surface appeared explosion earthquake collapse and fracture. The reinforced concrete plate with coating had a smaller pit on the contact blast face besides the softening of polyurea caused by the instantaneous high temperature. Moreover, the sparse tensile wave of the explosion reflection caused the damage of polyurea material, leading to the tearing of the coating material. As for the backburst surface coating, the polyurea coating weakened the effect of the explosion impact tensile wave, thus protecting the concrete material from breaking and preventing the explosion debris from splashing.

To study the dynamic response characteristics and protective effectiveness of sandwich composite structure subjected to internal explosion load in a cabin, small scale structure model experiments and finite element numerical simulations were performed, and the propagation and distribution characteristics of the explosion load in the cabin with different blasting distances were analyzed. The dynamic response and deformation mode of the aluminum foam sandwich structure under the initial shock wave, the superposition of reflected shock waves and the quasi-static pressure of the internal explosion were discussed. The experimental and numerical results showed that when the explosive was detonated near one end of the cabin, the localized deformation of the specimen caused by the initial shock wave is significant, while the deformation area of the specimen on the far wall is larger and smoother. Compared with the load conditions of explosions in the center of the cabin, the fluctuation of the shock wave are gentler. In addition, the deformation process of aluminum foam sandwich structure can be divided into three stages: foam core compression, local bulge deformation and overall deflection. The corresponding deformation modes include the facing blast panel with local rising on integral deformation, double panels with local rising on integral and large deformation of integral flexure.

Benefitted by the 3D printing technologies, metallic lattice materials have gained remarkable development. Energy absorption is one of the most important applications for lattice materials. This paper presents our recent work on the energy absorption of polycrystal-like lattice materials. Inspired by the grain boundary strengthening mechanisms of polycrystalline metals, the polycrystalline-like macroscopic lattice structures were designed and constructed by introducing the macro grain boundaries or twin boundaries. Attention will be paid to the crashworthiness and energy absorption properties of the new structures. Specifically, three types of polycrystal-like lattice structures with the simple cubic lattice, the face-centered cubic lattice, and the triclinic lattice cell configurations were created. A parametric study was carried out using the finite element simulations and the quasi-static compression tests based on additive manufacturing technology. The influences of the grain size (i.e., grain boundary density), the grain boundary mis-orientation angle, the interface orientation angle on the deformation modes and the energy absorption properties were investigated. It is found that the interfaces with high symmetry can mostly enhance the energy absorption capability of the lattice structures. Further study demonstrates that the Hall-Petch relationship that was usually used to describe the grain boundary strengthening mechanism of polycrystalline materials can also be applied to the macro polycrystal-like lattice structures. This paper is expected to provide guides for the development of new lightweight energy absorption structures.

In order to study the deformation and failure of the thin plate under impact of debris cloud in the multi-layer structure, a series of hypervelocity impact experiments on multi-layer structure are carried out. The experimental results showed that typical failure characteristics of the thin plate under impact of the high-speed debris cloud are central perforation, deflection and petalling. Considering the effect of bending moment and membrane force, an ideal rigid-plastic annular plate deflecting model is established, which can be used to describe large deflection of a thin plate under the strong axisymmetric impact load. The transverse and radial velocity fields of the thin plate under the strong axisymmetric impact load can also be calculated by the established ideal rigid-plastic annular plate deflecting model. With the Grady fragmentation theory, the number of petals can be calculated. The theoretical calculation result is consistent with the experiment. The research results can provide a basic theory for the damage assessment of the multilayer structure under the impact of hypervelocity projectiles.

In order to investigate the internal explosion damage effect of reinforced concrete frame-masonry wall, the dynamic response and failure characteristics of masonry walls under internal explosion were studied. Based on numerical simulation and theoretical analysis, the failure mechanism and failure transformation process of masonry wall under internal explosion with different TNT equivalence were analyzed. The results showed that under internal explosive with small mass of explosive, the failure of the masonry wall is mainly due to bending effect. With the increase of the mass of explosive, the failure dominated by shear deformation will happen due to the reflection of the first shock wave. For the cases with larger mass of explosive, compressive failure occurs because the overpressure of the first shock wave reaches the ultimate compressive strength of masonry wall. The research results can provide technical reference for explosive damage evaluation and protection design of masonry wall structures.

The dynamic compressive strength of concrete material not only has obvious strain rate strengthening (hardening) effect, but also has obvious temperature weakening (softening) effect. Under the combined condition of strain rate and temperature, there are not only clear strain rate inflection point in the process of compression strength changing with strain rate and temperature, the change of compression strength with strain rate is obviously different before and after the inflection point. Under the same condition, there also are significant differences in the strain rate values corresponding to the inflection points which are existed when the curve bends at different temperatures. Combined with theoretical analysis and references to the compression experimental data of concrete materials under the combined temperature and strain rate condition in recent years, the variation law of the joint effect factor K of concrete compressive strength under different temperatures (T) and different strain rates ($\dot {\varepsilon} $) is discussed. By fitting the experimental data, the prediction expressions of K(T)-$\dot{\varepsilon} $ at different strain rates and different temperatures were obtained, and the coupling effects of strain rate hardening and temperature softening on compression strength were determined. The relationship between the inflection point of strain rate and temperature is analyzed, and the combined rate-temperature boundary for strain rate sensitive and strain rate insensitive region is determined. The rate-temperature equivalent equation is established when the rate-temperature effect is equivalent (namely, K=1) and the rate-temperature equivalent parameters of concrete materials are determined.

In order to study the mechanical response characteristics of rubber under large loading strain rates, a strain-rate-dependent visco-hyperelastic constitutive model is established. The nonlinear and the strain-rate-dependent elastic behavior are characterized by the hyperelastic constitutive model and the viscoelastic constitutive model, respectively. Firstly, based on least square method, the fitting abilities of several hyperelastic constitutive models, i.e., Mooney-Rivlin model, the modified Mooney-Rivlin model, Yeoh model, the modified Yeoh model, Ogden model and Arruda-Boyce model, are compared. The results show that the modified Mooney-Rivlin model and the modified Yeoh model have similar fitting goodness as Ogden model and Arruda-Boyce model. Furthermore, the visco-hyperelastic constitutive model based on a modified Mooney-Rivlin model with a few parameters leading to good fitting results and the Maxwell model reflecting the strain-rate-dependent property of rubber is described. The fitting ability of the proposed model under uni-axial tension and uni-axial compression loading conditions at medium and high strain rates is assessed. It is concluded that the fitting goodness of the model is above 0.95 under both loading conditions. This study can provide a reference for the selection of constitutive models to characterize the mechanical behavior of rubber under uni-axial tension and uni-axial compression tests at different strain rates.

In order to study the rebar effect on perforation into concrete targets, the equivalent mixture model of reinforced concrete is established based on the mixture theory. Meanwhile, the model of steel equivalent to steel plate and the plain concrete slab model are given. The residual velocities, the pressure fields and perforation processes for the two models are compared. The results show that the equivalent reinforced concrete mixture model based on mixture theory can better reflect the rebar effect during the penetration, which can not only meet the calculation accuracy, but also simplify the modeling process and improve the calculation efficiency. It is an effective simplified method for numerical analysis of penetration. The distribution of rebar near the free surface of reinforced concrete slab can improve the resistance of target to projectile, but its role is limited.

In order to improve the damage effectiveness of aimed warhead, the influence of sequential initiation parameters on damage effectiveness of aimed warhead is studied. The initial power parameters of fragments under different sequential initiation parameters are studied by using LS-DYNA finite element program, methods of fragment velocity difference accumulation and dispersion angle accumulation. The damage probability method is used to calculate the damage effectiveness of warhead to ground military vehicles under different sequential initiation parameters. The results show that the number of initiation lines and the angle between initiation lines mainly affect the fragment velocity, and the initiation delay time mainly affects the fragment velocity and the positive and negative proportion of the dispersion angle. Compared with the eccentric one line and three lines sequential initiation, the damage area of eccentric two lines sequential initiation is 7.5–25 m² when the drop height is 7–9 m. When the angle of initiation line increases from 30° to 120°, the damage area of warhead to ground military vehicles is reduced by 3.9%–60.3% at the falling height of 4–8 m. The delay time of sequential initiation increases from 0 to 0.75 times of the propagation time of detonation wave between adjacent initiation points, and the damage area of warhead increases by 8.4%–87.2% when the drop height is 4–8 m. In the initiation mode, by adopting eccentric two lines sequential initiation, the angle between initiation lines of 30°–60°, and the delay time of 0.50–0.75 times of the detonation wave propagation time between adjacent initiation points, the fragment warhead has good damage efficiency to the ground military vehicle target.

To explore the accumulative damage problem of the hull girder subjected to multiple underwater explosions, the influences of explosive equivalent, stand-off distance, and the number of explosions to the hull girder were studied by ultilizing of AUTODYN software together with testing methods. The results show that under underwater explosive loadings, there are two deformation modes, i.e., local plastic deformation of middle depression and plastic bending deformation of global hogging. At a certain shock factor, the deflection values change linearly with the loading times of multiple underwater explosions, and they increase with the increase of explosive charge. The final deflection values of hull girders are different between the cases subjected to single and those to uniform three consecutive underwater explosions under the same stand-off distances and equivalent charges. The deflection values of hull girders decrease subjected to three-time uniform explosions, and are only half of the deflection values under single-time explosion loadings.

In order to study the energy output characteristics of the RDX-based aluminum explosive (JHL-X) and its energy level evaluation method, the explosion heat value and underwater explosion of JHL-X were tested through adiabatic calorimeter, underwater explosion system, and air blast system. Energy, ground overpressure. The results show that the explosion heat value of JHL-X in vacuum is basically the same as that in N₂, about is 1.75 times TNT equivalent; the explosion heat value in air is 8045.724 J/g, 1.93 times TNT equivalent, which is 10% higher than vacuum and N₂. The shock wave energy and bubble energy of JHL-X in an underwater explosion are 0.935 and 4.614 kJ/g, and the total energy is 1.83 times TNT equivalent. In an air blast, the TNT and JHL-X overpressure formulas derived from ground overpressure show that the TNT equivalents at 1.5, 2.0, and 2.5 m are 2.14, 1.70, and 1.75 times, respectively, and the average value is 1.86 times. In addition, the underwater explosion and the explosion heat in vacuum are not provided with oxygen from the external environment, so that the two experiment methods maintain consistency when evaluating the energy level of JHL-X explosives. The air blast and explosion heat in the air have oxygen supply from the external environment, which causes reaction of Al in the aluminum-containing explosive to increase, so the total energy increased, results of these two experiments are similar. Therefore, when evaluating the energy level of explosives, it is necessary to consider the explosive formulation design and practical use, then select different evaluation methods.

In order to study the expand-rupturing process and the radial velocity distribution of the elliptical cross-section natural fragment warhead shell driven by detonation, a three-dimensional model of the elliptical cross-section warhead was established. The AUTODYN-3D software was used to simulate the expansion and rupture process of the elliptical cross-section natural fragment warhead shell driven by detonation with Lagrange algorithm. The relationship between the minor-major axis fracture time difference and the minor-major axis ratio under the single-point central initiation mode of the end face was studied. The influence of initiation points, minor-major axis ratio and loading ratio (i.e. the mass ratio of charge and shell) on the radial velocity distribution of the elliptical cross-section warhead was studied. The results show that compared with the single-point initiation at the center of the end face, the double-point eccentric initiation at the major axis of the end face and the four-point eccentric initiation at the minor axis of the end face, the double-point eccentric initiation at the minor axis of the end face has the best effect on the radial velocity gain of the elliptical cross-section warhead shell. When the loading ratio is constant, the fracture time of the minor and major axes and the difference between the fracture time of the minor and major axes are linearly related to the minor and major axis ratio. Meanwhile, the real-time minor and major axis ratio of the cross-section shape during the expansion of the warhead shell varies linearly with loading time. The radial velocity distribution of warhead shell fragments decreases with the increase of minor-major axis ratio. When the ratio of minor axis to major axis is constant and the loading ratio is less than 1, the fragment velocity increases sinusoidally with the increase of azimuth angle, and the difference of fragment velocity in minor and major axes shows a linear relationship with the loading ratio.

In order to study the response law of composite charges with different structures in the process of slow cook-off, the cook-off bombs filled with $\varnothing $19 mm single charges of explosives JH-2 and JHB and $\varnothing $30 mm composite charges were designed. The temperature-time curves of single charges at 1 and 2 ℃·min⁻¹and composite charges at 1 ℃·min⁻¹ were obtained in tests, and combined with the numerical simulation to further analyzed the temperature field inside the bomb. The research results show that in the case of a single charge, the low-sensitive explosive can significantly reduce the response level of the bomb under thermal stimulation; while in the case of a composite charge, the response point of the bomb is located at the annular region of the outer low-sensitive charge near the shell. The response temperature increases with the increase of the high-energetic charge’s diameter, and the response level increases with the increase of the outer low-sensitive charge’s thickness. The heat transfer in the bomb is retarded due to the contact thermal resistance between the contact surface of composite charges, thus the inner high-energetic cylinder is rarely involved in the reaction.

According to the energy conversion mechanism of rock failure and the overall failure criterion of element, a multi-parameter rockburst criterion considering the releasable strain energy accumulated in rock, the critical value of surface energy required for rock failure, and the brittleness coefficient is proposed. Based on the numerical simulation platform of the three-dimensional discrete element code (3DEC), the above rockburst criterion is developed, and the response characteristics in deep underground engineering, including the principal stresses difference, the elastic strain energy density and the rockburst judgement index, are studied under excavation disturbance in different buried depths and different lateral pressure coefficients. Some conclusions are obtained from the simulations: the larger values of the principal stress difference of the surrounding rock are mainly concentrated at the vault of the tunnel, and the larger values of the elastic strain energy density are mainly concentrated at the vault and arch foot of the tunnel; the distribution range and the values of the rockburst criterion index increase with the augmentation of the buried depth and the lateral pressure coefficient. In order to verify the proposed rockburst criterion and the numerical calculation method, the rockburst disaster in 4^# headrace tunnel of Jinping Ⅱ Hydropower Station is simulated and analysed. It is found that the intensity and location of rockburst disaster simulated by the above method are consistent with the actual situation, which verifies the rationality and applicability of the method established in this paper. The research results provide a theoretical support and a technical guidance for effective prediction, prevention, and control of rockburst disasters in deep underground engineering.

In order to effectively reduce the disturbance derived from the vibration of the presplitting blasting in the slope rock mass and surrounding structures, it is important not only to pay attention to the vibration damping effect of the presplitting, but also to optimize the blasting parameters and initiation modes of the presplitting hole. The study adopts the orthogonal experimental method, which selects the C30 concrete as the similar simulation material of the blasting object to carry out the similar model test of the blasting process with presplitting hole. In this model test, three factors are considered as the non-coupling coefficient, which are delay time, and maximum single-shot charge, and four levels are set for each factor, taking effective half porosity, pre-fracture width and original rock damage rate as evaluation indicators. After the analysis of the sensitivity of each factor to evaluation indicators through range and variance calculations, the best blasting effect with the blasting parameters of the presplitting hole are finally achieved in this model test: non-coupling coefficient is 1.33, delay time is 12 ms, and maximum single-shot charge is 1.8 g. The research results provide guidance for the design of the parameters of on-site blasting with presplitting hole and precise delay time.

The quality of aquatic products decreases after fishing due to the action of microorganisms, endogenous enzymes, lipid oxidation, and other factors. Appropriate treatment can delay aquatic products deterioration. The ultra-high pressure technology (UHP) has the advantages of uniform pressure transmission, good sterilization and enzyme inactivation effect, low energy consumption, high efficiency, no secondary pollution, and simple operation. UHP can not only remain the original color, flavor and various nutrients of food, but also give food a new taste. Based on the introduction of main advantages, disadvantages and working principle of UHP, the research progress of UHP technology in sterilization, enzyme inactivation and processing modification of aquatic products were summarized. UHP combined with physical, chemical and biological preservation technologies can improve sterilization and enzyme inactivation effect and food quality, and the future development of UHP technology in aquatic products was prospected.