As an important rock-forming mineral of the rocks in the earth, garnet is one of the most important minerals in the upper mantle, transition zone and (ultra) high pressure metamorphic rocks.The study of its equation of state is therefore of great significance in laying a foundation for constraining the state and chemical composition of the earth interiors, and further understanding the geodynamical processes of the subducted oceanic lithosphere plate and Earth's mantle.This article summarized the recent advances in the studies of the p-V (pressure-cell volume) and p-V-T (pressure-cell volume-temperature) equation of state of the garnet, focusing on the phase stability, the effect of component and hydrogen on the thermal elastic parameters of the garnet at high pressure and high temperature.Finally, the existing problems and prospects of the garnet's equation of state studies were also evaluated.

Owing to their expected capability to reach metallization within the pressure range under the present laboratory conditions, hydrogen-rich compounds are considered promising candidates for potential high-T_c (superconductor critical temperature) superconductors.Both experimental and theoretical research have found that the critical high-temperature superconductivity can reach a record high-T_c as up to 203 K in compressed sulfur hydrides, thereby generating a new wave for searching for new hydrogen-rich superconductors.The present review focuses on researches of pressure-induced metallization and novel superconductivity in chalcogen hydrides, and discusses their differences in structures and various physical and chemical properties.Chalcogen atoms are isoelectronic but differ a lot in atomic mass and electronegativity, resulting in their great differences in stoichiometry, structure, and chemical bonding.The high-T_c superconductivity of Te/Po-H compounds originates from the strong electron-phonon couplings associated with the intermediate frequency of H-derived wagging and bending modes, a superconducting mechanism which differs substantially from those in S/Se-H compounds where the high frequency H-stretching vibrations make considerable contributions.

By using the developed particle swarm optimization algorithm on the crystal structural prediction, we proposed 6 novel carbon nitride phases with a 5:1 stoichiometry.Their structures, stability, mechanical and electronic properties were investigated by first-principle calculations with the density functional theory.Our calculations indicate that P62m-C₅N is energetically favorable in the 6 structures.Both elastic constants and phonon-dispersion calculations show that these structures remain mechanically and dynamically stable at 0 GPa.Electronic calculations indicate that I4₁-C₅N is metallic while the other 5 are semiconductive.The Vickers hardness shows that all the 6 structures are superhard materials except for I4₁-C₅N.Formation enthalpy calculations suggest that these 6 structures can be synthesized at attainable high pressures (19-83 GPa).

Transparent ceramics is a novel kind of inorganic non-metallic materials with a prospect of broad applications.In the present paper we present a novel method-ultra-high pressure sintering-for fabricating transparent ceramics, characterized by its low sintering temperature, short sintering time, high density and inhibition of grain growth which, compared with the sintering methods traditionally adopted, offers unique advantages in the preparation of nano-structured transparent ceramics.We reviewed the latest progresses made in the ultra-high pressure sintering of transparent ceramics, including the ultra-high pressure sintering of YAG, spinel and alumina under low temperature, and the ultra-high pressure synthesis of nano polycrystalline diamond (NPD), B-C-N, Si₃N₄ under high temperature, and analyzed and summarized the high pressure sintering mechanism of transparent ceramics.

The China-made hinge-type large volume cubic press is a high-pressure device independently developed in China.After 50 years of continuous development, it has achieved fruitful results in industrial synthesis and high-pressure scientific research and occupied a special place in the world.In this paper, we take the topic of China-made hinge-type large volume cubic press used in high-pressure scientific research at the High Pressure Science and Technology Laboratory of Sichuan University, and demonstrate its development and technical characteristics.The technical performance of the device will be continuously improved in the development process in the future, so that it will play a greater role in China's industrial high-pressure synthesis and high-pressure scientific research.

As a well-known insensitive explosive, TATB has been a hot issue in the field of energetic materials due to its sensitivity and reaction characteristics.In this work, using the ab initio molecular dynamics method, we simulate the decomposition process of TATB at different temperatures and under different pressures, and with or without a binder, and analyze the effect of these factors on TATB's decomposition mechanism and reaction rate.The results show that the reaction mechanism keeps unchanged at different temperatures, while the reaction rate is greatly influenced by temperature.Pressure has different influences at earlier and latter reaction stage.We found that, for a system containing fluoropolymer binders, the fluorine polymers participate in the TATB decomposition and change the components of the final products.

The miniature desktop pulse laser equipment can be used to drive shock wave and load dynamic high pressure (DHP) in materials, a technique marked by its low cost, high experimental repetition frequency and ultra high loading rate.The present paper presents the work we have done so far on the desktop laser driven shock wave technique and its corresponding application in exploring the molecular reaction mechanism of energetic materials under shock.We have built an experimental system using nanosecond laser pulses and developed a method to characterize the features of shock wave.The laser driven shock wave obtained in our experiment has a rise-time of only a few nanoseconds and a peak pressure of no less than 2 GPa.This experimental system has been used to study the shock sensitivity of the typical energetic materials RDX.It was found that the intramolecular charge transfer induced by DHP is a key factor influencing the sensitivity.Under high pressure, the electrons on the C-N heterocycle will transfer to the nitro group, leading to the increase of the sensitivity of NO₂.This result can provide experimental reference for understanding the shock ignition mechanism of RDX.Through the present and the future subsequent work, we expect to develop a comprehensive experimental technique that can support the investigation about the shock ignition mechanism of energetic materials on the molecular level.

High-pressure water diffusion experiments in olivine crystal were conducted in a piston-cylinder press in the present work to investigate systematically the diffusion coefficients of water in view of changes of pressure, temperature and oxygen fugacity.It was found that diffusion coefficients increase with elevated temperatures and decreased pressures, and become relatively larger at high oxygen fugacity.The rate of the diffusion along [100] axis is faster than that along [001] axis and the anisotropy becomes weaker with the increase of the pressure.The measured hydroxyl concentrations in the olivine under lunar mantle conditions are higher than 10^-4, thus indicating that the olivine could be a major water reservoir in the deep lunar mantle.By comparing the diffusion rate of the water in the olivine melt inclusions with the magma ascent and the eruption rates, we found that the water in the melt inclusions in the olivine xenocrysts will be well maintained during the magma ascent, whereas water will diffuse out of the xenocrysts during the magma eruption process.The estimated water concentration in the lunar mantle based on the melt inclusion data could be the lower limit.Our work provides significant thermodynamic parameters for exploring the moon evolution history.

The double-mode Richtmyer-Meshkov (RM) instability, when the incident shock (Ma=1.27) impacting on several groups of initial double-mode cosine interface formed by different amplitudes in initially nonuniform flows whose density is Gaussian distribution, was numerically investigated using the large-eddy simulation code MVFT (multi-viscous-flow and turbulence).The numerical results show that the coupling effects between different amplitudes in the nonuniform flows are weak and the evolution of the interface with a large initial amplitude in the low density nonuniform area grows fastest, while that with a small initial amplitude in the high density nonuniform area grows slowly.Further analyses reveal that within a certain initial amplitude range, the amplitude growth rate and energy in the low density zone of nonuniform flows is larger than those in the high density zone, thus the influence of the initial amplitude on the low density zone is more obvious, which eventually leads to a faster evolution process of the RM instability.Moreover, the changing phenomena of uniform flows are opposite to nonuniform flows.Thus, it can be concluded that the evolution mechanisms of the RM instability between the nonuniform and uniform flows are distinctive.

In the present study, to directly measure the radial strain of a metal sample loaded by the split Hopkinson pressure bar (SHPB) facility, we developed a new all-fiber displacement interferometer that could output signals of invariable strength by adopting a semiconductor optical amplifier (SOA) followed by an erbium doped fiber amplifier (EDFA) to control the light intensity reflected from the measured sample during the dynamic measurement process.The theoretical study showed that the displacement measurement resolution was free from the fluctuation of the output intensity, and the experimental results demonstrated that this new interferometer could measure the elastic and plastic strains of metal sample loaded by the SHPB with high resolution.

In this work, we propose a novel method for testing the dynamic mechanical properties of materials and for in-situ observation at ultra-high temperature (up to 1 600 ℃).The experimental devices used include a classical split Hopkinson pressure bar, a MoSi₂ heating source for obtaining ultra-high temperature, two piston rods added to complement the double synchronically assembled system and a high speed camera employed to observe the deformation.To verify the ability of the proposed method for operating at ultra-high temperature, we conducted our experiments on TC4 alloy at temperatures ranging from 20 to 1 400 ℃ and the strain rate of 2 000 s^-1, and SiC at temperatures ranging from 20 to 1 200 ℃ and the strain-rate of 250 s^-1.The results showed that the peak flow stress of the TC4 alloy specimen drops from 1.6 GPa at room temperature to 150 MPa at 1 400 ℃, and the compressive strength of the SiC specimen drops from 250 MPa at room temperature to 220 MPa at 1 200 ℃.Furthermore, the high speed images revealed that the oxide layer of the TC4 alloy specimen cracked in air but not in argon, and the initial cracks of the SiC specimen occurred at 80% of the compressive strength at room temperature and at 99% of the compressive strength at 1 200 ℃.

The split Hopkinson pressure bar (SHPB) tests are often conducted to obtain the dynamic compressive strengths of concrete-like materials which need to be interpreted or analyzed correctly as these data are very important for the construction of reliable constitutive equations used in numerical simulations.In the present work, a numerical study is performed on the influence of specimen size on concrete in SHPB tests using a rate-independent material model.A new empirical equation for the dynamic increase factor due to inertia (confinement) effect is also proposed which took account of specimen size effect through its volume.It is shown that the empirical formula agrees well with the numerical results for the SHPB tests on concrete with different specimen sizes, and the dynamic increase factor due to inertia (confinement) effect increases with the increase of specimen size.

Based on the Hayes multi-phase equation of state, non-equilibrium phase transition rate and damage evolution rate equation, and the constitutive relation of materials, the numerical simulation method considering the phase transition and damage was proposed and then used to analyze the interaction between phase transition and spall of iron in the symmetric impact experiment of iron.The results show that it is only when the phase transition of pure iron occurs that spall emerges.In addition, the free surface velocities and the spall positions of the sample are in agreement with the experimental results.

In the present study, analytical solutions were presented for the prediction of the penetration and perforation of composite glass fiber-reinforced plastic (GFRP) sandwich panels struck normally by flat-nosed cylindrical projectiles over a wide range of impacting velocities, projectile mass and core thickness.The analysis model involved a three-stage perforation process including perforation of the front steel skin, the GFRP core, and the back steel skin.The formulation were based on assumptions that the deformations of steel skins are localized and the projectile is considered as a rigid body in the perforation of GFRP composite laminate.The energy absorption of the front and back steel skins and the GFRP core were estimated with the upsetting effect of the projectile and the adiabatic shear effect of the steel skins taken into consideration.In addition, based on the energy balance, the ballistic limit of the sandwich panel were obtained and compared with the available experimental results.The results show that the analytical predictions are in good agreement with the available experimental data.

To study the air/water interface deformation and breakup, the water bubble and the blast waves in water, we launched a high-speed projectile using a vertical second-stage gas gun, and visualized the flow-filed close to the air/water interface using the laser shadow and schlieren photography.The images show that the high pressure air downstream the projectile overtakes the projectile at the speed of about 350 m/s and generates blast waves in the air.In the meantime, the blast waves and cavitation bubbles are also generated in the water.The air blast wave reflects on the air/water interface but cannot deform it due to water's large inertia at such a short time.The projectile traveling is not disturbed although the reflected blast wave interacts with it.The droplets cloud from the broken interface is produced after the projectile water entry.It is hard to distinguish the border between the bubbles and the droplets clouds.For projectiles with different head shapes, the bubbles are obtained in different shapes and sizes but the projectile trajectory is seldom disturbed.Similar flow-field characteristics can be identified for a projectile at the speed of 1.8 km/s but with different size and shape of clouds and bubbles.The results demonstrate that such a vertical two-stage gas gun can provide a way for experiments of projectile water entry.

To improve the axial lethality of focusing fragment warhead, we carried out a research on the axial dispersing characteristics of prefabricated fragments.Based on the Shapiro formula theory, we designed the shell and improved the charge structure of warhead, and simulated its explosion process using the LS-DYNA software and ALE algorithm.Considering the axial distribution of fragments on the target, we analyzed the relationship between the charge structure, the shell curvature and the dispersing characteristics of fragments.The results indicate that the scattering of the fragments can be controlled effectively by deferring the curvature of the shell and using the "I"-shaped charge structure.Our work has been proved to benefit researches on the control and application of the fragments scattering of warhead.

In the present work, to find out the mechanisms of the coupling effect for blast waves and fragments by fragmentation warheads exploding in the air, we developed a theoretical model by analyzing the motion patterns of the blast waves and fragments moving in the air in consideration of the influence of the shell on the intensity of the shock wave.Meanwhile, we carried out an analysis of an actual case and examined the factors that influence the coupling action spans.The results show that the warhead loading coefficients, detonation velocities, shell thicknesses and energy allocations have a great influence on the coupling action spans, whereas the influence of the explosion heats, masses and shapes of the fragments is relatively limited.The coupling action spans decrease with the increase of the loading coefficients, explosion heats and detonation velocities of the explosives, fragment masses and the energy ratio of the shock wave energy to the fragment kinetic energy.However, as the shell thickness gets bigger and the fragment shapes become more abnormal, the coupling action spans become larger.

In this work we simulated the process of the jet penetrating into a target with a V-shaped reactive armor using the three dimensional finite element code (LS-DYNA), and performed the corresponding experiment to study the effect of the impact point position on the jet.The numerical simulation results are in good agreement with the experimental data.The results show that the disturbance degree of the jet was obviously different when the impact point was positioned differently.With the increase of the distance between the impact point and the bottom in the center line of the V-shaped reactive armor, the penetration depth of the jet in the witness target exhibits a tendency to decrease first and then increase.When the distance between the impact point and the top of the V-shaped reactive armor is 6.25 times that of the jet diameter, the penetration depth is minimum and the protective capability at this point is optimal.Moreover, the protective capability of the top is superior to that of the bottom.