Hydrogen under extremely compressed conditions exhibits extraordinary richness in physics and chemistry.Its structural transitions and phase diagram are fundamental for understanding the high pressure behavior of condensed matters, and also for important applications in astrophysics and material science.In this paper, we reviewed the research progress on metallic hydrogen since it was proposed until to very recent years.Several key issues and possible future progress about dense hydrogen are analyzed and summarized.With density functional theory calculations and a model analysis using an equation of states, we explored and demonstrated:(1)the complex and novel atomic structures of dense hydrogen; (2)the novel behaviors of hydrogen molecules near the dissociation region; (3)the stability of metallic hydrogen under pressure and the possibility of recovery to zero pressure; (4)the advantages and disadvantages of the "DAC+shock" experimental method to achieve metallic hydrogen.Our results showed that it is impossible to quench the high pressure phases of metallic hydrogen to ambient conditions.The complex behaviors of dense hydrogen present as a great challenge for both experimental and theoretical studies, especially near the dissociation of hydrogen molecules, where sharp discrepancies were unveiled, implying that much effort is still required to improve the state-of-the-art experimental and many-body theoretical methods.

Three-dimensional polymetric cubic gauche nitrogen (cg-N) combined with covalent N─N single bonds is an ideal high energy density material (HEDM).A series of solid molecular state-to-solid molecular state transitions (β-δ-ε-ζ-η) in nitrogen were observed in experiment upon pressurizing the molecular nitrogen up to 135.6GPa in ambient condition.Under 133.9GPa and at 2000K, the transparent cg-N was successfully synthesized using the double-side laser heating diamond-anvil cell (LHDAC) without any laser absorbing material.In addition, the pressure coefficient of the Raman A mode for cg-N is 1.56cm^-1/GPa at about 134GPa.

The lattice constant and mechanical properties of cubic BC₃ under ambient and high pressure, including the elastic constants, the elastic modulus, and the mechanical anisotropy, were investigated using the first principle method in the framework of the density functional theory.The thermodynamic properties under high temperature and high pressure were calculated in terms of the quasi-harmonic Debye model.The results obtained show that the cubic BC₃ possesses a large elastic modulus and a high degree of anisotropy under ambient pressure.Under high pressure, the lattice constant, elastic constants, and elastic modulus of cubic BC₃ increase significantly.The results obtained from the thermodynamic calculations suggest that the cubic BC₃ has a large Debye temperature, and the molar heat capacity at constant volume and pressure exhibits obvious variation under high temperature and high pressure.Meanwhile, The Debye temperature of cubic BC₃ increases with the increase of pressure, but decreases with the increase of temperature.

As a class of stable low-resistivity and high-temperature materials, tantalum disilicide (TaSi₂) has been widely used in integrated circuits.Therefore, its electrical stability is as important as its structural stability.Here, we report the electronic transport properties of TaSi₂ based on structural stability under high pressure.Its stable crystallographic structure was studied by synchrotron X-ray diffraction and Raman spectroscopy experiments up to 20 GPa.In situ high-pressure resistance measurements revealed that the resistivity of TaSi₂ has a trend to be steady at the value of about 2 μΩ·cm under pressure increasing up to 16.3 GPa.Futher, the electronic structure of TaSi₂ under pressure was theoretically calculated to understand its metallic behavior.

The structural stability of LiAlH₄, a promising hydrogen storage material, under high pressure was researched using the ab initio pseudopotential plane wave method.It is found that the phase transition occurs at 1.6 GPa from the α-LiAlH₄ phase to the β-LiAlH₄ (space group I2/b) phase.This phase transition is identified as first-order in nature with volume contractions of 18%.Moreover, the analysis of the phonon dispersion curves suggests that phase transition is related to the phonon softening.Mulliken population analyses indicated that the ambient phase (α-LiAlH₄) is expected to be the most promising candidate for hydrogen storage.

In this research we presented a novel method based on frequency domain interferometry to in situ measure the cupping deformation of diamond anvils under high pressures.First we introduced the working principle of the cupping deformation measurements based on the frequency domain interferometry, and then we carried out the experiments under high pressures.The cupping deformation of diamond anvils is obtained under high pressures up to 42.1GPa, and its maximum value reaches 11.1μm.The experimental results show that the cupping deformation increases linearly with the pressure.Our work verify the recent finite element modeling calculations.

In the present work MoWC₂ was successfully fabricated under 5.0GPa/2000K with a holding time of 60min using, as the synthetic raw material, molybdenum, tungsten and graphite powder (whose purity are more than 99.8%).Then the physical properties of the synthesized samples were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, micro-hardness test, physical property measurement system and thermo gravimetric-differential thermal analyzer (TG-DTA).The results show that the MoWC₂ crystal thus synthesized has a hexagonal structure with a space group of P6-m2.It is highly crystalline with an average grain size of 1-4μm.Its convergence hardness value, oxidation temperature and the superconducting temperature are 15.3GPa, 450℃ and 6.8K, respectively.In addition, this MoWC₂ has a high hardness and oxidation resistance owing to its strong orbital hybridization.Furthermore, it is a superconducting material with a relatively high transition temperature since it has a higher density of states at the Fermi surface and Debye temperature, thereby making it a versatile material that is superconductive, highly heat-resistant, and superhard.

Due to its wide range of applications as a superhard material, polycrystalline diamond (PCD) has been used in oil-and gas-drilling, tool cutting, making of wear-resistant parts.At present, the average size of industrial synthetic PCD is above the micron dimension, but synthesizing the PCD with a size below the micron dimension remains a tough challenge.In this work, we succeeded synthesizing sub-micron polycrystalline diamond under high temperature and high pressure using the infiltrating technique.The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), energy dispersive spectrometer (EDS) and hardness test.These results show that the hardness of the PCD thus synthesized is 57.0GPa under 5.5GPa and 1500℃ when the hold time of temperature is 15min; that the Co can disperse uniformly in PCD as a round hole used the bi-layered assembly so that the PCD demonstrates uniform and excellent performance; and that it is found from its sintering process that the temperature and holding time play an important role in its synthetic process.

In the present work, pure polycrystalline cubic boron nitride (PCBN) sintered bodies were synthesized under different high pressure sintering conditions using 10 μm-sized cBN grains.The microstructure of the sintered pure PCBN bodies were investigated using the scanning electron microscope (SEM) and X-ray diffractomer (XRD).The wear ratio and compressive strength of the sintered pure PCBN bodies were tested, and the effects of the sintering pressure, temperature and holding time on the microstructure and properties of sintered pure PCBN bodies were examined.The results show that the factors exerting the most significant influence on the properties of the sintered samples are the pressure, the sintering temperature and the holding time, in order of their degrees of influence.When they are 9 GPa, 1 700 ℃ and 240 s, respectively, the optimal properties of the pure PCBN are achieved, i.e. with the wear ratio as 10 200 and the compressive stress as 2.52 GPa.

An aluminum bar with a dense degree of over 98% was fabricated using nano-aluminum powders in an improved sintering device capable of pressure relief to study the sintering molding of nanometer metal powders.First, the performance of the sintering aluminum bar at different detonation velocities were obtained by adjusting the ratio of the ammonium nitrate explosive to the wood powder.Then the microstructures of the aluminum bars were observed using metallurgical microscopy, and such mechanical properties as the density and hardness were measured.The results show that the Mach-hole can be reduced by reducing the detonation velocity.However, the excessively low detonation velocity decreases the mechanical properties such as the density and the hardness.Moreover, the sintering aluminum bar that is free from any Mach-hole, of higher hardness, higher dense degree and finer grain size can be fabricated from nano-aluminum powers whose detonation velocity reaches 2 158 m/s.

In present experiments, nitrate salts, sodium silicate, anhydrous ethanol and RDX were mixed with a certain proportion, and the detonation synthesis of FeO doped silica coating iron nano particles was completed in a closed container with argon as the protection gas.The composition, morphology and magnetic properties of the detonation products were tested by XRD (X-Ray Diffraction), TEM (Transmission Electron Microscope) and VSM (Vibrating Sample Magnetometer), respectively.Experimental results indicate that the metal particles are the core of the detonation products, and the silicon dioxide is the coating of the shell/core structure with the particle size of about 60 nm.And the analysis of the magnetic curve shows that the detonation products present weak ferromagnetism, high remanence and coercivity at room temperature, which should be regarded as an excellent magnetic storage material.

Sandwich cylinders cored with aluminum foam have been widely applied in the fabrication of blast protection containers.The experiment under internal blast loading was performed and, based on the Voronoi technique, finite element models of sandwich cylinders were constructed and then used to simulate the deformation process of the sandwich cylinders.The results show that the simulation results agree well with the experiment results.With the increase of the cores' relative densities, the deflections of the inner shells increase and the deflections of the outer shells decrease.Furthermore, the deflections of the shells and the relative density of the cores approximately satisfy a quadratic relationship.

Based on the numerical model established using the ALE algorithm in consideration of the influencing factors of the water surface and the water bottom, the shallow water explosion in different explosion depths was simulated using LS-DYNA, and the credibility of the simulation results were verified by the comparison of numerical results and empirical formula.Then the bubble pulsation's form and loading characteristics in different explosion depths were explored, and the influence of the explosion depth on the bubble pulsation in shallow water explosion was analyzed.The results show that with the increase of the explosion depth, the influence of the free surface and gravity diminish, the influence of the hydrostatic pressure and the boundary surface rise up, the jet flow direction constantly changes from downward to upward during the bubble shrinkage process, and the times of the maximum bubble radius and pulsation period also gradually increase; that the specific impulse-water depth curve increases at first and then decreases, and the load distributions are basically consistent with each other when the explosion depth is close to the water bottom; the decline of the load slows down with the explosion's spreading distance; and that the growing trend of hazard explosion depth tends to slow down after rising steeply along with the increase of the depth measured, becoming stable towards the water bottom.

To study the influence of the plexiglass-air interlayer structure on underwater explosion vibration, the foundation vibration signals for this structure caused by underwater explosion in the small pool (5.5 m in diameter and 3.62 m in height), the influence of different air interlayer thicknesses on the maximum vibration velocity was studied, HHT (Hilbert-Huang Transform) was used to analyze the vibration test signals by writing relevant programs based on Matlab software, studying the influence of different air interlayer thickness on the global frequency of vibration signals.Experimental results show that:under the condition of plexiglass-air interlayer structure, with the increase of air interlayer thickness, the maximum vibration velocity decreases first and then increases, and the vibration isolation effect is the best when the thickness is 120 mm.The amplitude corresponding to the global frequency can be obtained by means of HHT analysis, the amplitude attenuation of the 5-15 Hz low frequency section is obvious, the action time is shortened, which can effectively prevent the resonance phenomenon between the building and structure.The experimental results and analysis have certain theoretical reference value for underwater blasting engineering protection and structural design of lightning protection bunker for military ship.

Flyer shock-initiated HNS-Ⅳ explosive is an important topic in the research of the in-line explosive train.In this study, with the influence of the energy loading method, which may be electrical explosion, laser and micro charge detonation, and flyer material on the shock initiation taken into consideration, the parameters of pⁿτ and the James criteria for HNS-Ⅳ explosive were obtained according to flyer threshold velocity measured by literatures.Meanwhile, the process of initiating HNS-Ⅳ explosive the flyer driven by copper azides was simulated using the ANSYS/LS-DYNA program, based on whose results the parameters of pⁿτ and the James criteria for HNS-Ⅳ explosive were adjusted.It was found that the pⁿτ criteria for HNS-Ⅳ explosive should be adjusted to p^2.08τ>1.54 GPa^2.08·μs(0.001 μs <τ < 0.14 μs, 3.8 GPa <p < 28.0 GPa), while the James criteria should be adjusted to 0.215/Σ+0.108/E < 1.The two adjusted criteria, which might have a higher practicability, were consistent with the simulation results.

The prediction of the penetration depth of concrete in concrete damage effect is of great significance to the design and construction in protection engineering.However, the traditional methods for this prediciton involve such problems as requiring a great supply of samples, or suffering from a large prediction error, and so on.In this work, following the theory of the support vector machine (SVM) and according to the parameters optimized through the particle swarm optimization (PSO), the PSO-SVM for predicting the penetration depth was proposed.The corresponding programs were written and the prediction was verified by the experiment data.The results show that the PSO-SVM method has a great advantage for small samples and non-linear prediction.In comparison with the traditional grey theory, the relative predicted errors through the PSO-SVM method are smaller (the maximum relative error being 3.18%).As the number of the samples increases, the maximum relative errors decrease and the changing rate slows down whereas, however, the amount of calculation becomes larger.Above all, it is feasible to apply PSO-SVM method to the prediction of penetration depth of projectiles into concrete targets.

Hypervelocity penetration is an important issue for a weapon designer and protection engineering experts.With the increase of the impact velocity, a projectile may transition into a fluid penetration phase, and its depth of penetration (DOP) no longer rises monotonously with the velocity.Numerical simulation of the penetration processes of a long rod projectile at an elevated impact velocity was performed to analyze the variation and influencing factors of the transition point.Influences of the hardness, nose shape, material of the projectile and the target on the transition point of DOP were simulated.The simulation results show that, with the increase of the impact velocity, the DOP increases at first and then decreases at a certain velocity (called the transition velocity).The velocity of the transition point improves with the increase of the projectile's hardness.The Ogive-headed projectile has a higher transition point than the spherical-headed projectile.Moreover, the projectile/target material also has significant effects on the transition point.

In order to reduce the bullet destruction, the design of shrapnel, a new type of bullet based on the standard small bore bullet, is proposed.We performed the experiment of water penetration of the shrapnel to study the deformation of the projectile head at different speeds, and conducted the corresponding numerical simulation using LS-DYNA and obtained the projectile's velocity attenuation and displacement curve.The results show that the degree of deformation of the projectile's head is related to its speed, the higher the speed, the greater the warhead deformation.The warhead cracking into "petals" can effectively reduce the bullet velocity, and raise the penetration resistance.The displacement in high speed penetration is less than that in low speed penetration, which indicates that the shrapnel has a good low-penetrating characteristic.

In this paper, the influence of the aspect ratio on the penetration resistance in the target penetration process of the warhead was studied based on the classical cavity expansion theory, the modified Forrestal resistance model and the acceleration resistance model.The influence of the aspect ratio on the resistance term coefficient was analyzed and the range of applicability of the three theories was discussed by calculating the penetration residual velocities of the warhead with different aspect ratios.The results show that the variation of the acceleration resistance term coefficient has a significant influence on the penetration process when the aspect ratio is below 3;when the aspect ratio is above 5, the results of the three models tend to converge, and they are all applicable to engineering calculation.

The process of wedge-shaped charge's interference effect and that of sandwich charge's on the jet were numerically simulated using ANSYS/LS-DYNA software.The influence of the wedge angle and that of the charge mass on the velocity and the declination angle of the jet head, the velocity of the slug were analyzed and discussed.Comparison of the obtained results with those of the sandwich charge shows that the interference effects of the wedge-shape charge and the sandwich charge on the jet head are very much alike but their interference effects on the jet slug are different.The movement of the wedge shaped flying-plates can be seen as a 2D composite motion of translation and rotation.When the wedge angle is positive, the cutting jet effect of the wedge-shaped charge is better than that of the sandwich charge.In this case, the deflection of the jet head increases, the velocity of the jet slug decreases, and the effect is enhanced with the increase of the wedge angle.Moreover, as the charge mass increases under the condition that the angle remains unchanged, the contact position of the jet head gradually shifts to the front of the target, the contact time delays, the breakup time of the jet slug arrives earlier, and the rotation of the plates slows down.

The processes of shaped warheads penetration of post-impact targets with reaction armor at different flight speeds (150, 200, 300, 400, 500 m/s) and in different penetration angles (30°, 45°, 60°) were simulated using the LS-DYNA program, and the interference of the jet and the result of its penetration into the target plate were discussed.The results show that when the penetration angle is a constant, the cutting length of the target surface increases with the increase of the velocity and the rate of the increase is the fastest at 30°, but the penetration depth decreases and the rate of the decrease is the slowest at 60°.When the flight speed is a constant in the range of 150-500 m/s, both the cutting length of the target surface and the penetration depth decrease with the increase of the angle.The drop of the cutting length of the target surface tends to increase at first and then decrease with the increase of the velocity and the maximum decrease is 59.6% at 300 m/s, whereas the drop of the penetration depth tends to decrease at first and then increase with the increase of the velocity and the minimum decrease is 39.3% at 350 m/s.The theoretical analysis was carried out and the numerical simulation method was proved correct.

In this study, the deflagration and detonation parameters of RP-3 aviation kerosene in a vertical shock tube, 200 mm in inner diameter and 5 400 mm in height, was measured at different initiation energies, spray pressures and equivalence ratios in direct ignition by a high explosive to further explore the influencing factors of the combustion characteristics of the RP-3 aviation kerosene.The results show that the critical initiation energy of the aviation kerosene decreases sharply at first and then rises slowly with the increase of the equivalence ratio, and its changing trends are basically in an "L" shape.When the spray pressure varies from 0.20 MPa to 0.60 MPa, the detonation velocity and the explosion pressure are both in the shape of an inverted "U" along with the changing of the spray pressure at the same fuel concentration.The detonation velocity and the explosion pressure curves have a linear ascending tendency with the increase of the initiation energy.Moreover, when the initiation energy ranges from 0.37 MJ/m² to 1.68 MJ/m², the aviation kerosene cannot reach the state of detonation.The detonation velocity and the explosion pressure of the fuel at first increase and then decrease along with the rising of the equivalence ratio, also in an inverted "U" shape.

Setting spoilers in the tunnel is an effective way to accelerate its shock wave attenuation.In order to investigate the influence of the spoiler structural parameters on its shock wave's attenuation, numerical simulation was carried out using the ANSYS/LS-DYNA finite element software.First, based on the fluid-solid coupling algorithm, the equal scale model of Schardin's experiment was established.The simulation results were found to be in good agreement with the experimental results, which verified the validity of the simulation model.Then the numerical method was used to investigate the influence of the spoiler thickness, inclination angle and interval on the shock wave attenuation in a silo tunnel when the rectangular spoiler width was a constant.The results show that when the other parameters remain the same, with the increase of the spoiler thickness, the overpressure attenuation of the shock wave becomes increasingly more obvious.When the spoiler thickness is 40 cm, the spoiler with the inclination angle of 105° and the interval of 6 m is the most beneficial condition for the shock wave attenuation.These results can provide valuable reference for the design of the tunnel protection.