Using the plane wave pseudo-potential (PWP) and the general gradient approximation (GGA) methods based on the density functional theory, we performed an ab initio investigation of thermal dynamics of ZnSe in zinc-blende (ZB), rock-salt (RS) and wurtzite (WZ) phases.The lattice parameters, equation of state and phase transition properties of ZnSe in different phases were obtained from the calculated energy-volume curves.The results show that the RS structure is a stable phase at high pressure, and the transition pressure from ZB to RS phase is 14.95 GPa, which is well consistent with the experimental and theoretical results.In addition, the phonon spectra of ZnSe in ZB and RS phases were obtained through the quasi harmonic model, and the temperature dependence of their heat capacities, entropies, and free energies were also calculated.

In order to evaluate the structures of magnesium end-member pyroxene polymorphs (MgSiO₃) under different pressures, first-principles theoretical calculation on low- and high-pressure phases, with space group Pbca, P2₁/c, C2/c, P2₁ca respectively, was conducted under pressures up to 30 GPa.The bulk moduli of polymorphs were obtained from fitting the third-order Birch-Murnaghan equation with calculated pressure-volume data.The C2/c phase had the largest modulus (an increase of 3% compared to Pbca) under zero-temperature and zero-pressure, whereas little difference was observed between moduli of Pbca and P2₁/c, and the high-pressure phase P2₁ca showed a smaller value than Pbca.Moreover, the results of axial compression showed that the c-axis was harder to compress than a-axis in C2/c, which was opposite to the previous first-principle results on diopside (MgCaSi₂O₆).The angels of SiO₄ tetrahedral chains in P2₁/c, C2/c, and P2₁ca decreased monotonically as a function of pressure while in Pbca, which had two kinds of angles, one showed the same trend as the aforementioned three polymorphs and the other increased monotonically above 7 GPa, implying an unstable structure or the onset of a new phase transition.The static enthalpy differences among the four polymorphs indicated the possible phase transitions of the pyroxene under low-temperature and high-pressure.

To study the effect of gas concentration on kinetic characteristics of gas explosion in a closed space, we simulated the gas explosion with different gas concentrations using a constant volume reactor model.The results show that with the increase of the initial gas concentration, the final temperature increases at first till its maximum and then decreases, and the pressure increases continuously; the concentrations of ·OH, H· and O· increase at first to the maximum and then decrease; the remnants of CH₄ increase slowly and those of O₂ are gradually reduced to zero.For gas explosion, the optimum reaction concentration (about 10%-12%) is higher than the stoichiometric mole fraction and the temperature reaches the maximum at this time.In the case of the stoichiometric mole fraction, the primitive reactions which contribute to the consumption of methane and oxygen and the generation of free radical (O· and H·) is R32, R38, R85, R118, R119, R155, R156, R157;the primitive reactions which contribute to the generation of methane and oxygen and the reduction of free radical (O· and H·) are R53 and R158.

Adding aluminum powder into emulsion explosive can increase its explosion heat and work capability, but also raise its heat sensitivity.In order to study the effect of the aluminum particle size on the thermal stability of the emulsion matrix, the thermal decomposition characteristics of the emulsion matrix containing aluminum powders of different particle sizes were examined using differential scanning calorimetry (DSC) and thermal gravimetric (TG) methods at various heating rates, and the kinetic parameters of thermal decomposition were obtained.The results show that the addition of aluminum powder reduces the peak temperature, the activation energy and thermal stability.Moreover, this trend becomes more obvious with the decrease of the aluminum particle size.Compared with the case of the emulsion explosive without the powder addition, the aluminum powders with different particle sizes have no effect on the thermal decomposition mechanism functions of the emulsion matrix in the scope of experiments and they are controlled by nucleation and growth mechanism and the mechanism function could be described with Mample principle with a reaction order of n=1.The results can provide theoretical guidance for corresponding thermal stability research of aluminized emulsion explosive.

One-dimensional plate impact experiments were performed to study the double shocks to detonation transition and Hugoniot state in the HMX-based explosive JOB-9003.The flyer was a combination of sapphire and Kel-F, which could pass two different pressure waves after the impact.We measured the particle velocities at the interface and the different depths using the Al-based electromagnetic particle velocity gauge technique, and obtained the particle velocity-time diagram, according to which we calculated the impact velocity, the shock wave velocity, and then the Hugoniot relation of the explosive.By comparing them with the existing experiment data in the Pop plot, we can draw the conclusion that the explosives pressed by the double shocks will exhibit desensitization features.

The shaped charge jet can be applied to explore and enlarge the escapeway for drivers and passengers trapped in an ignited bus due to its special cutting ability.In this research, we established a numerical model of this scheme to study the performance of the shaped charge jet by using the ANSYS/LS-DYNA finite element software.Simulation results show that despite of the negative influence of both the asymmetry of the shaped charge and the diffraction of the detonation wave in curvature segments on the penetrating ability of jet, the cutting ability of the shaped charge jet can be sustained with reasonable parameters.It can smoothly explore and expand the escapeways within microseconds without any remaining obstacles for physical vulnerable groups.Thus the scheme can be used as an effective countermeasure for the ignited bus.

The technology of preparing coatings using a shaped-charge explosion was briefly introduced and employed to produce coatings of WC/Co (10%, mass fraction of Co) on the surface of the charge's substrates.The properties of the coatings were analyzed and characterized by means of X-ray diffraction analysis and optical microscopy.The results indicate that the uniform and compact coatings prepared from the mechanically mixed powder of WC/CoC₂O₄·2H₂O (21.7%, mass fraction of CoC₂O₄·2H₂O) by a shaped-charge explosion are better than those prepared from the mechanically mixed powder of WC/Co (10%), and the degree of oxidation and decarburization of the coatings was also lower than that of the later.With the increase of the gas dispersant in the mechanically mixed powder of WC/CoC₂O₄·2H₂O, the porosity of the coatings was gradually decreased whereas its uniformity and compactness were gradually strengthened.

The shock wave generation characteristics of underwater plasma intense sound source were analyzed and, based on the superposition of shock waves, a multi-electrode array bunching scheme was proposed using the interval consistency between the shock wave formation and the triggered switch flow.The multi-electrode array bunching sound field model of underwater plasma intense sound source was established, and the array bunching characteristics of different discharging sequences were obtained by numerical simulation.The results show that the multi-electrode array bunching scheme is feasible for coherent superposition.By controlling the discharging sequence of the multi-electrode array, the directivity of the array bunching area can be flexibly changed and the sound pressure level of the specified area can be effectively enhanced.The results provide a theoretical guide for further understanding of the superposition rule of underwater intense sound shock wave and optimum design of the multi-electrode array.

The two-stage light gas gun is a conventional device for accelerating a projectile commonly chosen for research owing to its wide range of launching velocities, good repeatability and flexible work environment, and is widely used in studies of high pressure physics, space debris protection, and mechanical properties and dynamic responses of materials.However, as the traditional light gas gun uses explosive as the energy source, it suffers from the disadvantages of comparatively heavy molecular weight and low sound velocity, poisonous products, requirement of special conditions for transportation and storage.In this work we developed a novel two-stage light gas gun, whose driving energy is supplied by the gaseous chemical reaction, and whose highest velocity in projectile-launching reaches 5.6 km/s.This novel technology is inexpensive, free from use of explosive and environment-friendly.

Granules can be accelerated to a high velocity using high-power lasers.We applied this technique to the process of mixing granules with gas to investigate the high speed gas-solid two-phase flow transportation.Optimization of target design and adjustment of laser parameters were adopted to control the laser-driven process.Diagnostic tools with high resolving power of space and time were set up to capture the high-velocity granule.The results indicate that the laser-driven launching technique is effective, and the shadow photographs of the high-velocity granule are successfully obtained.The experimental and diagnostic technology can also be used in the research of ejecta mixing, scramjet engine performance, and high-speed impact, dust explosion, and so on.

In the present work, based on the nonlinear dynamics software AUTODYN, we performed a three-dimensional simulation of the instability process of the aluminum honeycomb sandwich panels under blast loading.By establishing the solid model of aluminum honeycomb sandwich panels with different parameters, we studied the dynamic response of the front and back sheets under the TNT impact and the instability deformation in the plastic stage.The results achieved from our calculation show that with the increase of the thickness of the aluminum honeycomb panel, the height and thickness of the aluminum foil, the final residual deformation of the aluminum honeycomb panel under blast loading is obviously reduced and its deformation-resistance ability is enhanced.For the aluminum honeycomb panels with different cell shapes but the same relative density, the distinction of the panels' final residual deformation under blast loading is not significant because there is little difference in "inertia effect" under the uniaxial compression condition.

In this work different modification features were designed for the study of the fracture characteristic and mass abrasion of projectiles with local modification, normal impact experiments were performed on typical RHA targets at velocities ranging from 380 to 500 m/s, and the failure mode and mass loss of the penetrating projectile were examined.The results show that the length eroding and mass loss of the projectile increase as the impact velocity increases, yet the variation of the diameter eroding is small.The failure mode of the projectiles is mainly shear fracture, and the macroscopic damage degree of the projectiles by local modification processes is comparable to that of the unmodified projectiles, of which the main structure and modification parts remain stable.The local modification ① and ⑤ with better fragmentation performance can prevent the damage from occurring during ballistic impacts.

The damage modes and resistance performance of the annular pre-cut metal target impacted by the projectile were studied by experiments and numerical simulation.Influences of the projectile nose shape, the diameter as well as the depth of the annular groove on the resistance performance of the target were analyzed.The results show that there exist two kinds of damage modes for the target with an annular groove, one being the penetration of the inner part of the groove and the other the fracture along the bottom of the annular groove.The critical damage velocity (CDV) is closely related to the damage modes of the target.Generally, the grooved target was easier to be damaged than the intact one.The CDV decreases with the increase of the annular groove depth while it goes up with the increase of the annular groove diameter.Compared with the oval nose projectile, the CDV of the target is smaller for the flat nose projectile.The microscopic analysis shows that when the adiabatic shear band is formed inside the target, the plug is easier to be formed and the target is easier to be damaged.

The split Hopkinson pressure bar (SHPB) technique has been widely used to measure the dynamic strength enhancement of concrete-like materials at high strain rates ranging from 10 to 10³ s^-1.In this research, computational simulation models were employed to obtain a better understanding of this technique.The constitutive models of J₂ and the linear Drucker-Prager were employed to study the axial and lateral inertial effects on SHPB test.The results show that the axial inertia does not affect the DIF (dynamic increase factor) and the lateral inertia confinement is not the most important factor that causes an apparent increase of the DIF for concrete and concrete-like materials at high strain rates.