Understanding the physical and chemical properties, detonation properties and decomposition mechanism is very important for molecular design, safety assessment and practical utilization of energetic materials.Ab initio molecular dynamics can be used to not only study the physical and chemical properties, but also understand the decomposition mechanism of energetic materials.The theoretical studies on energetic materials using ab initio molecular dynamics have been reviewed in this paper.Firstly the current progress on crystal structure and basic properties, such as thermal, mechanical and electronic properties, the effect of pressure and temperature on crystal structure of energetic materials are summarized.Then unimolecular decomposition of energetic materials are discussed, especially the products, mechanism and dynamics properties.The main initial reactions of thermal decomposition include proton transfer, C—N bond fission and N—NO₂ bond cleavage.The effects of hydrostatic pressure, shock wave and other loading conditions on thermal decomposition are also discussed.In particular, shock wave loading may lead up to new reaction mechanism, for example, C—N bond fission.

As one of the most important ferroelectric ceramic materials, PbZr_0.52Ti_0.48O₃ (PZT) ceramic has been widely studied because of its extensive industrial application.We prepared the PZT ceramic using a simple water-based sol-gel method, and studied its Raman spectra as a function of high pressure.Raman spectroscopy analysis show that the phase transition pressure from rhombohedral-tetragonal (R+T) to tetragonal-cubic (T+C) phases is 2.61 GPa and the pressure for T+C to C phase is 8.5 GPa.We also measured the dielectric constant of the PZT ceramic, the result suggests that the Curie temperature of the PZT ceramic is 395 ℃.

In the high-pressure and high-temperature experiments with the diamond anvil cell and large volume press, metal powder (such as Pt, Au, Fe) is usually added for the purposes of pressure measurement, laser heating and mineral growth rate reduction.It is widely acknowledged that these metal additives should not react with the system under investigation.However, no enough attention has been paid to the issue whether or not these metal additives affect the reaction rate.Under appropriatep-T conditions, corundum and coesite combine to form kyanite.With the addition of different amounts of Pt powder into the system, we investigated the effect of adding Pt powder on the kyanite formation reaction.We found that adding Pt powder promotes the synthesizing reaction, and the promoting effect increases with the amount of added Pt powder.These results can provide important constraints in interpreting relevant high-pressure and high-temperature experiments.

Instrumented impact tests are carried out using precrack Charpy specimens of typical pressure vessel steel Q345R, the load-displacement curves are obtained.Based on the test data, the J-integral incremental equation procedure and Schindler method are used to estimate dynamic crack resistance curve of Q345R steel under impact loading respectively.The results of them are compared and verified each other.After comparing the dynamic J-R curve with the qusi-static curve, it is found that the J-R curve under dynamic loading is always higher than that obtained under quasi-static loading.Further analyses of test data lead to an equation which quantitatively describes the relationship between Q345R quasi-static and dynamic crack growth resistance curve.The equation may have important significance in engineering application.

An experimental platform is built to investigate the dynamic fragmentation of multiple metal rings, the layout of multiple metal rings, initiation system and principle, are detailed.Then the platform is applied to conduct the dynamic loading of pure aluminium and oxygen-free electronic copper materials, and the fractured strain and statistical distribution of reassembled fragments are obtained.It is shown that the experimental platform can achieve simultaneous and stable loading of multiple metal rings.Morever, the statistical distribution is well fitted by the Weibull function.

A zero-dimensional model is proposed to analyze the magnetic flux compression process of a thin cylindrical liner driven by electromagnetic force.The magnetic energy conversion efficiency and 3 optimal dimensionless parameters (h, A, Π) in the magnetic flux compression process are obtained by solving the equation set consisting of LC circuit equations and equations of motion of a thin cylindrical shell.It is shown that in order to achieve a 10-fold compression of cylindrical shell under the condition of steady current, the parameter h should be less than 0.2.To obtain a compressed magnetic field up to 1 000 T with high magnetic energy conversionefficiency, the dimensionless parameters are optimized on the condition that the capacitor bank's energy is about 1 MJ.These analyses and simulations are of great importance for both theoretical and experimental studies on magnetic flux compression.

The lattice structure, electronic sructure and electrical properies of the Mg doped ZnO have been systematically investigated by the ultro-soft pseudo-potentials based on the density functional theory calculations under the generallized gradient approximation.The calculational and analyzing results show the shrinked lattice and the increased direct band gap of 1.2 eV of the Mg doped ZnO system.There are newly formed bands near the -40 eV.The bands near Fermi level are composed by the Mgp, Zn p, Zn d, O p, Mg s, Zn s, O s electrons and strong hybridizations between them are found.The carriers of the bands formed by Zn p, Zn d, O p electrons hop to the bands formed by the s, and then the electrical conduction is accomplished.The carrier effective mass, density of states as well as the carrier concentration near Fermi level are increased for the Mg doped system.The electrical conductivity should be enhanced by Mg doping for ZnO.

A three-term equation of state for elemental solid materials is established, in which the cold energy and pressure are approximated by a fraction of the numerical solution of Thomas-Fermi theory at absolute zero-temperature, the thermal energy and pressure of ions are obtained from Cowan model, and the thermal energy and pressure of electrons are built on the basis of the screened hydrogenic average-atom model of Faussurier.Numerical results show that this model is applicable for elemental solid materials when their compression ratios of density are greater than 2.Moreover, the maximum compression ratios, the corresponding temperature and pressure on the shock adiabat are calculated and compared with other models for elemental solid materials with nuclear charge from 3 to 70.These results can be used to contrast with strong shock wave compression experiments.

A three-dimension numerical simulation subjected to gas-particle two phase flow method is implemented to simulate the particle-gas interaction in spherical ejection, in which particles are ejected from shocked sample interface.Particles initial distribution is modeled accroding to characteristics of ejection processes and reference data.And action of the moving sample interface on gas is simulated by using ghost fluid coupling Eulerian-Lagrangian method.Only steady drag force between particles and gas is considered at present.The evolutions of gas flow and particles movements are shown in this paper.It is concluded that the particles naturally redistribute to a high-density low-velocity region and a low-density high-velocity region, which qualitatively agrees with basic acquaintance obtained from ejection experiments.

In order to study the minimum ignition energy (MIE) of diesel, ignition experiments of -10^# diesel were carried out in the shock tube under condition of spray and in the external field diesel tank.Results of the shock tube experiment show that the MIE of diesel cloud is approximate to a L-shaped curve in relationship with equivalence ratios, and the minimal MIE reaches 0.16 MJ·m^-2(about 5.02 kJ) when the equivalence ratio is 1.31.Results of the external field experiment show that the MIE of the oil zone is 6.74 times of that of the oil-vapor zone, and it increases with diesel quantity linearly.However, the MIE of the oil-vapor zone does not change with diesel quantity.In addition, when the volume of diesel is 21 mL, the MIE of the external field experiment is 36.42 kJ, which is 7.25 times the minimal MIE of shock tube experiment.

When the convergent hypervelocity launcher is applied to measure the equation of states, the second stage flyer are required to have well impact planarity and high impact velocity. Taking this into consideration, our paralleled Eulerian code HVL-MFPPM is employed to investigate the hypervelocity launcher.According to the simulation results, the structure and dimensions of the first stage flyer are optimized.Finally, the best scheme (the diameter of the first stage flyer is 20 mm, and its thickness is 1.8 mm) is obtained, which leads to the successful launch of an intact gram magnitude tantalum flyer to a velocity over 14 km/s in numerical simulation, and significant improvements in the impact velocity and planarity of the second stage flyer.