高压物理学报

The Criterion for Crack of Tungsten Carbide Anvil Based on Finite Element Method

HAN Qi-Gang, MA Hong-An, LI Rui, ZHANG Cong, LI Zhan-Chang, JIA Xiao-Peng

2010, 24(1): 1-5 . doi: 10.11858/gywlxb.2010.01.001

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Abstract:
Based on finite element method, the model of tungsten carbide (WC) anvil and the criterion for crack of WC anvil used in China-type cubic high pressure apparatus have been founded successfully. The simulation results indicated that the criterion for crack of WC anvil should make the reference point at the end of bevel edge. According to the von Mises criterion, we know that in the area of anvil surface and bevel edge, the cracks are often arising around the bevel edge. In the axis of anvil, the cracks are often arising at the place which is 30 mm below anvil surface. This study may greatly help to design new type WC anvil and improve the large volume cubic anvil type high pressure techniques.

Morphology Investigation of the Extended-Chain Crystals in High-Pressure Crystallized Poly (Ethylene Terephthalate)-(Bisphenol-A) Polycarbonate Blends

Lü Jun, HUANG Rui, LI Liang-Bin

2010, 24(1): 6-14 . doi: 10.11858/gywlxb.2010.01.002

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Abstract:
Morphologies of extended- chain crystals with different characteristics, i.e. wedge-shaped crystals, bent crystals and wedge- shaped bent crystals, were disclosed with scanning electron microscopy (SEM) and atomic force microscope (AFM) in the high-pressure crystallized poly (ethylene terephthalate)/bisphenol-A polycarbonate (PET-PC) blends. The observations revealed that the thickening growth for the large polyester extended-chain single crystals should first undergo the nucleation step leading to the folded-chain nuclei, and then, the chain extension process which is an isothermal thickening resulting from transesterification and sliding diffusion. The morphological structures shed light on the fundamental nature of the large single crystals in the blends, which may be instructive to grow such large crystals in similar polymer systems.

Numerical Simulation of Suspended RDX Dust Detonation in a Shock Tube

HONG Tao, LIN Wen-Zhou, QIN Cheng-Sen

2010, 24(1): 15-20 . doi: 10.11858/gywlxb.2010.01.003

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Abstract:
Dust detonation of RDX particles suspended in air was numerically studied with two-phase flow model. Behind the leading shock front of detonation, RDX particles were accelerated and heated by the gas flow. Melt of RDX occurred on the surface of particles. It was assumed that melted part of particle was stripped by the gas flow and decomposition reaction happened instantaneously, during the energy is released to support the propagation of detonation wave. Development and propagation of dust detonation with different particle sizes and different concentration was numerically simulated and the parameters of detonation were obtained. Distribution of pressure, temperature, velocity behind leading shock front was calculated. Parameters of dust detonation were determined. When the concentration of RDX dust is low, pulsating mode of peak pressure history of detonation front occurred. Numerical simulation results showed that when the concentration of RDX dust was between 80 g/m3 and 150 g/m3, history of peak pressure of detonation wave front was regular pulsating. When the concentration was 70 g/m3, the pulsating was irregular.

Study on Numerical Methods for Particle Material Penetration Problems

LIU Xiao-Hu, ZHU Tao

2010, 24(1): 21-25 . doi: 10.11858/gywlxb.2010.01.004

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Abstract:
Four numerical methods, i.e., purely Continuum based Finite Element Method (C-FEM), Discrete Element Method (DEM), Discrete particle based Finite Element Method (D-FEM) and combination of FEM and DEM (FEM-DEM), were explored through numerical examples of steel sphere normally impacting on the sand target at 100 m/s and 200 m/s velocities. Comparing computing efficiencies and precisions of the methods, it is shown that FEM-DEM is the most suitable to simulate problems of sand target penetration.

The Parallel Computation Based on MPI for Explosion in Air

FEI Guang-Lei, MA Tian-Bao, NING Jian-Guo

2010, 24(1): 26-30 . doi: 10.11858/gywlxb.2010.01.005

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Abstract:
Euler algorithm, fuzzy interface method for three-dimensional multi-material and the data dependence of this algorithm were studied, and a method for settling the data dependence was presented. The parallel program of MMIC-3D based on message passing interface (MPI) was designed. The three-dimensional numerical simulation results of explosion field in an infinite air medium, which were obtained in this study, are in agreement with the experimental phenomena and the principle of physics. Test on the symmetrical multi-processing (SMP) shows a better speedup.

Optical Observation and Numerical Simulation on the Evolution of Adiabatic Shear Band in Structural Steel

CHEN Si-Ying, HUANG Chen-Guang, KONG Wei-Guo, NI Guo-Qiang

2010, 24(1): 31-36 . doi: 10.11858/gywlxb.2010.01.006

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Abstract:
Adiabatic shear band (ASB) may cause damages and failures of many metal materials under impact loading, which is a key issue in the research of damage mechanism. The theoretical study is mainly focused on the relationship among the strain, stress, speed of shear and the initial flaw size in one-dimension shear conditions, which is used to determine the possibility of the generation of ASB. By experimental investigations, the features of ASB of titanium alloy, tungsten alloy and high-strength structural steel, including deformation fields, local temperature and the threshold value for ASB generating, can be detected. However, since there is little study on the real-time and in situ measurements on the evolution process of ASB, the failure details according to the shear-localization are still unknown. In this paper, the real-time observations and visualizations on the evaluation of ASB in 45 steel under different impact conditions in SHPB are presented. The generating and evaluating processes in a single sample are detected and analyzed by a self-design optical system and the self-designed software, which is based on Digital Correlation method with high resolution. At the same time, the numerical simulations and micro-observations by SEM are obtained by LS-DYNA and the simulation results are in good agreement with the experimental ones.

High Temperature SHPB System with Heat Insulation for Short Ceramic Bars

XIAO Da-Wu, LI Ying-Lei, HU Shi-Sheng

2010, 24(1): 37-42 . doi: 10.11858/gywlxb.2010.01.007

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Abstract:
To obtain dynamic behavior of materials at very high temperature, a new experimental system of high temperature split Hopkinson pressure bar (SHPB) is investigated. The steel bars in the inside section of the furnace are replaced with relatively close acoustic impedance matched short ceramic bars. Compared to the traditional high temperature SHPB system, this system can be used under higher loading and higher experimental temperatures, and it is more convenient than the auto-assembling high temperature SHPB system. In addition, the effect of impedance mismatch is investigated by numerical simulation, which proves veracity of the results. The dynamic compressive properties of anti-hydrogen steel at high temperature up to 800 ℃ are tested by this system. Results show that the flow stress of material decreases with the increase of the temperature.

Finite Element Analysis on the Influence of PMMA Geometry on Explosion Cutting

WANG Zhi-Hua, LI Zhi-Qiang, REN Hui-Lan, ZHAO Long-Mao

2010, 24(1): 43-48 . doi: 10.11858/gywlxb.2010.01.008

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Abstract:
In order to improve the present aviation ejection lifesaving system and enhance success possibility of safe escape, the application of Miniature Detonating Cord (MDC) on the aviation ejection-escape- system is proposed. The explosion cutting process of plexiglass (PMMA) plate and Canopy by MDC is simulated employing nonlinear dynamic explicit program LS-DYNA3D. The variation of cutting depth with charge quantities is obtained, which agrees well with the experimental result. Simulation result shows that the geometry of PMMA has slight influence on the cutting effect. This study may provide the powerful foundation for the design of the aviation ejection lifesaving system.

Experimental Research on Compression Mechanical Properties of Ta-10W

ZHONG Wei-Zhou, SONG Shun-Cheng, XIE Ruo-Ze, HUANG Xi-Cheng

2010, 24(1): 49-54 . doi: 10.11858/gywlxb.2010.01.009

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Abstract:
Quasi-static and dynamic compression experiments of unannealed Ta-10W alloy specimen are implemented by MTS and split Hopkinson pressure bar equipments. Quasi-static compression yield strength is gained. In addition, the stress-strain history and dynamic compression yield strength are obtained when strain rate ranges from 700 s-1 to 3 100 s-1. The experiment results indicate that unannealed Ta-10W is preferably flexile. There is no crack on the surfaces of specimen after experiments. The quasi-static and dynamic compression strength of unannealed Ta-10W alloy is quite large. Quasi-static compression yield strength is about 930 MPa, and the dynamic compression yield strength is over 1 GPa. Dynamic compression yield strength of Ta-10W is dependent on strain rate, and it grows from 1.0 GPa to 1.3 GPa when strain rate increases from 700 s-1 to 3 100 s-1.

Further Study on JWL Equation of State of Detonation Product for Insensitive High Explosive

SUN Zhan-Feng, XU Hui, LI Qing-Zhong, ZHANG Chong-Yu

2010, 24(1): 55-60 . doi: 10.11858/gywlxb.2010.01.010

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Abstract:
The JWL equation of state of detonation product for insensitive high explosive JB-9014 was further studied. The particle velocity, displacement, and acceleration of the cylinder wall were obtained from the modified standard cylinder test. The parameters of JWL equation of state were derived from analytical analysis and non-linear curve fit. The cylinder expanding process was numerical simulated using the ANSYS/LS-DYNA3D. The simulation results are consistent with the experimental results, which indicate that the parameters of JWL equation of state derived in this work are suitable and reliable.

Numerical Analysis on Fragmentation Properties of the Steel Cylinder Subjected to Detonation of Internal Short Cylinderical Explosive Charge

WANG Xin-Zheng, ZHANG Song-Lin, ZOU Guang-Ping

2010, 24(1): 61-66 . doi: 10.11858/gywlxb.2010.01.011

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Abstract:
The characteristics of fragments, which are numerical studied with Smoothed Particle Hydrodynamic (SPH) algorithms, come from the steel cylinder subjected to the detonation of internal short cylinderical explosive charge. Grady spall model is employed to describe the spall failure of the steel cylinder. Stochastic failure is used to define the failure models, in which Mott distribution is used to depict the failure strain. Mass distribution and velocity of fragments are mainly discussed. The results show that the part near the head of explosive begins to fracture after the steel cylinder expands to a certain extent, and then the part around the explosive disaggregates to fragments. For the closed cylinder, the ends are the other weakness position. The fragments around the explosion centre are smaller with high velocity, while the fragments around cylinder ends are larger with low velocity. The fragments near the explosion centre are relatively concentrated in the space.

Study on the Pressure-Induced Phase Transition of g-C3N4

LI Xue-Fei, MA Yan-Mei, SHEN Long-Hai, ZHANG Jian, LEI Wei-Wei, LIU Wei, ZOU Guang-Tian

2010, 24(1): 67-70 . doi: 10.11858/gywlxb.2010.01.012

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Abstract:
Graphitic carbon nitride (g-C3N4) is prepared by pyrolysis of melamine. At room temperature, the structure change of the g-C3N4 is investigdted by in situ high pressure angle-dispersive X-ray diffraction with a synchrotron radiation source, which is in a diamond-anvil cell. The results show that structural phase transition occurred in g-C3N4 within 16.57 GPa pressure range. The crystal structure changes from graphitic to triclinic structure at 6.6 GPa. The isothermal equation of the state of C3N4 is fitted using the Birch-Murnagha equation of state.

Study on Thermal Stability of Ti2AlN-Al at High Pressure

AN Pei, KOU Zi-Li, LI Zi-Yang, QIN Jia-Qian

2010, 24(1): 71-75 . doi: 10.11858/gywlxb.2010.01.013

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Abstract:
Thermal stability of Ti2AlN-Al at high pressure is studied. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM), it was found that the thermal stability was mainly dependent on the temperature, but less on the pressure. When the pressure is 3, 4 and 5 GPa, the lowest reaction temperature of Ti2AlN-Al was between 500 and 600 ℃, and the decomposition products depended on temperature. When the temperature was up to 900 ℃, Ti2AlN-Al had completely decomposed and most of the final products were Al3Ti and TiN.

Experiment Research on the Hugoniot of JB-9014 Explosive Over-Driven Detonation Product

ZENG Dai-Peng, CHEN Jun, TAN Duo-Wang

2010, 24(1): 76-80 . doi: 10.11858/gywlxb.2010.01.014

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Abstract:
Over-driven detonation is achieved by high speed flyer impacting, which is driven by explosive. The time when the shock wave passes through the samples is detected. Using the impedance matching method, the Hugoniot of the product of the JB-9014 explosive can be obtained. It is shown that the simple D-u equation can not fit the Hugoniot data well. With relation to the explosive, it is better to use quadratic in D-u equation. Using conservation relations of physical variable before and after the shock wave, the D-u data can be translated to p-V data. Then the p-v equation can be obtained by fitting the p-V data.

2010 Vol. 24, No. 1

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