高压物理学报

An Experimental Study on the Micro/Macro Fracture Behavior of PBX Using Digital Speckle Correlation Method

ZHOU Zhong-Bin, CHEN Peng-Wan, HUANG Feng-Lei

2011, 25(1): 1-7 . doi: 10.11858/gywlxb.2011.01.001

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Abstract:
The micro/macro fracture behavior of a polymer bonded explosive (PBX) material was experimentally studied using a semi-circular bend test and digital speckle correlation method (DSCM). Brittle fracture occurred when a semi-circular disc sample of PBX with a preset crack was compressed. The whole strain field and displacement vector plot were obtained using the DSCM, and the plane strain fracture toughness of PBX material was acquired. In addition, real time microscopic examination was conducted to observe the process of deformation and failure of PBX material under semi-circular bend test using a scanning electron microscope (SEM) equipped with a loading stage. The localized damage and its evolution in PBX were obtained by the DSCM, demonstrating possible fracture route of microcracks. The results indicate that DSCM technique is a valid and effective tool to study the deformation and fracture mechanisms of PBX.

Mesoscale Simulation of Cavity Collapse Hot Spot Mechanism in HMX under Shock Loading

FU Hua, ZHAO Feng, TAN Duo-Wang, WANG Wen-Qiang, SHANG Hai-Lin

2011, 25(1): 8-14 . doi: 10.11858/gywlxb.2011.01.002

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Abstract:
The origin, ignition, growth of hot spot are the factors to understand shock initiation in heterogeneous explosive. The process of cavity collapse in HMX under shock loading was simulated using discrete element method. The results showed that the visco-plastic deformation formed hot spot mechanism and there was serious shear distortion around cavity under low impact. It was also found that the micro-jetting formed hot spot under high impact. The mesoscale process of hot spot formation and cavity collapse were gained.

The Failure Strength Parameters of HJC and RHT Concrete Constitutive Models

ZHANG Ruo-Qi, DING Yu-Qing, TANG Wen-Hui, RAN Xian-Wen

2011, 25(1): 15-22 . doi: 10.11858/gywlxb.2011.01.003

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Abstract:
The analyzed and calculated results indicate that the concrete failure strength will decrease under higher hydrostatic pressure, when the original failure parameters of HJC and RHT models implemented in LS-DYNA and AUTODYN are adopted. A new method is introduced which using the characteristic strength of concrete to confirm the modified failure parameters of HJC and RHT models. The same physical experiment of concrete penetration was simulated using the modified HJC and RHT failure parameters respectively, and the numerical results demonstrated that the RHT model matched the experiments much better. But the numerical results with the HJC modified failure parameters were not enough satisfied, because the third invariant of the deviated stress tensor was not considered in the HJC model.

Numerical Study on the Viscosity of Shocked Al vis Small-Perturbation Amplitude Damping Profile Measurement by Flyer Impact

MA Xiao-Juan, LIU Fu-Sheng, LI Yi-Lei, YU Ming, LI Yong-Hong, PENG Xiao-Juan, JING Fu-Qian

2011, 25(1): 23-28 . doi: 10.11858/gywlxb.2011.01.004

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Abstract:
Flyer-impact disturbance amplitude damping method of shock wave is one of practical method for viscosity measurement at high pressure and high temperature. The experimental results for shocked Al at two high pressures have been reported previously by Li, et al, instead of the analytical solution method, which was proposed by Miller and Ahrens, for treating same characteristic data from the measured profiles that was adopted in Li's analysis. Here we first put forward a two-dimensional Eulerian viscous fluid, to make a full-shock front perturbation evolution simulation. The measured profile at 78 GPa is used as an example in our re-analysis. The numerical simulated profile agrees well with the measured one, from which the determined effective viscosity coefficient of the shocked Al at 78 GPa is (2.80.1)kPas. This value is about twice of the Li's one ((1.30.3)kPas), but we believe the value in the present study might be more reasonable because it is obtained from a comprehensive simulation for the full-shocked perturbation evolving process.

Experimental Study on Shock Wave Demagnetization of Nd2Fe14B Hard Ferromagnetic

WU Jun-Ying, CHEN Lang, LI Wei, FENG Chang-Gen

2011, 25(1): 29-35 . doi: 10.11858/gywlxb.2011.01.005

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Abstract:
For the study of the demagnetization performance of Nd2Fe14B ferromagnetic under shock wave loading, the plane shock wave loading experiment device was established, and the shock demagnetization experiments were conducted. The electromotive forces were measured, and the shock demagnetization time and pulse width were obtained. The demagnetization rates with different shock wave pressures were discussed, and the effects of magnet sizes on the electromotive force were analyzed. The results show that the time is about 0.28 s between the shock wave loading Nd2Fe14B ferromagnetic and shock demagnetization occurring. The critical pressure of demagnetization is lower than 8.52 GPa. The electromotive force increases with the increase of the magnet diameter and the decrease of the magnet height.

Primary Experimental Study on Driving Technique of Strong Detonation Using Gas Gun

WEN Shang-Gang, ZHAO Feng, WANG Jian, ZHAO Yu-Gang, WENG Ji-Dong, WANG Xiang

2011, 25(1): 36-40 . doi: 10.11858/gywlxb.2011.01.006

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Abstract:
Using the loading technique of two-stage gas gun and the doppler pin system, the driving technique of strong detonation is studied. The velocity increment of the secondary flyer is obtained when the velocities of the first flyer surpass 5 km/s. The loading technique of two-stage gas gun and the driving technique of strong detonation are combined very well. The primary experimental results show that the velocity increment of the secondary flyer is considerably large if the two techniques are combined together.

The Numerical Simulation of 2-D Thermal Shock Wave Induced by X-Ray in Anisotropic Material

HUANG Xia, TANG Wen-Hui, JIANG Bang-Hai, GUO Xian

2011, 25(1): 41-47 . doi: 10.11858/gywlxb.2011.01.007

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Abstract:
Using anisotropic elasto-plastic constitutive model, the 2-D thermal shock wave induced by X-ray in anisotropic material is simulated by finite element method, and the thermal shock wave propagation rules are discussed. The results show that the thermal shock wave exhibits different shapes under the radiation of soft and hard X-ray, and there are great differences in some other aspects, such as thermal shock wave forming mechanism, wave peak value, penetration depth of X-ray, gasification phenomenon, tensile intensity and so on.

Quasi-Static Bursting Analysis of Gas-Filled Pressure Vessels on the Front Side under Hypervelocity Impact

GAI Fang-Fang, PANG Bao-Jun, GUAN Gong-Shun

2011, 25(1): 48-54 . doi: 10.11858/gywlxb.2011.01.008

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Abstract:
In a given set of impact velocity conditions, the numerical simulation is performed to analyze the effect of the projectile diameter on perforation of the front wall of gas-filled pressure vessels. Then the critical stress value is estimated based on the stress intensity factor which is determined by simplified linear elastic fracture mechanics, and the computational model is built. The model is presented by postulating the existence of two-radial cracks that emanate at the boundary of a circular hole. The result shows that a good correlation between experimental and computational results is obtained. If the ratio of single crack length to hole radius exceeds the value of 0.5, the hole with radial cracks can be considered as a straight crack. The projectile with small kinetic energy is likely to lead catastrophic burst of pressure vessels.

Fabrication of Nanocrystalline BaTiO3 Ceramics by Ultra-High Pressure Sintering

XIAO Chang-Jiang, JIN Chang-Qing, LI Zheng-Xin, DENG Xiang-Rong

2011, 25(1): 55-60 . doi: 10.11858/gywlxb.2011.01.009

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Abstract:
10 nm raw BaTiO3 powder was sintered by ultra-high pressure assisted method at 6 GPa. The grain size of sintering samples is about 30 nm. The microstructures of sintering samples were studied by scanning electron microscope and atomic force microscopy. The results indicated that owing to the ultra-high pressure, the agglomerates in nano powders were broken down, and the densification was significantly increased. Additionally, the nucleation rate was increased due to reducing the energy barrier for nucleation and the growth rate was reduced due to the decrease of diffusivity. Thus, ultra-high pressure enables the specimen to be fabricated under relatively lower temperature and shorter period that assures to obtain dense nanocrystalline ceramics. The piezoelectricity was investigated by piezoelectric force microscopy. There existed some full piezoresponse hysteresis loops at different areas in 30 nm BaTiO3 ceramics, indicating the presence of piezoelectricity. In addition, oxygen vacancies were produced in strongly reducing atmosphere during ultra-high pressure sintering. F+ centers were formed because oxygen vacancies caught electrons, and therefore, the color of BaTiO3 ceramics became block.

First-Principle Study on the Structural, Elastic Properties and Absorption Spectra on ZnO under High Pressure

WANG Qing-Bo, ZHENG Guang, HE Kai-Hua, CHEN Qi-Li, YU Li, LONG Guang-Zhi, ZENG Zhong-Liang

2011, 25(1): 61-67 . doi: 10.11858/gywlxb.2011.01.010

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Abstract:
The structural, elastic properties and absorption spectra of ZnO in wurtzite (B4), NaCl (B1) and CsCl (B2) structures are studied by plane wave pseudo-potential (PWP) method. The method is based on the density functional theory (DFT) within the local-density approximation (LDA) and generalized gradient approximation (GGA) approaches. The calculation gives out the respective structural phase transition pressures for two transitions (B4B1, B1B2). We investigate the behavior of the elastic constants C as function of pressure and show the relation between the behavior and the phase transition. The blue shifts of absorption spectrum of ZnO under high pressure are found. Comparing the results between experiment and computation, we can find that the calculation by LDA is in better agreement with the experiment.

Study on the Influence of the Outer Shell Thickness on the SEFAE Damage-Power

GAO Hong-Quan, LU Fang-Yun, LUO Yong-Feng, WANG Shao-Long, HU Jian, YUAN Wei, QIN Zhi-Qiang

2011, 25(1): 68-72 . doi: 10.11858/gywlxb.2011.01.011

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Abstract:
Based on the theoretical analysis of the SEFAE outer shell velocity and kinetic energy with different depths, the influence of the shell on the dispersed fuel was obtained. The relationships between the damage power and the thickness of the shells were obtained by different SEFAE explosion experiments. The theoretical and experimental results show that the TNT equivalent of the SEFAE and the utilization rate of the center charge can be improved by using the thinner shell and increasing the connection strength between the shell and the end cover, in which the experimental results were in agreement with the theoretical results.

Numerical Simulation on Initial Stage of Liquid Dispersed under Explosion Drive

XU Yu-Xin, WANG Shu-Shan, HAN Bao-Cheng, LIU Yong

2011, 25(1): 73-78 . doi: 10.11858/gywlxb.2011.01.012

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Abstract:
For fuze-warhead cooperation design on fire extinguishing warhead, characteristics on liquid (based-water extinguisher) dispersed under explosion drive were studied. The numerical simulation model was built based on representative fire extinguishing warhead structure. The numerical simulation was done by LS-DYNA program. The influence rule about loading coefficient (drive charge divide liquid mass) to the breach time on shell, the movement speed on liquid/air interface at the shell breach initial phase, and the movement characteristic on liquid-air interface after shell breach were obtained. With the same simulation condition, the experiment on basedwater extinguisher dispersed under explosion drive was done. For different loading coefficients, the liquid/air interface movement speed at shell breach initial phase was gained. The results between experiment and numerical simulation were in good agreement, which indicates that the numerical simulation method was correct and effective. The research outcomes may provide important reference to investigate the relevant problem.

Breeding of Bacterial Cellulose Strain Induced by Ultra-High Pressure and Optimization of Fermentation Medium

DU Shuang-Kui, LI Zhi-Xi, WU Rui-Qin, YANG Jia-Ping

2011, 25(1): 79-88 . doi: 10.11858/gywlxb.2011.01.013

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Abstract:
In order to obtain high-yield strains of bacterial cellulose (BC), the primary bacterial cellulose strain was induced by ultra-high pressure. Plackett-Burman design was employed to evaluate variables which were relevant to yield of BC which was produced by strain induced by ultra-high pressure. Fermentation medium composition was optimized through Box-Behnken experiment. The results show that mutagenic pressure and time on the strain of bacterial cellulose have significant or extremely significant influence. The mutagenic conditions of BC strain are pressure of 250 MPa, time of 15 min, and temperature of 25 ℃. The mutagenic strain M438 with high cellulose production capacity and genetic stability is obtained through the ultra-high pressure treatment. The key factors affected bacterial cellulose production of mutation strain M438 are yeast juice, MgSO4, and anhydrous ethanol. The optimistic fermentation medium is as follows, carbon source 5% (glucose∶sucrose=4∶1), yeast juice 1.25%, CaCl2 0.15%, ZnSO4 0.2%, K2HPO4 0.2%, MgSO4 0.93%, fumaric acid 0.3%, and ethanol 0.5%. BC yield of M438 cultured with optimized fermentation medium is as 1.84 times as that cultured with the initial fermentation medium, and is as 2.69 times as that of the unmutant strain. Ultra-high pressure technology for mutation breeding of bacterial cellulose strain is feasible. BC producing capacity of M438 can be significantly improved through fermentation medium optimization.

Effects of Combined High Pressure and Thermal Treatment on Protease Activities in Beef Muscle

MA Han-Jun, ZHOU Guang-Hong, YU Xiao-Ling, GAO Hai-Yan, PAN Run-Shu, D. A. Ledward

2011, 25(1): 89-96 . doi: 10.11858/gywlxb.2011.01.014

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Abstract:
The effects of combined high pressure (0.1～600 MPa) and temperature (20～60 ℃) treatment for 20 min on beef protease activities were studied. The results showed that the protease activities decreased with increasing pressure up to 400 MPa at room temperature, after which there was no significant change of them. The content of free amino acid increased significantly at 200 MPa and then the increased speed decreased with the pressure increasing. 400 MPa or higher pressure treatment at room temperature resulted in the increase of tryptic digestibility of protein in beef extract. There was no significant effect on protease activities and free amino acid content in beef after pressurized at 200 MPa, 40 ℃, but the protease was almost completely inactivated at pH 7.5 and free amino acid content reduced rapidly after treated at 600 MPa, 40 ℃. Part of protease activities survived in beef muscle when heated at 60 ℃. They did not change significantly when treated at 200 MPa, 60 ℃, but the free amino acid content increased obviously. Treatment of 600 MPa at 60 ℃ resulted in the inactivation of almost all the proteases and the free amino acid content also decreased markedly. The similar changes of tryptic digestibility of protein in beef extract were found when pressure applied at 40～60 ℃. 200 MPa treatment did not cause significant changes and 600 MPa treatment induced the tryptic digestibility of protein marked increase. These results suggested that high pressure treatment combined with heating could regulate proteases activities of beef and improve its quality.

2011 Vol. 25, No. 1

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