高压物理学报

Study on the Phenomena of the Mass Ejection from the Free Surface of Aluminum at Different Dynamic Loading Rates

HAN Chang-Sheng, JING Fu-Qian, DING Jing, ZHANG Wen-Ping, CHEN Sen-Hua, LU Jing-De

1989, 3(2): 97-106 . doi: 10.11858/gywlxb.1989.02.001

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Abstract:
The relation between the mass-ejection and the dynamic loading rate has been investigated with emphasis on the micro-jetting mechanism. Artificial wedged-grooves were made as the geometrical defects on the free surface, ramp-wave generator technique was employed to control the rate of dynamic loading, and quartz transducer was used to measure the ejected mass quantitatively. It is found that both the ejected mass and the maximum ejected velocity decrease with decreasing the loading rate if the wedged-groove size and the peak stress are fixed, and there is an indication that the ejected mass decreases with decreasing the geometrical defect volume if the dynamic loading condition, including peak stress and loading rate, is fixed. Using HELP code, we have carried out two-dimensional numerical simulation for the experiments aimed at micro-jetting mechanism study. The numerical results are in good agreement with the measured ones.

Direct Observation and Mechanism Study of the Dynamic Process of Thermal Expansion

TANG Da-Wei, ZHOU Ben-Lian, HE Guan-Hu

1989, 3(2): 107-114 . doi: 10.11858/gywlxb.1989.02.002

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Abstract:
In this work, CO2 laser pulse of 0.1 s was used to heat instantly the thin specimens of Al, constantan, BN with the thickness of 20~100 m, and a system of the slit diffraction using He-Ne laser was also adopted. By a photoelectric converting device, the change of the specimen length was transferred to the change of light strength, then to that of voltage. Using above method, we have observed and measured the changing process of the thermal expansion amount of the specimen with time during the specimen was heated instantly. For the first time, the dynamic-process of thermal expansion was observed directly and the oscillograms of the relaxation curves of thermal expansion were obtained. On the basis of above experiment, we have examed the relation between the relaxation time and the specimen length for Al. The mechanism of the dynamic-process of thermal expansion has also been discussed.

The Planar Dynamic Compaction of Tungsten Powder

XUE Hong-Lu, LU Fang-Yun

1989, 3(2): 115-124 . doi: 10.11858/gywlxb.1989.02.003

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Abstract:
In this paper we study the planar dynamic compaction of tungsten powder with the granular size of 3 m and 20 m. It is shown experimentally that the tungsten powder with smaller granular size cannot be well compacted. Its compacted sample has severe layer division. In order to obtain well-compacted sample, the tungsten powder must have the granular size more than 20 m, the velocity of compaction must be greater than 1 100 m/s, and the tungsten powder must be mixed with cohesive phase composed by the cobalt, nickel and iron powder. All these can be well explained by the numerical calculation which is performed by use of the spherical shell model proposed by Carroll and Holt in 1972.

The Surface Graphitization of Diamond Grains in the Process of Sintering Polycrystalline Diamond

ZHANG Xing-Dong, PENG Ying-Cong, QIU Shu-Zhen, LI Bo-Xun, ZUO Chang-Ming

1989, 3(2): 125-131 . doi: 10.11858/gywlxb.1989.02.004

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Abstract:
The surface graphitization of diamond grains, which is induced in the process sintering polycrystalline diamond under high pressure, is studied. The results of analysis by micro-area X-ray diffraction, XPS and laser Raman spectrum etc. show that no graphitization is detected in the area where the doped agents have not been liquefied or permeated although the sintering process was undergone. The most active period of the surface graphitization is at the moment when he doped agents are just liquefied and permeated into the spaces among diamond grains. The surface graphite of diamond grains will be eliminated and the sintering of polycrystalline diamond will be completed with the spaces being filled fully and the doped agents reacting with the diamond grains.

Crystal structure Stability Study by Molecular Dynamics Method with Variable Cell

HU Xiao-Mian

1989, 3(2): 132-142 . doi: 10.11858/gywlxb.1989.02.005

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Abstract:
In this paper, the crystal structure stability of metals irradiated by ion beam is investigated by molecular dynamics method with variable cell. The phase transformation process of copper, aluminum and silver metals under pressure are simulated. It is confirmed that for Cu, Ag, Al at normal conditions fcc structure is stable. In our three dimensional MD program, the leapfrog method is used and some of this difference scheme are duly revised. Through calculation, it is clear that present difference scheme spends less CPU time and occupies less storage units than both Euler-Cauchy and Runge-Kutta methods.

Molecular Dynamics Studies of Material Behavior at High Strain Rates

YU Wan-Rui

1989, 3(2): 143-147 . doi: 10.11858/gywlxb.1989.02.006

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Abstract:
Molecular dynamics is used to investigate the mechanical behavior of crystal material at high strain rates in this paper. Dislocation and plastic deformation was produced in crystal material under shock loading. Phase change could occur when shock loading was strong. It was obtained that the yield strength was increased as the strain rates were raised.

The Calculation of Thermal Expansion Coefficients of Several Alkali Halide Crystals

SUN Feng-Guo, LI Yong

1989, 3(2): 148-151 . doi: 10.11858/gywlxb.1989.02.007

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Abstract:
Using the method of P. Mohazzabi and F. Behrooz, we calculated thermal expansion coefficients of NaCl, KCl, RbBr and KBr at room temperature. The results are in agreement with experimental data approximately.

The Phase Transition of PSZT Ceramics under High Pressure

LI Feng-Ying, WANG Ru-Ju, GU Hui-Cheng, WANG Ji-Fang, ZHANG Liang-Kun, CHEN Zhi-Ming, LIAN Jing-Yu, QU Cui-Feng

1989, 3(2): 152-155 . doi: 10.11858/gywlxb.1989.02.008

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Abstract:
The phase transition of PSZT ceramics with vertical ferro-antiferroelectric phase boundary was studied by using ultra sonic pulse echo overlap method under high pressure. It was found that there was a first-order transition caused by pressure in those samples, and the phase transition was reversible. The changes of both v and a were large with phase transition. In this article, the experimental results are discussed.

Studies of Phase Transition in LADTGS Crystal with Ultrasonic Method

WANG Ru-Ju, LI Feng-Ying, YAO Yu-Shu, WANG Ji-Fang, LIN Xue-Shi

1989, 3(2): 156-158 . doi: 10.11858/gywlxb.1989.02.009

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Abstract:
The variation of the velocity and attenuation coefficient of ultrasonic wave with temperature in LADTGS crystal in the range from 20 ℃ to 90 ℃ under hydrostatic pressure up to 0.8 GPa has been investigated by means of ultrasonic pulse echo overlap techniques. The slope of the curve of the velocity vs temperature breaks at transition temperature. When the pressure is raised, shifting of Tc toward the higher side with a rate of 12 ℃/GPa was observed.

Measurement of High Pressure at the Temperature of 600 to 760 ℃ by Melting Point of Plumbum

HONG Shi-Ming, LUO Xiang-Jie, WANG Yong-Guo, SUN Zhu-Mei, JIANG Ren-Zhu

1989, 3(2): 159-164 . doi: 10.11858/gywlxb.1989.02.010

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Abstract:
Melting points of Pb under high pressure were measured with the NiCr-NiSi thermocouple, using the cubic anvil type high pressure apparatus, so that the relation between pressure in cell and oil pressure was obtained according to the melting curve of Pb in the range from 600 to 760 ℃ for two assemblies of pressure mediums. The contrast result was clear, that the pressure in the cell was higher about 10%, when NaCl was used as the internal pressure medium than the pyrophylite was used under the same oil pressure.

Studies of Crystallization of High Density Polyethylene under High Hydrostatic Pressure

WU Rui-Qi, WANG Hui, YANG Guang-Qun, HUANG Rui

1989, 3(2): 165-171 . doi: 10.11858/gywlxb.1989.02.011

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Abstract:
High density polyethylene has been crystallized under a pressure 1 GPa to 2 GPa and cooled at 5 ℃ per minute from the melting point. The solids were analyzed at atmosphere pressure by DSC, SEM and WAXD. The data show that the crystalline content of the samples by WAXD increases to 89.9% from 68.2% of the original material. Extended chain lamellae have thickened from 14 nm to 25 nm. DSC and SEM observations show the existence of the extended chain lamellae. Controlling of high pressure and temperature is the key of the formation of extended-chain crystals.

Second and Third Order Elastic Constants of Titanium Alloy TC-6

ZHANG Shu-Hua

1989, 3(2): 172-175 . doi: 10.11858/gywlxb.1989.02.012

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Abstract:
The second and third order elastic constants of titanium alloy (TC-6) had been measured using ultrasonic pulse echo overlap technique. Pressure derivative of shear modulus is found to be negative in the range p0.17 GPa and positive in the range p0.17 GPa.

1989 Vol. 3, No. 2

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