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排序方式: 共有142条查询结果,搜索用时 31 毫秒
31.
Deformation twins are often observed to meet each other to form multi-fold twins in nanostructured face-centered cubic (fcc) metals. Here we propose two types of mechanism for the nucleation and growth of four different single and multiple twins. These mechanisms provide continuous generation of twinning partials for the growth of the twins after nucleation. A relatively high stress or high strain rate is needed to activate these mechanisms, making them more prevalent in nanocrystalline materials than in their coarse-grained counterparts. Experimental observations that support the proposed mechanisms are presented. 相似文献
32.
为了提高激光弯曲过程数值模拟结果的验证精度,用图像处理技术对铝合金板料AA6056进行了激光弯曲变形过程的实时测量.自行设计了硬件测量系统和软件的测试系统,使用MV21300UM CCD拍摄板料上测量点在激光照射过程中的动态变化过程,通过软件测试系统中实时采集软件记录动态变化过程、图像处理软件进行图像处理,得到了测量点动态变化的实测曲线.实测曲线表明,板料厚度对激光弯曲过程的位移变化影响较大,板料越薄,边界效应越明显,使得位移的变化曲线越易出现突变.实验结果证明该实测方案是可靠有效的. 相似文献
33.
A. J. Cao Y. G. Wei Scott X. Mao 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(9):85-88
Microtwins are frequently observed in face-centered-cubic (fcc) metal nanowires with low stacking fault energy. The authors
have previously reported that the tensile yield strength of copper nanowires can be increased by the presence of twin boundaries.
In this work simulations are carried out under both uniaxial tension and compression loading, to demonstrate that the strengthening
effects are inherent to these nanowires, independent of the loading condition (tensile/compressive). It appears that the strengthening
mechanism of the twinned nanowires can be attributed to stress redistribution due to the change of crystallographic orientations
across twin boundaries, which requires larger external stress to make them yield as compared to the twin-free wire. 相似文献
34.
THE PRESSURE TRANSIENT ANALYSIS OF DEFORMATION OF FRACTAL MEDIUM 总被引:1,自引:1,他引:0
The assumption of constant rock properties in pressure-transient analysis of stress-sensitive reservoirs can cause significant errors in the estimation of temporal and spatial variation of pressure. In this article, the pressure transient response of the fractal medium in stress-sensitive reservoirs was studied by using the self-similarity solution method and the regular perturbation method. The dependence of permeability on pore pressure makes the flow equation strongly nonlinear. The nonlinearities associated with the governing equation become weaker by using the logarithm transformation. The perturbation solutions for a constant pressure production and a constant rate production of a linear-source well were obtained by using the self-similarity solution method and the regular perturbation method in an infinitely large system, and inquire into the changing rule of pressure when the fractal and deformation parameters change. The plots of typical pressure curves were given in a few cases, and the results can be applied to well test analysis. 相似文献
35.
An experimentally-validated approach for predicting fatigue crack initiation life of polycrystalline metals is developed based on crystal plasticity finite element (CPFE) simulations. In this approach, the microstructure used in the simulations possesses statistically the same grain size and crystallographic orientations as those obtained from electron back-scatter diffraction experiments. A backstress model is incorporated into the CP constitutive model to describe the mechanical behaviour of aluminium alloy (AA) 7075 under cyclic loading. The key variables of the prediction model, the energy efficiency factor and plastic strain energy density, are calibrated using a fatigue test on a round-notched AA7075 specimen at room temperature. The proposed approach is then validated by using another fatigue test to predict 69.1–87.3% of the experimentally measured fatigue crack initiation life. The effects of the microstructure and texture on the energy efficiency factor and fatigue life prediction are quantitatively determined. It is shown that for a given range of energy efficiency factors a similar range of life prediction is obtained. Since the proposed approach considers the heterogeneity of the microstructure, it can well capture the grain scale deformation localisation and therefore improve the precision of fatigue life prediction. 相似文献
36.
《Intermetallics》2007,15(5-6):706-710
The plastic deformation behavior and serrated flow in seven bulk metallic glass (BMG) systems were investigated through instrumented indentation. These materials include Ce65Al10Ni10Cu10Nb5, Mg65Cu25Gd10, Pd43Ni10Cu27P20, Cu60Zr20Hf10Ti10, Pt57.5Cu14.7Ni5.3P22.5, Ni60Nb37Sn3 and Fe43Cr16Mo16C15B10 BMGs, which show a glass transition temperature (Tg) ranging from 360 to 908 K at a heating rate of 0.33 K/s. Remarkable difference in deformation behavior was found among these BMGs in the load–depth curves during nanoindentation. Prominent serrations are observed in Mg-, Pt- and Pd-based BMGs with medium Tg during the loading process, whereas no distinct serrated flow was found in Ce-, Ni- and Fe-based BMGs with quite low or high Tg. The subsurface plastic deformation regions after indentation were investigated using depth-sensing microindentation to characterize the shear band feature developed in various BMG systems. The size of the shear band upset is found to be larger in the alloys with lower Tg. The effect of Tg on the operation of shear bands and the serrated flow behavior in various BMG systems were discussed. 相似文献
37.
The role of the interfacial strength in glass bead filled HDPE 总被引:3,自引:0,他引:3
Shu-Lin Bai Jiankang Chen Zhuping Huang Zhongzhen Yu 《Journal of Materials Science Letters》2000,19(17):1587-1589
38.
Wang Yanshuo Chen Nuofu Zhang Xingwang Yang Xiaoli Bai Yiming Cui Min Wang Yu Chen Xiaofeng Huang Tianmao 《半导体学报》2009,30(7)
Cs. A new SiO2/Ag-ZnS double-layer coating with better antireflection ability can be achieved if the particle volume fraction in ZnS is 1%-2%. 相似文献
39.
GUO Qiang CHENG Rui SILBER-LI Zhan-hua 《水动力学研究与进展(B辑)》2007,19(5):594-600
Nano-liter flowrate measurements in micro-tubes with displacement method were performed and the effect of capillarity force on the accuracy was investigated through lab experiments and theoretical analysis in this article. The experiments were conducted under the pressure drops ranging from 1 kPa to 10 kPa in a circular pipe with a diameter of 50 μm, to give the pressure-flowrate (P-Q) relation and verify the applicability of the classical Hagen-Poiseuille (HP) formula. The experimental results showed that there existed a discrepancy between the experimental data and the theoretical values predicted by the HP formula if the capillary effect was not considered, which exceeded obviously the limit of the system error. And hence a modified formula for the relation, taking the capillary effect into account, was presented through theoretical deduction, and after the HP formula had been modified the error was proved to be less than 3%, which was permitted in comparison with the system error. It was also concluded that only by eliminating the effect of the capillary force in experiments could the original HP formula be employed to predict the pressure-flowrate relation in the Hagen-Poiseuille flow in the micro-tube. 相似文献
40.
Surface rapid solidification microstructures of AISI 321 austenitic stainless steel and 2024 aluminum alloy have been investigated by electron beam remelting process and optical microscopy observation. It is indicated that the morphologies of the melted layer of both stainless steel and aluminum alloy change dramatically compared to the original materials. Also, the microstructures were greatly refined after the electron beam irradiation. 相似文献