共查询到16条相似文献,搜索用时 203 毫秒
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采用计算机模拟了位错和位错偶沿单一滑移系从裂纹尖端的发射,考察了滑移面取向、外加载荷、晶格摩擦力以及位错发射的临界应力强度因子对所发射的位错数量、塑性区与无位错区大小以及裂关残余应力强度因子的影响研究表明,位错从裂纹尖端发射的临界应力强度因子对无位错区的存在和其大小起决定作用,而外加载荷与晶格摩擦力主要影响位错发射的数量以及塑性区大小.在I型载荷作用下,滑移面与裂纹面的夹角越大,从裂尖发射出的位错数量越多,位错对裂纹的屏蔽效应也越大当裂纹发射位错后的残余应力强度因子仍然较大时,位错偶就有可能在裂纹尖端附近产生井沿着几个滑移面发射,但发射出的位错偶对裂纹没有明显的屏蔽作用在滑移面不垂直于裂纹面时,发射出的位错或位错偶关于裂纹面呈不对称分布 相似文献
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位和位错偶沿单一滑移系从裂纹尖端的发射 总被引:1,自引:0,他引:1
采用计算机模拟了位错和位借偶沿单一滑移从裂纹尖端的发射,考察了滑移面取向,外加载荷,晶格摩擦力以及位错发射的临界应力强度因子对所发射的位错数量,塑性区与无位错区大小以及裂尖残余应力强度因子的影响。 相似文献
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采用分子动力学方法研究了FeNiCu合金在单轴应力加载下的微裂纹扩展行为。分析了相对于裂纹不同角度位置的位错对微裂纹扩展的影响。结果表明,在微裂纹扩展过程中,裂纹在尖端主要的变形机制为滑移带和位错,裂纹尖端在滑移方向<110>发射位错。随着位错的连续增殖,位错密度逐渐增大,形成位错塞积,导致产生位错针扎,微裂纹沿此方向进行扩展。而预设不同滑移方向的位错对微裂纹扩展存在阻碍作用,在位错阻碍效果失效前,当位错相对位于裂纹30°时对裂纹的扩展运动阻碍效果最大,45°次之,60°最小。其中30°位错的滑移方向与裂纹的滑移方向垂直,且应力峰值最大,表示拉伸需要的外应力最大,表现出的阻碍效果最明显。这种抑制微裂纹扩展的效果越强,在裂纹尖端的应力集中现象越明显。而在抑制作用失效后,缺陷处会释放大量势能,使裂纹快速扩展,对材料造成破坏。 相似文献
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P.B.HirschFRS 《金属学报》1997,33(3):225-232
众多结晶体在低温环境下呈现解理断裂,在高温环境下呈现塑性断裂。在过渡温区,解理断裂的应力随温度增加而增加,反映了屈服应力的下降以及裂纹尖端区塑性的相应增加。裂尖塑性可钝化裂纹并因塑性区中的压应力而屏蔽裂纹。本文简短评述了脆-韧转变模型。在该模型中,计算屏蔽效应的塑性区是由位错的产生、运动和相互作用形成的,这些位错匀在含裂尖的滑移面上运动,并且服从速度/应力/温度定律。对模型在实验结果中的应用也进行 相似文献
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TC4ELI合金疲劳裂纹尖端塑性区对裂纹扩展的影响 总被引:2,自引:1,他引:1
研究了TC4ELI合金片层组织与短棒α组织中的疲劳裂纹尖端塑性区及裂纹扩展行为.首先通过SEM及TEM观察比较两种显微组织下的疲劳裂纹尖端塑性区,讨论两种显微组织中裂纹尖端塑性区对疲劳裂纹扩展路径及扩展断口的影响,分析裂纹扩展路径和裂纹尖端塑性区对裂纹闭合及裂纹扩展速率的影响.结果表明:与短棒α组织相比,片层组织中具有较大的裂纹尖端塑性区及曲折的裂纹扩展路径,并最终从疲劳裂纹闭合的角度,解释了片层组织具有较低的疲劳裂纹扩展速率的原因. 相似文献
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YAO Kefu TANG Naiyong CHEN Nanping Tsinghua University Beijing China Originally published in ACTA METALL SIN 《金属学报(英文版)》1989,2(6):433-438
The development of dislocation structures in the plastic zone ahead of a crack tip has been in-vestigated in a duplex stainless steel during in-situ deformation experiments in a scanningtransmission electron microscope.It was found that the dislocation distribution wassignificantly different in the ferrite and in the austenite.In the ferrite grains,the dislocationsemitted by the crack tip may cross-slip out of the original slip planes and form a broad plasticzone.However,in the austenite,the dislocation free zone is small and the dislocations emittedby the crack pile up in its slip plane.The selection of slip systems at the crack tip depends onthe crack tip Schmid factors in both phases.But after large deformation,the selection of thesecond slip systems at the craek tip in austenite does not depend on the Schmid factors. 相似文献
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《Acta Materialia》2008,56(16):4339-4348
Environment-assisted cracking is caused by enhanced crack-tip plastic deformation. Lattice resistance to shear slip is caused by the periodic fluctuation of the misfit energy across a slip plane. Lu et al. have shown that hydrogen reduces the misfit energy, slip resistance and resistance to dislocation motion. The 1s orbital of a hydrogen atom in a metal is not full, and the electron of the atom moves and reacts as a valence electron. The resistances to shear slip and dislocation generation at a crack tip are reduced by hydrogen electrons and hydrogen nuclei. Crack-tip plastic deformation is thus enhanced, and crack growth rate is increased. The model of reduced resistance to crack-tip dislocation generation and enhanced crack-tip plastic deformation can be extended to liquid metal-assisted cracking and stress corrosion cracking if the valence electron(s) of a liquid metal or chemical reduces the misfit energy and the slip resistance sufficiently. 相似文献
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《Acta Materialia》1999,47(2):661-669
The effect of grain boundary misorientation on the high-cycle fatigue performance of solution-treated, metastable-β titanium alloys was investigated. Initial damage during cyclic deformation was associated with the formation of coarse, planar slip bands, these often propagating through several grains without obstruction or redirection when intersecting with a grain boundary. This “continuous” slip through several grains was associated with the presence of a significant number of “low-angle” grain boundaries. Fatigue crack initiation was associated with crack initiation at intersecting planar slip bands at the free surface. The increase in operative slip length occasioned by the presence of low-angle grain boundaries lead to enhanced crack initiation and reduced lifetime. Fatigue crack propagation was characterized by step-like features formed through the interaction of the propagating crack and the coarse slip bands present in the plastic zone ahead of the crack tip. The direction of local fatigue crack propagation was also minimally affected when crossing low-angle grain boundaries. 相似文献
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C. Kahloun L.T. Le G. Monnet M.-H. Chavanne E. Ait P. Franciosi 《Acta Materialia》2013,61(17):6453-6465
In situ tensile tests were performed inside an atomic force microscope on commercially pure α-iron single crystals to examine the process of emerging slip at a free surface during plastic straining. The reported study corresponds to a crystal orientation which favors slip on a {1 1 0} plane. Statistical analysis of periodically stored images during the test allowed the collection of information on the planar and heterogeneous nature of slip, as well as on the evolution of this heterogeneity with strain. The average slip and the slip dispersion were step-wise estimated separately in each of the slip bands in a representative crystal observation zone. An estimate of the related heterogeneous evolution of the mobile dislocation density was also obtained. For the advanced microstructure-based modeling of intra-crystalline plastic behavior actually used in multiscale computational approaches of metal plasticity it is of interest to describe the relevant intra-crystalline slip process, which is not homogeneous even in single slip mode, although it is frequently simplified as such. These results also are of particular importance in validating the dislocation collective behaviour predicted by dislocation dynamics simulations. 相似文献
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《Intermetallics》1999,7(3-4):479-489
The room temperature brittleness of NiAl constitutes a major problem for technical applications. In order to investigate the micromechanisms of fracture in NiAl, we have carried out in situ tensile straining experiments on stoichiometric NiAl single crystals in a high-voltage electron microscope. According to our observations, crack propagation always involves dislocation activity around the crack tip, even in the hard orientation at room temperature. The Burgers vectors and the typical arrangements of the dislocations, as well as the extension of the corresponding plastic zone vary with the loading direction and the orientation of the microcrack versus potential glide systems. We observe that local concentrations of slip leads to irregular deviation of the cleavage plane from the {1 1 0} facets one usually observes at the macroscopic level. The results of our experiments help to understand why the mode I fracture toughness of NiAl is significantly larger for 〈1 0 0〉 loading directions than for non-〈1 0 0〉 directions. 相似文献