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Mechanism of the emission of shielding dislocations from a crack tip

裂纹尖端屏蔽位错的发射机制

基本信息

批准号：
10650652
负责人：
NARITA Nobutaka
金额：
$ 2.11万
依托单位：
Kyushu Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10650652/
关键词：
fracture fracture toughness dislocation crack stress shielding lattice defect ionic crystal semiconductor 破壊靱性

项目摘要

In this research project, the mechanism of dislocation emission from a crack tip in MgO, NaCl and Si crystals have been studied using microscopic techniques of a electron microscope and an atomic force microscope. The results obtained are summarized as in the following.(1) In thick crystals, hinge-type structures of slip bands are formed around a crack tip, while in thin crystals dislocation structures are observed on slip planes intersecting through a crack tip line.(2) Dislocations are emitted from a crack tip through the nucleation of half-loop dislocations, and in thin crystals, the half-loop dislocations are generated at the intersection of a crack tip to free surface as well as at a crack jog and kink.(3) Dislocations are introduced not only ahead of a crack tip, but also formed behind a crack tip.(4) The sign of dislocations emitted ahead of crack tip is opposite to that of dislocations behind a crack tip, when they are lying on the same slip plane.(5) In any cases, dislocations which shield the crack stress field from an applied stress are mostly emitted from a crack tip.(6) In the deformation of NaCl crystals at high temperature, microscopic cross slip takes place on indefinite planes, so that half-loop dislocations can be expanded along a crack tip line by the cross slip to shield all over the crack front, leading to the suppression of crack growth.

本研究利用电子显微镜和原子力显微镜等显微技术对MgO、NaCl和Si晶体中裂纹尖端的位错发射机制进行了研究。所得结果总结如下。(1)在厚晶体中，铰链型结构的滑移带周围的裂纹尖端，而在薄晶体中观察到位错结构的滑移面相交通过裂纹尖端线。(2)位错从裂纹尖端通过半环位错的成核而发射，并且在薄晶体中，半环位错在裂纹尖端与自由表面的相交处以及在裂纹弯曲和扭结处产生。(3)位错不仅在裂纹尖端的前方引入，而且在裂纹尖端的后方形成。(4)当位于同一滑移面上时，裂尖前位错和裂尖后位错的符号相反。(5)在任何情况下，屏蔽裂纹应力场免受外加应力影响的位错主要从裂纹尖端发射。(6)NaCl晶体在高温变形时，在不确定的晶面上发生微观横滑移，横滑移可使半环位错沿着裂纹尖端线扩展，遮挡住整个裂纹前沿，从而抑制裂纹扩展。