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Study on the dislocation emission around a crack tip by using high-voltage electron microscopy

裂纹尖端周围位错发射的高压电子显微镜研究

基本信息

批准号：
10650651
负责人：
HIGASHIDA Kenji
金额：
$ 2.18万
依托单位：
KYUSHU UNIVERSITY
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-10650651/
关键词：
fracture crack dislocation HVEM

项目摘要

Dislocation emission from a crack tip is most fundamental process to understand the toughening mechanism of crystalline materials. In the present study, dislocation emission from the tip of a crack in MgO thin crystals has been investigated based on the geometry of crack tip dislocations observed using high voltage electron microscope(HVEM). In-situ experiments in the HVEM using tensile holder were also made. The effect of crack tip shielding due to the dislocations was also calculated using 3-D Buekner-Rice weight function theory for crack-dislocation interaction.Dislocation image analyses showed that dislocations ahead of the crack tip observed in the present study were almost right-handed(R-H)screw dislocations lying on the(011)plane, while in the crack wake many of the dislocations were left-handed(L-H)on the (011)plane. Formation of such dislocation configuration can be understood by the emission of dislocation loops from sources at a crack tip, where crack jogs, crack kinks and intersections of crack planes with free surfaces may act as significant sources for dislocation emission. 3-D stress analysis exhibits that the largest component of crack tip stress intensities induced is mode I shielding type, and that mode II component is not negligible in the present case, suggesting the induction of the crack tip shielding for the mixed stress modes of I and II through the dislocation emission from the sources indicated above.

裂纹尖端的位错发射是理解晶体材料增韧机理的最基本过程。在本研究中，位错发射从MgO薄晶体中的裂纹尖端已被调查的基础上使用高压电子显微镜（HVEM）观察到的裂纹尖端位错的几何形状。在高压电磁法中使用拉伸保持器进行了原位实验。采用三维Buekner-Rice权函数理论计算了位错对裂纹尖端的屏蔽作用，位错图像分析表明，在裂纹尖端观察到的位错几乎都是位于（011）面上的右旋（R-H）螺旋位错，而在裂纹尾流中，许多位错都是位于（011）面上的左旋（L-H）位错。这样的位错配置的形成可以理解为位错环的发射源在裂纹尖端，其中裂纹凹凸，裂纹扭结和裂纹平面与自由表面的交叉点可以作为位错发射的重要来源。三维应力分析表明，裂纹尖端应力强度的最大分量是I型屏蔽型，而II型分量在本例中也不可忽略，这表明I型和II型混合应力模式的裂纹尖端屏蔽是通过上述源的位错发射引起的。