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.

裂纹尖端的脱位发射是了解结晶材料的坚固机制的最基本过程。在本研究中，已经根据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研究了MGO薄晶体裂纹的脱位发射。还使用拉伸固定器进行了HVEM中的原位实验。还使用3-D Buekner-Rice重量功能理论来计算了由于位错引起的裂纹尖端屏蔽的效果，以进行裂纹 - 脱位相互作用。DISTOSITATION图像分析表明，在本研究中观察到的裂纹尖端之前的位错几乎是右撇子的（R-H）位于（011）平面上的螺钉位错，而在裂缝中唤醒（011）平面上的许多位错（L-H）。可以通过从裂纹尖端处的源头排出循环来理解这种错位构型的形成，其中裂纹慢跑，裂纹扭结和裂纹平面与游离表面的交叉点可能充当脱位发射的重要来源。 3-D应力分析表明，裂纹尖端应力强度的最大成分是模式I屏蔽类型，并且在本情况下，该模式II成分不容易忽略II通过上述源的脱位发射。