权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

SIMULATION OF FATIGNE CRACK INTIATION AND PROPAGATION BASED UPON DISLOCATION DYNAMICS

基于位错动力学的疲劳裂纹萌生和扩展模拟

基本信息

批准号：
14550077
负责人：
MORITA Tatsuro
金额：
$ 0.9万
依托单位：
Kyoto 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：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14550077/
关键词：
fatigue crack initiation propagation dislocations dynamics simulation 入り込み・突き出し転位動力学遮蔽効果

项目摘要

(1) Fatigue Crack Initiation : The behavior of fatigue crack initiation was considered through the dislocation dynamics simulation based upon the movement of edge dislocations escaping from the surface under a cyclic applied shear stress. The result showed that no ship step was formed only by movable dislocations because the same number of dislocations with the opposite sign alternately escaped from the surface. However, the formation of a slip step occurred under the existence of sessile dislocations randomly distributed in the material since the stress field of the sessile dislocations disturbed the behavior of movable dislocations. Furthermore, in the case of plural slip planes, it was found a fatigue crack can be produced by the growth of each slip step under the existence of the sessile dislocations.(2) Fatigue Crack Propagation : The influence of the loading history and stress ratio on the behavior of fatigue crack propagation was investigated through the computer simulation based upon the emission and movement of dislocations from the crack-tip. The result of the simulation showed that is a power relation between the stress intensity range in the preceding cycles and the threshold value where is the crack stops propagating. It was also found that the threshold value obtained by the simulation is closely connected with the stress ratio through the Walker relation. The existence of those relations was explained from the viewpoint that the above two parameters control not only the maximum stress intensity but also the crack opening stress intensity level which is determined by the degree of the shielding effect to the residual dislocations.

(1)疲劳裂纹萌生：基于刃型位错在循环剪应力作用下从表面逃逸的运动，通过位错动力学模拟研究了疲劳裂纹的萌生行为。结果表明，由于相同数量相反符号的位错交替逸出表面，不存在仅由可动位错形成的船形台阶。然而，在材料中随机分布的固着位错的存在下发生滑移台阶的形成，因为固着位错的应力场干扰可动位错的行为。此外，在多滑移面的情况下，发现在固着位错的存在下，每个滑移台阶的扩展都可以产生疲劳裂纹。(2)疲劳裂纹扩展：通过对裂纹尖端位错发射和运动的计算机模拟，研究了加载历史和应力比对疲劳裂纹扩展行为的影响。模拟结果表明，前几次循环的应力强度范围与裂纹停止扩展的门槛值之间呈幂函数关系。通过步行者关系发现，模拟得到的阈值与应力比密切相关。这两个参数不仅控制最大应力强度，而且控制裂纹张开应力强度水平，而裂纹张开应力强度水平取决于对残余位错的屏蔽作用程度。