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Studies on Dislocation Dynamical Model having an Emitting Source at a Crack Tip on Supposition of Crack Propagation

假设裂纹扩展的裂纹尖端发射源位错动力学模型研究

基本信息

批准号：
05650081
负责人：
SAITO Kenji
金额：
$ 1.41万
依托单位：
Kyoto Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-05650081/
关键词：
Dislocation dynamics Criteria for the emission of dislocations Crack Inclusion Critical stress intensity factor Pile-up Fatigue crack growth Crack opening displacement CTOD

项目摘要

The present research deals with the analysis of the interaction between a crack and an inclusion from the standpoint of the dynamics of dislocations which are emitted from the crack tip and pile up against an inclusion. The criteria for emission of dislocations are assumed to be governed by the local stress intensity factor at the crack tip. The equations of motions for dislocations can be obtained by considering the swelling of the applied stress due to the inclusion, image dislocations in it, and the interactions between a crack and dislocations. The effects of the rigidity and the radius of the inclusion, etc., on the shear strain near the inclusion can be evaluated.In addition to this, in order to determine the effect of the orientation of crystal grains on the fatigue crack growth, the analysis of the model that edge dislocations emitted from a crack tip and located on an inclined slip plane pile up against a grain boundary is performed and both the angular dependence of crack tip opening displacement and the change of CTOD during the crack growth through a crystal grain are examined. It is suggested from the results that the fatigue crack most easily propagates through a crystal grain and its boundary when an angle between the crack front and the slip plane is between 70 and 80 degress.Furthermore, the analysis of the screw dislocations piled up against a thin-surface-layr is performed as one of the application of the dislocation dynamics and calculated the stress field generated in the layr by both the pile-up of dislocations and applied stress. The effects of the thickness of the layr, misfit of shear moduli, grain size and friction stress on the magnitude of the stress field in the thin-layr can be evaluated.

本文从位错动力学的观点分析了裂纹与夹杂物的相互作用，位错从裂纹尖端发射出来并堆积在夹杂物上。位错发射的标准被假定为由裂纹尖端的局部应力强度因子。位错的运动方程可以通过考虑由于夹杂物引起的应力膨胀、夹杂物中的像位错以及裂纹和位错之间的相互作用而得到。研究了夹杂物的刚度、半径等因素对夹杂物力学性能的影响，对夹杂物附近剪切应变的影响，此外，为了确定晶粒取向对疲劳裂纹扩展的影响，分析了裂纹尖端发射的位于倾斜滑移面上的刃型位错在晶界上堆积的模型，研究了裂纹尖端张开位移的角度依赖性和裂纹扩展过程中CTOD的变化检查通过晶粒的生长。结果表明，当裂纹前缘与滑移面夹角在70 ° ~ 80 °之间时，疲劳裂纹最易沿晶界扩展，作为位错动力学的应用之一，对薄表面层上堆积的螺型位错进行了分析，计算了薄表面层上螺型位错的堆积和螺型位错在薄表面层中产生的应力场。在位错和外加应力的作用下可以计算出薄层厚度、剪切模量失配、颗粒尺寸和摩擦应力对薄层应力场大小的影响。