Fatigue crack propagation under various kind of loading

各种载荷下的疲劳裂纹扩展

基本信息

批准号：
06555302
负责人：
TOYOSADA Masahiro
金额：
$ 8.19万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

A Simulation model of fatigue crack opening and closing phenomena is introduced by developing Dugdale model.It is confirmed that the simulated RPG load (Re-tensile plastic zone Generated load) is in good agreement with experimental one.It becomes clear that a delayd retardation effect on fatigue crack propagation just after decreased maximum load can be also quantitatively assessed by effective stress intensity factor range DELTAKAPPA_<RP> corresponding to the period in which the re-tensile plastic zone appears, and stopping condition of a fatigue crack propagation is that DELTAKAPPA_<RP>*0.It is also confirmed from the model that plastic zone size omega received fatigue damage is proportional to a two power of DELTAKAPPA_<RP>. It is reported that a fatigue crack propagation curve in residual stress distribution field and under "storm model" loading with changing mean load can be quantitatively assessed by using omega. However a problem occures in case of receiving very large spike load, which is assessed to unsafe side.In the early stage of fatigue initiation, small surface cracks emanate and repeat coalescence one after another. Therefore aspect ratio of each surface crack has a large scatter. However the aspect ratio of a flctitious representative surface crack of which K value at the deepest point is the same as an increased K value due to interference effect of vicinity surface cracks and the depth is the same of the same of the deepest surface crack among surface cracks changes to be linear to the depth before the completion of coalesence. Moreover the method of a surface crack to be modeled into two dimensional problem by series springs model is also introduced.

通过开发Dugdale模型，引入了疲劳裂纹张开和闭合现象的模拟模型。证实了模拟的RPG载荷（再拉伸塑性区生成载荷）与实验载荷吻合良好。很明显，延迟延迟效应最大载荷下降后疲劳裂纹扩展的影响也可以通过再拉伸塑性区出现时期对应的有效应力强度因子范围DELTAKAPPA_<RP>来定量评估，疲劳裂纹扩展的停止条件为DELTAKAPPA_<RP>*0。从模型中也证实，受到疲劳损伤的塑性区大小omega与DELTAKAPPA_<RP>的二次方成正比。据报道，使用omega可以定量评估残余应力分布场和平均载荷变化的“风暴模型”载荷下的疲劳裂纹扩展曲线。然而，如果受到很大的尖峰载荷，就会出现问题，被评估为不安全的一面。在疲劳萌生的早期阶段，表面会产生细小的裂纹，并不断重复合并。因此各表面裂纹的纵横比具有较大的分散性。然而，最深点的K值与由于邻近表面裂纹的干涉作用而增加的K值相同且深度与表面中最深的表面裂纹相同的虚构代表性表面裂纹的纵横比在合并完成之前，裂纹随深度呈线性变化。此外还介绍了用串联弹簧模型将表面裂纹建模为二维问题的方法。