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Study on Elastic-Plastic Fatigue Crack Growth under Service Loading Conditions

使用载荷条件下弹塑性疲劳裂纹扩展研究

基本信息

批准号：
60550054
负责人：
MASAHIRO Jono
金额：
$ 1.22万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-60550054/
关键词：
Elastic-Plastic Fatigue Crack Varying Loading Crack Growth Rate Crack Closure Cyclic Deformation One-Directional Deformation Effective Stress Intensity Factor 繰返しJ積分

项目摘要

Engineering structures are often subjected to large amplitude loads in service which exceed the yield conditions of materials. Therefore, it becomes important to know an estimation method of elastic-plastic fatigue crack growth rates under varying loading conditions, in order to secure the safety of structures in damage tolerant design. From this point of view, in this study, load controlled fatigue crack growth tests were carried out on several kinds of structural materials under constant and variable amplitude loads over a wide range from the linear elastic region to the post-yield one, and fracture mechanics parameters which governed the fatigue crack growth rates were investigated. Crack growth increment and crack closure behavior were monitored through fatigue tests by the minicomputer-aided unloading elastic compliance method.The effective stress intensity range, <DELTA> Keff, was found to be a governing parameter of fatigue crack growth rate even in the large scale yielding region within the limit conditions as well as in the linear elastic region. In the post-yield region, however, cyclic plastic deformation and fatigue induced one-directional deformation took place remarkably depending on materials, specimen configurations and stress ratios, and affected crack growth behaviors. It was found that these effects could be explained by considering the cyclic J-integral, <DELTA> J, and the maximum J-integral, Jmax, and the elastic-plastic fatigue crack growth rate could be expressted by the power law of <DELTA> J/E(1-Jmax/C) irrespective of materials, specimen configurations and test conditions. From the test results with repeated two-step loadings simulating several kinds of service loadings, it was found that the elastic-plastic fatigue crack growth rate under varying loading conditions could be well estimated based on the linear accumulation law of crack growth using the above mentioned fracture mechanics parameter.

工程结构在使用中经常承受超过材料屈服条件的大幅值载荷。因此，为了保证结构在损伤容限设计中的安全性，了解一种在不同载荷条件下的弹塑性疲劳裂纹扩展速率的估计方法具有重要意义。从这一角度出发，本文对几种结构材料进行了恒幅和变幅载荷作用下从线弹性区到屈服后的大范围载荷控制疲劳裂纹扩展试验，研究了影响疲劳裂纹扩展速率的断裂力学参数。用小型计算机辅助卸载弹性柔度法对疲劳试验中的裂纹扩展增量和裂纹闭合行为进行了监测，发现有效应力强度范围&lt；Delta&gt；KJeff是疲劳裂纹扩展速率的控制参数，即使在极限条件下的大屈服区和线弹性区也是如此。然而，在屈服后区域，循环塑性变形和疲劳诱导的单向变形显著地发生，这取决于材料、试件形状和应力比，并影响裂纹扩展行为。结果表明，这些效应可以通过考虑循环J积分&lt；Delta&gt；J来解释，最大J积分Jmax和弹塑性疲劳裂纹扩展速率可以用&lt；Delta&gt；J/E(1-Jmax/C)的幂定律来表示，而与材料、试件构型和试验条件无关。从模拟几种服役载荷的重复两步加载试验结果可以看出，根据裂纹扩展的线性累积规律，利用上述断裂力学参数可以很好地估计不同载荷条件下的弹塑性疲劳裂纹扩展速率。