A Probabilistic Approach to the Fatigue Crack Propagation under Non-stationary Random Loading

非平稳随机载荷下疲劳裂纹扩展的概率方法

基本信息

批准号：
60460146
负责人：
MACHIDA Susumu
金额：
$ 4.54万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1987
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-60460146/
关键词：
Fatigue crack propagation Random loading き裂開口応力

项目摘要

Crack extention by fatigue may sometimes cause a catastrophic failure of structure. For the safety assessment of structure, it is indispensable to estimate fatigue crack growth under service loading. In most cases actual service load are random, and the estimating methor for fatigue crack growth under random loading must be setablished.For practical use, it is very preferable that the prediction of fatigue behavior in real structures under random loading could be made using the data obtained by constant amplitude loading test which is simple and routine test. Many investigations have been carried out in order to clarify the releationship between fatigue behaviors under random loading and constant amplitude loading, recently based on the concept of "crack closure" proposed by Elber. In these investigations, however, pure random load has not been applied because of its complexity, and the relationship nas not been clarified yet.In this study, fatigue crack propagation tests under random loading are carried out as well as constant amplitude loading tests for comparison. Crack closure phenomna of the specimens are automatically recorded over a long period of fatigue cycles aided by micro-computer system. It is shown that consideration of crack closure is essential for examination of fatigue crack growth and fatigue behavior under random loading may be predicted from constant amplitude test. Furthermore, fatigue tests are carried out under the condition of the same constant stress amplitude on many specimens. The results are analyzed using Bogdanoff's probabilistic model (B model) based on Markov chain concept. It is shown that the B model has the possibility for proveding a useful tool for examining the statistical properties of fatigus crack growth.

疲劳引起的裂纹扩展有时可能会导致结构的灾难性失效。对于结构的安全评估，估计使用荷载下的疲劳裂纹扩展是必不可少的。在大多数情况下，实际使用载荷是随机的，必须建立随机载荷下疲劳裂纹扩展的估计方法。对于实际应用，最好使用数据来预测随机载荷下实际结构的疲劳行为通过等幅加载试验获得，试验简单、常规。最近，基于Elber提出的“裂纹闭合”概念，为了阐明随机载荷和恒幅载荷下的疲劳行为之间的关系，已经进行了许多研究。然而，在这些研究中，由于其复杂性，并未采用纯随机载荷，而且其关系也尚未明确。在本研究中，进行了随机载荷下的疲劳裂纹扩展试验以及等幅载荷试验以进行比较。在微机系统的辅助下，自动记录试件在长时间疲劳循环过程中的裂纹闭合现象。结果表明，考虑裂纹闭合对于检查疲劳裂纹扩展至关重要，并且可以通过恒幅试验预测随机载荷下的疲劳行为。此外，对多个试件在相同恒定应力幅的条件下进行疲劳试验。使用基于马尔可夫链概念的博格丹诺夫概率模型（B模型）对结果进行分析。结果表明，B 模型有可能成为检查疲劳裂纹扩展统计特性的有用工具。