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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.

疲劳裂纹扩展有时会引起结构的灾难性破坏。在结构的安全评价中，对结构在使用荷载作用下的疲劳裂纹扩展进行估计是必不可少的。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。在实际应用中，采用简单、常规的恒幅加载试验数据预测实际结构在随机载荷作用下的疲劳行为是非常可取的。近年来，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疲劳行为之间的关系，进行了许多研究。然而，在这些研究中，由于纯随机载荷的复杂性，它们之间的关系尚未明确，因此没有应用纯随机载荷。本研究进行了随机载荷下的疲劳裂纹扩展试验和等幅载荷试验进行对比。在微机系统的辅助下，自动记录试样在长周期疲劳循环过程中的裂纹闭合现象。结果表明，在检验疲劳裂纹扩展时必须考虑裂纹闭合的影响，随机载荷作用下的疲劳行为可通过等幅试验进行预测。此外，还对多个试件进行了相同恒应力幅条件下的疲劳试验。利用基于马尔可夫链概念的Bogdanoff概率模型（B模型）对结果进行了分析。结果表明，B模型有可能为检验疲劳裂纹扩展的统计特性提供一种有用的工具。