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Development of Statistical evaluation method for fatigue crack profagation under random loading

随机载荷下疲劳裂纹扩展统计评价方法的开发

基本信息

批准号：
61460086
负责人：
SAKAI Shinsuke
金额：
$ 4.22万
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：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

1) Exzmination of performance of developed statistical fatigue test machine;We finally completed a statistical fatigue test machine by which we can execute a test for 5 specimens simultaneously. Basic performance of the testing machine was examined. Response of gain and phase difference is shown to be flat between 020Hz and it is shown that frequency response prosperity is sat isfactory. Drift of mean load after long time usage is shown to be very small. Therefore, it is confirmed that there is no problem in executing fatigue test. In addition, multi-task real time system was developed on a personal computer to control this testing machine and to execute data processing efficiently.2) Execution of preliminary experiment for the statistical fatigue testing machine;Accuracy of automated crack length measuring by compliance method and the effects of random loading on fatigue crack propagation were examined preliminarily. It was confirmed that measuring accuracy of crack length was as good as one by visual observation and the relation between the statistical factor in random loading and the fatigue crack propagation characteristics were obtained. By using developed testing system, fatigue crack propagation data were obtained. 3) Application to reliability analysis;In addition to acquire fatigue crack propagation data, a reliability analysis has been done. Effects of scattering in fatigue crack propagation and initial shape of surface crack on final failure probability was analysed by Monte carlo simulation.4) Re-examining of usual data;Usually,data of fatigue crack propagation were collected on the basis of deterministic theory. However, those data are not sufficient to understand the probabilistic characteristics of crack propagation. Therefore,we tried to separate a scattering factor in data processing from the one in materials strength itselt and considered a contribution of each scattering factor to total scattering level.

1)研制的统计疲劳试验机的性能检验最终完成了一台可同时进行5个试件试验的统计疲劳试验机。对试验机的基本性能进行了检验。增益和相位差的响应在020Hz之间是平坦的，并且频率响应繁荣度是饱和的。经过长时间的使用，平均载荷的漂移是非常小的。因此，确认在执行疲劳试验时没有问题。另外，在微机上开发了多任务真实的实时系统，实现了对试验机的实时控制和数据处理。2）对统计疲劳试验机进行了初步试验，初步考察了柔度法自动测量裂纹长度的精度和随机载荷对疲劳裂纹扩展的影响。验证了裂纹长度的测量精度与目视观测相当，并得到了随机载荷下统计因子与疲劳裂纹扩展特性之间的关系。利用研制的试验系统，获得了疲劳裂纹扩展数据。3)在可靠性分析中的应用：除了获得疲劳裂纹扩展数据外，还进行了可靠性分析。用MonteCarlo模拟方法分析了疲劳裂纹扩展的离散性和表面裂纹初始形状对最终失效概率的影响。4）对常用数据的重新检验通常，疲劳裂纹扩展数据是根据确定性理论收集的。然而，这些数据不足以理解裂纹扩展的概率特性。因此，我们试图将数据处理中的散射因子与材料强度本身中的散射因子分开，并考虑每个散射因子对总散射水平的贡献。