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

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对5个试件进行疲劳试验的统计疲劳试验机。对试验机的基本性能进行了测试。幅值和相位差的响应在020赫兹范围内是平坦的，频率响应是异常的。长期使用后的平均载荷漂移很小。由此可见，进行疲劳试验是没有问题的。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准确性和随机载荷对疲劳裂纹扩展的影响。通过目测验证了裂纹长度的测量精度，得到了随机载荷下的统计因子与疲劳裂纹扩展特性之间的关系。利用研制的疲劳裂纹扩展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。通过蒙特卡罗模拟分析了疲劳裂纹扩展过程中的散射和表面裂纹的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基于确定性理论收集的。然而，这些数据不足以理解裂纹扩展的概率特征。因此，我们试图将数据处理中的散射因子与材料强度本身的散射因子分开，并考虑每个散射因子对总散射水平的贡献。

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.