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Life Predictions of Fatigue Crack Propagation Considering Fracture Surface Contact Under Residual Stress Fields and Quantitative Evaluation in Fractal Analysis on Fracture Surfaces

考虑残余应力场下断裂表面接触的疲劳裂纹扩展的寿命预测以及断裂表面分形分析中的定量评估

基本信息

批准号：
15560072
负责人：
TSUJI Masahiro
金额：
$ 2.3万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

Fatigue life predictions considering fracture surface contact under residual stress fields were made and our life prediction method was verified by employing quantitative evaluations by fractal analyses on fracture surfaces and an examination in its applicability was attempted. The results obtained are summarized as follows.1.Main results of experiments(1)Fatigue crack propagation experiments for SM and HT steel were conducted in different stress ratios Rs corresponding to residual stresses. Their fracture surfaces contacted were observed with SPM. Their data were used in fractal analyses and fractal dimensions Ds were calculated. It was found that D decreased with R increasing but that dependence was not large. Consequently it was concluded that the predictions making use of its correlation would have large errors. Additional researches and Ds corresponding to many kinds of fracture surfaces were needed.(2)Fractal analyses were made for SUS304 stainless steel employed for elevated tem … More perature experiments in a vacuum and the air in the past because of obtaining many kinds of Ds. Consequently clear correlations between Ds and their environments and temperatures could be obtained. Fractal analyses for Ni based-super-alloy were made. Their fracture surfaces were fractal in both environments. The other fracture surface analyses were made and root-mean-square method could distinguish a crack propagation direction from a direction perpendicular to that.2.Main results of simulationsFatigue crack propagation simulations were made for slant surface cracks, corner cracks toward a hole, and slant cracks emanating from a hole with and without considering fracture surface contacts. Consequently it was demonstrated that the consideration of fracture surface contacts often changed crack propagation rates and paths and then changed crack front shapes. It was confirmed that our fatigue life prediction method for three-dimensional cracks was applicable which combined "Uestimation method" with "Δσ_θ maximum theory". Less

进行了考虑残余应力场下断裂表面接触的疲劳寿命预测，并通过断裂表面分形分析的定量评估验证了我们的寿命预测方法，并尝试检验其适用性。主要研究结果如下： 1.主要实验结果 (1)在不同残余应力对应的应力比Rs下对SM和HT钢进行了疲劳裂纹扩展实验。用SPM观察它们接触的断裂面。他们的数据用于分形分析并计算了分形维数 Ds。结果发现，D随着R的增加而减少，但依赖性并不大。因此得出的结论是，利用其相关性进行的预测会有很大的误差。需要进行更多的研究和对应于多种断裂面的Ds。(2)由于获得了多种Ds，对过去在真空和空气中进行高温实验的SUS304不锈钢进行了分形分析。因此可以获得 D 与其环境和温度之间的清晰相关性。对镍基高温合金进行了分形分析。它们的断裂面在两种环境下都是分形的。对其他断裂面进行了分析，均方根法可以区分裂纹扩展方向和垂直于该方向的裂纹扩展方向。2.主要模拟结果在考虑和不考虑断裂面接触的情况下，对倾斜表面裂纹、朝向孔的角部裂纹以及从孔发出的倾斜裂纹进行了疲劳裂纹扩展模拟。结果表明，考虑断裂表面接触通常会改变裂纹扩展速率和路径，然后改变裂纹前沿形状。证实了我们提出的“估计法”与“Δσ_θ最大值理论”相结合的三维裂纹疲劳寿命预测方法的适用性。较少的