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Life Prediction of Three-Dimensional Fatigue Crack Propagation in Residual Stress Fields with PMMA

利用 PMMA 预测残余应力场中三维疲劳裂纹扩展的寿命

基本信息

批准号：
03650062
负责人：
TSUJI Masahiro
金额：
$ 1.02万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

An extended method for predicting fatigue lives of a 3-dimensional crack propagating in residual stress fields proposed by the present authors was examined with PMMA as follows.(1) Basic data of 2-dimensional cracks, a da/dN-DELTAK_<eff> and U-R relation, were obtained, which were to be employed in the 3-dimensional U prediction method. (2) During loading, Newton's rings could not be generated owing to difficulty of the experiments. In stead, observations of the crack closure phenomenon were made by making use of total reflection on the crack surfaces of sodium-vapor lamp developed by the present authors. However, by this method deformation aspects of the crack surfaces can not be observed in theoretically, but aspects in which the crack was closing from its crack front could be observed clearly. (3) Same experiments as (2) were conducted for specimens with residual stresses, and aspects that a crack was closing from the compressive residual stress field could be observed clearly. In n … More o-loading, Newton's rings could be generated, and it was confirmed that a crack surface bent in the tensile residual stress field. Consequently many informations on the crack closure phenomenon of 3-dimensinal cracks could be obtained. (4) A influence coefficient method by Shiratori et al and Newman-Raju's equations were mainly employed in calculating K values. F. E. M. was employed only for verifying those K values because a great deal of work it required. Without reference to this original program, the present life prediction method was applyed to PMMA, and its prediction results were in good agreement with experimental results.On the basis of these informations, this life prediction method could be applyed to metal specimens with residual stresses, and their results were compared with experimental results. Two kinds of residual stress distributions were employed in the experiments. One was caused by electronic beam welding of SM41B(instead of HT80 which was not available) and the other was in SUS-clad SPV steel. The experiments were conducted in the same way as PMMA.Consequently it was confirmed that the extended method for predicting fatigue lives of a 3-dimensional crack propagating in residual stress fields proposed by the present authors was in valid. Less

本文采用PMMA对三维裂纹在残余应力场中扩展的疲劳寿命预测方法进行了验证。(1)获得了二维裂缝的基本数据，即da/dN-DELTAK_<eff>和U- r关系，可用于三维U预测方法。(2)加载过程中，由于实验难度大，无法产生牛顿环。利用本文作者研制的钠蒸气灯裂纹表面的全反射，观察了裂纹闭合现象。然而，这种方法在理论上不能观测到裂纹表面的变形方面，但可以清楚地观察到裂纹从其裂纹前缘闭合的方面。(3)对有残余应力的试件进行了与(2)相同的试验，从压残余应力场中可以清晰地观察到裂纹闭合的方面。在n…+ 0载荷下，可以产生牛顿环，并证实裂纹表面在拉伸残余应力场中弯曲。从而获得三维裂纹闭合现象的许多信息。(4)计算K值主要采用Shiratori等人的影响系数法和Newman-Raju方程。f.e.m.只用于验证这些K值，因为它需要大量的工作。在不参考原程序的情况下，将本文提出的寿命预测方法应用于PMMA，预测结果与实验结果吻合较好。在此基础上，将该寿命预测方法应用于存在残余应力的金属试样，并与实验结果进行了比较。实验中采用了两种残余应力分布。一个是SM41B的电子束焊接造成的（而不是没有的HT80），另一个是susu包覆SPV钢造成的。实验的进行方式与PMMA相同。结果表明，本文提出的三维裂纹在残余应力场中扩展疲劳寿命预测方法是有效的。少