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

本文提出了一种预测三维裂纹在残余应力场中扩展的疲劳寿命的扩展方法，并用PMMA进行了检验。(1)得到了二维裂纹的基本数据，即da/dN-DELTAK_1关系<eff>和U-R关系，为三维U预测方法提供了依据。(2)在加载过程中，由于实验的困难，牛顿环不能产生。本文利用作者研制的钠蒸气灯裂纹表面全反射观测了裂纹闭合现象。然而，通过这种方法，在理论上不能观察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)对具有残余应力的试样进行与（2）相同的实验，可以清楚地观察到裂纹从压缩残余应力场闭合的情况。在n ...更多信息 o加载时，可以产生牛顿环，并确认裂纹表面在拉伸残余应力场中弯曲。从而获得了三维裂纹闭合现象的许多信息。(4)K值的计算主要采用了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有机玻璃，其预测结果与实验结果吻合较好，在此基础上，将本文提出的寿命预测方法应用于含残余应力的金属试件，并将其预测结果与实验结果进行了比较。实验中采用了两种不同的残余应力分布。一个是由SM 41 B（而不是HT 80，这是不可用的）的电子束焊接引起的，另一个是在SUS-复合SPV钢。实验结果表明，本文提出的预测三维裂纹在残余应力场中扩展的疲劳寿命的扩展方法是有效的。少

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