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Life Prediction Method and Experiments of Three-Dimensional Fatigue Cracks Propagating in Inhomogeneous Materials and Residual Stress Fields

非均匀材料和残余应力场中三维疲劳裂纹扩展的寿命预测方法与实验

基本信息

批准号：
11650091
负责人：
TSUJI Masahiro
金额：
$ 2.18万
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：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

1. Main results of experiments(1) Corner fatigue crack propagation experiments were conducted for a specimen fastened with a bolt, a kind of inhomogeneous material, in a residual stress field. These cracks were propagated from the edge of the bolt hole perpendiculary to a load axis. Consequently, it was found that crack-propagation-rates of the surface direction of the specimen were larger than the thickness direction slightly.(2) Three-dimensional slant corner fatigue crack propagation experiments were conducted for PMMA water-quenching specimens with residual stress fields by water-quenching. Direct observations of their crack opening behaviors were made. A partial elastic-contacts phenomenon of crack surfaces could be observed; the crack gradually closed from its crack mouth in the compressive residual stress fields with unloading.2. Main results of simulations(1) Horizontal and slant corner creeks in residual stress fields, horizontal and slant corner cracks propagating toward a hole, and horizontal and slant hole-corner cracks fastened with a bolt were used as models for analysis. We could confirm the effects of residual stresses, a hole and fastening with a bolt. As compared with some experimental results and simulated ones, documentation of three-dimensional fatigue crack life prediction method based on crack propagation simulations which combined "U-estimation method" with " Δσθ maximum criterion" made remarkable progress.(2) Crack opening simulations taking account of crack surface elastic-contacts were made only in the case of slant corner cracks. It was found that there was a case when crack propagation paths changed according to residual stress distributions by means of electron beam welding. However, all the models used for analysis couldn't be simulated because of a limit in our automatic mesh dividing program.

1.主要实验结果（1）对用非均匀材料螺栓紧固的试件在残余应力场中进行了角疲劳裂纹扩展实验。这些裂纹从螺栓孔边缘扩展到载荷轴。结果表明，试样表面方向的裂纹扩展速率略大于厚度方向。(2)对有机玻璃（PMMA）水淬试样进行了三维斜角疲劳裂纹扩展实验，研究了水淬残余应力场对裂纹扩展的影响。对它们的裂纹张开行为进行了直接观察。裂纹表面存在部分弹性接触现象，随着卸载，裂纹在残余压应力场中从裂纹口逐渐闭合.模拟的主要结果（1）以残余应力场中的水平和倾斜角裂纹、向孔方向扩展的水平和倾斜角裂纹以及用螺栓紧固的水平和倾斜孔角裂纹为模型进行了分析。我们可以确认残余应力、孔和螺栓紧固的影响。通过与一些试验结果和模拟结果的比较，基于裂纹扩展模拟的三维疲劳裂纹寿命预测方法--“U-估计法”与“Δσθ最大准则”相结合的文献研究取得了显著进展。(2)裂纹张开模拟考虑裂纹表面弹性接触的情况下，只有在斜角裂纹。结果发现，有一种情况下，裂纹扩展路径改变，根据残余应力分布，通过电子束焊接。然而，由于我们的自动网格划分程序的限制，无法模拟所有用于分析的模型。