Study on crack opening/closing behavior of fatigue surface crack and fatigue life priduction

建立焊趾表面裂纹疲劳寿命评估方法是本研究的目的之一。复合表面裂纹的寿命通常占总疲劳寿命的很大一部分。因此，有必要建立裂纹合并完成前的疲劳扩展寿命估算方法。考虑考虑近裂纹干涉效应的情况下，假设表面裂纹单独存在于缺口根部，其K值与K值相同。由此可见，假设裂纹的比值随K值的变化有一个重要的规律，它可以间接地表示焊接残余拉伸应力场下从缺口根部产生的多个表面裂纹的裂纹扩展行为。为了获得裂纹的开闭特性，研制了激光干涉位移指示器测量系统。然后对该系统存在的问题进行了分析，并提出了改进的地方。

It is that a purpose of this study establishes fatigue life assessment method of surface crack emanated from weld toe. The life during plural surface crack usually occupies the major portion of total fatigue life. Therefore it is necessary to establish the estimation method of fatigue propagation life before completion of crack coalescence. A supposed surface crack which exist alone at the notch root and of which K value is the same as K value with considering interference effect from near crack is considered. Then it becames clear that thereis a important law about the change of ratio for the supposed crack with respect to K value which may represent indirectly crack propagation behavior for multiple surface cracks emanated from notch root with welding tensile residual stress field.The measuring system using laser interference displacement indicator was developed for the purpose of obtaining the crack opening/closing behavior. Then problems of this system were investigated and some improved points were indicated.