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。多个表面裂纹的寿命通常占总疲劳寿命的大部分。因此，有必要建立裂纹贯通完成前的疲劳扩展寿命估算方法。在考虑裂纹附近干扰影响的情况下，考虑了缺口根部单独存在的表面裂纹，其K值与K值相同。结果表明，假设裂纹与K值的比值存在一个重要的变化规律，它可以间接反映缺口根部产生的多个表面裂纹在焊接残余拉应力场中的扩展行为。为了获得裂纹的张开/闭合行为，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，并提出了一些改进意见。

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.