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

本研究的目的之一是建立焊趾表面裂纹的疲劳寿命评估方法。在疲劳寿命中，多裂纹扩展寿命往往占很大一部分。因此，有必要建立裂纹贯通前疲劳扩展寿命的估算方法。考虑了一个假设的表面裂纹，该表面裂纹单独存在于缺口根部，其K值与考虑近裂纹干涉效应时的K值相同。在此基础上，提出了在焊接拉伸残余应力场作用下，缺口根部产生的多表面裂纹的裂纹张开/闭合行为随K值的变化规律，并研制了激光干涉位移计测量系统。然后分析了该系统存在的问题，并指出了改进的方向.

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.