A Prediction of Initial Fatigue Crack Propagation Life in a notched Component Taking Elasto-Plastic Behavior

J. Ocean Eng. Technol. 1988;2(2):61-70.

Cho Sang-Myung,Kohsuke Horikawa

탄소성 응력집중부에서의 초기피로균열전파수명의 예측

조상명,굴천조보

한국해기연수원,오사카대학

Keywords: Fatigue Design, Offshore Structure, Hot Spot, Fatigue Crack Propagation, Initial Fatigue Crack, Elasto- plastic Fracture Mechanics, Notch

핵심용어: 피로설계, 해양구조물, 절점, 피로균열전파, 초기피로균열, 탄소성파괴역학

Abstract

In order to consider the concept of the fitness for purpose'in fatigue design of offshore structure, fracture mechanics is applied to evaluate initial or weld defects. Generally, linear elastic fracture mechanics has been applied to tstimate initial fatigue crack propagation rate as well as long fatigue crack propagation rate. But, initial fatigue crack propagation rate in elasto-plastic notch field may not be characterized by application of stress intensity factor range .DELTA. K, because plastic effect due to stress concentration of notch may contribute to initial crack propagation. Therefore, to introduce the plastic effect into fatigue crack driving force, in this studty, the evaluating method of J-integral range .DELTA. J, was developed by willson was modified for application to notch field. In calculation of .DELTA. J obtained from the modified J-integral, stress gradient and crack closure behavior in the notch field were considered. The initial crack propagation rates in the notch fields of mild steels and high tensile strength steels were correlated to .DELTA. J. As the result, it was cleared that the present .DELTA. J is applicable to charachterize the fatigue crack propagation rates in both the elastic and elasto-plastic notch fields.