Abstract
Fatigue crack growth behavior under single-peak overloads is investigated for structural steel JIS SM520B. Fatigue test is carried out on seven center prenotched specimens. Three parameters, i. e. overload ratio, overload application stage and stress ratio are introduced to investigate the retardation effect. It is verified that fatigue crack growth rate is retarded after overloading and then gradually recovers to the normal. It is also observed that the retardation effect is intensified when the overload ratio and the stress range between overload stress and the following minimum stress increase. From the test results the crack length increment in which retardation occurs is compared with Irwin's and Dugdale's plastic zone sizes.
