Previously the authors investigated that the effect of low cycle fatigue on the brittle fracture propagation-arrest characteristics and brittle fracture initiation from fatigue crack in ordinary ship steels.
This paper concerns with some fundamental aspects of brittle fracture initiation from fatigue crack and fatigued plate in 60kg/mm2 class high strength steels.
The followings have been obtained conclusively : The material deterioration due to repeated plastic straining seems to be relatively slight. The specimens with low cycle fatigue crack showed higher toughness than that of the virgin plate specimen with machined notch, for which the tilting of fatigue crack and the residual compression stress developed in crack tip zone seemed to be responsible. On the other hand the same degree of fracture toughness is observed in the specimen with high cycle fatigue crack where the above two factors are almost absent.
