Abstract
Estimation of residual life due to the fatigue crack growth is taken to account for design or inspection of structures. The residual life is estimated by integrating the fatigue crack growth rate which is a power function of the range of stress intensity factor. It is well known that the cyclic life mainly depends on slow fatigue crack growth rate near fatigue threshold, ΔKth. This paper describes the relationships between fatigue crack growth rate, da/dn, and range of stress intensity factor, ΔK. The importance of welding residual stress induced around crack tip is pointed out based on experimental results which are obtained by using center cracked transverse butt welded specimens. These experimental results show that the relationships between da/dn and ΔK for welded joints are quite similar to each other in spite of the difference in welding conditions and materials. While the relationship for welded joints is inferior to that for base metal: ΔKth for welded joints is about a quarter of that for base metal. The difference between welded joints and base metal is revealed to arise from the stress ratio effect due to the high tensile residual stress in welded joints, Finally a guide in applying the fatigue crack growth data in design or inspection of structures is furnished.
