Abstract
Most structures have a region where stresses concentrate, and the probability of fatigue crack initiation may be higher than in other parts. Therefore, to improve the reliability of an LBB (Leak Before Break) design, it is necessary to evaluate the growth and through thickness behavior of fatigue cracks in the stress concentration region. In this paper, fatigue crack growth behavior in a stress concentration region has been studied on 3%NiCrMo and HT80 steels. Stress concentration was caused by a fillet on the plate. The main results obtained are as follows. (1) Before cracking through the plate thickness, stress concentration has a remarkable effect on the fatigue crack growth behavior and it flattens the shape of surface crack. The crack growth behavior can be explained quantitatively by using the Newman-Raju formula and the stress resolving method proposed by ASME B&P Code Sec.XI. (2) The da/dN-ΔK relation obtained in a stress concentration specimen shows good agreement with that obtained in a surface-cracked smooth specimen. (3) The stress concentration caused by a fillet has little effect on the crack growth rate after cracking through the plate thickness. (4) By using the K value based on Eqs. (1) and (2), particular crack growth behavior and the change in crack shape after cracking through thickness can be explained quantitatively.
