Fatigue Crack Propagation in Welded Joints under Random Loading

Abstract

Fatigue crack propagation properties of welded joints under random loading were investigated in air and synthetic sea water. The fatigue crack closure did not occur for whole excursion of loading, because the stress ratio around crack tip became high due to the tensile residual stresses around crack tips. That is, the applied range of stress intensity factor coincided with the effective range of stress intensity factor. The fatigue threshold in synthetic sea water was about a half of that in air. The fatigue crack propagation rates under random loading could be well estimated by the results obtained from constant amplitude tests assuming a linear cumulative damage law. That is da/dn=C{ΔK_eq^m-ΔK_th^m}, where ΔK_eq={Σ(ΔK_i^m·n_i)/Σn_i}^1/m, n_i=0 at ΔK_i≤ΔK_th or n_i=n_i at ΔK_i>ΔK_th.