Fatigue strength and fatigue crack initiation of steel notched plates under cyclic and random loading

Notched plates from JIS SM570Q high strength steel for welded structures were tested under cyclic and random loading. Double edge notches were machined on the specimens and stress concentration factors were 1, 2, 3 and 4. Random loading was corresponding to Rayleigh distribution of stress ranges and it was applied as randomized loading blocks. During the loading the maximum stress was kept constant and equal to yield strength thus it is considered that complex residual stresses are avoided. Fatigue crack initiation under constant amplitude loading and random loading was observed. A new damage parameter is proposed to correlate fatigue lives under random loading.