The Effect of Welding Residual Stresses on Fatigue Crack Prapagation Rate

Abstract

The purpose of this study is to clarify the effect of welding residual stresses on fatigue crack propagation rate. Materials used are steel of 800 MPa in tensile strength. Specimens are center cracked plate and consist of four kinds: base metal, welded joint with a longitudinal bead on center of specimen, this welded joint done post heat treatment and welded joint with longitudinal beads on both sides of specimen. Results obtained are summarized as follows:
(1) Tensile residual stresses increase fatigue crack propagation rate and compressive one decrease it.
(2) The effect of residual stresses on fatigue crack propagation rate (da/dN) is more remarkable when stress intensity factor range (ΔK) is small and stress-ratio is low.
(3) When tensile residual stresses are large and ΔK is small, da/dN-ΔK relation is unique and independent of stress-ratio.
(4) Above results are closely related with fatigue crack closure phenomena.