This paper describes the effect of the welding residual stress on the fatigue strength of welded joint. The fatigue strength was measured on Aluminum alloy, mild and stainless steels under the condition that the factors affecting the fatigue strength of welded joint were not changed except the residual stress produced by electron beam welding. When the residual stress at the initiation area of fatigue was compressive and did not vanish during the fatigue test, the fatigue strength was improved. When the tensile residual stress existed at the fatigue initiation area, the following two cases appeared: The fatigue strength of a non-quench hardening material as well as that of a quench hardening material with high ductility and low yield ratio were not influenced by the tensile residual stress. However, the fatigue strength of a quench hardening material with poor ductility and high yield ratio was lowered by the tensile residual stress.
