X-Ray Fractography on Fatigue Fracture Surface Formed by Crack Propagation in Initial Tensile Residual Stress Field

Abstract

Fatigue tests were performed using CCT specimens having initial tensile residual stress caused by welding. The residual stress distribution on the fatigue fracture surface was measured by X-ray diffraction method. The monotonic plastic zone depth corresponds to the K_{max, true} which is the sum of the K_max related to the applied maximum stress and the K_res caused by the initial residual stress. So, if the initial residual stress distribution is known, the K_max or the applied maximum stress can be estimated from the monotonic plastic zone depth. The residual stress on the fatigue fracture surface corresponds to the sum of the tensile residual stress related to the K_{max, true} and the compressive residual stress related to the ΔK_eff. So, even if the initial residual stress distribution is unknown, the ΔK_eff or the stress amplitude can be estimated from the residual stress on the fatigue fracture surface and the monotonic plastic zone depth.