Real‐time measurement of welding residual stress relaxation based on strain‐controlled fatigue test

Abstract Fatigue‐induced variation of residual stress (RS) in welded joints is inevitable and has significant influence on fatigue behavior. The widely used technologies (e.g., X‐ray diffraction) can only test surface RS of specimen at unloading or certain holding load condition. In this study, an approach of measuring equivalent RS in real time during fatigue cycling is proposed based on strain‐controlled fatigue with strain ratio of −1. Under applied waveform starting with tensile strain, tensile RS in a welded joint continuously relaxes with fatigue cycles, but compressive RS first increases then relaxes. Both tensile and compressive RSs rapidly change in the first few cycles and then gradually relax to a steady state in which accumulated plastic strain is linearly correlated to amount of RS relaxation during fatigue cycling.