The present work aims at investigating the effect of shot peening on the fatigue behaviour of welded joints made of advanced high-strength steel with a tensile strength of 600 MPa. Uniaxial fatigue tests were conducted on double lap welded joint specimens with both as-welded and shot-peened conditions for two loading ratios of 0.1 and − 1 . These tests were complemented by X-ray diffraction analyses and roughness measurements. The fatigue test results indicate that shot peening improves the fatigue strength of welded specimens, especially at R = − 1 . The beneficial effect at R = 0 . 1 is reduced because of the redistribution of the residual stresses induced by cyclic plasticity. The effects of residual stresses, work hardening and surface roughness on the fatigue strength were estimated separately by comparing the results obtained for heat-treated and preloaded specimens. According to the results, the generation of compressive residual stresses by shot peening is the major factor controlling the fatigue strength of lap joints. The effects of work hardening and surface roughness are negligible. To consider the effect of shot peening on the fatigue resistance, a numerical approach is proposed. The methodology includes a non-local multiaxial fatigue criterion that, when coupled with a S-N relationship, makes it possible to estimate the number of cycles to failure. The model successfully captures the beneficial effect of shot peening in the vicinity of the weld toe. The final result is a master S-N curve adapted to the fatigue design of double lap welded structures, tested under different loading conditions.
NABARA et al. (Fri,) studied this question.