Vibration residual stress relief and acoustic emission in resistance spot welded joints of advanced high-strength steels

It is well established that tensile residual stresses have a detrimental impact on components, as they promote crack nucleation and propagation. In welding processes, these stresses arise primarily due to contraction and phase transformation phenomena. Innovative stress-relief techniques, such as vibration stress relief, have been developed. During this process, acoustic emissions are detected as stresses are relieved. Resistance spot welding and Advanced High-Strength Steels, such as Complex Phase and Dual Phase steels, are widely employed in the automotive industry. This study aimed to investigate the vibration-induced residual stress relief in CP1000 and DP1000 resistance spot welded joints using X-ray diffraction and statistical analysis, while correlating the stress relaxation with acoustic emissions. In addition, microstructural characterization through optical and scanning electron microscopy, as well as Vickers microhardness analysis, was performed to assess the effects of the welding process on the welded joints. The results revealed a mean reduction of residual stresses of 43% in the analyzed samples. Statistical analysis using Analysis of Variance (ANOVA) indicated a statistically significant effect of the material and vibration condition factors (p < 0.05). Furthermore, real-time acoustic emission monitoring showed a strong correlation between acoustic emission activity and stress relief efficiency, indicating the feasibility of vibration-based stress relief monitoring via acoustic emission.