Numerical study on local residual stresses induced by high frequency mechanical impact post-weld treatment using the optimized displacement-controlled simulation method

Abstract

The High Frequency Mechanical Impact (HFMI) treatment is a reliable, effective, and user-friendly post-weld technique for fatigue life enhancement of welded structures. The working principle for HFMI can be characterized by impacts from cylindrical indenters with a high frequency which introduces the local work hardening and high compressive residual stresses (RS) and reduces the stress concentration at the weld toe. These beneficial effects are needed to be considered in the fatigue assessment and design of those HFMI-treated structures. This study proposes a multi-process numerical simulation model to estimate local RS and improved shape profiles induced by HFMI treatment in welded joints. Firstly, the welding simulation is performed by thermal-elastic-plastic finite element (TEPFE) analysis using a coarse finite element (FE) mesh model. The zooming technique is then applied to transfer simulated as-welded RS to the ultra-fine mesh used in HFMI analysis as initial stresses. Finally, the numerical analysis of HFMI-induced RS is carried out using the optimized displacement-controlled numerical simulation method. An HFMI-treated out-of-plate gusset welded joint specimen was fabricated using SM490 steel. The surface topography for the treated zone, RS before and after the HFMI process, and thermal cycles during the welding process were experimentally investigated to calibrate and validate the proposed simulation approach. Both simulated local deformed shape profiles and RS were in good agreement with the measurements. In this paper, the recommendations for FE modeling and the procedures for determining HFMI analysis parameters were discussed in detail.