Simulation of residual stress and fatigue strength of welded joints under the effects of ultrasonic impact treatment (UIT)

• A novel 3D numerical model to simulate UIT process for weld joints is developed.
• Ultrasonic impact and ultrasonic softening effect are considered in the FE model.
• The residual stress prediction before and after UIT are verified by experiments.
• A fracture mechanics based method is employed to predict fatigue strength.
• Effects of stress ratios and preloads on fatigue strength are simulated.

Ultrasonic impact treatment (UIT) is a remarkable post-weld technique, which applies mechanical impacts in combination with ultrasonic oscillations into welded joints introducing plastic deformation and beneficial compressive residual stress in the region of the weld toe. In this study, a novel 3D numerical analysis approach including thermo-mechanical welding simulation and dynamic elastic-plastic FE analysis of ultrasonic impact treatment process for welded joints is proposed. In the FE model, the actual process parameters and ultrasonic-induced material softening, which is appropriately adjusted to fit experimental results, are considered. The predicted residual stress distributions of a non-load-carrying cruciform joint before and after UIT are compared with experimental results, showing a fairly good agreement with each other. In addition, an evaluation of fatigue strength of welded joints based on fracture mechanics is carried out. The results not only clearly distinguish the fatigue strengths of as-weld and UIT processed weld joints, but also show the effects of preloads and stress ratios, so that the proposed solution method may provide an effective tool to simulate UIT process in engineering structures.