Most structures are fabricated using welded joints because of its low cost, structural strength and geometric flexibility. Welding is considered a highly complex metallurgical process that results in irregular geometries, material imperfections/flaws and tensile residual stresses. High tensile residual stresses and stress concentrations resulting from the weld process have a significant impact on fatigue life of structures, and thus a topic of great concern in product design. Ultrasonic impact treatment (UIT) is regarded as one of the most effective post welding treatment techniques to enhance the fatigue performance of welded structures. The UIT aims to introduce fatigue-beneficial compressive stresses by plastically deforming the weld toe and reduce stress concentrations by modifying local weld geometries. In this study, 3D modeling and simulation using finite element (FE) method has been performed to simulate welding process and numerical modeling of the UIT process to predict weld residual stress distribution of butt and T weld joints. The predicted numerical results under as-welded and UIT treatment conditions were compared to present weld residual stress improvements. Compared results shows that the UIT has potential applications on the fatigue design of welded structures, can lead to lighter structures and products, in which structures can be down-sized and optimized to reduce weights.

Introduction

Welding technology has been widely applied in the fields of automobile, aviation, nuclear, vessel manufacturing and other industrial sectors due to its low cost, geometrical flexibility and desirable mechanical properties [1]. On the other hand, welding comes with the expense of some detrimental effects on welded structures such as microcracks/flaws, high stress concentration and tensile residual stresses. Hence, from the point view of fatigue design, welded areas are deemed as weak structural joints where cracks and tensile residual stresses are easily to be found [2]. Over the past several decades, numerous post-weld treatment techniques, including grinding, TIG dressing, hammer peening and shot peening, have been developed to address this vexing issue and improve fatigue performance of weld joints, [3]. These treatments are generally classified into two different categories: geometry improvement and residual stress modification techniques. Geometry improvement techniques such as TIG dressing and grinding focus on eliminating flaws and reducing stress concentration of welded components. While residual stress modification techniques like hammer peening and shot peening lay emphasis on introducing beneficial compressive residual stresses and improving residual stress distributions of welded joints[4]. Ultrasonic impact treatment (UIT) is a recently developed treatment technique by Statnikov et al. in former Soviet Union [5].