13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Comparative Study on Fatigue Properties of Friction Stir Welding Joint and Lap Joint Teng Zhang1, Yuting He1,*, Qing Shao1, Haiwei Zhang1, Liming Wu1 1 Aeronautics and Astronautics Engineering College, Air Force Engineering University, Xi’an 710038, China * Corresponding author: hyt666@tom.com Abstract Friction Stir Welding (FSW) is a new type of solid-state connection which can reduce structural weight significantly. In this paper, fatigue tests and finite element analysis were employed to study fatigue properties of aerial aluminum alloy 2524-T3 FSW joint and lap joint. The S-N curves of specimens show that the fatigue strength of FSW joint is better than that of lap joint. Finite element models of two joints were established by ANSYS software. The residual stress of FSW joint were obtained by a nonlinear direct coupled-field analysis, and the detailed stress distribution of lap joint which under pulling force were simulated. On the basis of finite element analysis results, the fatigue lives of two types of joints were estimated. It is verified that the analytic and estimated results agree with that of experiment. The residual stress is the main factor affecting the fatigue life of FSW joint and the failure of lap joint is mainly caused by stress concentration of hole edge. Keywords Friction stir welding, Fatigue test, S-N curve, Finite element analysis, Lap joint 1. Introduction Friction stir welding (FSW) [1] is a new solid-state joining technology invented at the welding institute (TWI) of Britain in 1991. It is a technique well suit for joining many hard-to-weld metals without filler materials. Compared with traditional bolt or rivet jointing techniques, FSW can reduce connective weight significantly and has higher link efficiency. In order to reduce design, manufacture, and maintenance costs, FSW is applied to the fabrication of aircraft primary structures. In North America, Eclipse Aviation has developed the Eclipse 500 business jet, utilizing FSW in both wing and fuselage skin-stiffener-frame fabrication [2]. Extensive research has been carried out on FSW with the wide application of this technology. In order to improve the mechanical properties of FSW joint, many studies have been performed on welding procedure and microstructure of joint, and many researchers have explored the thermomechanical numerical simulation technology of FSW. Thermal and mechanical behaviors are mutually dependent during the FSW process. Many researchers [3-7] have simulated this process by finite element method and have obtained the distribution of residual stress, but they didn’t discuss the relationship between residual stress and fatigue life of FSW joint. Furthermore, reference [8] pointed out that the influence of residual stress on fatigue life of FSW joint is a problem need to be solved. Reference [9] has studied the fatigue properties of aerial aluminum alloy 2524-T3 base metal specimens and three different sizes of FSW joints, fatigue tests have been carried out and the S-N curves have been obtained. Although the fatigue properties of base metal specimens and FSW joints have been compared, the fracture mechanism of FSW joints has not been identified. Nowadays, structures such as skins and stringers are jointed together by bolts or rivets in most aircrafts, however, the comparative study on fatigue properties of FSW joint and bolt or rivet
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