13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Property for Fatigue Crack Propagation of Friction Stir Welded 2024-T3 Aluminum alloy Masakazu Hirose1,*, Motoo Asakawa2, Takao Okada3, Shigeru Machida3, Toshiya Nakamura3, Shuji Kishishita4, Kazuya Kuwayama5, Shinya Fujita5, Takuya Noguchi1 1 The Graduate School of Science and Engineering, Waseda University, Tokyo 169-8555, Japan 2 Department of Applied Mechanics and Aerospace Engineering, Waseda University, Tokyo 169-8555, Japan 3 Japan Aerospace Exploration Agency, Tokyo 181-0015, Japan 4Advanced Engineering Services, Tsukuba 305-0032, Japan 5 Alumnus of the Graduate School of Waseda University, Tokyo 169-8555, Japan * Corresponding author: m_hirose1989@ruri.waseda.jp Abstract In this study, crack propagation tests were conducted to clarify property for the fatigue crack propagation of Friction Stir Welded (FSW) 2024-T3 aluminum alloy. FSW panel has residual stress around weld line and the longitude residual stress is higher around it. The peak tensile residual stress is about 180 MPa in this case. To understand fatigue crack growth property on FSW panel, crack opening stress measurement of the base material and FSW joint using an extensometer with the modified tool is also conducted during the crack growth test. The modified tool is jig to mount the extensometer to the specimen with magnets. The test results indicate that the accuracy of crack opening stress measurement is improved. In addition, the crack growth acceleration and decelerate around the FSW line under the low applied stress range (25 MPa) is bigger than that under high applied stress range (50 MPa). This means the effect of residual stress under low stress range is relatively larger than that under high stress range. Keywords: Friction Stir Welding, Fatigue Crack Growth Propagation, Residual Stress, Crack Opening Stress 1. Introduction Friction stir welding (FSW) is one of recently developed welding process[1] as shown in figure 1. It has the capability of welding high strength Aluminum alloys of 2xxx and 7xxx type which are difficult to weld by conventional welding. FSW has applied many structures such as trains, rockets and ships. From point of reducing production cost and structural weight, FSW is expected to be applied to commercial aircraft primary structures as an alternative to riveted joints. FSW was firstly used on a normal category aircraft “Eclipse 500” by Eclipse Aviation in 2006. However, the safety factor of FSW joint is estimated high in this aircraft. So far the study of FSW has been not sufficient to meet a damage tolerance. The Federal Aviation Regulations (FARs) on damage tolerance and fatigue evaluations of aircraft structures require understanding of the locations of fracture origin and the fatigue crack propagation property of the materials for aircrafts. To apply the structures jointed by FSW on aircrafts, the investigation of relationship between fatigue crack propagation property and residual stress on FSW panel is particularly significant. In case of FSW, the fatigue crack propagation rate is accelerated by the tensile residual stress around weld line as a result of non-uniform deformation caused by welding heat. Therefore, the explanation is required to determine an effect of residual stress on the crack propagation in the FSW panel. The aim of this study is to accurately evaluate the crack growth rate on FSW panel. The significance of this study is to focus on the crack opening stress to predict crack growth rate on FSW panel. Our final goal of this research is to accurately predict the crack growth rate using FEM analysis. To achieve this goal, we have conducted the crack growth test[2-5]. In this paper we report the crack growth test results of the FSW panel with different applied stress and crack opening stress of the base material and FSW joint using an extensometer with the modified tool.
RkJQdWJsaXNoZXIy MjM0NDE=