13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- Figure 1. Schematic scheme of Friction Stir Welding 2. Material, specimen and method The crack propagation tests were conducted, in accordance to the procedure in ASTM E647-08[6] standard test method. Sheet of 2024-T3 with a thickness of 2 mm were joined by FSW to form a butt joint. It is fabricated by Japanese aircraft manufacturer. The situations of Base metal panels and FSW panels are shown as Figure 2. Table 1 shows the list of specimens. All specimens have a center hole and notches as the initial flaw. All FSW panels have been welded by same welding procedures. So the level of residual stress is presumed to become same as each FSW panels. Figure 3 shows the result of measuring the residual stress in the vicinity of the weld line. The crack growth test is subject to cyclic load with stress range: = 25, 50, 75 MPa, stress ratio: R = 0.1 and load frequency: f = 5 Hz. The crack length was measured using a CCD camera. And we have installed the extensometer on specimens to measure crack opening displacement in order to evaluate the crack opening stress based on the compliance method which is improved by Chung et. al.[7]. In this test, the displacement above and below the hole was measured by an extensometer; the crack opening stress was determined on the basis of the change in the compliance of the specimen. We had installed the extensometer with bolts. In this study, the extensometer has been installed with modified tools. The modified tool is jig to mount the extensometer to the specimen with magnets. Table 1. The list of specimens No. Base metal or FSW panel Specimen size stress range MPa 1 Base metal Large size 50 2 Small size 25 3 FSW panel Large size 75 4 Large size 50 5 Small size 25 Pressure Stir Rod Direction of the welding Rotation
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