13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 8. Schematic diagram of FEA model The material properties of aluminum alloy 2524-T3 are shown in Table 2. Table 2. Material properties of aluminum alloy 2524-T3 Temperature(℃) 25 150 300 500 Young’s modulus(GPa) 68 60 51 38 Poisson’s ratio 0.31 0.32 0.33 0.35 Density(kg/m3) 2810 2785 2750 2708 Coefficient of thermal expansion(um/m℃) 23 25.5 29 33 Yield stress(MPa) 370 330 115 50 Tangent modulus(GPa) 23.5 22 19.8 17 Thermal conductivity(W/m℃) 120 134 146 159 Specific Heat(J/kg℃) 860 920 980 1050 The temperature rises at the contact interface due to frictional contact between the tool and workpieces. FSW generally occurs when the temperature at the weld line region reaches 70 to 90 percent of the melting temperature of the workpiece material [10]. A moving heat source was used to simulate the heat generated by friction. Meanwhile, a moving pressure of 1.5kN is applied synchronously to simulate the forging pressure of tool. According to reference [11] and [12], the heat flux density of shoulder is expressed as, 2 2 1 1 2 2 1 2 ( ) 45( ) s P R RR R q R R , (3) and the heat flux density of stirring pin is, 2(1.5 1) 45 p PR h q . (4) where, : Rotating speed of tool, : Friction coefficient, P: Forging pressure of tool, 1R: Radius of shoulder, 2R : Radius of stirring pin, h : Height of stirring pin. The boundary conditions include thermal boundary conditions and mechanical boundary conditions. On the top and side surfaces of the workpiece, convection and radiation account for heat loss to the ambient [4], the value of the convection coefficient is set as 30 W/m2℃. Conduction losses also occur from the bottom surface of the workpiece to the backing plate, and a high heat-transfer coefficient of 300 W/m2℃ is set. The workpiece is fixed by clamping plate [4], and the clamped portions are constrained in all directions. To simulate support at the bottom of the backing plate, all bottom nodes of the workpiece are constrained in the Z direction. The simulated FSW process consists of three primary phases: dwell, traverse and cool. Three load
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