24.2.1 Temperature Measurement The thermal history and the temperature field have been acquired during welding by the infrared camera NEC H2640 (Range 0–2,000 C; Resolution 0.06 C; Accuracy 2 C or 2 %). In Fig. 24.1, the specimen painted with matte black acrylic spray paint is shown. The coating reduces the reflection of the aluminium and increases the emissivity of the surface (ε ¼0.95 after painting). Figure 24.2 shows the experimental setup. The infrared camera has been placed in front of welding machine, normal to the weld direction with an angle of 30 between the optical axe of the camera and the normal direction at the aluminium sheet. 24.2.2 Numerical Model To describe the FSW thermal history, a three-dimensional transient thermal analysis has been developed using the finite elements commercial code ANSYS 14.5. Due to the symmetry of the problem, just a half plate model has been implemented, in order to decrease the elements number and reduce computational time. The model has been meshed using 6000 SOLID90 elements [26]. In order to describe more accurately the thermal behavior near the tool area, to take into account the higher gradient of temperature, a thicker mesh has been used near the plane of symmetry (Fig. 24.3). Fig. 24.1 Bead on plate welding and clamping system Fig. 24.2 Experimental setup 24 Temperature Field in FSW Process: Experimental Measurement and Numerical Simulation 179
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