br Results and discussion Fig a depicts

Results and discussion Fig. 2(a) depicts the computed temperature distribution during FSW of AA2014-T6 using a regular triangular pin. The region heated above 600 K, which is nearly 0.8 times the solidus temperature of the workpiece material, is represented in red color and presumed to be the softened zone to primarily experience the traction by the rotational motion of the tool pin. The size of the high temperature region is wider underneath the shoulder and tends to reduce along the length of the pin in the thickness direction. This can be attributed to higher rate of frictional heat generation along the shoulder-workpiece interface in comparison to the same around the surfaces of the tool pin. The rate of frictional heat generation on the vertical surface of the pin is slightly higher than that Bafilomycin A1 on the bottom surface due to larger surface area of the former. Similarly, Fig. 2(b)–(d) depict the computed temperature distributions for the regular square, pentagon and hexagon pins, respectively. A comparison of Fig. 2(a)–(d) depicts an increase in the high temperature region, which is above 600 K, in the vicinity of the pin vertical surface with the increase in the number of pin sides that is attributed to the increase in the rate of frictional heat generation along the pin vertical and bottom surfaces. Fig. 3(a)–(d) depict a comparison between the numerically computed and experimentally measured thermal cycles during FSW of AA2014-T6 using a regular triangular, square, pentagon and hexagon pins, respectively. The increase in the peak temperature from the triangular pin profile towards the hexagon pin profile is attributed to the enhanced rate of frictional heating around the pin vertical and bottom surfaces with the increase in the number of pin sides. Overall, a fair agreement between the computed and corresponding measured thermal cycles can be noted in Fig. 3. The slight deviation between the computed and corresponding measured thermal cycles may be attributed to the neglect of heating due to mechanical deformation and the presumed thermophysical properties of AA2014-T6 (Table 3). Fig. 4 depicts the variation in the computed peak temperature for four different regular polygonal pins. It is noted that the peak temperature increases with the increase in the number of pin sides from the triangular pin to the hexagon pin. Higher number of pin sides increases the overall pin-workpiece contact area, resulting in greater rate of frictional heat generation, in particular, on the pin vertical surfaces, which leads to a higher peak temperature. Fig. 5(a) and (b) depict a comparison between the analytically estimated and corresponding experimentally measured torques and traverse forces, respectively, for four different regular polygonal pins. The total torque remains nearly unchanged while the traverse force decreases with the increase in the number of sides from the triangular pin to hexagon pin. For a given shoulder diameter and pin circumradius (c), the increase in the number of pin sides reduces the shoulder-workpiece contact area while increases the pin-workpiece contact area, resulting in a nearly steady tool torque. However, the increase in the number of pin side enhances the rate of frictional heat generation and the resulting softening of a greater amount of deformed material around the pin surfaces, leading to the decrease in traverse force. A fair agreement between the computed and corresponding measured torques and traverse forces for various regular polygonal pins can be noted in Fig. 5. Fig. 6(a) depicts the estimated variations in the components of mechanical stresses (σB, τB, τT and τmax) experienced by FSW tool with triangular pin at different orientations (ξ) during one complete rotation. The values of σB, τB, τT and τmax at 30° are estimated for the regular triangular pin, as indicated in the plot of τmax for clarity. The analytically evaluated values of σB, τB, τT and τmax indicate the apparent trend of the component of stresses during one complete rotation of the tool. Fig. 6(a) shows hydrogen bond τT is constant for all values of ξ while σ is the highest and lowest at ξ = 60° and 240°, respectively, and τB assumes multiple occurrences of low and high values during one complete rotation of the tool pin. The resultant maximum shear stress, τmax, is the highest at ξ = 120° and 180° where τB is at its maximum and the component of τT along τB is in the same direction as that of τB. In contrast, τmax, is the minimum at ξ = zero and 300° where τ is also the maximum while the component of τT along τB is in the opposite direction as that of τB. The estimated maximum value of τmax is 581.76 MPa for the regular triangular pin. Fig. 6(b) depicts the estimated results of the largest magnitude in τmax for four different regular polygonal pins for the welding conditions considered here. The largest magnitude of τmax reduces from the triangular pin profile to the hexagon pin profile, which is attributed to the enhanced structural stiffness and the decrease in traverse force with an increase in the number of pin sides.