PSI - Issue 46

Gaurav Singh et al. / Procedia Structural Integrity 46 (2023) 149–154 Gaurav Singh et al. / Structural Integrity Procedia 00 (2021) 000–000

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Fig. 4. Residual stress at varying die angles for a feed rate of (a) 1.25 m /min and (b) 2 m/min from surface to centre of Zr-4 alloy.

It was observed that beyond the die angle of 10 o , there is a pattern of irregular deformation. The results are not consistent beyond this die angle, and the mechanical properties are abnormal. Moreover, when observed in the simulation window, irregular deformation has occurred as the billet slipped outwards on each iteration and never got into the deformation zone. 4. Discussion The residual stress observed across different die angles, and feed rates followed a similar trend of being compressive at the surface and became tensile at the center of the billet. Moreover, it can be concluded from the plots that samples produced with a 1.25 m/min feed rate exhibit lower residual stresses over samples produced at 2 m/min at the same die angle. Among all the die angles, the die with a die angle of 4 o has the least tensile residual stress at the center and more compressive residual stress at the surface. Hence, it is the best choice for carrying out an experimental test to validate the simulation results. The horizontal axis plots at the surface and center of the test sample produced with a die angle of 4 o and a feed rate of 1.25 m/min are plotted in Fig. 5, respectively. It can be observed that the residual stresses values are consistent across the axial (length) of the billet sample. The samples beyond the die angle of 10 degrees have irregular deformation. They do not enter into the deformation zone. It keeps sliding on each iteration, making it a bulged irregular shape unsuitable for post-processing with these samples. A possible explanation for this behavior is the shift of the neutral plane beyond the deformation zone, leading to the load applied is distributed more on the horizontal axis. There is not enough resisting force to keep the billet moving inwards into the dies. For further studies, the frictional coefficient could be varied to evaluate this behavior as increasing the frictional coefficient between the die and billet would enable the billet to stay inside the dies at increased die angles of 12 and 14 o .

Fig. 5. Residual stress along the length of the billet at centre and surface of axis for 4o die angle at 1.25 m/min feed rate