Effect of friction welding conditions on joint properties of austenitic stainless steel joints by friction stud welding

ABSTRACT

This study focuses on the opening mode of induction bends; this mode represents the deformation outside a bend. Bending experiments on induction bends are shown and the manner of failure of these bends was investigated. Ruptures occur at the intrados of the bends, which undergo tensile stress, and accompany the local reduction in wall thickness, i.e. necking that indicates strain localization. By implementing finite element analysis (FEA), it was shown that the rupture is dominated not by the fracture criterion of material but by the initiation of strain localization that is a deformation characteristic of the material. These ruptures are due to the rapid increase in local strain after the initiation of strain localization and suddenly reach the fracture criterion. For the evaluation of the deformability of the bends, a method based on FEA that can predict the displacement at the rupture is proposed. We show that the yield surface shape and the true stress–strain relationship after uniform elongation have to be defined on the basis of the actual properties of the bend material. The von Mises yield criterion, which is commonly used in cases of elastic–plastic FEA, could not predict the rupture and overestimated the deformability. In contrast, a yield surface obtained by performing tensile tests on a biaxial specimen could predict the rupture. The prediction of the rupture was accomplished by an inverse calibration method that determined the true stress–strain relationship after uniform elongation.

KEYWORDS:

• Friction stud welding
• austenitic stainless steel
• friction welding conditions
• joint efficiency
• bend ductility

Acknowledgments

We would like to express our profound gratitude to Takumi Kawakami, President of Kawakami Seisakusho, for the provision of some of the test materials for this study. We are also grateful to the Fabrication Center of the Graduate School of Engineering, University of Hyogo for the fabrication and modification of the equipment used in this study. We would also like to thank Masataka Kishiguchi of the Systems Engineering Department, Engineering Faculty of University of Hyogo for his enthusiastic assistance with this study.