Effects of Residual Stress on Elastic Plastic Behavior of Metallic Glass Bolts Formed by Cold Thread Rolling

Abstract

Metallic glass (MG) has unique mechanical properties, combining high strength and low Young’s modulus. By applying MG to the fabrication of fastening bolts, high resistance against bolt loosening is expected. However, MG components are thought to be brittle because MG exhibits poor ductility when subjected to uniaxial loading at room temperature. We have developed hexagonal cap bolts made of zirconium-based MG by cold thread rolling. The MG bolt showed a 1.6% plastic strain with a tensile strength of more than 1550 MPa. In addition, the load-strain curve was similar to that of a strain hardening material although MG itself is free of strain hardening. In this study, we attempt to clarify the reasons for the behavior, which are advantageous for bolts in terms of toughness and reliability. Various experiments and numerical analysis indicate that residual stress plays an important role in the behavior.