Effects of residual stress on elastic plastic behavior of metallic glass bolts formed by cold thread rolling

Metallic glass (MG) has unique mechanical properties, combining high strength and low Young's modulus. By using MG to fabricate fasteningbolts, high resistance against bolt loosening is expected. However, MG components are considered 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 bolts 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 attempted to clarify the reasons for these characteristics, which are advantageous for bolts in terms of toughness and reliability. Various experiments and numerical analysis indicated that residual stress plays an important role in the behavior.