様々な金属材料を用いた断続引張試験と Bridgman の式による破断直前までの真の応力-ひずみ関係の推算

Abstract

True stress (σ)-true strain (ε) relationships until just before fracture, i.e., the plastic deformation limit, were estimated by the stepwise tensile test and the Bridgman equation for various metals and alloys with different crystal structures. The estimated σ-ε relationships were different from the nominal stress-strain curves including the conventional tensile properties. In the relationships between the true stress (σpdl) and true strain (εpdl) at the plastic deformation limit, SUS304 and SUS329J4L indicated a better σpdl-εpdl balance. On the other hand, SUS329J4L, tempered martensite, and an ultrafine-grained steel showed superior results in the yield strength-εpdl balance. The estimated σ-ε relationship for the ultrafine-grained steel suggests that grain refinement strengthening can improve σ and ε up until the plastic deformation limit. The value of εpdl became larger with increasing the reduction in area and a decrease in the fracture stress. The products of σpdl and εpdl became larger with increasing work-hardening rate at the plastic deformation limit.