부산대학교 도서관

The strain-rate sensitivity exponent m and activation volume υ∗ are often used to characterize the strain-rate sensitivity of strength behavior in metals and alloys. Complications can arise when the m and υ∗ values become indeterminate, due to factors such as an inherent scatter in the mechanical property data. The study of commercial Ti-alloy wires is considered wherein to overcome this limitation, the formulation of the Kocks–Mecking (K–M) model is modified to provide a parameter cb that characterizes the microstructural scale responsible for the observed plasticity and work hardening behavior. The softening factor cb is found to be independent of strain-rate for the Ti-alloy wires of this study. It is proposed that cb !can offer a versatile and complementary computation to the activation volume υ∗ since its formulation includes the yield and ultimate strength values along with the plastic strain. For the tensile testing of Ti-alloy wires, a low cb-value of 14 is calculated for Ti-6Al-4V that is consistent with >10 % plasticity during work hardening whereas a high cb-value of 135 for Ti-6Al-7Nb corresponds with