Strain Rate Dependence of Stress-Strain Curves in a Ti-Fe-O Alloy

Quantitative expression of stress-strain curve including strain rate dependence in a Ti-Fe-O alloy was studied at temperatures between 77 and 293 K. In order to evaluate the strain-rate-independent component, in the first place, the authors endeavored to obtain the stress-strain curve as the curve at 0 strain rate through relaxation tests under constant crosshead displacement. The relaxation-saturated stress-strain points made a single curve. The authors named this single curve as "Base Curve". The Base Curve was good fitted to the Swift's equation in the following form: σBase(ε)=A(ε+b)n, where σBase(ε) is the stress on the Base Curve, ε the plastic strain, n the exponent, and A and b are coefficients. The stress-strain curves at the strain rate between 2.8×10-5 and 3.0×10-2 s-1 were parallel to the Base Curve. Namely, the strain-rate-dependent component, σ*, was independent of strain at a constant strain rate. The relation between σ* and strain rate, γ, was expressed in the following form: σ *=Bγm, where B coefficient and m exponent. Finally, the equation, σ=A(ε+b)n+Bγm, is derived for the expression of flow stress-plastic strain relation under the deformation at a constant strain rate.