Selecting a dependence for the approximation of experimental data on secondary creep and creep rupture strength

Abstract

As a rule, for the evaluation of the mechanical characteristics of a metallic material by secondary creep and creep rupture strength, tests are carried out for uniaxial tension of cylindrical specimens under the influence of a stationary axial force. These mechanical characteristics include the experimental dependence of constant strain rate on nominal stress and the experimental dependence of rupture time on nominal stress. In order not to conduct a large number of experiments, so that these mechanical characteristics can be determined at any nominal stress, one of the two empirical dependencies is used, allowing the corresponding experimental dependences to be approximated with the smallest total error. As such empirical dependences, a power dependence with two material parameters and a fractional power dependence with four material parameters are considered, two of which acquire the definite physical meaning of starting creep stress (the maximum stress at which the strain rate is zero) and break creep stress (the minimum stress at which instantaneous rupture occurs). When choosing an empirical dependence, the author used experimental data obtained by him from mechanical tests for uniaxial tension of cylindrical VT5 and VT6 titanium alloy specimens at 650 °C. The calculated total errors testify that both empirical dependences satisfactorily approximate the considered experimental data.