Creep Constitutive Equations for 1CrMoV Bolt Material

Abstract

Creep constitutive equations were developed for 1CrMoV bolt material using the NRIM creep data at temperatures of 450°C, 500°C and 550°C. The creep constitutive equations were those used by the ANSYS FEM stress analysis program. Three types of creep equations were developed: (1) primary, (2) secondary, and (3) primary plus secondary. The primary creep equation had a power law in stress and time with an exponential inverse temperature dependence. The secondary models for log minimum creep rate had either log stress alone or stress and log stress terms. Two primary plus secondary models were used: (1) a power law primary and (2) the rational polynomial. For the rational polynomial, the constant p was estimated as nineteen over the time to the end of primary creep. The time to end of primary creep was defined by the attainment of a low value for the ratio of the primary creep rate to minimum creep rate. The primary creep rate was calculated using the power law primary component of the power law primary plus steady state creep equation. To evaluate the fits, comparisons of calculated and observed creep curves were made as well as plots of residual in log creep strain. Based on these comparisons and the statistical measures (R2 and standard deviation), the derived creep equations were judged to be a good description of the creep behavior.