Basic model for primary and secondary creep in copper

Abstract

A model for primary and secondary creep is established. The starting point is a combination of basic models for tensile stress–strain curves and for secondary creep. The derived model can describe experimental creep strain curves for Cu 50 p.p.m. P in the temperature interval 75–250 °C with the same precision as the variation in the experimental creep strain curves for identical conditions. No fitting parameters are involved in this representation. The model has also been applied successfully to creep specimens with round notches, where multiaxial stress states are present. One main aim of deriving a basic creep model is to improve the accuracy of extrapolation. That this is possible has been demonstrated for creep tests with estimated secondary creep rates down to 5 × 10 −22 s −1. In conventional creep rupture testing strain rates down to 1 × 10 −12 s −1 can be recorded. As a background, a summary of empirical methods for the extrapolation of creep strain data is given.