Estimation of Norton-Bailey parameters from creep rupture data

Abstract

It is often hard to find creep constants or extensive creep data from the literature for a specific material at a certain temperature. If data are available they are usually the results from standard creep rupture testing, i.e. rupture time and reduction of area at a given nominal stress. Two different methods are discussed for estimating the parameters of the Norton-Bailey strain rate relation from creep rupture data. The first method is based on a series expansion of the Kachanov formula for the creep rupture life at low stress levels where the brittle rupture mode is dominating. The basis for the second method is an average creep strain rate, calculated as the rupture strain divided by the rupture time. Four examples are given, where the methods are applied to published data sets for different materials. The conclusion is that both methods give fair estimates of the Norton- ailey parameters.