Creep deformation in modified 9Cr-1Mo steel - dynamical systems approach to prediction of creep properties

Abstract

In a recent publication it has been suggested that creep deformation can be described as a dynamical system, using the equation (dS/dt) + ωS=0 where S is the strain rate at time t and ω is a damping coefficient. The damping coefficient was found to be a function of strain rate and time, and a procedure was described by which the creep curve could be analysed to determine the various constants in the dynamical systems equation. However, while this procedure may produce a good description of individual creep curves, for it to be useful it is necessary that the constants be predictable for any combination of temperature and stress. It has been found that for a modified 9Cr-1Mo steel, whose creep properties have been considered elsewhere, the stress and temperature variations of the constants in the dynamical systems equation are complex. These variations have been discussed, but the complex nature of the variations, combined with the relatively small number of test results make a detailed explanation and extrapolation to low stresses, difficult for the present limited set of data. However, it is considered that the results show sufficient promise to suggest that further work on this and other alloys, may produce a viable mathematical model for creep deformation.