The constitutive equations of continuum creep damage mechanics

Abstract
When metals are subjected to stress at temperatures in excess of about one third of their melting temperature, it is found that they deform continuously and that they can sustain the stress for a limited time referred to as the rupture life. Constitutive equations are proposed which describe the macroscopic behaviour of metals when subjected to multiaxial states of stress. In these constitutive equations it is necessary to introduce the concept of an internal state parameter w referred to as the damage parameter. It is shown that under certain loading conditions this damage parameter is a normalized form of the actual physical damage which is defined as the integral of nucleation and growth rates of voids which grow on the grain boundary. The constitutive equations are used to determine the characteristics of certain load-bearing components operating at temperature. It is shown that the reference rupture stress and the isochronous rupture surface are the material properties which are responsible for component performance.