Intergranular fracture during power-law creep under multiaxial stresses

Abstract

Approximate methods are used to calculate the growth of grain-boundary cavities by power-law creep, under multi axial stress states. The time to fracture at constant stress is given by t f =t n+ɑ/n+1)εss1n(1/(n+1)f i )where t n is the nucleation time (the time at which the voids first appear), εss is the steady-state creep rate, n is the creep exponent and f i is the original area fraction of cavities. The quantity α is defined by:ɑ=1/sinh-{2(n-½)/(n½)P/σe}where p is the hydrostatic pressure and σe the von Mises equivalent stress. Differential equations are given which allow the times and the strains to failure under variable loading histories to be calculated.