Intergranular fracture during power-law creep under multiaxial stresses

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)ε_ss1n(1/(n+1)f _i )

where t _n is the nucleation time (the time at which the voids first appear), ε_ss 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/σ_e}

where p is the hydrostatic pressure and σ_e 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.