Density measurements as an assessment of creep damage and cavity growth

The change in density during creep of several polycrystalline metals may be correlated through the expression —Δρ/ρ =B(∈t/d)(σ/G)^q exp (—Q _gb /RT) where —Δρ is the density change, p is the original density, e is the strain,t is the time,d is the linear intercept grain size,σ is the applied stress,G is the shear modulus,Q _gb is the activation energy for grain boundary diffusion,R is the gas constant,T is the absolute temperature, andB andq are constants withq ≃2 to 3. This expression is consistent with the theory of unconstrained grain boundary diffusion growth of cavities provided there is also concomitant strain-dependent nucleation. The expression does not support the power-law growth of cavities, growth by surface diffusion, or constrained grain boundary diffusion growth. Formerly Research Associate, University of Southern California.