Dimensional transitions in creeping materials due to nonlinearity and microstructural disorder

Abstract

Abstract The transition from extremely brittle to very ductile behaviours of creeping materials is discussed, where analogies with power-law hardening materials are pointed out. Considering Norton's Law as a viscous constitutive law, it is possible to define a generalized stress-intensity factor Kc ―characterizing the intermediate asymptotic behaviour under steady-state creep conditions― with physical dimensions depending upon the Norton stress exponent n. In the two limit cases of creep resistant materials (n≅1) and creep sensitive materials (n ≫ 1), Kc assumes respectively the dimensions of an elastic stress-intensity factor ( F L − 3 / 2 ) and of a stress ( F L − 2 ). Such a dimensional transition, with consequent stress-singularity attenuation, is completely analogous to that occurring through the introduction of a fractal stress-intensity factor (Kc)*, when the influence of microstructural disorder is considered.