Multiaxial Creep Equations for Nonlinear and Volume-Nonconservative In-Reactor Creep

Stress state dependence of in-reactor creep and swelling

“…The constitutive equations developed here provide a phenomenological model that is consistent with the early experimental observation of Hall [11] that a deviatoric stress can affect volumetric creep (stress-affected swelling) in the absence of a hydrostatic stress. The equations moreover predict that both deviatoric and volumetric components of irradiation creep each are functions of both deviatoric and hydrostatic invariants of stress for both linear and non-linear creep.…”

“…Derivation of a volumetric creep equation that is a function of the deviatoric stress in the absence of a hydrostatic stress component can be accomplished phenomenologically by extending Hall's effective stress expression [11] to include a term that couples deviatoric and hydrostatic stress invariants:…”

“…The principles of continuum plasticity, sometimes guided by mechanistic models, previously have been used [9][10][11] to derive multiaxial constitutive equations for neutron irradiated materials undergoing void swelling. By analogy to the multiaxial stressstrain equations for linear elastic behavior, Wire and Straalsund (WS) [10] developed a multiaxial, linear creep equation that includes stress-affected swelling.…”

“…Hall [11] extended the WS equations to include non-linear creep of a material undergoing stress-free and stress-affected void swelling. Using microstructural modeling estimates of equation parameters, obtained from the work of SGW [8], the predicted effects of stress state triaxiality, stress exponent and plastic Poisson's ratio on deviatoric strain rate were explored parametrically.…”

Stress state dependence of in-reactor creep and swelling. Part 2: Experimental results

“…Constitutive equations capable of describing such effects were first proposed in 1979 by Hall [8]. Hall that the deviatoric and stress-affected swelling components each are functions of both deviatoric and hydrostatic components of stress, but only for non-linear creep and a mixed stress state having both deviatoric and hydrostatic stress components.…”