Effect of Load Redistribution in Transient Plastic Flow.

Creep transients are commonly described either by a change in the isotropic strength of a material due to an increase in dislocation density or by a change in directional hardening, often described by a backstress. Here we look at transients as developed by load redistribution among regions of material with differing local strength in finite element simulations. No strain hardening or backstress exists in our material description. Two types of material models are used. The first contains grains of binary strength; the other uses grains with a continuous distribution of strengths. Both 2D and 3D analyses were performed. It was found that the load redistribution process is an important source of the transients in both creep and tensile testing. An equivalent stress quantity to track the strength of a sample during deformation is proposed. Using this quantity, a single load-shedding curve can be obtained that describes both the tensile and creep tests. This unifies the material constitutive behavior for the very different boundary conditions seen in creep and fixed-rate testing. Lastly, it is shown that from this general model we can also develop realistic anelasticity and Bauschinger transients. [ABSTRACT FROM AUTHOR]