Dislocation-based length-scales in crystal plasticity: Experiments and modeling

Considered is a dislocation-based plasticity model that includes both temperature- and strain-rate effects, and heavily draws from a body of experimental data on various metals over broad ranges of strain rates, from quasi-static to 10(4)/s and greater, and temperatures from 77 to 1,300K and greater. In this model, the role of the strain gradient is embedded in the nature of the dislocations, their density and distribution, and the manner by which they produce slip in crystal plasticity and affect the overall flow stress. The model includes length scales that are directly related to the dislocation densities and hence change with temperature and the strain-rate histories. The model can be used to calculate the force-deformation relations at micron to continuum dimensions. For plastic deformation of small polycrystalline samples involving only a few grains, geometric and textural incompatibilities will most likely manifest themselves through a size effect, and may affect the overall materials' resistance to deformation (flow stress). This size effect is distinguished from the length scales in plasticity, and the size effect is viewed as a problem-dependent phenomenon. For a few interacting crystals, the proposed model of slip-induced crystal plasticity should adequately account for any such size effects.