A Phenomenological Model for Transient Deformation Based on State Variables

The state variable theory of Hart, while providing a unified description of plasticity-dominated deformation, exhibits deficiencies when it is applied to transient deformation phenomena at stresses below macroplastic yielding. It appears that the description of stored anelastic strain is oversimplified. Consideration of a simple physical picture based on continuum dislocation pileups suggests that the neglect of weak barriers to dislocation motion is the source of these inadequacies. An appropriately modified description incorporating such barriers allows the construction of a modified phenomenological model including transient effects. The applicability of the modified model to aluminum has been investigated at room temperature. A consistent set of parameters describing the mechanical properties of the material has been determined experimentally. Agreement between experiment and model predictions for fairly complex loading histories is good. Although the constitutive equations for microplastic flow could not be established unambiguously, the results indicate that the general structure of the transient deformation model represents the deformation properties well.