A viscoplastic theory is developed that reduces analytically to creep theory under steady-state conditions. A viscoplastic model is constructed within this theoretical framework by defining material functions that have close ties to the physics of inelasticity. As a consequence, this model is easily characterized—only steady-state creep data, monotonic stress-strain curves, and saturated stress-strain hysteresis loops are required. The model is applied to the copper alloy NARloy Z.

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