A unified constitutive model for strain-rate and temperature dependent behavior of molybdenum

In this paper, a constitutive model proposed by Cheng and Nemat-Nasser [Acta Mater. 48 (2000) 3131] is extended to describe both the dynamic and quasi-static stress-strain response of a commercially pure molybdenum over the temperature range 300-1100 K. Experimental results of Nemat-Nasser et al. [Acta Mater. 47 (1999) 3705; Scripta. Mater. 40 (1999) 859] suggest that molybdenum behaves plastically differently at high and low strain rates. Within the framework of the classical theory of thermally activated dislocation motion, different models and model parameters must be used for high and low strain-rate deformations, indicating that different rate-controlling deformation mechanisms may be involved. In the present paper, a unified constitutive description of the mechanical behavior of molybdenum is developed. The activation energy and the maximum strength of the local barriers to the dislocation motion, change gradually with the changing strain-rate and temperature, due to the increased solute mobility with increasing temperature. Therefore, no change in the deformation mechanism is actually included. Only the configuration of the local obstacles is assumed to change because of the change in the solute mobility. The model predictions are in good agreement with the experimental results. (C) 2001 Elsevier Science Ltd. All rights reserved.