Effect of viscoplastic relations on the instability strain, shear band initiation strain, the strain corresponding to the minimum shear band spacing,and the band width in a thermoviscoplastic material

We study thermomechanical deformations of a steel block deformed in simple shear and model the thermoviscoplastic response of the material by four dif ferent relations. We use the perturbation method to analyze the stability o f a homogeneous solution of the governing equations. The smallest value of the average strain for which the perturbed homogeneous solution becomes uns table is called the critical strain or the instability strain. For each one of the four viscoplastic relations, we investigate the dependence upon the nominal strain-rate of the critical strain, the shear band initiation stra in, the shear band spacing and the band width. It is found that the qualita tive responses predicted by the Wright-Batra, Johnson-Cook and the power la w relations are similar but these differ from that predicted by the Bodner- Partom relation. The computed band width is found to depend upon the specim en height. (C) 2001 Elsevier Science Ltd. All rights reserved.