A re-formulation of the exponential algorithm for finite strain plasticityin terms of cauchy stresses

The role of the stress measure to be chosen as the argument in the definiti on of yield functions is discussed in the context of finite strain plastici ty theory. Motivated by physical arguments, the exponential algorithm for m ultiplicative finite strain plasticity is revisited such that Cauchy stress es are adopted as arguments in the yield function. Using logarithmic strain measures, the return map algorithm is formulated in principal axes. The al gorithmic tangent moduli are obtained in a slightly modified, unsymmetric f ormat compared to the standard formulation in terms of Kirchhoff stresses. However, the global structure of the exponential algorithm is unchanged. Th e algorithm is applied to the re-formulation of the Cam-Clay model in terms of Cauchy stresses. The typical calibration procedure of the Cam-Clay mode l based on Cauchy stresses is demonstrated. As an alternative, a modificati on of the Cam-Clay model, which allows re-calibration of Cauchy stress-base d test data to be used within the framework of a Kirchhoff-based finite str ain model is also dicsussed. The relevance of the adequate choice of the st ress measure is illustrated by means of selected numerical analyses. (C) 19 99 Elsevier Science S.A. All rights reserved.