APPROPRIATE MATERIAL SOFTENING AND FAILURE MODELS FOR NUMERICAL CALCULATIONS

Abstract

Structures exposed to loads involving high stresses and/or large deformations often fail by softening, localization, and failure in regions of load concentration or imperfections. Finite element (FEM) computer codes therefore need material models (constitutive relations) that can describe such localized behavior with internal variables. Since the material elements, represented by computational cells, often undergo large deformations, rotations, and nonelastic deformations, care must be taken to choose constitutive relations that, when combined with the equations for conservation of mass, momentum, and energy, form a well-posed problem. The constitutive relations must be cell size-independent. Furthermore, to describe the localization process, the above set of equations must be stable. Finally, the constitutive relations must use measures of stress and strain that obey the usual requirement for frame-indifference (objectivity). In this paper we review the above requirements, and describe a class of material failure models that appears to satisfy those requirements.