Implementation of plasticity models into flnite element code

Abstract Several commercial flnite element software packages (e.g. ABAQUS, LSDyna, and MARC) provide the facility for users to specify their own material models. In ABAQUS, the user is required to provide a Fortran subroutine called a ‘UMAT’. This chapter is concerned with the implementation of plasticity models into flnite element code, which is carried out, by example, in using ABAQUS. In particular, we start by developing an ABAQUS UMAT for elasticity, and discuss the tests necessary to verify the model implementation into ABAQUS. We go on to consider isotropic hardening plasticity with explicit and implicit integration, with continuum and consistent tangent stiffnesses, large deformation formulations using rotated variables provided by ABAQUS, and from first principles using the deformation gradient. We use the problem of simple shear with elasticity to verify the large deformation implementations. We then present an implicit implementation for elasto-viscoplasticity (and creep). All the Fortran coding, together with the necessary ABAQUS input files, are available through the OUP wepsite.