Numerical implementation of finite strain elasto-plasticity without yield surface

In the present study, the finite element (FE) implementation of elasto-plasticity without
a yield surface is discussed. For that purpose, the method of perturbing the deformation
gradient tensor is employed to calculate approximate tangent moduli. The development of a
user subroutine that enables one to use the proposed model within the FE programABAQUS
is covered. A number of exemplary numerical simulations is conducted in order to check the
performance of this subroutine. Material parameter values determined for different materials
are utilized. Finally, the presented constitutive equation is examined upon its ability to
capture the shear-softening process.