Nonlocal Finite Element Implementation for Anisotropic Viscoplastic Gurson Model for Thermoplastic Polymer in ABAQUS

Strain softening and localization lead to spurious energy dissipation and size effect of load responses using FEA. The purpose of this paper is to introduce the nonlocal integral theory with a length scale into the anisotropic viscoplastic Gurson model to capture objective void growth mechanisms and shear bands. A nonlocal finite element formulation for the anisotropic Gurson model is presented, where nonlocal averaging on the equivalent plastic strain is involved in the implicit stress return algorithm. Semi-implicit numerical strategy by combining ABAQUS-UMAT, USDFLD, and UEXTERNALDB subroutines is used to perform nonlocal FEA. The maximum principal stress-based scaling approach is used to eliminate the boundary effect to some extent due to nonlocal averaging. In terms of the dog-bone plate and the double-edge notched plate under tension, the effects of the evolution of void shape and orientation as well as the plastic softening of glassy polymer on the void growth, the evolution of shear bands and the load responses are studied. Results show that local model is shown to fail to predict the contour of the shear band accurately and the developed nonlocal model circumvents mesh dependency well.