A localizing gradient plasticity model for ductile fracture

Abstract

The conventional gradient enhanced plasticity model uses a nonlocal gradient regularization to avoid mesh sensitivity issues present in the continuum-based local plasticity models. These conventional gradient plasticity models are found to manifest spurious spreading of localization zone during the post-peak regime, leading to non-physical structural and fracture response. Therefore, in the present work, a localizing gradient plasticity (LGP) model is proposed to avoid these non-physical responses. The LGP model avoids spurious responses by including the effects of the fracture processes (at micro and macro level) in the model description through the micromorphic framework. The fracture processes are typically found to initiate as a diffused region of plastic deformation (called necking region), which localizes to form cracks upon further loading. An interaction function is adopted in the LGP model to incorporate the localization of the fracture processes. The enhanced capability of the LGP model is demonstrated through one-dimensional and planar problems with tensile, compressive and mixed-mode loading. The numerical results show that the LGP model can arrest the spurious widening of the localization region resulting in a narrow region of high deformation representing failure.