Gradient strengthening effects in mode I tearing of ductile plate at the engineering scale

The present study aims to quantify the influence of void size effect on crack initiation and growth in mode I tearing of large ductile plates. Specifically, the aim is to demonstrate how size effects influence the transition from crack initiation to steady-state tearing and reveal the evolution in both the traction-separation relation and the fracture energy dissipated in the tearing process when related to large-scale cohesive modeling. The study investigates mode I tearing by adopting the gradient enriched Gurson-Tvergaard-Needleman (GTN) model by Niordson and Tvergaard (2019), where the novelty lies in accounting for strain gradient hardening near growing micro-voids in relation to large-scale plate tearing. The steady-state crack growth conditions are compared to a 2D plane strain model setup, while the transition from crack initiation to steady-state is analyzed using full 3D plate tearing calculations. A discussion about the 2D versus 3D models’ capability, their differences, and agreement is presented. The results are related to the traction-separation relations fit for efficient large-scale simulations, e.g., using cohesive zone modeling. The present study shows that the material length parameter incorporated into the constitutive model has a negligible impact on the onset of plate thinning (or necking) but delays the onset of shear localization and, thus, increases the total cohesive fracture energy.