Modelling of localized ductile fracture with volumetric locking-free tetrahedral elements

Finite element analysis of ductile fracture with tetrahedral elements faces two numerical issues: volumetric locking and mesh sensitivity. In this paper, two widely adopted remedies for volumetric locking (F-bar and mixed field) are evaluated, and the superior performance of the mixed field method is demonstrated. Building on the mixed field formulation, a gradient enhancement is further incorporated to resolve the mesh sensitivity. It is shown that a localizing gradient enhancement can avoid a spurious spreading of damage induced by the conventional gradient approach. A locking-free, regularized ductile fracture is first presented via a uniformly tapering plate example. Finally, a shear plate test on ferrite-bainite steel is considered. Numerical results obtained with the proposed approach are shown to capture the rapid strain softening and localized shear fracture phenomenon observed experimentally.