Comprehensive study of ductile damage behavior and formability in hole expansion process

Abstract

This study presents a comprehensive finite element analysis coupled with experimental validation to address the individual and coupled effects of critical parameters on ductile damage and formability in the perforated hole expansion process. A high-fidelity computational model is developed via an explicit dynamic formulation and shell elements, integrating both the stress-state-dependent ductile damage criterion (DUCTCRT) and the strainpath-dependent forming limit diagram criterion (FLDCRT) to accurately capture large plastic strains, contact nonlinearities, and the evolution of material damage leading to fracture. A systematic parametric investigation is undertaken, focusing on punch geometry, interfacial friction coefficient, and sheet material. The results definitively establish punch geometry as the paramount factor with the conical punch yielding the highest formability, due to its favorable combined bending-stretching mode. In contrast, the cylindrical punch characterized by an abrupt line contact provides the most premature failure. The influence of friction is profoundly geometrydependent, exhibiting stable behavior for the conical punch but complex nonmonotonic trends for the others. Material substitution reveals a critical trade-off, while aluminum universally reduces flow stresses and failure strains because of its lower strength, it significantly enhances damage tolerance under specific stress states. Furthermore, a comparative analysis of damage criteria confirms that the FLDCRT conservatively predicts failure at much earlier stages, while the DUCTCRT accurately captures the ultimate formability up to fracture, closely aligning with empirical tests. This research presents a validated simulation-driven framework for optimizing the hole expansion process in industrial applications.