The Influence of Shear-Induced Damage on the Formability of High-Strength Steel Sheet: A Particle-based Numerical Study

Shear cutting is the primary method for preparing blanks in sheet metal forming, widely used across various sheet materials. However, when applied to advanced high-strength steels (AHSS), the process introduces additional challenges. While AHSS offer superior strength-to-weight performance, their limited ductility makes them highly sensitive to shear-induced edge damage, which can lead to premature edge cracking and reduced formability. Accurate numerical modelling of shear cutting and its effects is therefore essential for optimising manufacturing processes and improving formability predictions. In this thesis, the Particle Finite Element Method (PFEM) was employed to develop a numerical framework for modelling of the shear cutting process, addressing challenges associated with extreme deformations and localised strain effects. PFEM provided a robust approach for modelling large localised deformations and material separation while preserving detailed information in critical regions along the cut edge. The method was validated against experimental sheet punching tests, demonstrating its ability to accurately capture key aspects of the shear cutting process. The developed PFEM model was further extended to examine the influence of cutting conditions on sheared edge formability, providing insights into how variations in cutting parameters affect edge cracking. A hybrid modelling approach was introduced, combining numerical shear cutting results with experimental observations to assess circumferential variations in cut edge morphology. This approach enabled a more detailed analysis of local heterogeneities in sheared edges, which are often overlooked in conventional numerical assessments. Additionally, a critical investigation of continuum-based ductile damage modelling for pre-cracked AHSS sheets highlighted the limitations of strain-driven failure models in capturing crack evolution. This study suggested that fracture mechanics approaches could provide a more reliable alternative for predicting crack propagation in edge cracking scenarios. The findings of this thesis enhance the understanding of shear-induced damage mechanisms and their role in subsequent forming defects, providing valuable insights for minimising edge cracking in AHSS. The successful application of PFEM, combined with ductile damage and failure modelling, demonstrates its effectiveness as a robust and computationally efficient method for capturing extreme deformations and fracture evolution in shear cutting, contributing to the advancement of state-of-the-art shear cutting simulations. Moreover, the results highlights the significance of circumferential variations in sheared edge morphology, emphasising the need for precise cutting conditions and tool maintenance. These advancements contribute to the optimisation of shear cutting processes and broader applications of PFEM in large deformation solid mechanics, supporting the development of lightweight, high-performance AHSS structures.