The study examines the shear cutting process of Advanced High Strength Steel using the Particle Finite Element Method. Shear cutting, a crucial process in sheet metal forming, often leads to microcracks and plastic deformation that degrades the material performance in subsequent applications, such as cold forming, crashworthiness, and fatigue resistance. This work utilises the Particle Finite Element Method as an alternative to conventional Finite Element Methods to address the challenges of large deformation solid mechanics, offering high predictive accuracy in localised shearing deformation and fracture. The model was validated against experimental data from sheet punching tests, with evaluations at both macroscopic and mesoscopic levels, including cut edge profiles and microstructural deformation within the shear-affected zone. The Particle Finite Element Method approach demonstrated a high level of accuracy in predicting cut edge shape and shear-induced damage across various cutting conditions. As an unconventional numerical technique, usage of the Particle Finite Element Method advances modelling of large deformations solid mechanics and providing a robust tool for optimising manufacturing processes of materials sensitive to sheared edge damage.

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.

Shear cutting introduces residual strains, notches and cracks, which negatively affects edge-formability. This is especially relevant for forming of high-strength sheets, where edge-cracking is a serious industrial problem. Numerical modelling of the shear cutting process can aid the understanding of the sheared edge damage and help preventing edge-cracking. However, modelling of the shear cutting process requires robust and accurate numerical tools that handle plasticity, large deformation and ductile failure. The use of conventional finite element methods (FEM) may give rise to distorted elements or loss of accuracy during re-meshing schemes, while mesh-free methods have tendencies of tensile instability or excessive computational cost. In this article, the authors propose the particle finite element method (PFEM) for modelling the shear cutting process of high-strength steel sheets, acquiring high accuracy results and overcoming the stated challenges associated with FEM. The article describe the implementation of a mixed axisymmetric formulation, with the novelty of adding a ductile damage- and failure model to account for material fracture in the shear-cutting process. The PFEM shear-cutting model was validated against experiments using varying process parameters to ensure the predictive capacity of the model. Likewise, a thorough sensitivity analysis of the numerical implementation was conducted. The results show that the PFEM model is able to predict the process forces and cut edge shapes over a wide range of cutting clearances, while efficiently handling the numerical challenges involved with large material deformation. It is thus concluded that the PFEM implementation is an accurate predictive tool for sheared edge damage assessment.

The shear cutting process, which is the most common cutting technique in the sheet forming industry, is known for introducing damage to the cut edges of high strength metal. This damage may impair the forming- or fatigue properties of the material and can cause edge-cracking during forming or in-service part failure. The edge formability of a sheared edge is strongly linked with the appearance of large notches arising due to unfavorable process parameters. By numerical modelling of the shear cutting process with the possibility to vary important process parameters, the sheared edge damage can be detected and avoided in the manufacturing process. This work present numerical modelling of shear cutting in Advanced High Strength Steel using a novel Particle Finite Element Method approach. Numerical modelling of shear cutting processes over a large range of cutting clearances were conducted and validated against laboratory experiment results. The results showed that the PFEM modelling could detect the cut edge damages with the largest negative impact on formability, thus narrowing the feasible cutting clearance range.

The use of Advanced High Strength Steel (AHSS) allows for lightweighting of sheet steel components, with maintained structural integrity of the part. However, AHSS grades show limitations in edge crack resistance, primarily influenced by sheared edge damage introduced by the shear cutting process. Numerical modelling of the shear cutting process can aid the understanding of the sheared edge damage, thus avoiding unforeseen edge cracking in the subsequent cold forming. However, the extreme deformations of the blank during the shear cutting process are likely to cause numerical instabilities and divergence using conventional Finite Element modelling. To overcome these challenges, this work presents the use of a particle-based numerical modelling method called the Particle Finite Element Method (PFEM). PFEM accurately solves some of the challenges encountered in shear cutting with the standard Finite Element method, such as large deformation, angular distortions, generation of new boundaries and presents an efficient way of transfer historical information from the old to the new mesh, minimising the results diffusion. The present work shows prediction of cut edge morphology of AHSS using a PFEM modelling scheme, where the numerical results are verified against experiments. With these results, the authors show new possibilities to obtain accurate numerical prediction of the shear cutting process, which promotes further advances in prediction of edge damaged related to shear cutting of AHSS.

An efficient way of reducing CO2 emissions from the transportation sector is to reduce the vehicle weights, i.e. lightweighting. A common strategy for lightweighting of vehicles is to replace the steels used to build structural parts of the vehicle, usually manufactured by metallic sheets, with stronger, advanced high strength steel (AHSS) grades. Using stronger steel grades enables down-gauging while the structural integrity of the parts remain unchanged. However, the increase in strength of AHSS typically comes with a loss of ductility, affecting their forming properties. A common AHSS manufacturing defect is edge cracking occurring when a sheared edge (damaged by the shearing operation) is bent or stretched. It is known in the sheet metal forming industry that the shear cutting process introduces damage, in terms of micro-cracks and notches, to sheared edges from which edge cracks can grow. Conventional forming analyses do not include the effects from sheared edge damage and therefore can not predict edge cracking during forming. Numerical modelling of the shear cutting process can aid the understanding of sheared edge damage and how it affects the AHSS edge cracking phenomena.

This thesis presents experimental and numerical methods for calibration of acommercial damage- and failure model, intended for shear cutting simulations. Crack initiation and propagation govern the shear cutting process of AHSS sheets. Therefore, a commercial numerical damage- and failure model was studied regarding its ability to predict shear edge damage. The investigation shows that the damage and failure model has limitations concerning prediction of crack initiation, thus concluding that modelling of processes including formation of cracks using the said damage- and failure model risks to generate erroneous results. This phenomena was also seen in modelling of shear cutting, where the crack-driven fracture process following burnish formation was delayed. Through sensitivity analysis of uncalibrated areas on the failure locus could accurate correlation between numerical and experimental cut edge morphology be obtained. Such results show that additional calibration experiments are necessary, but also the need for development of stress-state dependent failure modelling of AHSS that includes the effect from cracks.

In the present work, numerical models are developed for the shearing and cutting process of advanced high strength steel-blanks which can predict the edge morphology in the shear effected zone. A damage model, based on the modified Mohr-Coulomb fracture surface, is calibrated. To increase the predictability of the numerical models, the fracture surface is fine-tuned in areas corresponding to the stress-state of cutting, a methodology called Local calibration of Fracture Surface (LCFS). Four cutting cases with varying clearance are simulated and verified with experimental tests, showing good agreement. It is thus found that the suggested methodology can simulate cutting with adequate accuracy. Furthermore, it is found that solely using plane-stress tensile specimens for calibrating the fracture surface is not enough to obtain numerical models with adequate accuracy.

This article discusses the fracture modelling accuracy of strain-driven ductile fracture models when introducing damage of high strength sheet steel. Numerical modelling of well-known fracture mechanical tests was conducted using a failure and damage model to control damage and fracture evolution. A thorough validation of the simulation results was conducted against results from laboratory testing. Such validations show that the damage and failure model is suited for modelling of material failure and fracture evolution of specimens without damage. However, pre-damaged specimens show less correlation as the damage and failure model over-predicts the displacement at crack initiation with an average of 28%. Consequently, the results in this article show the need for an extension of the damage and failure model that accounts for the fracture mechanisms at the crack tip. Such extension would aid in the improvement of fracture mechanical testing procedures and the modelling of high strength sheet metal manufacturing, as several sheet manufacturing processes are defined by material fracture.