It is well recognized in the literature that the fracture process of thin metal sheets involves three energy dissipation mechanisms i.e., plasticity, necking and surface separation. However, the complex stress state in thin structures hinders the experimental assessment of these quantities and, consequently, the failure modelling. This work evaluates the contribution of these mechanisms to the ductile damage of a thin advanced high strength steel sheet under different stress triaxiality ranges. The essential work of fracture test was carried out on a set of different notch geometry specimens that cover a wide range of stress states. The experimental trend of these specimens was simulated in ABAQUS/Explicit using a VUSDFLD subroutine. Bai and Wierzbicki uncoupled fracture model, which is a function of fracture plastic strain to stress triaxiality (η) and normalized Lode angle (, was selected as damage initiation criterion. A quantitative relationship of the fracture energy (G0) as a function of (η) was proposed in this work and implemented in the model as a damage evolution law. The model captures well the experimental response and the influence of (η) on the softening behavior of the material. It was found that the sensitivity of G0 to η is significant between 0.7 and 1.5. Above this rage, it seems that (η) has no influence on G0. The model showed also the relationship between the two local damage parameters (G0) and the necking (Gn) with respect to the stress state. G0 represents less than 10% of the total work of fracture, while the largest contribution comes from (Gn).

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 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.

Characterising fatigue delamination in composite materials following standardised testing protocols is often associated with high costs and significant time investment. Therefore, it can be helpful to have a testing strategy to reduce the testing time and easily assess the fatigue delamination of multiple materials and conditions. This work shows how to apply one of the new rapid testing techniques known as the stiffness method on composite materials. The method has been developed to predict the fatigue delamination of composite materials by monitoring the fatigue damage through the compliance of the specimen. The obtained data in terms of displacement and force is used to obtain the fracture toughness, fatigue crack onset, fatigue crack threshold, and crack propagation parameters by using a reduced number of specimens and a few testing hours. The testing procedure has been developed on carbon fibre-reinforced polymer used in aerospace structures. The obtained results in a short time are promising, reporting a deviation below 10% compared to the values obtained in the standardised fatigue delamination tests.

Forming of aluminium-CFRP hybrid structures into complex shapes is key to decrease environmental impact in automotive industry. However, challenges such as preserving joint integrity after forming operations must be assessed. Therefore, the authors of this work have cold stamped hybrid aluminium-CFRP panels into omega shaped profiles with and without a mechanical interlocking joining technology. The effect of lubricant application, of the CFRP positioning (inside or outside the omega profile), and of the number of mechanical joints were studied. It was concluded that it is possible to cold stamp aluminium-CFRP prepreg panels even with mechanical joints into complex profiles when lubricant is used. Moreover, the position of the CFRP prepreg has a strong impact on the flange springback of the stamped part.

The present work investigates the influence of pre-strain on the fracture toughness of 3rd Generation Advanced High Strength Steels (AHSS). Specifically, a Carbide Free Bainitic (CFB) and a Quenching and Partitioning (Q&P) steel have been studied, the properties of which are crucial for lightweight vehicle construction. Fracture toughness, which is a key parameter for crash performance applications, is assessed using the Essential Work of Fracture methodology. The study investigates the pre-straining states of uniaxial tension, plane strain, and equibiaxial tension in 1.5 mm Q&P and 1.4 mm CFB sheet-form steels of 1180 MPa tensile strength. Overall, Q&P steel demonstrates superior fracture toughness compared to CFB steel. Remarkably, the specific essential work of fracture (we) remains unaffected by pre-straining across different strain states. Nevertheless, pre-straining exerts a notable influence on the non-essential plastic work (βwp) due to the plastic energy consumed during pre-deformation. These results suggest that prestrain has little or no influence on the fracture properties of AHSS, which is relevant for the design and manufacturing of high crash-performance and safety-related components.