This study investigates shear cutting of high-strength steel sheets, a process known to negatively impact the forming and fatigue properties of the material. The localized deformation near the cut edges imposes sheared-edge damage, especially in advanced high-strength steels where severe shear deformation occurs in the very vicinity of the cut edge. In this work, an extensive experimental investigation was carried out on punched holes of thin sheets, using light optical microscopy and metallographic techniques for sheared-edge damage assessment. These methods provided detailed insights into the sheared-edge damage and offer a thorough understanding of the deformation behavior in the shear-affected zone. Advanced engineering cut-edge investigation methods have been developed based on 2D and 3D stereo light microscopy for non-destructive panoramic cut-edge parameters and cut-edge profile determination along cut-hole circumference. Such methods provide an efficient evaluation instrument for challenging close-cut holes, with the possibility of industrial in-line monitoring and machine learning applications for Industry 4.0 implementation. Additionally, the study compares grain shear angle measurement and Vickers indentation for deformation assessment of the cut edge. It concludes that grain shear angle offers higher resolution. This parameter is therefore postulated as relevant for assessing the sheared-edge zone. The findings contribute to a deeper understanding of sheared-edge damage and improve evaluation methods, potentially enhancing the use of high-strength steels in automotive and safety-critical applications.

Forming hybrid structures into complex shapes is key to address lightweighting of automotive parts. Recently, an innovative joining technique between aluminium and Carbon Fibre-Reinforced Polymer (CFRP) based on mechanical interlocking through sheet punching has been developed. However, scaling up the solution requires the assessment of challenges, such as multi-material forming and joint integrity, after forming operations. Therefore, this work proves the feasibility of forming aluminium–CFRP prepreg panels into complex omega-shaped profiles following a conventional cold-stamping process. Forming without defects was possible even in specimens featuring mechanical joints generated through punching. The effect of the CFRP position (in the inner or the outer side of the formed profile), the number of mechanical joints, the addition of a Glass Fibre-Reinforced Polymer (GFRP) intermediate layer to prevent galvanic corrosion and adequate lubrication on necking, cracking, springback behaviour and the final geometry after curing were studied. Compression tests were performed to assess the mechanical response of the hybrid profile, and the results showed that the addition of CFRP in the aluminium omega profile changed the buckling behaviour from global bending to axial folding, increasing the maximum compression load. Additionally, the presence of mechanical interlocking joints further improved the mechanical performance and led to a more controlled failure due to buckling localization in the geometric discontinuity.

Single-Step Punch Interlocking (SSPI) is a recently developed joining methodology between aluminium and Carbon Fibre Reinforced Polymer (CFRP) aiming to contribute to multi-material design of structural parts. This hybrid joint technology combines adhesive bonding with mechanical interlocking. Elucidating the failure mechanism of the developed joint is relevant to provide insights for future enhancements in performance, increase its lifespan and prevent premature failure. Therefore, the different subcritical failure events were identified through interrupted Single-Lap Shear (SLS) tests and subsequent non-destructive ultrasonic inspection, and the global failure mechanism was described. Results indicate that the addition of the SSPI joint delayed the onset and propagation of adhesive failure between both substrates, providing residual strength and increasing the ultimate load in a 65 % and the absorbed energy of the joint in a 156 %.

Advanced high-strength steels (AHSSs) are used as lightweight solutions for vehicles, mainly focusing on the Body-in-White. However, the implementation of such steels for chassis parts requires a profound knowledge of the key design parameters for these components, particularly those concerning fatigue performance. Manufacturing of chassis parts include mechanical cutting operations. Therefore, the deformation and damage induced at the cut edge may affect the fatigue resistance of the parts in service. To characterize and study this critical area, damage and micromechanical properties have been evaluated at the cut edge for three different AHSS grades, CP800, CP980, and DP600, analyzing the impact of cutting parameters and post-processing treatments, such as sandblasting. Large high-speed nanoindentation maps of 400 × 200 µm2 have been carried out along the cut edge in the three different target zones: burnish, fracture, and burr. In the hardness maps, the deformation lines and the gradient of hardness with increasing distance from the cut edge are perfectly observed. Residual stresses at the target zones of the cut edges were measured using the FIB-DIC method for CP980 to complement the micromechanical study in these critical areas. The results found show that reduced cutting clearance leads to larger hardened zones and favorable compressive stress distributions, correlating with improved fatigue resistance. Hardened zones extending up to 100 µm from the cut edge and compressive residual stresses exceeding −300 MPa were observed at low clearance. These findings are consistent with numerical simulations and previous fatigue tests, highlighting the potential of combining high-speed nanoindentation and local stress analysis for optimizing shear cutting processes in AHSS components.

Surface roughness and process-induced defects, such as gas pores and lack of fusions, make additive manufacturing parts vulnerable to fatigue failure. As the conventional fatigue testing methods are time-consuming and require many specimens, several novel rapid fatigue test methods have emerged in recent years, including the stiffness method. In this work, the applicability of this method for AlSi10Mg parts printed by the laser powder bed fusion process is investigated. It is demonstrated that the stiffness method can obtain the fatigue limit of AlSi10Mg specimens with a small number of tests and has a minimal (1%) difference from conventional fatigue test method results. Furthermore, this methodology was applied to a fatigue demonstrator component obtained through a topology optimisation process. The fatigue limit of the demonstrator had less than a 10% difference compared to the conventionally tested ones and highlights the benefit of the stiffness method. In addition, these results led to the development of a framework which combines rapid fatigue testing and finite element modelling and can accurately predict the component fatigue life based on the results at the specimen scale, with a reported difference below 3%. This framework opens up a new avenue for faster qualification and certification of additively manufactured industrial components. 

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.

This study investigated how geometrical variations along the perimeter of sheared edges influenced the formability of advanced high-strength steel sheets during hole expansion. A combined numerical and experimental approach was employed, based on the standardised ISO 16630 Hole Expansion Test. The shear cutting process prior to cut edge forming was modelled using the Particle Finite Element Method, which enabled accurate prediction of edge morphology and deformation within the shear affected zone. The resulting geometries and residual fields were transferred to three-dimensional blank meshes for hole expansion simulations. A cold-rolled complex-phase steel was used, processed with varying cutting clearances to produce distinct edge conditions. Circumferential heterogeneities, including burr-to-no-burr transitions and irregular burnish patterns, were shown to significantly reduce edge formability and promote early crack initiation. These effects were found to be more detrimental than damage distributed through the thickness of the sheared edge. To represent such irregularities in numerical modelling, a hybrid meshing strategy was introduced, incorporating three-dimensional microscopy data into the simulation workflow. This approach improved the accuracy of predicted hole expansion ratios and allowed reproduction of experimentally observed fracture patterns. Stress analysis showed that geometric imperfections around the hole perimeter elevated local stress triaxiality and accelerated damage development. The findings emphasised the importance of achieving uniform cut edge quality to ensure reliable forming performance and reduce the risk of edge cracking during manufacturing.

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.