The automotive industry is currently in a paradigm shift transferring the fleet over from internal combustion vehicles to battery electric vehicles (BEV). This introduces new challenges when designing the Body-In-White (BIW) due to the sensitive and energy-dense battery that needs to be protected in a crash scenario. Press hardening steels (PHS) have emerged as an excellent choice when designing crash safety parts due to their ability to be manufactured to complex parts with ultra-high strength. It is however crucial to evaluate the crash performance of the selected materials before producing parts. Component testing is cumbersome and expensive, often geometry dependent, and it is difficult to separate the bulk material behaviour from other influences such as spot welds. Fracture toughness measured using the essential work of fracture method is a material property which has shown to be able to rationalise crash resistance of Advanced High Strength Steel (AHSS) grades and is thereby an interesting parameter in classifying steel grades for automotive applications. However, most of the published studies have been performed at quasi-static loading rates, which are vastly different from the strain rates involved in a crash. These higher strain rates may also lead to adiabatic self-heating which might influence the fracture toughness of the material. In this work, two PHS grades, high strength and very high strength, intended for automotive applications were investigated at lower and higher strain rates to determine the rate-dependence on the conventional tensile properties as well as the fracture toughness. Both PHS grades showed a small increase in conventional mechanical properties with increasing strain rate, while only the high-strength PHS grade showed a significant increase in fracture toughness with increasing loading rate. The adiabatic heating in the fracture process zone was estimated with a high-speed thermal camera showing a significant temperature increase up to 300 degrees Celsius.

The gradually more stringent environmental and safety regulations in the transport sector have made third generation Advanced High Strength Steel (3rd-gen AHSS) grades excellent alternatives to lower strength steel grades and have continuously been adopted by the automotive industry for body-in-white parts and energy absorbing safety components. Recently, essential work of fracture (EWF) has emerged as a viable material characterisation method to rationalise edge crack resistance and crashworthiness. However, much of the published data is still based on quasi-static conditions, which do not reflect the conditions during crash situations typically involving high deformation rates. This paper presents an experimental study on the deformation rate-dependence of fracture characteristics of three 3rd-gen AHSS grades. The results show that the fracture toughness, measured using the EWF method, increases significantly with the loading rate, although the differences in conventional tensile properties are modest. The increase is due to a combination of rate-dependent hardening combined with a much more ductile failure at a higher loading rate.

The usage of recycled alloys in the high pressure die casting (HPDC) applications for automobiles is gaining rapid interest. Even though the skin microstructure, which is typically induced on the casting surface during the HPDC process, is believed to improve the properties of the HPDC castings, it may not always form continuously throughout on the casting surface, and thereby can influence the mechanical properties. Thus, the current study evaluated and compared the effects of inhomogeneously formed surface skin with that of other defects on the ductility exhibited by the HPDC castings of a recycled secondary AlSi10MnMg(Fe) alloy. The formation of inhomogeneous skin in the current study was attributed to a phenomenon related to the “waves and lakes” type of defects created by the HPDC process. Such skin structure limited the ductility of the HPDC castings, irrespective of the tested strain rates in the current case, by undergoing abrupt fracture due to its poor bonding with the adjoining matrix resulting from the aforementioned inhomogeneity. Even if the investigated AlSi10MnMg(Fe) alloy contained an abundance of porosity, cold flakes and intermetallics, which are usually considered the driving factors behind the fracture of HPDC processed alloys, the effect from the inhomogeneous skin layer dominated all other factors in the current case. The order of detrimental effect on the ductility of HPDC processed AlSi10MnMg(Fe) alloy followed a sequence of inhomogeneous skin, cold flakes and pores, with the inhomogeneity in skin turning out to be the most harmful one.

The current study investigated the microstructure evolution, mechanical properties, and fracture behavior of a high pressure die cast (HPDC) novel secondary alloy. The as-cast microstructure comprised (i) Primary α-Al, (ii) α-Al15(FeMn)3Si2 intermetallics, and (iii) Al–Si eutectics. The microstructure starting from the surface through the depth of the HPDC casting consisted of (i) fine-grained skin at surface, (ii) increased Al–Si eutectics at intermediate location, and (iii) coarse α-Al dendrites at center. Accordingly, the hardness increased from skin to the intermediate section and then decreased toward the center of the casting. The formation of skin layer was highly discontinuous, which was attributed to the complicated fluid flow pattern inside the die cavity. The skin layer indicated to slightly improve the strength of the HPDC alloy; however, it restricted the ductility of the material with a large variation. Such ductility behavior resulted from a fracture mechanism triggered by the inhomogeneous skin because of its poor bonding with the adjacent matrix. Even though the secondary alloy contained casting defects and α-Al15(FeMn)3Si2 intermetallics that are known to be driving factors for the fracture in such materials, the effects from the inhomogeneous skin turned out to be predominant in the current study. 

The lightweighting of heavy-duty vehicles (HDVs) is an effective strategy to reduce fuel consumption and lower CO2 emissions in the transport sector. The widespread application of ultra-high-strength steels (UHSSs) in HDV construction offers a viable solution, particularly for thick-walled chassis components. This study aimed to support the lightweighting of heavy vehicles by developing a methodology capturing the entire warm-forming process in the range of 430–580 °C for thick-walled UHSSs—from material characterisation, including elastoplastic and fracture properties, to downstream forming process simulations. A novel 7 mm thick UHSS grade, WARMLIGHT-980 (ultimate tensile strength (UTS) of 980 MPa), intended for warm forming was investigated at 430, 505, and 580 °C using samples of reduced thickness. The results showed that thickness reduction had minimal influence on mechanical response at elevated temperatures, enabling flexible specimen design. The thermal uniformity improved in thinner samples, enhancing testing reliability. The calibrated hardening and fracture models demonstrated strong agreement with experimental data. Validated simulations of thick-walled components confirmed the accuracy of the modelling approach. The findings support the development of reliable, temperature-dependent models for warm-forming applications and contribute to the design of lighter, more sustainable HDV components without compromising structural integrity.

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.

Numerical modelling and simulation can be used to gain insight about rock excavation processes such as rock drilling. Since rock materials are heterogeneous by nature due to varying mechanical and geometrical properties of constituent minerals, laboratory observations exhibit a certain degree of unpredictability, e.g. with regard to measured strength and crack propagation. In this work, a recently published heterogeneous bonded particle model is further developed and used to investigate dynamic rock fracture in a Brazilian disc test. The rock heterogeneities are introduced in two steps—a geometrical heterogeneity due to statistically distributed grain sizes and shapes, and a mechanical heterogeneity by distributing mechanical properties using three Weibull distributions. The first distribution is used for assigning average bond properties of the grains, the second one for the intragranular bond properties and the third one for the bond properties of the intergranular cementing. The model is calibrated for Kuru black diorite using previously published experimental data from high-deformation rate tests of Brazilian discs in a split-Hopkinson pressure bar device, where high-speed imaging was used to detect initiations of cracks and their growth. A parametric study is conducted on the Weibull heterogeneity index of the average bond properties and the grain cement strength and evaluated in terms of crack initiation and propagation, indirect tensile stress, strain and strain rate. The results show that this modelling approach is able to reproduce key phenomena of the dynamic rock fracture, such as stochastic crack initiation and propagation, as well as the magnitude and variations of measured quantities. Furthermore, the cement strength is found to be a key parameter for crack propagation path and time, overloading magnitudes and indirect tensile strain rate.