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 European Commission has set a target to reduce greenhouse gas (GHG) emissions from road transport by 60\% compared to 1990 levels by 2050, as outlined in the Transport White Paper. In 2012, passenger cars accounted for about 60\% of GHG emissions from the road transport sector, a figure expected to decline to 45\% by 2030. Meanwhile, heavy-duty vehicles (HDVs), including trucks, buses, and coaches, contribute around 26\% of total CO$_2$ emissions in the European Union, with trucks alone responsible for over 85\% of this share. To achieve the 2050 goal, the European Commission has identified key strategies, including improving vehicle efficiency, developing sustainable propulsion systems, and using advanced lightweight material solutions. A promising approach to reduce fuel consumption and increase payload capacity in HDVs is to reduce vehicle weight. One method is the integration of ultra-high strength steels (UHSS) into chassis structures, enabling thinner, lighter components. However, the limited ductility of UHSS in cold-forming requires exploring alternative forming techniques. Warm forming of thick-walled UHSS sheets presents a viable solution. This thesis focused on the mechanical characterisation of WARMLIGHT-980, a novel 7~mm thick UHSS grade (UTS 980~MPa), developed for warm forming in the 430–580\textdegree C range. The goal of the forming process is to produce lightweight components with high stiffness and fatigue resistance, specifically for HDVs. The elastoplastic and ductile failure properties of this UHSS grade were investigated at elevated temperatures to support numerical simulations of warm-forming processes. Failure strains under various stress triaxialities and specimen geometries were determined by digital image correlation. Due to the thickness of the material, conventional full-scale specimens were impractical; thus, scaled-down 1.2~mm specimens were tested and validated against full-thickness tensile tests. Inductive heating was used to reach target-forming temperatures, with thermal photography confirming uniform distribution. A modified Mohr-Coulomb ductile failure model, calibrated at 3D stress states, was used to predict crack formation during forming. The thermo-mechanical simulation model was validated through three-point bending tests by comparing force-displacement responses. Thickness distribution from simulations was also compared with demonstrator components. Findings indicate UHSS can be effectively warm-formed into complex components at elevated temperatures. The calibrated material model accurately describes material behaviour, with simulation results closely matching experimental force measurements. This research supports the development of lightweight, high-performance HDV structures through improved forming processes and material modelling.

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.

For the reduction of the environmental footprint of Heavy-Duty vehicles (HDV), lighter chassiscomponents can be considered. A lighter HDV chassis gives the opportunity of lower fuel consumption, increased payloads, and savings of material resources. One way of achieving this, is to reduce thicknesses of components in combination of using higher strength steels. For the aim of forming UHSS into complex geometries the need to characterize thick sheet metal at elevated temperatures arises. This work aims at expanding earlier research of characterization of thinner sheet metal and create a testing methodology for tensile tests of 7 mm thick steel sheets at elevated temperatures. An experimental methodology for evaluating high strength steel under warm conditions have been developed and demonstrated. A Digital Image Correlation system is used to extract strain fields for all three testing temperatures. This together with an automatized induction system pre-defined temperature cycles are applied. When the desired Hollomon-Jaffe constant is obtained the tensile test is executed. The methodology shows promising results with good repeatability of stress-strain curves. The methodology shows good stability and are promising for future development and investigations of high strength steels under warm forming conditions.

Stålpartier i Norr AB (SPINAB) är ett företag som tillhör gruppen små och medelstora företag. De har företagsidén att tillverka och sälja CE-märkta fönster, dörrar och skräddarsydda produkter i stål. Företaget har identifierat en för dem ny marknad i säkerhetslösningar inom handelssektorn. SPINAB har uppmärksammat att antalet smash and grab-rån har ökat de senaste åren och att de befintliga skyltfönstren inte står upp till de krav försäkringbolagen tillsammans med Svenska Stöldskyddsföreningen satt upp. SPINAB har i och med detta utvecklat ett skyltfönster för att stå emot dessa angrepp.

Syftet med examensarbetet är analysera skyltfönstret med fokus på deformationszonen. Arbetet har genomförts genom ett utföra en olinjär FEM-analys av ett krasch-förlopp, där kraschförloppet motsvarar en bil som kör in i skyltfönstret. Geometrierna är modellerade i Siemens NX och FEM-analyserna är simulerade i LS-DYNA Två olika polyuretan-skum för deformationszonen har simulerats och utvärderas. Till vederbörande simuleringar har materialparametrar tagits fram genom materialtester i laboratorium.

Resultatet från analyserna visar på att polyuretan-skummet BRAND tar upp mer energi än ÅRET RUNT. Polyuretan-skum BRAND sänker hastigheten med 21,5 % innan genomslag i förhållande till ÅRET RUNT. Deformationszonen ger i detta skyltfönster en möjlighet att forma den kraftpåkänning som skyltfönstrets balkar samt fastighetens fasad och grund upplever. Således kan man med materialvalet i deformationszonen konstruera och optimera en lastkurva för att motverka att bakomliggande konstruktion går sönder på grund utav den uppkomna chocklasten.

Stålpartier I Norr AB (SPINAB) is a company belonging to the group of small and medium-sized companies. They have the business idea to manufacture and sell CE-marked windows, doors and tailor-made steel products. The company has identified one for them new market in security solutions in the commerce sector. They have noted that the number of smash and grab robberies has increased in recent years and the existing storefront windows do not meet the requirements of the insurance companies and the Swedish Anti-Theft Association. With this, SPINAB has developed a storefront window to resist these attacks.

The purpose of the thesis work is to analyze the storefront window with focus on the deformation zone. The work has been carried out by performing a nonlinear FEM analysis of a crash process, where the crash process corresponds to a car that crash into the storefront window. The geometries are modeled in Siemens NX and the FEM analyzes are simulated in LS-DYNA. Two different polyurethane foams for the deformation zone have been simulated and evaluated. For the relevant simulations, material parameters have been gathered by laboratory tests.

The results from the analyzes show that the polyurethane foam BRAND absorbs more energy than ÅRET RUNT. Polyurethane foam BRAND reduces speed by 21.5% before impact relative to ÅRET RUNT. The deformation zone in this window gives an opportunity to shape the stress of the storefront window, as well as the facade and foundation of the property. Thus, with the material selection in the deformation zone, one can design and optimize a stress curve to prevent the underlying structure from breaking due to the resulting shock load.