Andreas Frehn

Luftvergütende hochfeste Stähle für mehr Crashsicherheit

Steigende Rohstoffpreise und hohe Energiekosten sind Triebfedern fur Innovationen im Automobilbau. Neue hochfeste und kosteneffiziente Stahlsorten konnen im Leichtbau einen wichtigen Beitrag leisten. Ein Innovationsbeispiel ist der bei Benteler gefertigte Achstrager aus lufthartendem Stahl BAS100 der neuen Mercedes-Benz C-Klasse, bei dem eine Leichtmetallkonstruktion aus Aluminium durch Stahl-Leichtbau abgelost wurde.

The Deformation Behavior of Functionally Graded TWIP Steel under Monotonic Loading at Ambient Temperature

A processing route for the generation of functionally graded parts from steels showing twinning-induced plasticity is proposed. The procedure employing pre-deformation and local heat treatment allows for tailoring local properties with a high degree of freedom. Quasi-static tension tests revealed that no process-induced drawbacks are present, so that functionally graded parts of unprecedented performance become feasible.

The twist beam rear axle

Twist beam axles by Benteler are being used not only in vehicles of the A-, B- and C- segment but also in the D-segment, in Mini Sport Utility Vehicles and four-wheel drive cars. Due to the low costs, the compact design, the reduced weight and the good axle kinematics it often represents an unrivalled solution. The trend towards improvements of the axle design as well as of the optimised and partly newly developed manufacturing technologies will continue.

The Role of Notches on Fatigue Life of TWIP Steel in the HCF Regime

The present paper reports on the fatigue response of a commercial high manganese steel that features the twinning-induced plasticity (TWIP) effect in the high-cycle fatigue (HCF) regime. Specifically, attention was paid to the influence of the degree of pre-deformation and notches on the damage initiation and propagation in the TWIP steel studied. As monotonic pre-deformation significantly increases the fraction of twins and concomitant the strength of the steel, the fatigue properties and notch sensitivity are altered drastically. A thorough experimental approach including mechanical testing and microstructural characterization was employed to shed light on the microstructure-mechanical properties-relationships in order to deepen the understanding of the critical damage mechanisms. The current study clearly lays out that competing mechanisms effect the fatigue response of the TWIP steel, i.e. pre-deformation leads to strengthening but also induces damage. Since both effects evolve differently upon pre-deformation, fatigue performance can be optimized by appropriate amounts of pre-deformation.

Low-Cycle Fatigue Behavior of TWIP Steel - Effect of Grain Size

The effect of different grain sizes on the fatigue performance of high manganese TWIP steel (Twinning-Induced Plasticity) in the low-cycle fatigue regime was investigated. The average grain sizes in the fine grained condition were 2 5 μm and after heat treatment in the coarse grained condition about 80 μm were obtained. Pronounced twin-dislocation interactions especially in small grains strengthen the steel during monotonic deformation. Twin boundaries act as obstacles for dislocation slip, and thus, further reduce the effective grain size, which affects the fatigue response as well. The samples were monotonically and cyclically deformed at room temperature. The results reveal that the grain size has a significant influence on the mechanical as well as on the cyclic performance. Especially under cyclic loading differences in the resulting stress levels and cyclic stability can be observed. To clarify the microstructure evolution before and after fatigue with different constant strain amplitudes the samples were analyzed by means of transmission electron microscopy (TEM).

Herausforderungen bei der Auslegung und produktionstechnischen Umsetzung von Verbundlenkerhinterachsen fuer Pkw

Abstract Aufgrund der immer kürzer werdenden Entwicklungszeiten und des zunehmenden Kostendrucks bei der Entwicklung von Fahrzeugen und Komponenten wird die virtuelle Entwicklung weiter an Stellenwert gewinnen. Am Beispiel einer Verbundlenkerachse wird gezeigt, welche Kriterien bei der Auslegung dieses Bauteils berücksichtigt werden müssen, deren Verifizierung und Optimierung kontinuierlich über geeignete Test- und Untersuchungsverfahren erfolgen muss. Durch die virtuelle Validierung werden die Fertigungsprozesse variabel festgelegt, die notwendig sind, um die Anforderungen hinsichtlich Betriebsfestigkeit sicher zu erfüllen. In Kombination mit geeigneten Werkstoffen und Halbzeugen leisten diese einen wichtigen Beitrag zum Leichtbau und zur damit verbundenen Einsparung von CO2.

Air-hardening, high-strength steels for more crash safety

Increasing costs of materials and high costs of energy are driving innovation in automotive engineering. New high strength and cost effective steel grades contribute significantly to lightweight design. One innovation example is the chassis subframe of the new Mercedes-Benz C-Class produced by Benteler and made of the air-hardening steel BAS100. A light-alloy based design made of Aluminum was substituted by a lightweight design made of steel.

Determination of input data for numerical design of auto body sheet steels

With 20 steel grades serving as a basis, elastic, plastic and fatigue characteristic values were determined for FE simulation purposes in a joint project between the steel and automotive industries. The research with the aim of obtaining input characteristic values for FE calculations yielded a considerable increase in information with regard to measuring and testing methods and the collection and further processing of data. This article gives an overview over the investigation and its results.