Innovative concepts for the usage of veneer-based hybrid materials in vehicle structures

Abstract

A promising approach to the development of sustainable and resource saving alternatives to conventional material solutions in vehicle structures is the use of renewable raw materials. One group of materials that has particular potential for this application is wood. The specific material properties of wood in the longitudinal fiber direction are comparable to typical construction materials such as steel or aluminum and, due to its comparatively low density, there is a very high lightweight construction potential especially for bending loads. Structural components of the vehicle body are exposed to very high mechanical loads in the case of crash impact. Depending on the component under consideration, energy has to be absorbed and the structural integrity of the body has to be ensured in order to protect the occupants. The use of natural materials such as wood poses particular challenges for such applications. The material characteristics of wood are dispersed, and the material properties also depend on environmental factors such as humidity. The aim of the following considerations was to develop a material system that is as robust as possible by means of targeted hybridization, ensuring the functional reliability of the component. The test boundary conditions for validation also have a key role to play in this context. The potential of wood-steel hybrid design based on laminated veneer lumber and steel was investigated for use in a component subject to crash loads such as the door impact beam. The chosen solution involves a separation of functions. A laminated veneer lumber-based beam is hybridized with a steel strip on the tension side. The steel strip is designed to compensate for the comparatively low elongation at fracture of the wood and ensure the integrity of the beam. The function of the wooden component is to absorb as much energy as possible during the impact due to delamination and controlled failure, while maintaining the surface moment of inertia – i.e. the bending stiffness of the entire component. This approach is designed to ensure the functional safety of the component, prevent fatal component failure and make optimum use of the potential of both material systems. The tests carried out provided initial functional proof of the chosen solution. The hybridization allowed significantly greater deformations to be achieved without fatal failure of the beam. In addition, bending capabilities were significantly increased as compared to a beam without hybridization. In a direct comparison with a state-of-the-art beam, however, it was clear that the hybrid beam was not able to match the levels of the reference component under consideration in terms of maximum deformation and the target weight of the hybrid beam. Further optimization of the hybrid beam is therefore necessary.