Industrial framework for hot-spot identification and verification in automotive composite structures

Sammanfattning: The automotive industry needs to reduce energy consumption to decrease environmental impact. This can be achieved by reducing the weight of cars, which would consequently reduce the energy consumption and emission of greenhouse gases. A promising way to lose weight of automotive primary structures is to introduce carbon fibre composites, as they show outstanding specific properties. However, design of cars are made in virtual environments while composite designs today rely on methods and guidelines that require large amounts of testing. To be able to introduce composite materials in primary structures, the industry needs an efficient design methodology that can be used in virtual development processes. In addition to this, the automotive industry needs new material systems, and production methods to be able to produce composite structures in high volume at a profitable cost. In this thesis, a design methodology for composite structures within the automotive industry is proposed. A methodology that combines numerical models at multiple scales to first find potential hot-spots in global models and then assess only these using high fidelity models. The important part is to ensure that all potential failure modes can be captured both in the global model as well as in the local models. The first step in the methodology is to find accurate failure modes for material systems that are likely to be used within automotive industry. A possible material system for the automotive industry is Non Crimp-Fabric (NCF) reinforced composite materials. Compared to Uni-Directional (UD) reinforced composite materials, NCF composite materials have been found not to be transversely isotropic but orthotropic. This is valid for both stiffness and strength. Current state-of-the-art set of failure initiation criteria are based on the assumption of transverse isotropy. In this thesis, a set of criteria for assessing failure initiation of NCF reinforced composite materials are proposed. The failure criteria are compared and verified against data from literature and numerical models. The set of criteria have also been implemented into a commercial finite element code and verified against physical experiments.