Failure prediction of orthotropic Non-Crimp Fabric reinforced composite materials

Licentiatavhandling, 2016

The automotive industry needs to reduce the energy consumption to decrease the impact on the environment. One part of this is to reduce the weight of cars, thereby reducing the fuel consumption. A promising way to be successful with this is to introduce carbon fibre composites in the structural parts. This as carbon fibre composites have outstanding properties. However, design of cars are made in a virtual environment while composite designs are today made using guidelines that require large amounts of testing. The automotive industry needs an efficient design methodology for carbon fibre composite structures that can be used in the virtual development. In addition to this, the automotive industry needs new material systems and production methods to be able to produce in large scale at a profitable cost. In this thesis, the basis for a design methodology for composite structures within the automotive industry is given. A methodology that uses numerical models at multiple scales is proposed. Assessing failure on full scale models cannot be done as analysis of composite structures needs to be done with more detailed models due to the different failure mechanisms. An approach with global models for screening for critical locations and local higher fidelity models for verification is outlined. The first step in the methodology is to find accurate failure modes for the intended material systems. A strong candidate material for the automotive industry is Non Crimp-Fabric (NCF) reinforced composites. Compared to Uni-Directional (UD) reinforced composite materials, NCFs have been found not to be transversely isotropic but orthotropic. This is valid for both stiffness and strength. Current state-of-the-art failure criteria are based on the assumption of transverse isotropy. In this thesis and the appended papers a set of criteria for assessing failure initiation of NCF reinforced composites are proposed. The proposed failure criteria are compared and verified against data from literature and numerical models. It have also been implemented into a commercial finite element code and verified against physical testing. Keywords: Design methodology; Carbon fibre composite; Non crimp-fabric; Failure initiation; Orthotropic