Physically based fibre kinking model for crash of composites

Licentiate thesis, 2016

Passenger cars are a major emitter of global warming gases which has led to tighter regulations being imposed on car manufacturers. An efficient way to reduce emissions is to reduce the weight of the cars. Composite materials, due to their high strength and energy absorption to weight ratio, are a suitable material choice to reduce the weight without affecting passenger safety. A major challenge today is the fast development times and low costs required by the automotive industry. An efficient design phase using more virtual tools and less physical testing allows time and cost-savings during the design phase. Fibres oriented longitudinally with the load and subjected to compression fail mainly by kinking, which is the damage mode responsible for most of the energy absorption. In this thesis the focus is on developing a physically based fibre kinking model for crash of composites. Fibre kinking is shear dominated, i.e. strongly influenced by the properties of the matrix as well as the alignment level of the fibres and the transverse loads. Modelling the complex physical mechanisms involved in crash at the microscale will result in prohibitively expensive simulations for the automotive industry. Therefore, in the present thesis, we homogenize the material while capturing the physical mechanisms involved, such as fibre rotation. The model parameters are physically meaningful and avoid cumbersome tests to obtain input for the model. Furthermore, the model is implemented in commercial Finite Element (FE) software together with a mesh objective methodology. The results show that the proposed model can be used to predict the whole kinking response in a 3D framework and thus account for the correct energy absorption.