Load Introduction in Carbon Fibre Composites for Automotive Applications

The introduction of carbon-fibre reinforced plastics in load bearing automotive structures provides a great potential to reduce vehicle weight and fuel consumption. A reduction in overall manufacturing cost can be realised through part integration and use of cost-effective materials such as heavy tow carbon fibre. There is a current drive within the automotive industry to develop the technologies necessary to allow the introduction of carbon-fibre components in mass production vehicles. One key technology is the development of reliable and cost-effective joining techniques. This thesis addresses several important aspects of joining and load introduction in carbon-fibre reinforced plastics. The introduction of in-plane and out-of-plane loads in composite laminates based on non-crimp fabrics has been investigated experimentally and numerically. The bearing strength of composite laminates has been investigated considering the effects of the laminate stacking sequence, geometry and lateral clamping load and bolt-hole clearance. The laminate failure mode and ultimate bearing strength were found to be significantly dependent upon the laminate stacking sequence, geometry, lateral clamping load. The influence of initial bolt-hole clearance on the bearing strength, at 4% hole deformation and at ultimate load, was determined experimentally. Significant reduction in bearing strength at 4% hole deformation was found for both pin-loaded and clamped laminates. It was concluded that the effect of bolt-hole clearance is significant with regard to the design bearing strength of mechanically fastened joints. A three-dimensional non-linear finite element model was developed to investigate the effects of bolt-hole clearance on the stress field in the laminate adjacent to the hole. The magnitude and distribution of stress at the hole was found to be significantly dependent on the level of clearance. The importance of minimising bolt-hole clearance through machining of high tolerance, defect free holes was highlighted. The introduction of out-of-plane concentrated loads is commonly avoided in composite laminates due to their poor interlaminar and through-thickness strengths. However, these loads occur frequently in automotive structures and thus knowledge of the behaviour of composite laminates subject to transverse concentrated loading is necessary. Transverse load introduction in carbon fibre reinforced plastic was investigated considering the effect of the specimen size, thickness and stacking sequence. The load-displacement behaviour was found to be essentially linear with initial failure of the laminates occurring at 20-30% of the ultimate failure load. The governing failure modes were determined by fractographic analysis and found to be matrix intralaminar and interlaminar shear failure. The finite element method was used to successfully predict the structural behaviour and first-ply failure of the laminates. Load Introduction in Carbon Fibre Composites for Automotive Applications v