Joining of Carbon Fibre Reinforced Plastics 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. To enable the manufacture and assembly of composite structural parts, reliable and cost-effective joining technologies must be developed. This thesis addresses several aspects of joining and load introduction in carbon-fibre reinforced plastics based on non-crimp fabric reinforcement. The bearing strength of carbon fibre/epoxy laminates was investigated considering the effects of bolt-hole clearance. The laminate failure modes and ultimate bearing strength were found to be significantly dependent upon the laminate stacking sequence, geometry and lateral clamping load. Significant reduction in bearing strength at 4% hole deformation was found for both pin-loaded and clamped laminates. The ultimate strength of the joints was found to be independent of the initial bolt-hole clearance. The behaviour of hybrid (bolted/bonded) joints was investigated both numerically and experimentally. A three-dimensional non-linear finite element model was developed to predict the load transfer distribution in the joints. The effect of the joint geometry and adhesive material properties on the load transfer was determined through a parameter study. An experimental investigation was undertaken to determine the strength, failure mechanisms and fatigue life of hybrid joints. The joints were shown to have greater strength, stiffness and fatigue life in comparison to adhesive bonded joints. However, the benefits were only observed in joint designs which allowed for load sharing between the adhesive and the bolt. The effect of the environment on the durability of bonded and hybrid joints was investigated. The strength and fatigue life of the joints was found to decrease significantly with increased ageing time. Hybrid joints demonstrated increased fatigue life in comparison to adhesive bonded joints after ageing in a cyclic freeze/thaw environment. The strength and failure mechanisms of composite laminates subject to localised transverse loading were investigated considering the effect of the specimen size, stacking sequence and material system. Damage was found to initiate in the laminates at low load levels, typically 20-30% of the ultimate failure load. The dominant initial failure mode was intralaminar shear failure, which occurred in sub-surface plies. Two different macromechanical failure modes were identified, fastener pullthrough failure and global collapse of the laminate. The damage patterns and ultimate failure mode were found to depend upon the laminate stacking sequence and resin system. Finite element analysis was used to analyse the stress distribution within the laminates and predict first-ply failure. Joining of CFRP for Automotive Applications v