The strength of adhesive-bonded joints between fibre-reinforced plastics and metals: Analysis, shape optimization and experiments

The behaviour of adhesive-bonded joints between fibre-reinforced plastics (FRP) and metals was investigated using numerical methods as well as experiments. Various joint types were considered: single-lap joints, T-joints and two actual cases. Non-linear finite element methods were used in the analysis of the joints. The importance of allowing for both geometric and for material non-linearities is shown. The single-lap joints were optimized by modifying the geometry of the joint ends. Different shapes of adhesive fillet, reverse tapering of the adherend, rounded edges and grooves were applied in order to increase the joint strength. The influence of the joint-end geometry is shown for different metal/FRP adherend/adhesive combinations. Depending on the material combinations, the strength of the joints can be increased with a careful joint-end design by 90 - 250%. The same modifications of the joint ends were applied to the T-joints. The strength of T-joints can be increased by 200% using a proper joint-end design. To verify the analytical results, static tests were performed with single-lap joints and two actual cases. Both cases were tested at elevated temperature. One case was tested in fatigue. The effect of defects on the strength of single-lap joints was investigated experimentally. The influence of defects in the adhesive layer on the strength of the joints was remarkably low for the chosen material combination. The reduction of strength was not higher than the reduction in joint area.