Adhesive bonding of carbon fibre/epoxy laminates: Correlation between surface and mechanical properties

The effect of several surface treatments on the surface properties (roughness and surface free energy) of carbon fibre/epoxy laminates has been analysed. Then, the adhesive joints of these treated laminates have been tested in order to determine their mechanical properties (shear strength and mode I fracture energy) and failure mode. It was found that the mechanical properties of the adhesive joints depend on the surface characteristics of the substrates. Several correlations were established, allowing the determination that mechanical interlocking is the main adhesion mechanism for the mode I testing, whereas the shear strength does not increase with a rougher surface. In fact, this property is directly correlated to the polar component of the surface free energy, indicating that in this case the main adhesion mechanisms are those influenced by the chemical composition of the surface. The best mechanical properties have been obtained when the failure mode was delamination of the substrates.