Characterisation of GFRP surfaces amenable for bonding and their effect on the strength of co-cured vacuum resin infused single lap joints

The choice of a fabrication method is of primary importance in order to optimise and control the performance of composite materials. This becomes increasingly crucial when the fabrication method itself becomes in parallel an adhesive bonding co-cure technique. In this paper, the manufacturing process of the vacuum resin infusion jointing is introduced and specimens of co-cured single lap joints are fabricated and tested under a tensile load. The aim is to show the correlation between the surface characteristics of mechanically treated composite laminates and the adhesion performances of the corresponding surface assemblies using the vacuum resin infusion as a jointing procedure. The mechanisms that govern adhesion are investigated by measuring several physical and chemical parameters of the bonded surfaces with techniques such as surface profilometry, contact angle and surface energy measurements, X-ray photoelectron spectroscopy and scanning electron microscopy. These methods qualitatively and quantitatively measure the influence of surface characteristics towards adequate interfacial bond strength and reveal the importance of the mechanical interlocking, kinetics of wetting, chemical reactivity and intermolecular adhesion of the vacuum resin infusion joint interfaces. The results clearly demonstrate the major influence of the surface contamination and surface topography but also the role of the joining process itself, having no distinct adhesive layer, on the adhesion properties. It is shown that the interfacial adhesion qualities alter significantly the fragmentation process and the strength of the vacuum resin infused joints.