A cold atmospheric pressure plasma source was used to pre-treat the surface of carbon fibre reinforced epoxy substrates prior to bonding. Surface pre-treatments prevent or remove contaminants from the substrates. These pre-treatments also activate the surface of the adherends, and this could lead to higher bond strengths.
For comparison purposes, current surface pre-treatments used by the aerospace industry were also investigated (peel ply, manual abrasion, and grit blasting). In the aerospace industry, a synthetic cloth, called peel ply, is usually added on one of the sides of the composite during manufacture, and it is then peeled off prior to bonding. The aim of this ply is to prevent foreign materials from becoming integrated into the finished parts. This ply also textures the surface of the composite structure. The strength of the bonded joints of the different pre-treatments was assessed through tensile lap shear tests. It was found that protecting the composite laminates with peel ply doubles the performance of the joints. Manual abrasion and grit blasting improved the strength of the joints by 15% and 20% respectively, while plasma improved the strength of the joints 10%.
The other side of the composite substrates (without peel ply) was also investigated to analyse the effects on the other side of the composite laminates. The strength of the bag side of the composites without any pre-treatment was increased by pre-treating the samples through manual abrasion, grit blasting, and plasma.
All the pre-treatments studied in this research have shown their effectiveness at removing contaminants.
In order to have a better understanding of the effects of the different pre-treatments on the surfaces of the substrates, a surface characterization of the substrates (surface roughness examination, surface tension measurements, and analysis of potential chemical changes) was also conducted.