UV laser surace activation in co-bonding of CFRP elements. Comparison with other certified methods

Abstract

There is an increasing trend towards the substitution of mechanical joining by adhesive bonding in carbon fibre elements (CFRP) in aeronautical sector. However, it is mandatory to perform a previous step of surface preparation in order to obtain the best adhesive properties to the surface. There are some certified superficial preparation methods by the aeronautical sector, being shot peening, grinding and peel-ply the most used ones. All of them have the disadvantage of not being automatable. Hence, new potentially automatable methods for surface activation are being studied. In this work it has been studied the use of UV laser radiation as a surface activation method previous to adhesive bonding, and its behaviour has been compared to peel-ply activated samples. To this end, an advanced surface characterization has been performed, by means of surface free energy determination, surface chemical composition determination by XPS measurement, surface roughness and morphology observation with SEM. Mode I fracture toughness test have been performed for all surface activation methods. The obtained results show that adhesive bonding of UV laser treated samples have mode I fracture toughness comparable values to those obtained for peel-ply and peel-ply plus grinding samples. Furthermore, all the failure modes observed are accepted by the sector normative. This makes that UV laser surface preparation could be considered as an alternative for certified surface method of CFRPs.

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