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.

Abstract

In aeronautical sector, the step of removing damaged fabrics included in the process of reparison of carbon fibre elements is performed via manual grinding.  This procces is few automatable and shows high level of dificulty in depth control of removed material. Owing to the trend to procceses automation, different automatable technologies are being studied as alternatives that enable to obtaing higher control of this process. This work studies the use of an UV laser system to perform this task. This technologies led to a salective and controlled revomal of fabrics by the control of processing paramenters. Firstly, values of power, processing speed and frequency have been optimised in order to obtain an acceptable rermoved material amount to time ratio. Furthermore, the influence of fibre relative orientation with respect to processing direction on the amount of removed material has been studied. For that purpose, unidirectional tape samples have been laser processed with different processing direction, and the amount of removed material for all of them has been measured. Once optimized the processing direction, the number of shadows required to remove one entire fabric has been determined. Processing conditions that enable to remove selectivley and controlled fabrics of composite material have been determined. This would allow to automate the process of removing fabrics included in bonded breparison of elements of carbon fibre.