A new approach to assess delamination in drilling carbon fibre-reinforced epoxy composite materials

The development of efficient, high-quality joining techniques is still considered an obstacle to the wide application of composite materials as structural components. Mechanical fastening is one of the most common joining techniques. However, this requires the composite material to be drilled, which introduces significant damage to the material. The improvement of drilling techniques is dependent on the accurate analysis of the induced damage. Moreover, concerning repair activities, the assessment of the machining-induced damage enables the determination of its significance, identifying the immediacy of repair. The delamination factors described in the literature quantify the damage but neither has achieved full acceptance to create international standards, which are yet to be defined. This work proposes a new approach to assess the delamination factor by using an image processing methodology, based on digital radiography, to characterize the drilling-induced damage. This approach reconsiders the assumptions made prior to the application of the delamination factor, by reducing the affected area to a quantified damaged area ratio. The obtained results highlight that the minimization of the quantified damage for the most irregular delamination shapes to a single, unequivocal value creates an unambiguous delamination factor for quantifying drilling-induced damage. Simultaneously, the preferential direction of the damage is identified. Additionally, since it is a fully automated method, it is an expeditious method that can be used in situ, being valuable either for manufacturing or repair activities.