Exit delamination failure modelling during drilling of CFRP laminates

Drilling of CFRP components is a key manufacturing process in the aircraft manufacturing industry. Airframe structures and fuselage skins are often assembled using riveted joints, which require pre-drilling of composite parts. However, drilling CFRP can be challenging due to the inhomogeneous and anisotropic nature of the material, which can lead to major defects such as delamination, fiber pull-out and uncut fibers. In particular, push-out delamination at the hole exit is considered critical, as it can compromise the structural health of the components and even lead to their rejection. Therefore, the development of monitoring and modeling techniques to predict push-out delamination is of great importance to the industry. In this regard, the present work introduces a theoretical model for the prediction of exit delamination and thrust force evolution during CFRP drilling. The results are evaluated in comparison to part delamination and thrust force data obtained from experimental drilling tests. The results indicate that the proposed model can provide valuable insight into the CFRP drilling for process optimization, enabling the aerospace industry to improve current drilling practices towards delamination free drilling of CFRP components.