New analytical model for delamination of CFRP during drilling

Abstract

Drilling of composite material structure is a widely used process in aeronautical assembly due to itsbest manufacturing value (ratio quality/cost). However, delamination which can be generated at the holeexit is still a problem and is directly related to the drill axial force, the composite material mechanicalcharacteristics and the load distribution along the cutting and chisel edges. This paper analyzes thedistribution of the load along the drill edges and points out a triangular distribution associated to anadditional load located at the centre of the drill. This additional load depends strongly on the feed rate.An orthotropic analytical model is then proposed in order to determine the delamination critical thrustduring drilling for different combined loadings. This new model is compared with the existing ones inthe literature and with experimental results. This analysis highlights that delamination occurs in a mixedmode and not in mode I only. The use of the B-K criterion for the determination of the equivalent criticalenergy release rate GCand a cutting edge combined loading (triangular distribution associated to anadditional load) allow a close correlation between experimental measurements and the prediction ofthis new model.