New analytical model for delamination of CFRP during drilling

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. This is an author-deposited version published in: https://sam.ensam.eu Handle IDa b s t r a c tDrilling of composite material structure is a widely used process in aeronautical assembly due to its best manufacturing value (ratio quality/cost). However, delamination which can be generated at the hole exit is still a problem and is directly related to the drill axial force, the composite material mechanical characteristics and the load distribution along the cutting and chisel edges. This paper analyzes the distribution of the load along the drill edges and points out a triangular distribution associated to an additional 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 thrust during drilling for different combined loadings. This new model is compared with the existing ones in the literature and with experimental results. This analysis highlights that delamination occurs in a mixed mode and not in mode I only. The use of the B-K criterion for the determination of the equivalent critical energy release rate G C and a cutting edge combined loading (triangular distribution associated to an additional load) allow a close correlation between experimental measurements and the prediction of this new model.

Drill-exit temperature characteristics in drilling of UD and MD CFRP composites based on infrared thermography

“…This in theory facilitates the effective cut of any unremoved materials. However, drills are usually designed with a small helix angle for reasons like chips evacuation, and such geometry would lead to a strong peripheral cutting action, inducing severe Mode II or Mode III cracks and exacerbating the drill-exit splintering [26,47]. (2) Since only unremoved materials were cut off by the minor cutting edge, it would generate less cutting heat after P-III.…”

A new analytical critical thrust force model for delamination analysis of laminated composites during drilling operation

“…The delamination mode for layers of different orientations may however be more appropriately represented by a coupled loading as the stress fields near the crack tip becomes more complex. The reality of the mixed-mode assumption is even suggested when it is considered that the composite material is subjected to coupled axial force and bends during drilling operation [54]. The fracture initiation criterion which is expressed mathematically in Eq.…”

“…However, peel-up delamination which is associated with the geometry of the drill may occur by sliding of the plies up the flute of the drill due to unfavourable cutting conditions resulting in insufficient cutting of the fibre (see Fig. 2) [54]. It was pointed out that this type of defect constitutes 6% of the total damage of the drilling process and 27% for oval holes resulting in poor quality of drilled holes and increased manufacturing cost [55].…”

“…This phenomenon leads to the distribution of the energy release rates into different failure modes arising from different orientation of the plies around the cracked region leading to oscillatory stress and displacement around the crack tip. In this regard, analysis of critical thrust force based on mixed mode delamination is essential [54]. In addition, Silversides et al [60] reported that delamination damage involves combination of mode I, II and III (Fig.…”

Comparative analysis of wobble milling, helical milling and conventional drilling of CFRPs

“…In case improper machining technology is applied when machining CFRPs, many micro-and macro-geometrical damages can be generated easily: such damages include delamination [6,7,[14][15][16][17][18][19][20][21][22][23][24], uncut fibres and pull-outs [13,[25][26][27][28][29][30][31] as well as microcracks on the machined surfaces [30,[32][33][34]. In order to minimize the above-listed damages, there are many process and technological parameters that have to be optimized including (i) the geometry and coating of the cutting tool [18,33]; (ii) the cutting speed, feed rate and the depth of cut [7,18,35]; (iii) the tool path [7,13,32]; (iv) the cooling [36][37][38][39]; and (v) the type of support plate [40][41][42].…”