A study of the drilling of advanced carbon fibre composites

Khan, ZM

Abstract

Carbon fibre composites are increasingly being used in
aircraft structures due to their superior physical and
mechanical properties. The process of drilling of carbon
fibre composites in aircraft manufacture is economically
important since the extremely abrasive nature of the fibres
limits drill life. The hole quality produced by drilling
in terms of fibre pullout and matrix cracking affects the
notch sensitivity of the hole.
The present thesis describes an experimental and analytical
study of drilling of the carbon fibre composites carried
out with the support of British Aerospace (Military
Aircraft Division). Full drill life testing was carried out
using four low cost commercial cemented carbide drills,
three of which had brazed inserts, and drill life was
determined by measuring the outer drill corner wear. Hole
quality was measured in terms of diametrical tolerance
using accurate plug gauges. Drill forces were measured
using a two component Kistler dynamometer and attempts were
made to measure residual stress in the workpiece using the
birefringent photoelastic technique. The hole quality was
related to drill wear, cutting forces and heat generated
during drilling.
Independent tasks were carried out to relate cemented
carbide physical and mechanical properties to wear using
several standard sliding wear experiments. Three different
cemented carbide tool materials were investigated in terms of cobalt layer thickness, carbide distribution and
physical properties including hardness and fracture
toughness. Independent sliding wear tests were performed
using a Pin-on-Disc machine, lathe and machining centre.
These tests allowed the materials to be ranked in terms of
wear resistance when rubbing against carbon fibre
composite. The fracture toughness was measured using the
techniques developed by Palmqvist. The wear resistance was
correlated to the physical and mechanical properties of the
tool materials.
Hole quality was studied experimentally using scanning
electron microscopy and fibre pullout shown to be primarily
dependent on the fibre-matrix interface bond strength and
the intrinsic strength of the fibres. The surface
morphology of the fractured fibres in areas of fibre
pullout showed inultimode damage due to anisotropy of the
carbon fibre composite and the dynamics of drilling. The
degree and pattern of damage developed in the drilled holes
was found to be highly directionally dependent. The
experimental results and theoretical analysis showed that
the degree of hole damage depends not only on drilling
parameters but also on the material composition and the
manufacturing process of the carbon fibre composite.

Citation

Khan, Z. A study of the drilling of advanced carbon fibre composites. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Sep 19, 2011
• Publicly Available Date: Sep 19, 2011
• Award Date: Jan 1, 1991