JEC COMPOSITES MAGAZINE - Issue #102 - January/February 2016 - 40

impact resistance
suitable for use in conjunction with liquid moulding techniques.
In addition to this, prepreg materials that incorporate interleaving
films tend to be stiff, tack-free and are difficult to use.
Microfibre interleaving veils used in laminates can improve impact
resistance but often have detrimental effects on other composite
mechanical and physical properties. Furthermore, the addition of
bulky microfibre veils can result in undesirable increases in weight
and thickness of the laminate.

A new solution to an age-old problem
Revolution Fibres, an AS9100c-certified advanced materials
manufacturing company based in New Zealand, has developed
an electrospun polyamide (PA66) nanofibre interleaving veil
that addresses some of the problems associated with traditional
composite toughening systems. This product, marketed as Xantu.
Layr™, is a non-woven web consisting of kilometre-long nanofibres (Fig. 1), and is currently the only commercially available nanofibre veil on the market for use in composite materials. Xantu.
Layr™ has been shown to improve the interlaminar fracture
toughness (ILFT), compression after impact strength (CAI) and
fatigue resistance of composite laminates.
Xantu.Layr™ nanofibre veils have the advantage of being highly
porous and thus do not impede the flow of resin during cure.
They have very high specific surface areas to promote good
bonding with the matrix resin. They are also thin and lightweight,
meaning they do not significantly affect laminate thickness and
weight. The nanofibres do not move once inside a laminate, and
they do not increase the viscosity of the matrix resin. Nanofibre
veils can also be easily cut to size and placed in critical areas of a
laminate that require localized toughening.
Unlike some of the other commonly used toughening systems,
the physical and mechanical properties of the composite - such
as Tg, interlaminar shear strength, flexural strength and modulus,
and tensile strength and modulus - are not negatively affected by
the inclusion of Xantu.Layr™.

Mode I interlaminar fracture toughness
Fracture toughness is a property that describes the ability of a
material containing a crack to resist fracture, and is used as a

Fig. 2: Mode I interlaminar fracture toughness (onset) for composites interleaved
with different Xantu.Layr™ veils. Error bars represent ±1 standard deviation

measure of delamination resistance in composites. One common
mode of delamination failure, referred to as Mode I, involves
a crack opening up as a result of a tensile stress normal to the
plane of the crack. In this evaluation, the Mode I crack energy
release rates (crack onset) were obtained for 12-ply unidirectional
laminates made from MTM57/T700S (24K)-300-35%RW using
the double cantilever beam test and the modified beam theory in
ASTM D 5528.
The effect of nanofibre veil areal weight on the Mode I ILFT
of composites interleaved with various Xantu.Layr™ veils can
be seen in Fig. 2. It can be seen that the nanofibre veils had a
dramatic effect on increasing the Mode I ILFT, with 4.5g/m2 veils
showing an improvement of 156% over the control. PA66 has a
high elongation to break in relation to epoxy resin (30% and 4%,
respectively) and it is thought that the plastic deformation of the
nanofibres in the interlayer region diminish the crack energy and
thus increase the Mode I ILFT [3]. In other words, the nanofibre
veils reduce the brittleness and increase the crack energy absorbing characteristics of the epoxy resin in-between the reinforcing
layers of the composite.

Mode II interlaminar fracture toughness
A second mode of delamination failure, referred to as Mode
II, is characterised by a crack sliding through the laminate as a
result of a shear stress acting parallel to the plane of the crack and
perpendicular to the crack front. In this evaluation, the Mode II
crack energy release rates (crack onset) were obtained for 12-ply
unidirectional laminates made from MTM57/T700S (24K)-30035%RW using the end notch flexure test and the method stated in
ASTM D7905.
The Mode II ILFT of composites interleaved with various Xantu.
Layr™ veils can be seen in Fig. 3. It can be seen that all of the
nanofibre veils resulted in significant increases in fracture toughness, with the 4.5g/m2 nanofibre veils resulting in improvements
of 69% over the control.
According to Xia and Hutchinson [4], Mode II failure occurs
as a result of combined shear and tensile micro-crack growth.
While the toughening mechanisms of this type of system are
still not fully understood, it is believed that the nanofibres act to

Fig. 3: Mode II interlaminar fracture toughness for composites interleaved with
different Xantu.Layr™ veils. Error bars represent ±1 standard deviation

40 jec composites magazine / No102 January - February 2016

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #102 - January/February 2016