JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014 - 44

infusion

- Wet preform relaxation.
This method mimics the preform compaction/relaxation
behaviour in the VI process at different compaction pressures, and allows monitoring the change in Vf. The change
in preform thickness during a typical compaction experiment for a reasonably thick (~12mm) non-crimp glass fibre
preform is presented in Figure 7.

Fig. 6: Illustration of the preform characterisation rig

and the samples are cured in the oven under low vacuum
pressures according to the cure cycles presented in Table 1.
Due to the phenolic content, the blends need complex cure
cycles at different and high temperature steps.

Preform characterisation
The purpose of this investigation is to aid VI process
simulations. To represent the resins, non-toxic liquids such
as corn syrup or mineral oil are used. Preform characterisation is performed in terms of permeability measurements
and compressibility tests using a rig (Figure 6) developed
at Southampton University. A saturated channel flow inplane permeability measurement method (Figure 6) similar
to Reference [3] is used in the experiments. The aim of
this setup is to obtain permeability as a function of fibre
volume fraction (V_f ) from one continuous experiment.
This is achieved by developing a mould able to hold an
initial set of fabric layers and once the mould is closed, it
can continuously decrease the cavity height, which in turn
increases the fibre volume fraction inside the cavity. For
this purpose, a high-strength compressible closed-cell foam
material is used to support the preform in the mould, in a
similar manner to Reference [3]. This mould is used in an
Instron test machine in order to change the cavity height
with precision. Using the Instron test machine and highstrength compressible closed-cell foam, fine-tuning of the
gap height can be achieved for different fibre volume fractions. Once the desired Vf is obtained, the liquid is injected
continuously at a constant flow rate. Measurements of the
pressure change (∆P) in the steady state period allows inplane permeability values to be calculated.
For preform compressibility experiments, the same mould
is used on an Instron machine in load control mode to
resemble the preform compaction/relaxation behaviours in
the VI process. A typical test procedure is:
- Loading the preform to 1bar pressure,
- Preform settling at 1bar compaction pressure,
- Preform wetting,
- Unloading to different lower compaction pressures,

44 jec composites magazine / No90 June - July 2014

Fig. 7: Compaction and relaxation behaviour using the preform characterisation rig

Process simulation
The liquid composite moulding process simulation
software PAM-RTM 2011 is used for flow and cure simulations. The University of Southampton is also undertaking cure kinetics, cure modelling and viscosity analysis
studies in order to provide resin input data for cure and
flow simulations. The aim is to couple the resin data and
the preform characterisation study outputs to obtain more
realistic simulation results. The University of Southampton's team have performed preliminary research to explore
the processability of novel resin systems in the VI process,
and presented their methodology in this article. The global
aim is to manufacture good quality composites for fire
testing. The resin systems are still under investigation by
the university's partners to improve the compatibility and
quality of UP/phenolic blends. n
More information:
A.Aktas@southampton.ac.uk
References
[1] Novel co-blended polymer matrix systems for fire resistant structural marine composites. http://gow.epsrc.ac.uk/NGBOViewGrant.
aspx?GrantRef=EP/H020926/1
[2] Deli D, Kandola BK, Ebdon JR, Krishnan L. (2013) Blends of
unsaturated polyester and phenolic resins for application as fireresistant matrices in fibre-reinforced composites. Part 1: identifying
compatible, co-curable resin mixtures. Journal of Material Science,
48, p.6929-6942, DOI: 10.1007/s10853-013-7498-z.
[3] Stadtfeld HC, Erninger M, Bickerton S, Advani SG. (2002) An
experimental method to continuously measure permeability of fibre
preforms as a function of fibre volume fraction. Journal of Reinforced
Plastics and Composites, Vol. 21, No. 10/2002, p.879-899.

http://gow.epsrc.ac.uk/NGBOViewGrant.aspx?GrantRef=EP/H020926/1

JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014