JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 37

high temperature

- High hot/wet property retention for
higher service temperature applications
- Increased toughness

Environmentally
compatible processing
Preform resin infusion technology is the
main target when trying to avoid prepreg and
autoclave processing. This alone is beneficial
by eliminating the need for pre-impregnation processes, cold storage and wastage of
specially treated materials. The Quickstep
process was chosen to cure the laminate and
the demonstrator. This process is based on
the principle of conduction heating. It utilizes
a heat transfer fluid (HTF) to apply heat and
pressure to the uncured component during
processing. Rapid transfer of heat energy into
the curing substrate (fibre and resin) is the
heart of this technology.
Conventional mould heating, such as that
in an oven or autoclave, causes uneven
temperature distribution over the mould
surface. The use of the fluid-based Quickstep
process solves this problem, while achieving
fast ramp-up rates. Uneven temperature
distribution over the laminate also affects
resin shrinkage and may cause changes in
polymer morphology. The Henkel benzoxazine resins have lower heat of cure compared
to conventional resins and therefore can be
heated rapidly without risk of uncontrolled

exotherm. A heated fluid and slightly pressurized Quickstep process (up to 0.8 bar)
accurately achieves the required mould temperature all over the surface with faster ramp
rates and effective utilization of energy. This
helps to modify the cure cycle and dwell time
without affecting the physical and chemical
nature of a polymeric resin. By combining
the cure kinetics of the selected resin, OoA
curing and online temperature monitoring
during the process, the dwell times to complete the laminate curing can be shortened
to a great extent. Ultimately, this also causes
lower energy consumption during the
manufacturing processes. Additionally, fewer
moulds are required for serial production,
as well as reduced machine work hours and
maintenance, etc., resulting in lower costs.

Production of a prototype
demonstrator
In order to demonstrate the capability of the
resin and infusion/curing techniques on a
scale larger than flat laminates, a demonstrator panel (approximately 1 m²) was
produced and infused. This panel consisted
of 5 layers of 370 gsm 5HS carbon fabric for
the skin plies, resulting in a skin thickness of
2 mm, onto which a series of four hat-shaped,
or omega-type stiffeners were placed using
removable mandrels. The assembly was
bagged and placed into the Quickstep curing
chamber for infusion and cure.

Fibre volume and laminate
quality measurements
After moulding and post-cure, the panels
were tested by Henkel. Thickness measurements were in the expected range for woven
fabric panels produced using the VARTM
process. The hat-stiffened demonstrator
panel was inspected for thickness and any
evidence of dry spots. Visual inspection indicated no evidence of dry areas throughout
the panel. Microscopy analysis of trimmed
edges confirmed no visual internal voids in
the panel or stiffeners.

Promising results
The processing of the Loctite BZ 9130
AERO resin proved to be "infusion-friendly" in the Quickstep process, and void-free
panels were produced with fibre volumes in
the 55-57% range, which is considered high
for a woven fabric laminate. A mechanical
evaluation of the panels confirmed values
similar to or higher than those achieved using
standard oven-based VARTM processing.
The Quickstep process provided faster heating and cooling of the laminate and uniform
temperature during the infusion process. The
results demonstrated the synergistic benefits
of the Henkel benzoxazine infusion resin and
the Quickstep process technology. n
More information:
www.henkel-adhesives.com/aerospace

-

www.jeccomposites.com

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No96 April 2015 / jec

Feature Aeronautics

Carbon fibres:

composites magazine 37
http://www.henkel-adhesives.com/aerospace/aerospace.htm http://www.jeccomposites.com/product/carbon-fibres-history-players-and-forecast-2020?type=70&type_old=71 http://www.jeccomposites.com
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

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