SAMPE Journal - May/June 2017 - 24

Feature Article

Figure 6. Tensile modulus and strength as a function of the compression force during
injection with glass fiber.

Figure 7. Volume fraction and Young's modulus measurements as a function of injection flow rate for both epoxy and polyurethane matrix composites with glass fiber.

in areas away from the runner was
significantly reduced using a flow
rate of 40 g/s instead of 20 g/s, which
resulted in the increase in observed
tensile strengths. No further increase
of the tensile strength could be
achieved for the epoxy parts at a flow
rate of 60 g/s. As previously stated,
it was not possible to manufacture
polyurethane parts using a flow rate
of 60 g/s. The rise in internal pressure
caused by the increased injection
rates allowed more resin to stay in
the tool cavity, dropping the fiber
volume fraction and subsequently
the Young's modulus as well.
24

Overall,
the
epoxy
and
polyurethane behaved in similar
fashion in terms of both the polymer
processing and resulting mechanical
properties.
These
composite
properties are summarized in Table
4 for both the glass and carbon
composites for the datum test
parameters. The datum test was the
test constant through all the studies
using an injection rate of 40 g/s, a
compression force during injection
of 3000kN and a compression force
during cure of 3000 kN.

Summary and Next Steps
The HP-RTM equipment at the
Fraunhofer Project Center was
utilized to fabricate glass- and
carbon-fiber composites of both
epoxy and polyurethane matrices.
These composites were tested to
determine the impacts on processing
by modifying the injection flow
rate, the compression force during
injection, and the compression force
during cure.
Based
upon
the
measured
mechanical
properties,
the
compression forces during injection
and cure do not impart significant
effects on the processed panels.
However, as the injection flow rate
increases, the composite strength
and stiffness increase due to the
improved removal of entrapped
air during fiber impregnation. The
improvement is minor, and only to
the point that the air is removed as
there were no further gains at higher
flow rates.
From these observations, as long
as the component requirements are
met, it is recommended that future
trials select the gentler processing
parameters that obtain good
properties since no improvement
was seen using higher processing
values. Future trials will examine the
impregnation characteristics over
a range of panel thicknesses and
possibly adapting the equipment for
the use of vinyl ester resins.
Acknowledgements
Special thanks are given to
Steve Greydanus of Hexion and
Michael Connolly of Huntsman for
trial materials, their support, and
expertise.
References
1. Chaudhari
R.
et
al.,
"Characterization of High-pressure
Composites
Manufactured
by
using High-pressure RTM Process
Variants." Automotive Composites
Conference and Exhibition, ACCE 2012;
Troy, MI, 11 - 13, September 2012.

SAMPE Journal, Volume 53, No. 3, May/June 2017

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