SAMPE Journal - January/February 2022 - 25

INTRODUCTION
Resin Transfer Molding (RTM) is a composite
fabrication method, which enables high
throughput production of composites.
The
primary steps in a typical RTM process are the
production of a fiber preform, resin injection,
curing, and demolding. RTM is widely preferred
for the fabrication of complex composite parts
through the use of appropriately designed molds
and preforms. Various adaptations of the RTM
process include vacuum assisted resin transfer
molding (VARTM) and high-pressure resin transfer
molding (HP-RTM). VARTM involves vacuumassisted
resin injection for the production of
thicker laminates such as those used in aerospace
applications. HP-RTM is a unique process that
enables high throughput part production with very
high fiber volume fractions through a combination
of rapid, pressurized injection and cure processes,
which can lead to cycle times that are less 10
minutes. Hence, HP-RTM represents a significant
advancement in high volume manufacturing of
composite parts for automotive and aerospace
applications.1,2
Various aspects of the HP-RTM process and
the impact of specific process parameters on the
part quality and process speed have been studied
in the literature3,4,5
to improve the robustness and
the reliability of the process. In addition, process
monitoring capabilities have also been developed to
track the progression of cure behavior and achieve
cycle time enhancements6
. Apart from the impact
of process parameters, the resin system also plays
a key part in the efficacy of the HP-RTM process. In
spite of the fast injection time involved in HP-RTM,
the rheology of the resin should be appropriately
tailored to facilitate sufficient time for complete
impregnation of the fiber preform, which should
then be followed by a rapid cure under pressure.
The additional challenge in design and formulation
of resins for HP-RTM involves achieving a balance
between cure speed and exotherm development,
at desired cure temperatures to ensure production
of composite articles with the desired surface
quality and performance characteristics. While the
cure speed of a thermoset can be increased with
increasing reaction temperature, the magnitude
of the exothermic temperature rise would also
be higher at higher processing temperatures. An
uncontrolled reaction exotherm could lead to
poor surface quality, delamination, and premature
cracking of the composite part7
. Hence, in this work,
we present a novel epoxy resin system that can
be cured at nominal temperatures between 100115°C.
The rapid curing epoxy system, which offers
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Process parameter
Mixing head pressure (bar)
Resin injection temperature (o
Hardener injection temperature (o
Injection time for 980 g mix (s)
Mold temperatures (o
C)
C)
Value
120
60
C) 30
30
100-115
Mold pressure during injection (kN) 1500
Mold pressure during cure(kN)
4500
Table 1. HP-RTM process parameters employed
for panel production.
a balance of tailored rheology and rapid cure was
used to fabricate glass fiber reinforced composite
panels at various cure temperatures between 100115°C,
to confirm processability during the HPRTM
process. In this work, we also examine the
impact of nominal variations in the degree of cure
for the resin matrix on the mechanical properties
of laminate panels, as this remains an unexplored
topic in the literature to the best of our knowledge.
The effect of resin cure level variations on the
mechanical properties will b investigated in this
work through an in-depth evaluation of tensile,
flex, and short beam shear strength (SBSS).
EXPERIMENTATION
Materials
The epoxy system used was LITESTONE™ 4100
resin with LITESTONE 4103H amine hardener.
The mix ratio used was 100 parts by weight resin
to 17.1 parts by weight of the hardener. The glass
fiber mat used were C1500/1001 bidiagonal(0/90)
fabric from Owens Corning with an areal weight of
534.4 gm/m2
.
Processing
The HP-RTM process equipment consisted of
RTM Rimstar Thermo with two mixing heads. The
hydraulic press was Dieffenbacher CompressPlus
DCP-U 2500 with a maximum closing force of 25000
kN. The fabrics were precisely sectioned according
to the requirements using Dieffenbacher preform
center. The processing parameters used for panel
production are listed in Table 1.
Panel Fabrication
The mold used for production of panels is shown
in Figure 1. The flat panel plaque mold with
full fiber clamp consisted of center-fed fan gate
injection inlet and vacuum-assisted injection.
The dimensions of the panels (w x l xt) were
500x900x3.175mm. The panels were produced with
an overall fiber volume fraction of 61.7%. The front
JANUARY/FEBRUARY 2022
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SAMPE JOURNAL |
25
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SAMPE Journal - January/February 2022

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