SAMPE Journal - January/February 2016 - 21
FEATURE ARTICLE
Figure 4. Three steps of CRTM modeling as
flow in porous media2. The deformation rate
is driven kinematically and determines the
magnitude of resin sources in filled domain.
Note that the term "compression" RTM is sometimes
applied to infusion into fully closed mold, but not
fully compacted preform. In this case, the preform
permeability is higher - possibly by an order of
magnitude than in the fully compacted case. Resin
injection is then completed by the compacting step.
Flow Modeling in LCM
In all cases, the flow of the resin through the preform
is very important. If inlets and vacuum vents are not
properly located, particular sections of the preform
may remain dry after the injection is complete. This will
result in poor mechanical properties or even render the
part unsuitable. As the flow patterns in more complex
geometries are not necessary intuitive, numerical
flow process modeling has been used for some time to
determine suitable resin injection and vent locations.
The RTM process was the first one to be used in
practice and the first one to be modeled. Many reliable
computer simulation tools have been developed for
this process5-12. Originally, the models were used just to
verify the pre-existing process designs. More recently,
their application has been extended to address process
optimization and control. These numerical tools have
been reasonably validated and proven to be useful for
design of manufacturing process of composite parts
for various applications by several LCM variations. The
change of thickness in VARTM and RTM light has been
partially addressed, either by more complex models,
or, more successfully, by use of "equivalent" material
properties. The latter approach facilitates using the
well-developed RTM numerical tools to be used as
well (Figure 3).
CRTM Process Modeling Using RTM Numerical
Tools
The nature of CRTM, complex process, costly tooling
and time constraints, calls for reliable predictive
SAMPE Journal, Volume 52, No. 1, January/February 2016
modeling, first to simulate the resin infusion and then,
beyond the scope of this paper, cure. If the modeling
is available, one can find the optimal processing time
and minimize manufacturing defects. Unfortunately, a
rigorous modeling of the CRTM process is significantly
more complex to create and requires measurement
of many material constants needed to model the
constitutive relationships of preform deformation2.
Consequently, simplifications tend to be applied, such
as the assumption of uniform through-the-thickness
preform deformation2. We will examine briefly
the work under these assumptions and then try to
quantify their validity.
Current Modeling Approach
In more conventional LCM approaches - RTM,
VARTM or RTM Light - the resin flow can be described
as a single process, similar throughout the infusion.
By comparison, in CRTM the infusion exhibits three
distinct stages2. Essentially, all of the phases can be
modeled by a single code as a Stokes flow through
gap and Darcy's flow through porous media. However,
if one desires to use existing tools this may be very
impractical. Instead, it is modeled as flow in porous
media but within different domains (mesh) and having
different boundary and initial conditions. These three
stages are:
1. Resin injection into the gap between the mold
platen and the fiber preform in the mold. This
is over when needed resin volume has been
injected.
2. Closing of the gap. This ends when contact
occurs between the tool and the preform in
some locations. During this phase the resin is
still distributed mainly in the remaining gap.
3. Compaction of the reinforcement by the mold.
Displaced resin impregnates the regions that
are still dry.
21
Table of Contents for the Digital Edition of SAMPE Journal - January/February 2016
Contents
SAMPE Journal - January/February 2016 - Cover1
SAMPE Journal - January/February 2016 - Cover2
SAMPE Journal - January/February 2016 - Contents
SAMPE Journal - January/February 2016 - 2
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