A modiﬁed rule of mixture for the vacuum-assisted resin transfer moulding
Department of Mechanical Engineering, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
Received 31 August 2007
Received in revised form 18 January 2008
Accepted 18 March 2008
Available online 1 April 2008
A. Polymer–matrix composites (PMCs)
C. Computational simulation
E. Resin transfer moulding
Rule of mixture (ROM)
The vacuum-assisted resin transfer moulding process (VARTM) offers many advantages over the tradi-
tional resin transfer moulding such as lower tooling cost, room temperature processing. Computer sim-
ulation has become a powerful tool for liquid composite moulding process design and optimisation. In
the VARTM process simulation, due to the presence of HPM and ﬂow channels, the conventional simula-
tion will require 3-D geometric model and mesh generation. The extensive computation load and com-
plexity of pre-processing limit the usage of simulation in the process design and optimisation. In this
paper, a two-step method for improving the efﬁciency of VARTM process simulation is presented. First,
a design of experiment approach was coupled with 2-D CVFEM (control volume ﬁnite element method)
simulation to calculate the equivalent permeability and porosity for various process variable combina-
tions. Based on the data from DOE, a modiﬁed rule of mixture for calculating the equivalent permeability
and porosity was developed, with which the mould ﬁlling can be simulated in 2-D. Second, the algorithm
for the through-thickness ﬂow front construction was developed. The presented method was validated by
comparing the result against that from the 3-D simulation. It shows that the accuracy is within 5% while
the computation time saving is over 99%.
Ó 2008 Elsevier Ltd. All rights reserved.
The vacuum-assisted resin transfer moulding process (VARTM)
offers many advantages over the traditional resin transfer mould-
ing such as lower tooling cost, room temperature processing. This
process has been employed to manufacture many large compo-
nents ranging from turbine blades and boats to rail cars and bridge
This study focuses on one of the common VARTM processes: the
Seemann Composite Resin Infusion Moulding Process (SCRIMP),
which was invented and patented in the late 1980s by Bill See-
mann. As shown in Fig. 1, in this process, a highly permeable dis-
tribution medium is incorporated into ﬁbre preform as a surface
layer. During infusion, resin ﬂows preferentially across the surface
and simultaneously through the preform thickness, which enables
large parts to be fabricated.
Complete ﬁlling of the mould with adequate wetting of the ﬁ-
brous preform is critical in the VARTM. Incomplete impregnation
in the mould leads to defective parts containing dry spots. In order
to achieve good quality, processing parameters such as the loca-
tions and numbers of gates and vents need to be properly designed.
Traditionally, trial-and-error techniques are widely applied in
the composite industry, which largely depend on the experience
and skills of operators. It is very costly and time-consuming. With
the development of computing technology, simulation has become
a powerful tool for the process design and optimisation. Among the
various simulation techniques, the control volume ﬁnite element
method (CVFEM) has been the predominant method [1–5]. It forms
and solves a set of equations for nodal control volumes as if they
were ﬁnite elements. Mesh regeneration is not required, which
makes the computation more efﬁcient.
In the conventional RTM process, ﬁbre is the only ﬂow medium.
The part can often be regarded as a shell and simulated in 2-D. In
the VARTM process, due to the existence of two distinct ﬂow med-
ia, ﬁbre preform and high permeable medium (HPM), usually 3-D
models are required for simulation. When a 3-D model is used, be-
cause the distribution medium is usually much thinner than the
preform, a ﬁner mesh is needed to avoid the high aspect ratio,
which may result in poor conditioning in simulation, as well as
from discretization errors. This uses a large amount of computer
hardware resources and increases the computer load, especially
for large parts. The simulation time increases signiﬁcantly and
makes the simulation not feasible.
The VARTM process simulation has been studied extensively.
Mathur et al.  developed an analytical model, which predicts
the ﬂow times and ﬂow front shapes as a function of the properties
0266-3538/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
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Composites Science and Technology 68 (2008) 2125–2133
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