222
8
Typical parts manufactured by VARTM include airframes, fuselages, and automobile parts where tighter tolerances and high
mechanized properties are required. The size and shape of the
moulding play an important role in the VARTM process, and the
cost of big moulds is prohibitive. VARTM is a batch process, and the
production volumes are low. There are quicker and more efficient
versions of VARTM called RTM Lite, VARI, and Vacflo.
8.2 Processing-Induced Defects in Polymeric
Composites
Defects in composites occur during either processing or their service life. Processing-induced defects in composites may occur due
to the following reasons.
8.2.1 Unprepared Reinforcement or Matrix
It was discussed previously (7 Chap. 4) that the surface of the
reinforcement must be hydrophobic for its compatibility with a
hydrophobic matrix. If the surface treatment for compatibility
with the matrix is poor, the composite will be of poor quality, having low strength, low modulus, and low interlaminar shear
strength (ILSS) . Also, the surface treatments are responsible for
efficient handling of the reinforcement. If the surface coating of
carbon fibre is defective, then, during the filament winding of the
carbon fibre, a fuzzing of carbon fibre is observed at the payout
eye. Usually, a coating of polyimide or epoxy resin is placed on the
carbon fibre surface to make it compatible with the organic resins
and easy to handle.
As far as matrices are concerned, all of the components of the
matrices (in two- or three-component systems) must be mixed in
correct proportion to provide optimum properties. In the cases
where a hardner is mixed more, the cross-link density increases,
and high exothermic reactions occur, causing a poor quality of
composites. Similarly, low hardner contents lead to under or no
curing of the composite, affecting its glass transition temperature
and mechanical properties. In one component matrix system, such
as phenol formaldehyde resin (popularly known as phenolic resin),
lumps of resin due to ageing are observed, which cause a poor composite quality. The processing-induced defects for open and closed
mould processing are given here.
8.2.2 Improper Storage Conditions
Storage of a resin is important because resin matures with heat and
time. The maturity of resin is nothing but the initiation of a low
degree of cross-linking, which reduces the flowability of the resin
matrix in the composite. Resin matrices are susceptible to moisture
absorption. The ingress of moisture causes bulk and surface defects
Chapter 8 · Processability in Closed Mould Processing of Polymeric Composites
8
Typical parts manufactured by VARTM include airframes, fuselages, and automobile parts where tighter tolerances and high
mechanized properties are required. The size and shape of the
moulding play an important role in the VARTM process, and the
cost of big moulds is prohibitive. VARTM is a batch process, and the
production volumes are low. There are quicker and more efficient
versions of VARTM called RTM Lite, VARI, and Vacflo.
8.2 Processing-Induced Defects in Polymeric
Composites
Defects in composites occur during either processing or their service life. Processing-induced defects in composites may occur due
to the following reasons.
8.2.1 Unprepared Reinforcement or Matrix
It was discussed previously (7 Chap. 4) that the surface of the
reinforcement must be hydrophobic for its compatibility with a
hydrophobic matrix. If the surface treatment for compatibility
with the matrix is poor, the composite will be of poor quality, having low strength, low modulus, and low interlaminar shear
strength (ILSS) . Also, the surface treatments are responsible for
efficient handling of the reinforcement. If the surface coating of
carbon fibre is defective, then, during the filament winding of the
carbon fibre, a fuzzing of carbon fibre is observed at the payout
eye. Usually, a coating of polyimide or epoxy resin is placed on the
carbon fibre surface to make it compatible with the organic resins
and easy to handle.
As far as matrices are concerned, all of the components of the
matrices (in two- or three-component systems) must be mixed in
correct proportion to provide optimum properties. In the cases
where a hardner is mixed more, the cross-link density increases,
and high exothermic reactions occur, causing a poor quality of
composites. Similarly, low hardner contents lead to under or no
curing of the composite, affecting its glass transition temperature
and mechanical properties. In one component matrix system, such
as phenol formaldehyde resin (popularly known as phenolic resin),
lumps of resin due to ageing are observed, which cause a poor composite quality. The processing-induced defects for open and closed
mould processing are given here.
8.2.2 Improper Storage Conditions
Storage of a resin is important because resin matures with heat and
time. The maturity of resin is nothing but the initiation of a low
degree of cross-linking, which reduces the flowability of the resin
matrix in the composite. Resin matrices are susceptible to moisture
absorption. The ingress of moisture causes bulk and surface defects
Chapter 8 · Processability in Closed Mould Processing of Polymeric Composites