139
5
the processing temperature is less than their ignition
temperature.
5 Thermal and Hygrothermal Stability—The thermal stability
of synthetic fibres (such as glass, carbon, and Kevlar fibres)
is good, and they can be used under any thermal processing. Natural fibres are thermally less stable, and care must
be taken for their processing as mentioned previously.
Moisture affects all fibres, and the ingress of moisture in
Kevlar deteriorates its mechanical properties. In glass
fibres, moisture causes depletion of the coupling agent. In
carbon fibres, moisture affects the polyimide or epoxy over
the polymeric sizing. Natural fibres absorb moisture; thus,
their mechanical properties are diminished.
5 Post-processing Operations—The role of reinforcement and
its machinability is important for post-fabrication operations. Kevlar-reinforced composites are difficult to
machine, and they require water jet or laser cutting
operations for smooth cutting edges. Kevlar, having a fibril
structure, causes the fibrillization of fibres and gives a
rough surface to mechanical machining using standard
cutting tools, such as a hacksaw, milling cutter, turning
tool, etc. The processability of composites does not end
with striking the correct combination of raw materials and
processing methods to just get the product moulded. The
designer and process engineer must be prudent enough to
also plan the processing of the composite products for postfabrication finishing. Thus, the raw materials, moulding
surfaces, and processing technologies need to be chosen in
such a manner that they ensure a minimum of post-fabrication operations on moulded composite products.
5 UV Resistance—UV radiation does not affect natural fibres
and most synthetic-reinforcing fibres (except polyolefin
fibres, such as PP, UHMWPE, etc.).
2. Processing Technology Driven by Selection Criteria
5 Compatibility with the Form of Reinforcement—The forms
and weave patterns of reinforcement have a direct effect on
the processability of composites. Fabrics, CSM, and staples
cannot be used for filament winding and tape winding
processes. Staples cannot be used for the VARTM process.
Natural vegetation fibres are not compatible with hightemperature processing, and they also have limitations for a
filament winding process due to their limited tensile
strength.
5 Flow of Matrix—The weave of a reinforcement must allow
the resin to flow through it so that complete wettability is
achieved.
5 Production Rate—The production rate of composites also
has a bearing on the type of reinforcement to be used. In
order to achieve high production rates, prepregs or
performs are preferred to be used. For fewer batches (e.g.
ten pieces) of composite products, the hand layup method
may be the best in order to minimize mould costs, leading
5.3 · Thermosetting Composites
5
the processing temperature is less than their ignition
temperature.
5 Thermal and Hygrothermal Stability—The thermal stability
of synthetic fibres (such as glass, carbon, and Kevlar fibres)
is good, and they can be used under any thermal processing. Natural fibres are thermally less stable, and care must
be taken for their processing as mentioned previously.
Moisture affects all fibres, and the ingress of moisture in
Kevlar deteriorates its mechanical properties. In glass
fibres, moisture causes depletion of the coupling agent. In
carbon fibres, moisture affects the polyimide or epoxy over
the polymeric sizing. Natural fibres absorb moisture; thus,
their mechanical properties are diminished.
5 Post-processing Operations—The role of reinforcement and
its machinability is important for post-fabrication operations. Kevlar-reinforced composites are difficult to
machine, and they require water jet or laser cutting
operations for smooth cutting edges. Kevlar, having a fibril
structure, causes the fibrillization of fibres and gives a
rough surface to mechanical machining using standard
cutting tools, such as a hacksaw, milling cutter, turning
tool, etc. The processability of composites does not end
with striking the correct combination of raw materials and
processing methods to just get the product moulded. The
designer and process engineer must be prudent enough to
also plan the processing of the composite products for postfabrication finishing. Thus, the raw materials, moulding
surfaces, and processing technologies need to be chosen in
such a manner that they ensure a minimum of post-fabrication operations on moulded composite products.
5 UV Resistance—UV radiation does not affect natural fibres
and most synthetic-reinforcing fibres (except polyolefin
fibres, such as PP, UHMWPE, etc.).
2. Processing Technology Driven by Selection Criteria
5 Compatibility with the Form of Reinforcement—The forms
and weave patterns of reinforcement have a direct effect on
the processability of composites. Fabrics, CSM, and staples
cannot be used for filament winding and tape winding
processes. Staples cannot be used for the VARTM process.
Natural vegetation fibres are not compatible with hightemperature processing, and they also have limitations for a
filament winding process due to their limited tensile
strength.
5 Flow of Matrix—The weave of a reinforcement must allow
the resin to flow through it so that complete wettability is
achieved.
5 Production Rate—The production rate of composites also
has a bearing on the type of reinforcement to be used. In
order to achieve high production rates, prepregs or
performs are preferred to be used. For fewer batches (e.g.
ten pieces) of composite products, the hand layup method
may be the best in order to minimize mould costs, leading
5.3 · Thermosetting Composites