224
8
8.2.6 Improper Closing of the Mould
Improper closing of mould can lead to dimensional instability of
the cured product, and also it may lead to resin oozing out upon
curing. The oozing out of the resin leads to an imbalance in the
volume fractions of the reinforcement and the matrix. Thus, the
composite will have low mechanical properties.
8.2.7 Demoulding Temperature
A moulding (product) must be taken out of the mould at room temperature or at a prescribed demoulding temperature. If the moulding is removed from the mould at a higher temperature than the
demoulding temperature, warpages may occur in the product due
to the generation of residual stresses. The residual stresses are
caused due to a thermal nonequilibrium between the reinforcement
and the matrix at high temperatures, even though curing is complete. The reason for thermal nonequilibrium is the difference in
linear thermal expansion between the reinforcement and the
matrix. This problem is observed most in carbon fibre-reinforced
composites because the conductivity of carbon is much higher than
the conductivity of the matrix. Therefore, the coefficient of linear
thermal expansion of the carbon fibre is more than the matrix.
8.2.8 Post-fabrication Finishing Operations
In many composite products, there is a need to carry out postfabrication finishing operations, such as surface painting, metalizing, and fitment of assembly. All of these operations demand care in
handling so that no damage to the surface is caused. Many a time,
surface defects are not visible, but they remain in the form of microcracks or surface crazing. Microcracks or surface crazing leads to
debonding and delamination, which eventually causes failure of the
composite.
8.3 Future Composite Manufacturing
Technologies
Composites are primarily used for their good properties and to
replace conventional materials. In order to make composites competitive against metals (especially steels), cost reduction has to
occur in three areas: nonrecurring costs, recurring costs, and direct
operating costs (DOC) (e.g. durability, maintainability, reliability,
and reparability). The DOC are a major issue because many highend products (aircrafts, automobiles, yachts, etc.) depend heavily
on the use of composites. There is always a debate on the costeffectiveness of composites for commercial use; however, such
debates can only be put to an end with the development of newer
cost-effective processing technologies. The cost-effective processing
Chapter 8 · Processability in Closed Mould Processing of Polymeric Composites
8
8.2.6 Improper Closing of the Mould
Improper closing of mould can lead to dimensional instability of
the cured product, and also it may lead to resin oozing out upon
curing. The oozing out of the resin leads to an imbalance in the
volume fractions of the reinforcement and the matrix. Thus, the
composite will have low mechanical properties.
8.2.7 Demoulding Temperature
A moulding (product) must be taken out of the mould at room temperature or at a prescribed demoulding temperature. If the moulding is removed from the mould at a higher temperature than the
demoulding temperature, warpages may occur in the product due
to the generation of residual stresses. The residual stresses are
caused due to a thermal nonequilibrium between the reinforcement
and the matrix at high temperatures, even though curing is complete. The reason for thermal nonequilibrium is the difference in
linear thermal expansion between the reinforcement and the
matrix. This problem is observed most in carbon fibre-reinforced
composites because the conductivity of carbon is much higher than
the conductivity of the matrix. Therefore, the coefficient of linear
thermal expansion of the carbon fibre is more than the matrix.
8.2.8 Post-fabrication Finishing Operations
In many composite products, there is a need to carry out postfabrication finishing operations, such as surface painting, metalizing, and fitment of assembly. All of these operations demand care in
handling so that no damage to the surface is caused. Many a time,
surface defects are not visible, but they remain in the form of microcracks or surface crazing. Microcracks or surface crazing leads to
debonding and delamination, which eventually causes failure of the
composite.
8.3 Future Composite Manufacturing
Technologies
Composites are primarily used for their good properties and to
replace conventional materials. In order to make composites competitive against metals (especially steels), cost reduction has to
occur in three areas: nonrecurring costs, recurring costs, and direct
operating costs (DOC) (e.g. durability, maintainability, reliability,
and reparability). The DOC are a major issue because many highend products (aircrafts, automobiles, yachts, etc.) depend heavily
on the use of composites. There is always a debate on the costeffectiveness of composites for commercial use; however, such
debates can only be put to an end with the development of newer
cost-effective processing technologies. The cost-effective processing
Chapter 8 · Processability in Closed Mould Processing of Polymeric Composites