38
2
14. Radar Transparency—Composites may be designed with a low
dielectric constant and a low loss tangent so that they will
cause a minimum attenuation of EM radiation to pass through
them. This property makes composites ideal materials for
application in radomes and nose cones. The composite will
protect the antenna from damaging operational and environmental effects, while at the same time allow an EM signal to
pass through it. Radar- transparent composites are made from
glass or Kevlar fibre- reinforced polymers, such as epoxy resin,
low loss polyester resin, phenolic resin, or polyimide resin.
Carbon fibres are never used as reinforcement for radartransparent applications due to their conducting and semiconducting behaviour. Radio-frequency identification devices
(RFID) used for high frequency (HF), very high frequency
(VHF), and ultra-high frequency (UHF) that are embedded in
composites are used in various applications.
15. Low Thermal Conductivity—Composites are good insulators
due to their constituent phases, which do not easily conduct
heat. Composites exhibit a low thermal conductivity because
of their relatively low density, weak chemical bonding,
amorphous structure, and high anharmonicity in their
molecular vibrations. The main mechanism of heat conduction in most polymers is through phonons. The interaction
among phonons and their interaction with subatomic particles
cause a transfer of heat energy. The phonon scattering is
caused by anharmonicities due to lattice imperfections, voids,
and impurities.
16. Durability—Structures made of composites are durable and
have a long lifespan. They need little maintenance. Polymeric
composites may be designed for required performance. By
using a hybrid reinforcement and the choicest of matrices,
polymeric composites have the possibility of ensuring that a
product lasts for its designed lifespan.
17. Fire Retardancy—The fire resistance of composites is
dependent on the fire resistance of the matrix. Common
matrices are not inherently fire-resistant. Therefore, fire
retardants are added to make it fire-resistant. The matrices
containing ether group (-O-) are inherently fire-resistant,
and these matrices are PEEK, PEI, etc. Among reinforcements, glass fibre is fire-resistant, whereas carbon and
graphite fibres are not.
18. Ablation Property—Composites may be designed for ablation
applications. Common reinforcements for ablative composites
are glass fibres (preferably with high silica content) and
carbon fibres (preferably rayon based). The preferred matrices
for ablative composites are phenolic resin, epoxy resin, and
polyimide resin. The mechanism of energy exchanges in the
ablation process is shown in . Fig. 2.10.
Among all matrices, phenolic resin is used the most
because of its good ablative properties. Ablative composites are
used in re- entry aerospace vehicles, as liners for rocket motors,
in hypersonic vehicles, etc.
Point to Ponder…
Ablative composites made
possible the manufacturing and
flying of space shuttles, rockets,
and intercontinental ballistic
missiles (ICBM).
Chapter 2 · Advantages and Applications of Polymeric Composites
2
14. Radar Transparency—Composites may be designed with a low
dielectric constant and a low loss tangent so that they will
cause a minimum attenuation of EM radiation to pass through
them. This property makes composites ideal materials for
application in radomes and nose cones. The composite will
protect the antenna from damaging operational and environmental effects, while at the same time allow an EM signal to
pass through it. Radar- transparent composites are made from
glass or Kevlar fibre- reinforced polymers, such as epoxy resin,
low loss polyester resin, phenolic resin, or polyimide resin.
Carbon fibres are never used as reinforcement for radartransparent applications due to their conducting and semiconducting behaviour. Radio-frequency identification devices
(RFID) used for high frequency (HF), very high frequency
(VHF), and ultra-high frequency (UHF) that are embedded in
composites are used in various applications.
15. Low Thermal Conductivity—Composites are good insulators
due to their constituent phases, which do not easily conduct
heat. Composites exhibit a low thermal conductivity because
of their relatively low density, weak chemical bonding,
amorphous structure, and high anharmonicity in their
molecular vibrations. The main mechanism of heat conduction in most polymers is through phonons. The interaction
among phonons and their interaction with subatomic particles
cause a transfer of heat energy. The phonon scattering is
caused by anharmonicities due to lattice imperfections, voids,
and impurities.
16. Durability—Structures made of composites are durable and
have a long lifespan. They need little maintenance. Polymeric
composites may be designed for required performance. By
using a hybrid reinforcement and the choicest of matrices,
polymeric composites have the possibility of ensuring that a
product lasts for its designed lifespan.
17. Fire Retardancy—The fire resistance of composites is
dependent on the fire resistance of the matrix. Common
matrices are not inherently fire-resistant. Therefore, fire
retardants are added to make it fire-resistant. The matrices
containing ether group (-O-) are inherently fire-resistant,
and these matrices are PEEK, PEI, etc. Among reinforcements, glass fibre is fire-resistant, whereas carbon and
graphite fibres are not.
18. Ablation Property—Composites may be designed for ablation
applications. Common reinforcements for ablative composites
are glass fibres (preferably with high silica content) and
carbon fibres (preferably rayon based). The preferred matrices
for ablative composites are phenolic resin, epoxy resin, and
polyimide resin. The mechanism of energy exchanges in the
ablation process is shown in . Fig. 2.10.
Among all matrices, phenolic resin is used the most
because of its good ablative properties. Ablative composites are
used in re- entry aerospace vehicles, as liners for rocket motors,
in hypersonic vehicles, etc.
Point to Ponder…
Ablative composites made
possible the manufacturing and
flying of space shuttles, rockets,
and intercontinental ballistic
missiles (ICBM).
Chapter 2 · Advantages and Applications of Polymeric Composites