Explain fiber reinforced composite and write its applications and limitations.

Fibre-reinforced composites (FRC) are composites in which the dispersed phase is in the form of fibres, i.e. long, thin filaments with a high length-to-diameter ratio, embedded in a matrix. The fibres carry most of the load. The matrix binds them, transfers the load to them and protects them.

• Fibres: glass (E-glass, S-glass), carbon or graphite, aramid (Kevlar), boron, SiC, natural fibres (jute, sisal).
• Matrix: polymers (epoxy, polyester), metals (Al, Ti) or ceramics.
• Types by fibre arrangement: (i) continuous, aligned fibres, which are strongest along the fibre direction (anisotropic); (ii) discontinuous (short) fibres, either aligned or randomly oriented, which give nearly isotropic properties.

  continuous aligned        discontinuous aligned      discontinuous random
  ================          == == == == ==             / -- \ | / --
  ================          = == == == ==              \ | -- / \ |
  ================          == == == == ==             -- / | \ -- /

Properties: high strength-to-weight and stiffness-to-weight ratios, good fatigue and corrosion resistance, and properties that can be tailored by choosing the fibre type, fraction and orientation.

Applications: GFRP in boat hulls, car bodies, pipes, tanks and helmets; CFRP in aircraft parts, racing cars, bicycles and sports goods; Kevlar composites in bullet-proof vests and helmets; wind-turbine blades; PCB laminates; reinforced concrete and building panels.

Limitations

• High cost, especially of carbon and aramid fibres, and of fabrication.
• Anisotropic properties: they are weak across the fibre direction.
• Delamination, and poor resistance to impact damage that cannot be seen.
• Polymer-matrix FRCs have limited service temperature and can absorb moisture.
• They are difficult to repair, recycle and join, and their brittle failure gives little warning.