Define Matrix phase and dispersed phase of composites.

A composite has two constituents:

1. Matrix phase – the continuous phase that surrounds and binds the other phase. It may be a polymer, metal or ceramic.

• Binds the dispersed phase together and gives the composite its shape.
• Transfers and distributes the applied load to the reinforcement.
• Protects the reinforcement from abrasion, moisture and chemical attack.
• Keeps fibres apart and stops cracks from spreading from one fibre to the next.

Examples: epoxy and polyester resins (polymer matrix), aluminium and titanium (metal matrix), SiC and alumina (ceramic matrix).

2. Dispersed (reinforcing) phase – the discontinuous phase embedded in the matrix, as fibres, particles or flakes.

• Carries most of the load and raises strength and stiffness (modulus).
• Improves properties such as hardness, wear resistance, thermal stability and toughness.

Examples: glass, carbon and aramid (Kevlar) fibres; SiC and alumina particles; carbon black in rubber tyres; gravel in concrete.

Example of a whole composite: glass-fibre reinforced plastic (GFRP), where the matrix is polyester or epoxy resin and the dispersed phase is glass fibre.