In one line
Based on the reinforcement, composites are classified into particle-reinforced, fibre-reinforced and structural composites, each with sub-types.
Explained simply
Classify composites by asking "what shape is the strengthening ingredient?" Grains or pebbles → particle composite. Threads → fibre composite. Layers or sheets → structural composite. This is the standard classification used in materials science textbooks.
How it works
- Particle-reinforced composites
- Large-particle composites: particles are relatively large; the particles restrain matrix movement and share load. Examples: concrete (cement + sand + gravel), cermets such as tungsten carbide (WC) in cobalt matrix for cutting tools, carbon black in rubber tyres.
- Dispersion-strengthened composites: very fine particles (roughly 10–100 nm) uniformly dispersed in a metal; they block dislocation motion, giving strength retained at high temperature. Examples: thoria-dispersed nickel (TD nickel), sintered aluminium powder (SAP: Al with Al2O3).
- Fibre-reinforced composites
- Continuous and aligned fibres: highest strength along fibre direction.
- Discontinuous (short) fibres: aligned or randomly oriented; random gives nearly equal properties in all directions in a plane.
- By fibre type: glass-fibre reinforced polymer (GFRP), carbon-fibre reinforced polymer (CFRP), aramid (Kevlar) composites.
- Structural composites
- Laminar composites: layers (laminae) with different orientations bonded together; e.g., plywood with alternating grain directions.
- Sandwich panels: two strong, stiff thin face sheets bonded to a light thick core (honeycomb, foam, balsa wood); very high stiffness-to-weight. Used in aircraft floors, walls and doors.
Key formula
No formula for classification. Fibre effectiveness depends on aspect ratio (length/diameter); long fibres transfer load better.
| Type | Reinforcement shape | Example |
|---|---|---|
| Large particle | Coarse particles | Concrete, WC–Co cermet |
| Dispersion strengthened | Fine (nano-sized) particles | TD nickel, SAP |
| Fibre reinforced | Continuous or short fibres | GFRP, CFRP, Kevlar–epoxy |
| Laminar | Bonded sheets | Plywood |
| Sandwich | Faces + light core | Honeycomb aircraft panels |
Quick example
A cricket bat handle with carbon fibre, a car tyre with carbon black, a building column of reinforced concrete and an aircraft cabin floor of honeycomb sandwich panels each use a different class from the table.
Common mistakes
- Putting reinforced concrete (with steel rods) only under particle composites; plain concrete is a particle composite, and the steel rods add a further reinforcement.
- Confusing dispersion-strengthened (fine particles, dislocation blocking) with large-particle composites.
- Missing structural composites entirely.
How MU asks it
"Classify composites with examples" (5 marks) or "Write a note on fibre-reinforced composites" (3–5 marks). For full marks: a classification tree (diagram), a two-line explanation for each class and sub-class, and one example each.