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Classification of engineering materials

Short answer

Metals have metallic bonding, are ductile and conductive; used for shafts and wires. Ceramics have ionic/covalent bonding, are hard and brittle insulators; used for cutting tools and spark-plug insulators. Polymers have covalent chains and weak secondary bonds, are light and low-melting insulators; used for pipes and packaging. Composites combine matrix and reinforcement, giving high specific strength; used for glass-fibre panels and carbon-fibre aircraft parts.

Classify engineering materials into their main groups. Differentiate between metals, ceramics, polymers and composites with respect to bonding, typical properties and two applications each.

Engineering materials are grouped by the type of atomic bonding and structure into metals, ceramics, polymers and composites (semiconductors and biomaterials are sometimes added as special groups).

Classification

Engineering materials
 |-- Metals      : ferrous (steels, cast irons), non-ferrous (Al, Cu)
 |-- Ceramics    : oxides, carbides, nitrides, glasses
 |-- Polymers    : thermoplastics, thermosets, elastomers
 `-- Composites  : fibre, particle and laminar composites

Differences

PropertyMetalsCeramicsPolymersComposites
BondingMetallicIonic / covalentCovalent chains, weak secondary bonds between chainsCombination of two or more materials
StrengthGood, toughHigh compressive strength, weak in tensionLow to mediumHigh specific strength (along fibres)
DuctilityHighBrittleVaries, often highUsually low in direction across fibres
Melting pointMedium to highVery highLowLimited by matrix
ConductivityGood thermal and electricalInsulatorsInsulatorsDepends on constituents
DensityHighMediumLowLow to medium
Examples of useShafts, gears, frames (steel); wires (Cu)Cutting tools, refractory bricks, spark-plug insulatorsPipes, gears, insulation, packagingGlass-fibre panels, carbon-fibre aircraft parts

Key points

  • Metals have free electrons, so they conduct well and deform plastically.
  • Ceramics have strong directional bonds that resist dislocation motion, so they are hard but brittle.
  • Polymers are light and corrosion resistant but soften at low temperature.
  • Composites combine a matrix and a reinforcement to give properties that neither has alone.

✓ Answer checked by Claude Opus 5.5 (high effort)

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