Materials

• The two broad categories the structure of a material is split into

  • Crystalline
  • Amorphous
• Crystalline structure


  Regular, organised structure
• Amorphous structure


  Random and disordered arrangement
• Polycrystalline structure


  Regular crystalline fragments (grains) arranged in a disordered way
• Structures in a pure metal that help them be malleable and ductile

  • Dislocations
• Alloying


  Process that can make metals less ductile
• How alloying reduces the ductility of a metal

  • Alloying produces a less regular structure due to different sized atoms
  • This can pin dislocations into position and reduce the metal's ductility
• Polymers


  Long repeating chains of monomers
• Structure that reduces the rotation and flexibility of monomer chains in a polymer

  • Crosslinks
• Types of materials


  • Metals
  • Polymers
  • Composites
  • Ceramics
• Metals


  • Tough
  • Ions can slip
  • Dislocations allow for more plastic deformation
• Alloys


  • Pin dislocations
  • Stiffer/stronger
  • More brittle
• Polymers


  • Flexible
  • Can coil and uncoil (elastic)
  • Slide over each other (plastic)
  • Stiffen up as strands align (crystalline)
  • Crosslinks bind strands together (stiffer/stronger but more brittle)
• Composites


  • Mix 2 or more materials to balance properties
  • Steel in concrete
  • Steel = is good in tension and Concrete = good in compression
• Ceramics


  • Stiff
  • Strong
  • Brittle
  • Fixed, directional bonds in lattice (stiff/strong)
  • Stress focuses on cracks, making them propagate quickly through lattice
  • Pre-stress to keep in compression
  • Surface treat to stop cracks
• Strength is typically measured by the stress required to cause permanent deformation or fracture