4.2 MATERIALS MATERIALS, CLASSIFICATION AND PROPERTIES Classification Materials Science is one of the fundamental fields of engineering because each material has to be specifically processed and manufactured according to the end product or purpose that it has been selected for. Materials can be classified into five categories: , , , , and . The properties of a material determine its for certain applications, so these properties have to be analysed during the design process. broad metals 1 polymers ceramics composites smart materials suitability DO List at least four metals you use daily. 1 Physical and chemical properties Physical and chemical properties determine how materials react to external factors such as electricity or heat. The main properties are: : the ability to conduct heat; Thermal conductivity : the temperature at which a material , that is, when it changes its state from a solid to a liquid; Melting point melts 2 : the ability to conduct electricity; Electrical conductivity : the ability to resist oxidation. Corrosion resistance DO At what temperatures do iron and glass melt? If you don’t know, look it up on the web. 2 Mechanical properties Mechanical properties define the ability of a material to resist an external force (for example, a ) or a stress. load : the ability to or resist forces without breaking. Strength withstand : the ability to resist abrasion and . Hardness scratches : the ability to resist deformation. Stiffness : the ability to the original shape when the force is . Elasticity regain removed : the ability to deform when . Ductility stretched : the ability to deform under compression and take on a new shape. Malleability : the tendency to break when subjected to stress. Brittleness 3 DO How many brittle objects do you know of? 3 Examples of materials Examples of applications Properties Metals Copper Electrical conductor wires; high electrical conductivity Ceramics Silica Optical fibres; high refractive index, low optical loss Polymers Polyethylene Food packaging; easily formed into flexible films Composites Graphite epoxy Aircraft components; high strength-to-weight ratio Smart materials Dielectric elastomers Robotics; used for high stress operations