U N I T 1 PROPERTIES OF MATERIALS This Unit looks at the properties of materials that make them suitable for certain uses, the most widely used engineering materials and their applications. You will also learn about more advanced materials and their treatments. A. MECHANICAL PROPERTIES OF MATERIALS When studying materials and especially when selecting materials for a project/design, it is important to consider their properties, which can be classified in 4 groups: 1. mechanical (strength, hardness, toughness, elasticity, plasticity, brittleness, ductility and malleability) 2. thermal (conductivity, expansion, melting point) 3. electrical (conductivity, magnetism, resistivity) 4. chemical (atomic volume, density, corrosion resistance, flammability). Strength, hardness, toughness, elasticity, plasticity, brittleness, ductility and malleability are mechanical properties used as measurements of how materials behave under a load. These properties are described in terms of the types of force or stress that the metal must withstand (see Chapter B). Strength is the property that enables a metal to resist deformation under load without breaking, bending, shattering or deforming. Tensile strength is a measurement of the resistance to being pulled apart when placed in a tension load. Fatigue strength is the ability of material to resist various kinds of rapidly changing stresses. Impact strength is the ability of a metal to resist suddenly applied loads. Hardness is the property of a material to resist cutting, penetration or abrasion. Toughness is the property that enables a material to withstand shock and to be deformed without cracking. It may be considered as a combination of strength and plasticity. Elasticity is the ability of a material to absorb a force and flex in different directions before returning to its original shape after the load is removed. Copper wire is used for its good electrical conductivity 46