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Strength – the limiting loads which the structural and machine member can stand before failure of the material or excessive deformation occurs.
Elasticity - The property which enables a material to return to its original shape and dimension after the load is removed.
Plasticity - The ability of a material to be deformed extensively without rupture.
Ductility - The property of a material that permits it to be reduced in cross sectional area without fracture. In a tensile test, ductile metals show considerable elongation eventually failing by necking, with consequent rapid increase in local stresses.
Hardness – the ability of a material to resist surface abrasion/deformation. A number of methods are employed including Brinell, Vickers and Rockwell. The steel to be tested is indented by a hardened steel ball or diamond under a given load and the size of the impression is then measured. For steel there is an empirical relationship between hardness and tensile strength and the hardness number is often used as a guide to the tensile strength, e.g. 229 Brinell = 772N/mm2 (50 tons/sq.in).
Use of these Mechanical Properties
All these properties of a material enable us to design structural or machine members to suit our particular application.