The mechanical properties of a material are those properties that involve a reaction to an applied load. The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected. Mechanical properties are also used to help classify and identify material.
STRENGTH: The strength of a material is its ability to withstand an applied load without failure or plastic deformation.In machine design yield point or ultimate tensile / shear / compressive strength is used while designing.
Stiffness: Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.
Hardness: Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials (e.g. metals) are harder than others (e.g. plastics).
Elasticity: the ability of an object or material to resume its normal shape after being stretched or compressed. On a stress-strain diagram it is considered to be below proportional limit.But widely this point is taken as the yield point by drawing a line offset by 0.2% parallel to the straight line until it intersects the curve.
Plasticity: It describes the deformation of a (solid) material undergoing non-reversible changes of shape in response to applied forces.
Brittleness: A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength.