Important Mechanical Properties
Elasticity:- It is the poperty by virtue of which a material deformed under the load is enabled to return to original dimension when the load is removed.
♦ If the body regains completely its original shape it is called perfectly elastic body.
♦ Elastic limit marks the partial break down of elasticity beyond which removal of load result in a degree of permanent deformation.
♦ Steel, Aluminium, Copper, Concrete may be considered to be perfectly elastic within certian limit.
Plasticity:- The characteristics of the material by which it undergoes inelastic strain beyond those ar the elastic limit is known as plasticity.
♦ This property is particularly useful in operation of pressing and forging.
♦ When large deformation occurs in in a ductile material loaded in plastic region, the material in said to undergo plastic flow.
Ductility:- It is property which permits a material to be drawn out longitudinally to a reduced section, under the action of tensile force.
♦ A ductile materialmust posses a high degree of plasticity and stength.
♦ Ductile material must have low degree of elasticity.
♦ This is useful in wire drawing.
Brittleness:- It is lack of ductility. Brittleness implies that it can not be drawn out by tension to smaller section.
♦ in brittle material failure take place under load without significant deformation.
♦ Ordinary glass is nearly ideal brittle material.
♦ Cast iron, concrete and ceramic material are brittle material.
Malleabillity:- It is property of a material which permits the material to be extended in all direction without rupture.
♦ A malleable material posses a high degree of plasticity, but not necessarily great strength.
Toughness:- It is the property of end material which enables it to absorb energy without fracture.
♦ It is desirable in material which is subject to cyclic or shock loading.
♦ It is represented by area under stress-strain curve for material up to fracture.
♦ Bend Test used for common comparative test for toughness.
Hardness:- It is the ability of material t resist indentation or sufrace abrasion.
♦ Brinell hardness test is used to check hardness.
♦ Brinell hardness number,…
Hardness number = P / πD/2 x [D-(√D2 – √d2)]
where, P= Standard load
D= Diameter of steel ball(mm)
d= Diameter of indent(mm)
Strength:- This property enables material to resist fracture under load.
♦ This is most important property from design point of view.
♦ Load required to cause fracture, divided by area of test specimen, is termed as ultimate strength.