Mechanical Properties Solids- Stress & Strain

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.

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