explain stress strain curve for metall wire?with the help of digram
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Answer:
Stress-Strain Curve for Metallic Wire
The curve shows variation of stress with strain when a metallic wire of uniform cross-section is subjected to an increasing load.
Region of Proportionality OA is a straight line which indicates that in this region, stress is linearly proportional to strain and the body behaves like a perfectly elastic body.
Elastic Limit: If you increase the strain a little beyond A, the stress is not linearly proportional to strain. However, the wire still remains elastic, i.e. after removing the deforming force (load), it regains its original state.
The maximum value of strain for which a body (wire) shows elastic property is called elastic limit. Beyond the elastic limit, a body behaves like a plastic body.
Point C: When the wire is stretched beyond the limit B, the strain increases more rapidly and the body becomes plastic. It means that even if the deforming load is removed, the wire will not recover its original length. The material follows dotted line CD on the graph on gradual reduction of load. The left over strain on zero load strain is known as a permanent set. After point E on the curve, no extension is recoverable.
Breaking point F: Beyond point E, strain increases very rapidly and near point F, the length of the wire increases continuously even without increasing of load. The wire breaks at point F. This is called the breaking point or fracture point and the corresponding stress is known as breaking stress.
The stress corresponding to breaking point F is called breaking stress or tensile strength. Within the elastic limit, the maximum stress which an object can be subjected to is called working stress and the ratio between working stress and breaking stress is called factor of safety.
In U.K, it is taken 10, in USA it is 5. India has adopted UK norms. If large deformation takes place between the elastic limit and the breaking point, the material is called ductile. If it breaks soon after the elastic limit is crossed, it is called brittle.
