Stress-Strain Curve

Stress-strain graph:

  It's a graph which represents stress value against strain value of the given material,when the material is subjected to increasing pull. It is the characteristics properties of the Materials.

1.    proportional limit: it is the point upto which hookes law is applicable ie., stress is directly proportional to strain i.e. Portion OA. Stress and Strain are linearly proportional.

2.  Elastic limit: there is always the limiting value of load up to which strain totally disappears on removal of load i.e. Point B. If we unload  on point B , unloading curve will be B-A-O  i.e. no permanent deformation happens but Stress is not linearly proportional to strain.

a.      material posses elastic nature and properties till elastic limit.

b.      upto this point material obtains its original configuration on removing load.

3.  Yield point: The stress beyond which material becomes plastic.

Point “C”          Upper yield point i.e. Load just before yielding starts.

Pont “ D”          Lower yield point i.e. Actual point where yielding will take place.

 # For practical purpose we take C and D as same.

# yield point for particular material is defined with Point “D”.

4.  Ducticle point: beyond this point neck forms where the local cross sectional area becomes significantly smaller than original. Point D onwards till point E . Rate of strain is very high i.e. strain is increases at rapid rate as compared to stress.

a.      material acquires plastic nature .

5.  Ultimate point: The point at upto which material can withstand maximum load and ultimate strength with maximum elongation i.e.  Point E . Strain hardening of material occurs due to the change in crystalline structure of material.

a.      large deformation possible before failure.

6.  Point of rupture: the stress which makes the material failure or break. Zone EF. After point E cross-section of the  specimen starts to reduce known as necking.