Elasticity and Plasticity

Elasticity:

       External loads tend to deform materials from their original shape and size. Elasticity is the ability of a material to return to its original shape and size after removing the load applied. Elastic deformation (change of shape or size) lasts only as long as a deforming force is applied to the object, and disappears once the force is removed.This is so because the atoms in the metal change their position due to external stress but can't take new positions because the change of position is too small (or in acceptable range)

     Steels and other such materials are elastic over good range.

Plasticity:

     External loads tend to deform materials from their original shape and size. Plasticity is the ability of a material to retain the deformation even after external load is removed.In plastic deformation, the atoms in the material due to external force are displaced and take up new positions. They cannot come back to their natural positions once force is removed.

     This is very desirable property in machine tools. Lead has good plasticity at room temperature. Cast Iron has no plasticity even at very high temperature.    

PS: Some of the info here is taken from science.jrank.org & from Wikipedia. Please do refer to them for further info

with warm regards

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