Area under the strain-stress curve up to fracture:

Area under the strain-stress curve up to fracture gives the toughness of the material.

Explanation:

When a material is loaded by external forces stresses are developed in the material which produce strains in the material.

The amount of strain that a given stress produces depends upon the Modulus of Elasticity of the material.

Toughness of a material is defined as the energy absorbed by the material when it is loaded until fracture. Hence a more tough material absorbs more energy until fracture and thus is excellent choice in machine parts that are loaded by large loads such as springs of trains, suspension of cars.

The toughness of a material is quantitatively obtained by finding the area under it's stress-strain curve until fracture.

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