TENSILE STRENGTH

The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure.

There are three typical definitions of tensile strength:

Yield Strength/Yield Point: The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently. Knowledge of the yield point is vital when designing a component since it generally represents an upper limit to the load that can be applied
Ultimate strength: The maximum stress a material can withstand.
Breaking strength: The stress coordinate on the stress-strain curve at the point of rupture.

Necking: After a metal has been loaded to its yield strength it begins to "neck" as the cross-sectional area of the specimen decreases due to plastic flow. When necking becomes substantial, it may cause a reversal of the engineering stress-strain curve, where decreasing stress correlates to increasing strain because of geometric effects.This is because the engineering stress and engineering strain are calculated assuming the original cross-sectional area before necking.