INDIAN INSTITUTE OF TECHNOLOGY KANPUR Department of Materials and Metallurgical Engineering Virtual Laboratories for Thermal Processing and Characterization of Materials

Conversion of Load-Displacement Curve to Engineering Stress-Strain Curve

Figure below show a typical engineering stress-strain curve:

The salient observations from the above curve are listed below:

• As the tensile sample deforms the load initially increases and subsequently goes through a maximum.
• Beyond the maximum point the sample shows visible constriction in the gauge - this constriction is called the neck.
• At a particular load beyond the maximum point the sample would undergo fracture.

The load-displacement curve suffers from the disadvantage that it would vary as the sample size is changed. Therefore, the curve is normalized to make it independent of sample size. Load, F, is replaced by engineering stress: S = F/A_o. The displacement, u, is replaced by the engineering strain: e = u/L_o. The resulting, engineering stress-strain curve is shown below: