Background

For extensive background see

EngineeringToolbox.com and other sources.

An Elongation Curve represents Position vs$.$ Load. This illustrates the raw data as collected.

A Stress Strain Curve represents Strain vs$.$ Stress. Although the

Stress Strain

elongation curves looks visually very similar to the Stress Strain

Curve, the axes are different.

Stress $(MPa)=\frac{\text{L}\text{o}\text{a}\text{d}(\text{N}\text{e}\text{w}\text{t}\text{o}\text{n}\text{s})}{\text{C}\text{r}\text{o}\text{s}\text{s}-sectional\text{A}\text{r}\text{e}\text{a}(m^2)}$

Strain $=\frac{\text{E}\text{l}\text{o}\text{n}\text{g}\text{a}\text{t}\text{i}\text{o}\text{n}(m)}{\text{G}\text{a}\text{u}\text{g}\text{e}\text{L}\text{e}\text{n}\text{g}\text{t}\text{h}(m)}$

Modulus of elasticity is the slope of the early linear portion of the

curve. Sometimes there is a small phase prior to the linear

portion, which is usually ignored, as it is where some slack in the

sample is taken up$.$

Ultimate stress is the maximum stress measured.

Fracture stress is the stress value when the sample fractures

$($breaks$).$