Suppose a question starts by pointing that a cylindrical sample of a certain metal (in my case it is brass alloy) was put under a load. This piece has an initial diameter and length of 1.263cm and 5cm respectively.
It then provides a table showing the Gauge length, Stress, and Strain of this piece with respect to the varying Loads it is being subjected to.
Finally, the question states that the piece has fractured and was at a Diameter of 0.935cm and gage length of 7.535cm when this happened. It then proceeds to ask to draw an Engineering Stress Strain curve for this sample of metal.
My question here is, what is the formula that expresses the relation between stress and strain to use for this plot, and is it the same for the plastic and elastic deformation of this sample?