Why does the number changed Modulus of Elasticity We must ca

Modulus of Elasticity We must calculate the slop straight-line portion of the graph. Using the magnified shown in blue, this line extends from point O to an estimate which has coordinates of approximately (0.0016 in Therefore,

Solution

This is a way of calculation of yield stress for materials which does not show a defined yield point like steel (which has distinct upper and lower yield). For these materials, the stress corresponding to a certain percentage of strain in called yield stress or proof stress.

In this example yield stress is considered corresponding to 0.2% strain which means 0.002 in/in of strain. Such a small value of strain is difficult to plot if the stress-strain curve is taken as original. Instead it is magnified in the elastic region to capture the elastic portion more precisely.

So the curve OAA\' is the enlarged view of the original curve OA\'. As they are plotted on the same graph, there must be two scale: one corresponding to original (black) stress-strain curve and the other one (blue) corresponding to magnified curve.