Question

Use the following data to plot the true stress-strain curve in EXCEL for the material with original cross sectional area Ao = 0.056 in2, and original length Lo = 2 in. Assume the material volume does not change during the testing.

Load, P (lb)               Extension, ∆L (in)

0                                  0

1600                            0.01

2500                            0.02

3000                            0.08

3600                            0.20

4200                            0.40

4500                            0.60

4600 (max)                  0.86

4586 (fracture)             0.98                            

In the SAME graph, plot the engineering stress-strain curve using the same data.

What is your finding when comparing these two curves? Which curve is preferred to describe the large strains?

Answer 1

In the above figure, The red line shows " true stress-strain curve " and the blue line shows " engineering stress-strain curve" .

From the above plots, the " engineering stress-strain curve " is plotted with the original cross sectional area of the material and " true stress-strain curve " is plotted with the cross sectional area of the material at which the load is applied ( so, the load is continuously changing at this time).

So, the " engineering stress-strain curve " is preferred for large strains. Where as " true stress-strain curve " is used to find some critical properties of manufacturing problems.