The data for these equations would come from a tensile test. Let’s start by mathematically defining the true and engineering stress-strain curves, talk about why you might want to use one versus the other, and then dive into the math and show how to convert from one to the other. That is because the material never gets weaker! The decrease in the engineering stress is an illusion created because the engineering stress doesn’t consider the decreasing cross-sectional area of the sample. The most obvious thing you may notice is that the true stress-strain curve never decreases. True stress correctly accounts for the changing cross-sectional area. When deforming a sample, engineering stress simplifies by neglecting cross-sectional change. So, what is the difference between engineering and true stress-strain curves? Normally I write these articles to stand alone, but in this case, I’ll assume you’re here because you googled a homework question 🙂 If you don’t understand the basics of the stress-strain curve, I recommend reading that one first. So, now you know all about engineering stress-strain curves.
