Question

After the experiment of Aluminum, Copper and Nylon specimens, data shows that the tangent modulus is lower than the Young's modulus.
What does that physically mean?
Are the specimens showing signs of softening or hardening?

Answer 1

Hi, thanks for the question.

The tangent modulus is defined as the slope or the rate of change of a stress-strain curve at an instantaneous moment. The usage of tangent modulus comes in handy when you need to define the stiffness of material in the plastic range.

As a general rule of thumb, since the tangent modulus is defined at an instantaneous point on the curve, it is always less than Young's modulus, since Young's modulus is defined as the stiffness of a material through its stiffness range.

So, if the experiment says that Tangent modulus is lower than Young's modulus, then it means that at that point, the material is showing signs of plasticity, and hence, work hardening and straining hardening start taking place within the material. And hence, this means, the material is starting to get stiffer and will not revert back to its original shape. Hence, the specimens are showing signs of hardening.