Good morning,

Our laboratory makes tensile testing on steels. We often observe Young's Modulus (initial slope of the tensile curve) very different of the expected
value of 207 GPa (we observe 140 GPa to 230 GPa) on Carbon Steel materials
in different metallurgical states (Q, QT, N, ...).
This seems to occur since years (I have asked former workers), independently
of tensile testing machines, operator, sample geometry.
We have also asked INSTRON, the supplier of our testing machine, and they
have no ideas.

To live with the problem, it was decided to make an hysteresis loop after 2% deformation and use that slope as Young's modulus. The value so obtained is only slightly less dispersed, but a recent experiment with multiple hysteresis loops (after 1% 2%, 3%, ...) shows that doing so, the Young's Modulus seems to decrease with the deformation performed before the hysteresis.

Do you have any ideas or references about : - why the initial slope and the hysteresis slope differ so much from 207 GPa - why Young's Modulus seems to decrease as the inital deformation increases.

I have done search on the Web with google and Copernic, but got no helpful answer.

Thank you very much for your help,

Michel

Our laboratory makes tensile testing on steels. We often observe Young's Modulus (initial slope of the tensile curve) very different of the expected

To live with the problem, it was decided to make an hysteresis loop after 2% deformation and use that slope as Young's modulus. The value so obtained is only slightly less dispersed, but a recent experiment with multiple hysteresis loops (after 1% 2%, 3%, ...) shows that doing so, the Young's Modulus seems to decrease with the deformation performed before the hysteresis.

Do you have any ideas or references about : - why the initial slope and the hysteresis slope differ so much from 207 GPa - why Young's Modulus seems to decrease as the inital deformation increases.

I have done search on the Web with google and Copernic, but got no helpful answer.

Thank you very much for your help,

Michel