Stress vs logarithmic strain plot from Abaqus

Question

Stress vs logarithmic strain plot from Abaqus

compe_ad (Civil/Environmental)

(OP)

30 Oct 23 17:23

Hi all! I am trying to understand the stress vs strain plot for my model. I am using Abaqus/Explicit so 'LE' is the strain that I selected for output. I am trying to understand the trend of stress vs LE plot. Why am I getting opposite that expected? Can anyone please help me to understand this? The loading and unloading branch are mirror image of what I am expecting. Also, why I am getting positive strain?

rb1957 (Aerospace) · Answer 1 · 2023-10-30 17:34:44

why plot stress vs log (strain) ? why not stress vs strain ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

FEA way (Mechanical) · Answer 2 · 2023-10-30 17:46:47

About strain output in Abaqus/Explicit (from the documentation, of course):

Quote:
Logarithmic strain (output variable LE) is the default strain output in Abaqus/Explicit; nominal strain (output variable NE) can be requested as well. The “integrated” total strain is not available in Abaqus/Explicit.

SWComposites (Aerospace) · Answer 3 · 2023-10-30 17:49:21

You can’t just look at results from one element.
Suggest running the model with a simple static load first and ensure the mesh, loads, bcs are all generating appropriate and understandable results before trying to sort out the dynamic results.

compe_ad (Civil/Environmental) · Answer 4 · 2023-10-30 18:00:28

Thank you all! Even if I convert log strain to true strain. The trend will be the same.
If I were to generate stress-strain plot for concrete, then how should I do it without looking at one element?

SWComposites (Aerospace) · Answer 5 · 2023-10-31 01:44:53

It might help to explain what the purpose is for the model, and why you are looking at stress-strain at that particular location.
You should first review the overall stress distribution in the concrete, and figure out the specific locations of interest based on the purpose for the model.

swimfar (Mechanical) · Answer 6 · 2023-11-06 18:07:31

Stress and strain are tensors. You are plotting scalars. Which components of stress and strain are you actually plotting? Unless you're simulating a uniaxial tensile test, you shouldn't expect your results to look like a uniaxial stress-strain curve.

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Stress vs logarithmic strain plot from Abaqus