To whom it may concern,

I have a technical calculation question regarding the difference between the constitutive response of cohesive compared to continuum elements when NLGEOM is ON compared to OFF. 

I created a beam and added a layer of zero thickness cohesive elements in the center. The beam is being ran in implicit and in compression.

(on the left shows the layer of cohesive elements that are zero thickness) on the right it shows compressive and fixed boundary conditions.

**the cohesive elements have the same material properties as the continuum ones.

When it is OFF, I am seeing the stress and strain in the continuum and cohesive elements is the same (expected values from hand calculations).

When I add NLGEOM ON I see differences in continuum element (as expected as the true strain is calculated now with ln(1-e)).

However, what is not expected is the change in cohesive element response.

Max principal absolute stress:

continuum = -435.019

Cohesive = -448.584

I am wondering how these values are being calculated. It is unclear in the online documentation.

See photos below of 1. cohesive elements, 2. boundary conditions, 3.results

Thank you,

Allison Clement

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