Hello,
The interface layer does not add any material. It does not have any influence on the stiffness matrix and so this is why it is not part of the sampling point. The interface layers allows the simulation of delamination by putting interface elements betweent the solid elements. Without the interface layer, the solid elements are connected at the node and cannot separate.
You want to know the stiffness matrix when some solid elements in a laminate are no longer connected (delaminated). This is not possible in ACP.
I did not fully understand your question at first.
Yes, I think you will have to perform the delamination simulation in Mechanical and calculate the stiffness matrix manually based on the loads, BCs, and displacements obtained.
Have a good day!
Reno.
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