Cohesive Analysis with Abaqus/Explicit

Hello all,

I'm trying to model composite delamination under non-severe impact on layered composites in ABAQUS/Explicit.

To begin with, I've modeled a 2D aluminum with a finite very low thickness cohesive layer with traction-separation behavior between. Then, I give some displacement to the middle-top node to simulate an impact scenario. However, even in this simple configuration, I'm having stress distribution problems when the models with cohesive layer between and without cohesive layer are compared.

The problem is, I'm having some ridiculous stress distribution and meaningless bubbles when I model with cohesive elements, at the beginning of the step. I'm also having different stress outputs for the cases with and without cohesive layer.

I noticed that the stress output result varies with:

Cohesive layer in-plane thickness
Cohesive layer density
Cohesive layer penalty stiffness (Knn, Kss, Ktt)

From what I've read from literature, the common belief is using default thickness, very low density and very high penalty stiffness for those fields. However, with any try with those values, I couldn't get meaningful results.

Here's my input file for the cohesive & non-cohesive cases and the pictures of the problem I'm experiencing: https://www.dropbox.com/sh/igpidoms47xdvf4/MGHg3Gi...

Thanks in advance.