Lap shear test with silicone adhesive

TBauTBau PisaMember

Dear community,

For my thesis I am modeling (3D) a lap-shear test for an adhesive-bonded joint. Two metal plates (one steel, one aluminium) - bonded together by a silicone bead - are clamped at the machine at their ends. The lower clamp is fixed, while the upper one moves upward. As during the experiment we reached large displacement, a hyper-elastic Ogden1 material model is set for the silicone, and Large Deflection is switched ON in the analysis setting. For the elements, I chose SOLID185 adding an u-P formulation to avoid distorsion. For the bonded regions, I chose not to merge the geometry on space clam, but to define a comtact region in the modeler. The contact region is "bonded" with MPC formulation.

What I am trying to get is the strain along three path in Z direction (find attached):

- very close to the bonded region between silicone and the steel plate

- very close to the bonded region between silicone and the alum. plate

- in the middle of the silicone bead

Despite the global force-displacement curve really well follows the experimental one, I have some problems when I check the solution: should I check the strain values on the SCS or on the GCS? The SCS gives me negative values in the middle of the silicone bead, while the GCS positive values. Furthermore, both solution disagree with the displacement field: if I try to derive the strain from the displacement in Z direction along the path, the solution is closer to reality.

How can I solve this problem? Should I define another type of CS? Is possibile to have a CS which follows the deformed shape of the path point by point?

 

Thank u!

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