Reply To: Honeycomb Shear modulus Calculation based on Analysis – ASTM 273

[peteroznewman]

Fixed Joints could be a problem, they behave differently to Bonded Contact. Fixed Joints can be defined with the Behavior set to Rigid or Deformable. I believe the default is Rigid. Check to see what you have used and reply with the setting used.

After the model has solved, you can visualize the constraint equations the Rigid Fixed Joints created. Click on the Solution Information folder in the outline, the graphics window switches to the Worksheet tab at the bottom. Click on the Geometry tab at the bottom of the graphics window and you should see the red spider legs of the contraint equations representing the Fixed Joint. Reply with a screen image of that.

Fixed Joints are different to Bonded Contact. Fixed joints take all the nodes on the reference side and connect them to one node at the center, and do the same for the mobile side so all the forces and moments are transfered through that pair of nodes at the center. If you have a Rigid Fixed Joint, then none of the nodes can move out of the plane they start in, meaning that the test plate cannot flex. This may be okay since the test plate is supposed to be much stiffer than a typical thin facesheet, but if you were modeling a thin facesheet, using a Fixed Joint to connect the edges at the top of the core to the top facesheet would be a huge mistake. Bonded contact acts locally, so the facesheet can flex due to the applied loads.

Bonded contacts also have a Pinball radius and that would be one way to represent the effect of the adhesive supporting the cell wall for some height above the test plate. You can do some testing with progressively larger values of Pinball radius and plot the curve of Shear Modulus vs Pinball radius.

Bonded contacts have several formulations. You are using Bonded Contact for the cell wall to cell wall bond to create the 2t wall.  One formulation that does not use “springs” to connect the two sides is MPC which is the default unless the model has an exclusion that causes it to use the Augmented Lagrange, which does use “springs”. A Rigid Joint may be an example of an exclusion.

The preferred way to connect the edges of the core to the test plates and the cell walls to each other to get 2t is to use Shared Topology in SpaceClaim and delete all the contacts and joints.

You haven’t described how you are supporting and loading the test plates to solve the model to obtain the shear modulus.