Abaqus issue: simulation fails when adding fat layer

[adamkilroy10]

Hi,

I am working on a 2D simulation to model the interaction between a wheelchair cushion and the user's leg when they sit on it. I created this model by tracing over an MRI scan of the leg in Fusion 360 and then importing into Abaqus. The simulation runs successfully when I model the leg with only one deformable layer and the bone. However, I want to model the leg with 2 deformable layers (muscle and fat). When I add this second layer, the simulation no longer works even if I set the 2 layers as the same material. I have attached a screenshot of the simulation working with one layer, and then how it looks with the 2 layers (which does not work).



Model setup

• 2D deformable leg model (imported from MRI scan tracing)
  • Bone (inner layer)
  • Muscle (middle layer)
  • Fat (outer layer)
  • Cushion

Boundary conditions

• Pressure load on top surface of bone
• Bottom surface of cushion fixed
• Bone displacement fixed downwards
• Tie constraints between each layer

Warnings/errors

• I get this warning for all the elements in the bone (I also get these warnings when the simulation works well with one tissue): Solver problem. Zero pivot when processing element BONE
• Error: Too many attempts made for this increment

If anyone has any ideas for this problem they would be greatly be appreciated, thanks!

 

[FEA way]

Are the layers modeled as separate parts ? It might be better to use a partition instead.

 

[adamkilroy10]

Thanks for your response. I have tried modeling it as one part with partitions, and also as separate parts with tie constraints. The simulation does not work for either of these unfortunately. For both cases, the simulation works when it is just bone and one soft tissue, but does not work when I add the second soft tissue... which I do not understand why this is the case.

 

[GregLocock]

I suspect you need to solve the warning about zero pivot.

 

[FEA way]

When I add this second layer, the simulation no longer works even if I set the 2 layers as the same material.

If it fails with the new layer having the same material and modeled as a partition then it seems to be a matter of the mesh.