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ABAQUS Modelling of tissues under compression

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Hi All

Im currently modelling a hyperelastic cube

(10 x 10 x 10mm) liver tissue under uniaxial compression.

Attached is are two pictures illustrating the problem.

My model consists of

1. Liver tissue (Deformable) ( 10 x 5mm ) Symmetry in Y axis ONLY

2. Two reference planes (Analytical Rigid)

3. Material Properties : Hyperelastic Reduced Polynomial N=2 inclusive of test data

4. Step Time: General Static

5. Mesh: Tri-Structured

6. 4 BCs - X symmetry on left edge, fixed top reference plane (Ux=Urz=0), fixed bottom plane (Ux=Uy=Urz=0), Displacement compression load acting on the top plane(Uy = -5mm) 50% strain rate.

The purpose of the two reference planes is to act as the compression platens seen in laboratory and the friction coefficient between plane and tissue is 0.25.

Problems that Im facing are:

1.The liver tissue seen in the visualisation module was spilled out of the reference plane. I noticed that the right edge of the liver do not slide to the right as i would expect them to. This caused the top and bottom right nodes to overload which may be unrealistic [see pictures].

2.Selection of plane stress or plane strain elements does vary the sliding of the model. However, as the model is experiencing large deformation, only plane strain elements have the hybrid formulation options. May anyone advice which elements should i use and what could be possible problem about the model?

The analytical rigid plane should not allow any deformable tissue to pass through. hence my model cannot converge.

Thank you for your kind reply!

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