## General Mechanical

#### Convergence of nearly incompressible material – non-linear analysis

• dzz0
Subscriber

Hi everyone,

I have a problem with the simulation of nearly incompressible material (v=.495) and i hope someone may help me with this. I have searched older topics but could not find a suitable solution.

Specifically, this involves the simulation of a radially symmetrical silicone bond between to adherends under tension loading. For this purpose I use a USERMAT based on the Ogden model. Large deflections are activated (NLGEOM,ON).

I want to increase the maximum displacement i can apply. I already have tested many things:

- other elements (185,186,187,285)

- different keyopts

- finer mesh, which actually makes it worse somehow

- more substeps and cumulative iterations

- different type of symmetry and modelling adherends (flexible and rigid)

- 2D model

Does someone have another idea to increase the convergence?

Kind regards

Ben

• peteroznewman
Subscriber

I recommend using/continue using:

• Hyperelastic material model

• 2D Axisymmetric geometry. Axis of rotation is Y axis, surface on + X side of Y axis.

• Half symmetry at the center of the length

• Displacement in Y on the end face, with X = 0

• Linear elements, but not too small. PLANE182

• Mesh with element shapes that deform to better shapes, not worse shapes. Start as wide rectangles, end up square.

• uniform reduced integration keyopt, 1, 1

• mixed u-p formulation keyopt, 6, 1

• more substeps and cumulative iterations

• dzz0
Subscriber

Hello Peter,

thank you very much for your tips. I will try this.

Regards
Ben

• peteroznewman
Subscriber

Ben,

Note that with a half symmetry condition at the center, a 1 mm displacement of the end is equal to a 2 mm displacement of the full length sample.

Regards,
Peter

• dzz0
Subscriber

Hello Peter,

thank you for the advice. I will consider this in the evaluation.

Regards,
Ben