# hyperelastic modelling

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• Last Post 25 April 2018
trayC posted this 18 April 2018

Hi all,

I am trying to squeeze a hyperelastic mooney rivlin material sphere through a cylinder which gets slightly narrower, I was wondering if anyone had any tips that could my results converge?

At the moment my results are unable to converge.

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peteroznewman posted this 18 April 2018

Hi trayC,

I ran your model in 18.2 and it ran without problems and finished in 108 increments.

I have some other suggestions for changing the boundary conditions, and possibly using symmetry. It would help if you could describe the results you want to obtain from the model.  I don't currently have 18.0 but I have an old machine that I will install it on.

trayC posted this 21 April 2018

hi thank you for the reply, I ran it again and it worked !

I was wondering if you knew how i could measure the change in length across an edge on the sphere  e.g.

it seems like deformation probe also measures the displacement the sphere body undergoes as well

peteroznewman posted this 21 April 2018

A plane intersecting a sphere constructs a circle. A part of a circle is an arc. The arc has an arc length and end points.  If the plane is through the center, and the arc has 180 degrees of span, then the distance between the end points is the diameter. When a sphere is compressed, the arc length is shortened and the diameter is reduced.

When you say you want to "measure the change in length across an edge on the sphere", I don't know if you mean the change in arc length or the change in diameter. Please clarify.

trayC posted this 25 April 2018

I meant the change in diameter. This is because i want to compare the deformation in finite element analysis to an experiment that was conducted in real life, where a photographic method was used to measure 6 different diameters of a newborns head after passing through the vaginal canal.

thank you

peteroznewman posted this 25 April 2018

Okay, just create two deformation probes on two points on opposite sides of the head. The points should have about the same Y and Z coordinates, but opposite X coordinates. The difference in X coordinate is the initial diameter. Then during the solution, you can plot the X deformation of each point. The difference in X deformation of the two points is the change in the diameter.

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