Gasket FEA with PrePoMax

General Questions
1

Hi,

I am running a 3D bolted joint FEA using PrePoMax.

Is it possible to define 2 different Young’s modulas for a material under different conditions or steps.

I was aiming for defining a loading and a separate unloading modulas for the gasket? Step 1 of the analysis will see the gasket getting loaded while in step2 some of the load will come off.

Can we change material properties when moving from Step 1 to Step 2 of the analysis?

Any tricks or comments will be helpful.

Thanks in advance.

Fatehjit

2

You can use temperatures for that:

  1. Define temperature-dependent elastic properties.
  2. Apply initial temperature (by default, it will be zero).
  3. Apply defined temperature field and vary it with amplitude or between steps. This will change the material properties.

This approach can be used in a static analysis without any actual thermal or thermomechanical effects. Then the temperature is used as a field variable to vary the material properties and doesn’t affect anything else in the model.

Alternatively, you could try the *CHANGE SOLID SECTION keyword to replace the material definition assigned to the model.

Of course, you may want to include plasticity too. Then you could see how much deformation stays as permanent.

Moreover, rubber gaskets are often modeled using hyperelasticity (nonlinear elasticity) so consider this material model too.

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3

if compression or tension only behavior needed, CalculiX capable using material model and using nonlinear spring or gap element.

4

Compression only and tension elasticity is IMO not the best choice in this particular case. It’s too one-sided and doesn’t really allow two different stiffnesses for loading and unloading, just the allowable tensile/compressive force for the other direction.

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5

There’s a very good article on the Simulia website that covers some of the complexities of gasket modelling.

I’m not so familiar with Calculix to know what is possible to implement with keywords.

6

Yeah, but it focuses almost exclusively on gasket elements, which aren’t available in CalculiX.

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