Contact between Solids

General Questions
1

Hello,

I am a new user of PrePoMax (and CAE), and I’m using it mostly for structural analysis. Basically, I have an assembly with several solids and I want to know if, to evaluate the stress on the bottom solid, it’s necessary to include the contact regions or it’s not necessary? Do i have to insert something else for the mesh understand the interface of the solids? The following image will help to understand (since I forgot my computer at work).

Captura de tela 2026-03-17 204818
Captura de tela 2026-03-17 204818446×561 11.8 KB

2

You have the following options:

  1. Create a compound of these parts - this will merge their geometries and results in a continuous mesh so it only makes sense if you don’t need them to move independently.
  2. Apply tie constraints between them - this is equivalent to the first approach, but can be used even if there are gaps and incompatible meshes. It won’t allow for any relative motion either. You have to pick master (coarser mesh) and slave surfaces.
  3. Define tied contact between them - another approach where the relative movement of the surfaces is not possible, but you will be able to evaluate the contact stresses. Definition is similar to tie constraints.
  4. Hard or softened contact - same as above, but with different surface behavior. This will allow relative movement (separation and sliding with or without friction), but very often causes convergence issues, especially in models with force control.

Of course, you can mix these approaches and define some interfaces as merged/tied while applying contact to others.

So, use compounding (or tie constraints when compound fails/prevents hex meshing) if you don’t need the parts to slide/separate and choose contact only if you need to account for that.

There’s a built-in Search Contact Pairs tool that can be used to automatically define tie constraints and contact pairs between the parts if you decide to use them.

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