Surface to Surface Contacts

Assembly Analysis
When using the NX Nastran solver, the capability to analyze assemblies becomes available to the user. If you simply specify boundary conditions and set the assembly file up as you would in a single part analysis you'll realize that the nastran allows you to run through the simulation without errors. However, you will never get any results. This is because the surface to surface interations between the parts need to be specified.

How to use Surface to Surface Contacts...
This is located in the fourth level of the navigator under "Simulation Object Type" button. There are two different types of functions that you can choose from here: "Surface to Surface Contact" and "Surface to Surface Glue". As the name implies, the surface to surface gluing option prevents all types of motion in every direction between the two surfaces. Obviously choose the one that best simulates the interaction between your surfaces.

Surface to Surface Glue

  • Under "Type" there are two options "Automatic Pairing" or "Manual". Both are very similar to each other and will get you the same thing. I don't see much difference here at all.
  • The next step is to pick the face pairs that you desire to be "glued" together.
  • Once you click on the button for "Face Pairs" you specify the two faces in contact and that you want glued. The "quick pick" feature becomes extremely useful here since you can rarely see both faces you want to glue together.
*in the "Face Pairs" menu under "Properties" there are two important options...
->*"Grouping Option" - Simply specifies how to group these pairs of faces for the "Simulation Navigator".
->*"Distance Tolerance" - If any part of the two surfaces are within this tolerance of touching it will treat the interaction between the two as rigid.
  • Now back to the "Surface to Surface Gluing" menu...
  • There is not much left here to explain except for the "Boundary Condition Generation", which tells the program to automatically recalculate the face pairs when the model is modified.

Surface to Surface Contact

  • Use the same process as you would with a Surface to Surface part, except you have additional properties to choose from.
  • The "Coefficient of Static" specifies the coefficient of static friction that exists between the two surfaces that you are touching. For this to have any meaning the surfaces need a normal load between the two and my understanding is that it simply calculates that from the boundary conditions that are applied.
  • The rest of the property options are confusing and don't understand fully. I think an understanding of "NX Cards" is necessary to understand these fully.