Patran Fastener Idealization

[marketto]

Hi guys,

I'm new in the forum and in using Patran&Nastran.
Sorry in advance about my english.
I was just wondering how to create a fastener between 2 rectangular plates.
I would like to create a fastener (or more) to joint the 2 plates: the nodes on 1 edge of the bottom plate will be constrained (no trasl, no rotat) and on the nodes on the opposite edge, but upper plate, will be applied the force (along the longitudinal axis of the plate).
I m able to mesh and create the surface, to apply the BC and the forces, but I have problems to idealise the fastener that join the 2 plates.
How can I simulate the fastener? Which mesh element? Do i have to create a curve between upper and lower node?
Sorry again for the english, I can explain again the problem..
Thanks

 

[ESPcomposites]

The first thing is to determine what the equivalent spring constant ("fastener flexibility") is. There are many formulations available.

For the FEM, the standard methods are to use either a spring element or a beam element.

Spring - Simple and direct. However, if your problem is 2D, you will need coincident springs, which require extra tracking.

Beam - Able to automatically handle 2D, but you must first calibrate the beam's inertia properties to generate the equivalent fastener flexibility. Ultimately, you are after F=kx, which can be achieved with a beam element in an indirect manner.

*If you are attaching to a shell element, there is a small amount of local deformation that affects the overall response. In theory, you should make a single fastener case and calibrate this deformation out (for both the spring or beam element approach). I have found that roughly a 20% extra increase in stiffness is needed to account for the local softening where the fastener directly attaches. This may or may not be important to your model. Also, there is quite a bit of scatter in fastener flexibility tests, so this extra bit of calibration may be in the noise (again depending on the problem).

Brian

http://www.espcomposites.com

 

[ESPcomposites]

Forgot to mention, you can also use a CBUSH element to represent the fastener. However, you should first become familiar with it and the various types. There are a few subtle nuances that could affect your model.

Brian

http://www.espcomposites.com