CATIA GSA (Generative Structural Analysis) Assembly Question

[lildaveyboy]

Hello. I am running some FEA analysis in Catia using the GSA module of a rivet installed through two plates. I believe I am getting the correct stress value from my model for the large plate. But the secondary plate and rivet show 0 stresses. I am wondering if anyone thinks this is correct. Also the maximum stess is located in the plate on the side of the hole, in line with the load instead of perpendicular to it as the open hole case shows. I'm also wondering if this is correct. Please see attachment. Thanks.

 

[ESPcomposites]

The structural analysis and modeling of joints is not a trivial task. What are you trying to achieve with this model?

In this case, your rivet may perfectly fill the hole (is it a contact solution?). This would create a path for the load to travel through. If you were to create a clearance hole, you would see a different story. A close tolerance hole would be different as well.

Are you loading the rivet/fastener? If so, this will also change the local stresses.

But the better question is what do you want to do with this stress? It may be relevant for metal fatigue or composite structures, but is not useful for static strength calculation in metals. Furthermore, there are classical ways to treat problems like this (which should be your first step). I would encourage you to investigate those avenues as opposed to using what is called a "push button" FEA by the industry.

Brian

http://www.espcomposites.com

 

[lildaveyboy]

I am trying to get the stresses at the hole to calculate stress concentration factors. These factors will end up being used in a fatigue analysis. My question is really on what connection properties to use the in CATIA Generative Structural Analysis module that will simulate the effect the fastener hole fill has on the stresses in the plate at the edge of the hole. Any insight is appreciated.

 

[ESPcomposites]

I don't know much about the approach in CATIA, but if you want the answer to the Kt problem, that should be straight forward. Have a look at Peterson's Stress Concentration Factors or try a google search. They may call the fastener/rivet an "inclusion" or "elastic inclusion". There are many such publications on this topic.

Alternatively, if you have access to a more common FEM software package, it can be done with relative ease. For example, you could just run it as a 2D solid (plane stress) element. It is relatively simple for a neat fit. If you want to look at the effect of small clearances, a contact solution would be appropriate. The CATIA solution could probably do this as well, but there are few structural analysts (sole duty) who are familiar with that approach (and hence less support).

Brian

http://www.espcomposites.com

 

[lildaveyboy]

Thanks. I'll keep playing with the contact and constraint properties in the models. I'm aware of the effect of the fit condtions on Kts. However, I am wanting to model these fasteners/joints in the FEM/FEA software to develop these factors for comparison to know values. Some of the models I am running include 3D features so I really need to be able to run a 3D FEA analysis.

 

[lildaveyboy]

I am using the Fastened Connection Property in CATIA GSA in my FEM but the max stress is shifted and it occurs in line with the load at the edge of the hole unstead of at the sides of the hole. The max stress looks to be shifted 90 degrees to where it should be located but the value appears to be correct. I was wondering if anyone had any ideas about what may be causing this. See the attachment. Thanks.