FEA analysis of a tube frame

[kikiturbo]

Hi, I am just starting using SW 06 and am having some problems with modeling and analysis of a spaceframe construction for the car I am making.. as I want to model it in SW and analyse its torsional stiffness properties...

now, the easiest way for me is to use a 3D sketch and make my tube frame, then use the weld profiles tool and assign each section of the sketch with a tube.

now, when I do the analysis in COSMOS it doesn't understand that the tubes are actually connected togeather, so there are two ways of doing it, that I see:

1. use fillet welds and weld the tubes in SW
2. use the restraint tool in COSMOS and "tell" cosmos that the tubes are rigidly connected in the frame..

the first solution doesn't always work, in fact once I have a real 3D spaceframe, where I have joints wit several tubes going in, the SW fillet weld feature just will not weld some tubes togeather...

the second solution is very time consuming, and makes COSMOS block and crash from time to time...

I have also tried exchanging the tubes in the model with solid bars of equal cross section area (as I presume that tension/compression of the tube swill have much greater influence on the frame torsional stiffness than tubing bending) but that does make it much faster but the problems persist...

does anyone use SW to model tube frames and analyse it's properties... care to share some tips? or should I look for other software...?

best regards

vlado

 

[Theophilus]

Are you using Cosmos or Cosmos Express? If Express, I think you'll need the various parts to become a single part (much like it will be in its real-life assembly).

I'm not sure how accurate you'll need the analysis to be, but one thing you can do is save your assembly/part as a part and then join the various bodies. Run the analysis on the part file with the joined bodies. This won't take into account weld strength, so may not be quite what you're looking for.

Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe trumps reason.

 

[Heckler]

You might want to post this in the cosmos section. What you're trying to accomplish is a complex task one that requires a considerable amount of knowledge in the area of FEA. Also, you should be able to understand and complete these calculations by hand before attempting to set this up in Cosmos. Cosmos is only a tool and will give you the wrong answer over and over again. Do you have a copy of Roark's Formulas for Stress & Strain? if not consider buying a copy if you want to understand FEA.



Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 5.0 & Pro/E 2001
Dell Precision 370
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Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

 

[kikiturbo]

thanks for the tips guys... I will post the same thing in the cosmos section...

I am using full COSMOS... by the way..

as for my understanding of FEA, well, I understand the physics of it, as I had it in my lectures some time ago while I was studying... hell, I could even do the calculation for my tube frame by hand, but I need to experiment with my design a bit (optimize the various tubing thickness/diameters) so I need a relatively fast tool..
I did some experimental models, very simple spaceframe structures, and I noticed some problems that SW had with displacement plots, especially on the load points... will look into this..

cheers

vlado

 

[handleman]

One reason that Cosmos is not seeing the tubes as joined may be because they are not. When you use Weldment features in SolidWorks it creates multi-body parts by default. You may need to use some additional features (joins, etc) to actually make a single solid body. Even the fillet weld feature only creates a little triangular shaped separate solid there at the boundary between the two "welded" bodies.

 

[kikiturbo]

wen I did first experiments with cosmos, fillet weld feature worked a treat... the problem was when I wanted to do a bunch of fillets on a real frame... then I had problems with the fillet weld feature...

cheers

vlado