HELP WITH COSMOSXpress

I'm not a student of FEA and I'm trying to use COSMOSXpress for the first
time. I modeled a bracket, run the COSMOSXpress wizard, and set the
restraint as the surface of bracket that will bolt to the wall. I then set
a force of 25 lbs acting on the surface and in the direction of the weight
that the bracket will support. Oh and yes I did set the material for plain
carbon steel. When the results are calculated I get a FOS of 323.255. I'm
not sure what this number means. When I look at the html report it says
that the Max is 6.824e+005 and the min is 1.845e000 and the deformation
scale is 12712.3. Like I said, I'm ignorant as to what these numbers mean.
Looking at the visualization of the deformation of the bracket I find it
hard to believe that a 25# weight would cause that much. I must be doing
something wrong and I'm hoping that some of the power users out there will
explain it all to me.

Thanks in advance fo sharing your knowledge

Jeff

 

If the weight would be evenly distributed over the whole bracket,
this setup should be right. However, if it were toward the outer end,
you should select another surface. With such a high FOS, your bracket
is either way over-designed or you are not modeling the force on the
right location (or both).

 

Thanks for your help. Maybe now I can design a bracket my customer can
afford.

Jeff

 

FEA is a dangerous tool, and Cosmos Express is infinitely dangerous.

The limitation of one constraint type makes it diffcult to correctly
model many situations.

You should only use any FEA program in tandem with tradional
engineering analysis (one method should verify the other), esp. in
something as simple as a bracket. In any event, a person that is not
qualified to perform tradional engineering analysis should never use
FEA as a tool.

 

The first step to knowledge is to ask questions.

Well you got an answer. We can say with a reasonable sense of certainty the
the answer is correct insofar as the problem was posed. The real question
is, what was the problem posed? Was it the problem you thought it was?

Given that the max is about 700,000 we can assume that you are working in
metric units because there are no known materials that in english units
(psi) would have that high a stress and at the same time a Factor of Safety
(FOS) of 300+. Are you sure you input 25 lb, or was it 25 newtons?

Since you didn't know what FOS meant we can assume you haven't really done
much in the way of stress or strength calculations up till now. If this is
true, you might want to seek some local help in this area before you get
yourself in trouble. Sorry if I am being blunt, but someone could get hurt.
I would suggest at the very least getting a copy of Roark and Young and
reading it very carefully, especially the first few chapters. Roark has
nothing to do with FEA. It is a book of hand calculations and likely
contains a better solution to your problem than CosmosXpress does.


Regards,
Grumpy Analyst.

 

I see a bunch of answers here. As for the Deflection issue, there IS a
deflection scale, and NO it is not changeable. The deflection on the screen
does not really change. No matter the load, the part in its bent state is
still the same distance if you measured your screen. But the Deformation
Scale shown will be different.

You CAN get the actual deflection though. If you want to know how, I wrote
it up in our User Group newsletter once last year. If you want to see it,
here is a link to the PDF, and the Deflection issue is in the middle (or so)
of the PDF. Others have asked for it and it helped them.

http://www.okswug.com/images/News_Jul_2003.PDF

Mr. Pickles

 

Ahh, the .out file. A bunch of useful information and a big caveat.

THE .OUT FILE IS IN METRIC UNITS. KMS UNITS TO BE EXACT.

The actual deflection would be the deflection in metres divided by
..0254.

Even more important to knowing that you are solving the right problem
is the reaction data. The reaction in Newtons should match what you
think your loads were in pounds, stone or whatever.