# HELP WITH COSMOSXpress

• posted

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.

Jeff

• posted

I'm pretty ignorant of it too, but I've tinkered enough to settle your nerves...

FOS is Factor of Safety, yours being 323.25 means you can load a roughly

323 of your 25 pound weights on it before it breaks.

The Max & Min numbers are the stresses being put on the part, with different colors representing the range of numbers, you can adjust the settings to show you where your 'hot spots' are, where you may need a larger fillet or radius, etc.

The deformation you are seeing is being magnified 12712.3 times, that's why it looks like a squashed bug, fear not. You can change the deformation scale somewhere in there.

hope this helps

• posted

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).

• posted

Expanding a bit- I use 'Insert> Curve> Split Line' to create the area the force is applied to. Start a sketch on the face the force is applied to (just like you were going to extrude or cut) then use do Insert>

Curve> Split Line- this creates a surface the size of your sketch which you can then apply the appropriate loads and restraints to.

Say you have a ladder step secured only at the ends and you want to simulate the effects of a 300lb man stepping on it, well his foot isn't likely to cover the entire step- just the area his shoe covers. Using the above method on the surface of the part representing the step will get more realistic results, you may need to create other 'Split Lines' for the mounting ends.

Also- It had been a while since I'd messed with it, so I looked again this AM, and I don't see any way to alter the deformation scale, so you can stop looking :o)

Have fun.

Gary Reichl> If the weight would be evenly distributed over the whole bracket,

• posted

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

• posted

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.

• posted

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.

• posted

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.

Mr. Pickles

• posted

Or, if you like to live dangerously, download 05 beta4 from the subscription site. It gives deflections. I'd recommend you do a separate install, and be very careful to only work on copies of your files in order to do this.

• posted

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.

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