Need advice on simple FEA task

[QuestionBoy]

I need to compare the strength of a .5" OD, .040 wall tube made of 4130 with that of a .55" OD, .079 wall tube made of 6061 (the same length, about 4" long). Think of a telescopic motorcycle fork in miniature and you have a good idea what the setup is. I know the bend will be concentrated just below the lower triple tree (or yoke), but it would be helpful to know the approximate force required to bring each material to the yeild point.

I attempted to use COSMOSXpress, but my computer crashes after every attempt. On top of that I'm not so sure I'm setting things up correctly, or that the simulation can be done with COSMOSXpress.

Lives are not on the line with my products, and I don't usually need to do this type of work. However, I'm working on a new product and knowing this basic information could save me some headaches.

Provided I had a computer that could do this without crashing, will COSMOSXpress do the simulation?

TIA

QB

 

[prost]

Is it anyone else's opinion that QuestionBoy is making this too hard? For a first try at it, try a simple hand calculation. If the piece is telescoping, then there probably is very little bending except where the fork is. From what you describe, this looks to be mostly axial loadings on the various pieces in this structure. Did you do a hand calculation first, to get some good estimates?

What are the yield stresses of the various materials you are considering? There is often a very wide range of yield stresses even for the same alloy, say 6061, but with a different heat or temper, say T351. Which materials and heat/tempers are you considering?

 

[GregLocock]

"will COSMOSXpress do the simulation?"

Maybe, if you can model the constraints correctly.

As it is a tube in tube type loading it will actually fail in a fairly complex fashion, involving contacts, which CX won't handle, but with a bit of thought you should be able to get close.

Try running some of the tutorial models so that you can prove to yourself that it is not an installation problem. Assuming those work then the next problem is to figure out what is wrong with your model. Having said that I'm surprised a modelling error crashes the whole program.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[prost]

Isn't "Model crashing" usually indicative of "improperly constrained" Greg? For instance, if you don't not remove all the rigid body modes, your stiffness matrix is singular so that the FE solver 'crashes'.

 

[JStephen]

It sounds to me like you just want to compare bending strength of two tubes, simple Mc/I type calculations. Am I missing something here?

(and unless there is a LARGE difference in allowable stress, the larger thicker tube is stronger)

 

[GregLocock]

Well, he said his /computer/ crashes. I've often had bad models, but I don't remember one so bad that it attacked my PC!

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.