FEA model for VALVE body

[socolp86]

Dear all,
I meet a problem, when we do the FEA for a vlave body, we found it needs a minimum material condition model.How to understand it?Does it is the same as the ASME b14.5 LMC(least material condition)?
In advance to thank you for all of your answers.

What's your plan, How to do, What do you receive after review.

 

[btrueblood]

"it needs a minimum material condition model"

This means the FEA model is defined by the smallest/thinnest dimensions allowable per the drawing tolerances. I.e. if the drawing specifies a wall thickness of 10mm +/- 1mm, you would model the wall thickness at the worst-case, weakest condition allowed, or 9mm.

 

[socolp86]

Thanks a lot , but I found using the dimensions per the tolerance on the drawing is diffrent from the notification of the least wall thickness on the drawing. For example , I make the model by the method you mentioned, the wall thickness is 0.25 inch, but on the drawing it notified " the allowable wall thickness is 0.15-0.30 inch".
Should I make the model by the notification or the tolerances of the dimensions?

What's your plan, How to do, What do you receive after review.

 

[dwallace1971]

I would think the note "the allowabel wall thickness is 0.15-0.30 inch" would over-ride the general tolerances for the drawing-the whole "unless otherwise stated" thing. Your minimum thickness model should have a wall thickness of 0.15 inches.

 

[btrueblood]

"but on the drawing it notified " the allowable wall thickness is 0.15-0.30 inch""

Then the tolerance on the wall thickness, per the drawing, is .15 to .30 inches. Make the model at the minimum allowable thickness, or .15 inches. That is what I said, regardless of how you interpreted it.

Note that other dimensions than just the wall thickness may affect the valve strength, and it's up to the engineer to figure out what those may be. In other words, you may want to investigate other parameters that are allowed to vary per the drawing, in order to determine what the real worst case (lowest strength) configuration is.

I hope, given your apparent knowledge of the subject, that somebody is going to overlook/review your efforts?

 

[socolp86]

Thanks a lot, but there is a formula to modify the result of the FEA from normal dimension to a minimum material condition. When we can use this formula?(in the condition of the stress and strain is linear)
When I use btrueblood's method, how to deal with the problem that the wall thickness is less than the allowable dimension?
For example, we model a pipe, the OD=18, th ID=10, so the minimum wall thickness is 4, but on the drawing, the allowable wall thickness is 3, what should I do , to change the ID, or change the OD, or anything?
Thanks a lot

What's your plan, How to do, What do you receive after review.

 

[rb1957]

how about FEMstress*thkFEM/thkMIN ?