FEA Material Prop Requirments?
FEA Material Prop Requirments?
(OP)
It's been a while since I've performed an FEA analysis. Usually I'll perform an analysis on material info provided by the FEA software.
I'm trying to perform an FEA analysis on a plastic part (in the linear range), and the Material Prop Sheet does not have a poisson's ratio. Is this a problem? Can you get away from not having a p.r. to perform an FEA analysis? I always thought you needed this propoerty.
I'm going to perform an analysis using Ansys 10 inside SW 2007. What are the min req to perform an analysis?
The material is supplied by UMG ABS Ltd (I believe out of China). It is a plating grade ABS that is licensed from GE Plastics. I do not know's it's equivalent on the GE side.
http://www.umgabs.co.jp/en/data/index.htm
http://www.umgabs.co.jp/en/data/ed/3001m.pdf
I checked some GE Cycolac ABS data on Matweb. The poisson's ratio is also not supplied there.
I'm trying to perform an FEA analysis on a plastic part (in the linear range), and the Material Prop Sheet does not have a poisson's ratio. Is this a problem? Can you get away from not having a p.r. to perform an FEA analysis? I always thought you needed this propoerty.
I'm going to perform an analysis using Ansys 10 inside SW 2007. What are the min req to perform an analysis?
The material is supplied by UMG ABS Ltd (I believe out of China). It is a plating grade ABS that is licensed from GE Plastics. I do not know's it's equivalent on the GE side.
http://www.umgabs.co.jp/en/data/index.htm
http://www.umgabs.co.jp/en/data/ed/3001m.pdf
I checked some GE Cycolac ABS data on Matweb. The poisson's ratio is also not supplied there.





RE: FEA Material Prop Requirments?
2)First two google hits say 0.39 to 0.42
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: FEA Material Prop Requirments?
RE: FEA Material Prop Requirments?
Thanks for the info.
So it's absolutely necessary to have Poisson's ratio inorder to perform an FEA analysis? I wonder how Matweb can export out data to solvers without having the PR listed?
RE: FEA Material Prop Requirments?
If the Poisson ratio is not set, and it assumes zero, then it probably won't act much like a part made of plastic. Since plastic generally has a Poisson ratio close to 0.5, I'd guess you'd get some pretty odd behavior if you don't set the Poisson ratio (PR) and it assumes PR=0.0. What will happen? Say you pulled (with tension, that is) on a flat piece of this plastic. If the PR was set to 0.0, the bar would not contract at all; very odd behavior, don't you think? Aphysical even.
RE: FEA Material Prop Requirments?
RE: FEA Material Prop Requirments?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: FEA Material Prop Requirments?
RE: FEA Material Prop Requirments?
cameprak
RE: FEA Material Prop Requirments?
RE: FEA Material Prop Requirments?
yes, as E, G and nu are correlated (in other terms, only two are independent), then a FE engine won't use the three of them.
What the FE needs to know is the "rigidity to shrink" and the "rigidity to elongate" (OK, I express it very roughly), and this info can be provided by either of the two moduli together with "something" which undirectly expresses their ratio (i.e. Poisson ratio), OR by the two moduli altogether (without nu). If you provide the three altogether, then either you have them consistent or the FE program will have a built-in "preference" about how to use them. YOU MUST know how your FE works IF you want to specify the three values altogether, or you will most likely get unexpected / unwanted results !!!
Regards
RE: FEA Material Prop Requirments?
Calculate 0.5*(E/(1+PR))=3947 ksi. Or you can calculate PR from E and G: PR=0.5*E/G-1=0.3125
These E and PR results are probably the means of the E and PR from many many tests, right? (2024 is a oft used material, I ASSUME that many many tension tests for E and PR have been run and used in MIL5). Is G measured or calculated? I can think of a few reasons why the G calc. from MIL5 is not the same as the G quoted, but no one seems to really know:
1) 'G' can be measured directly with the right kind of strain gage arrangement--if this is so, G is measured, not computed from E and PR.
2) Roundoff error
3) Calculating G from E and PR for each individual test, then taking average of those calculated Gs. Obviously
G=1/N *sum(0.5*E/(1+PR), i=1 to N) is not equal to
G=(1/N)*sum(E)/(1/M *sum(PR)), where there are N tests to measure E and M tests to measure PR. There's an additional complication--there might be different number of tests to measure E than those to measure PR.
4) typo--not likely, every G I have tested by calculating from E and PR fails this test--my immediate conclusion is that they are all this way.
RE: FEA Material Prop Requirments?
I tend to think that different experimental methods & error also might play a role (even more so when measuring PR? - smaller lateral strain range, etc.).
I would say the accuracy of PR is the less important parameter for normal structural materials & case studies but very important when analysing rubber applications.
Regards