Part passing FEA but failing lab test
Part passing FEA but failing lab test
(OP)
I am designing brake pedal.
Its made of plastic, I am using CATIA/ANSYS for FEA analysis.
Part is within stress limits and sress counters are under yield stress, but during lab test, it fails.
I think that I am not modeling plastic correctly in FEA, I am using non linear model.
Any Ideas?
Its made of plastic, I am using CATIA/ANSYS for FEA analysis.
Part is within stress limits and sress counters are under yield stress, but during lab test, it fails.
I think that I am not modeling plastic correctly in FEA, I am using non linear model.
Any Ideas?





RE: Part passing FEA but failing lab test
TTFN
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RE: Part passing FEA but failing lab test
1) your model does not capture the test correctly
2) there is something wrong with your material properties
there are many more possibilities but without more specific information that's where I would start looking.
Marcus
RE: Part passing FEA but failing lab test
I will ask for ASTM dog-bone test done on material, I am looking for its stress-strain curve. That might tell me something.
I can refine my mesh further.
should I use linear model or non linear model?
Thanks
RE: Part passing FEA but failing lab test
TTFN
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RE: Part passing FEA but failing lab test
www.Roshaz.com
RE: Part passing FEA but failing lab test
How does the part fail: does it deform excessively, or does it break? Where does it fail - near a change in section for example?
RE: Part passing FEA but failing lab test
RE: Part passing FEA but failing lab test
Tobalcane
"If you avoid failure, you also avoid success."
RE: Part passing FEA but failing lab test
There is of course the possibility of something wrong in the FEA model. That can be wrong settings (unsuitable element selection, coarse mesh), or the FEA model not matching the physics of your problem (wrong boundary conditions, wrong loads, material model, material properties, etc). In that case you're getting the right solution to the wrong problem!
Nagi Elabbasi
Veryst Engineering
RE: Part passing FEA but failing lab test
Did you measrure the actual force on the pedal during the test? Without this feedback, how can you be sure your loading is correct?
Google "fea plastics". There is a link called "Why is FEA of plastic parts so often wrong?" that seems informative.
The material model is highly non-linear, but personaly i think this has more effect on the displacements than on the stress.
"If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack."
Winston Churchill
RE: Part passing FEA but failing lab test
If its a FEM problem: More times than not, the problem will be with poor choice of boundary conditions and not mesh density.
What about producibility issues? I remember having a great variance in strength between injection molded parts. Have you tested enough samples to determine what type of statistical distribution you might have? If there is a lot of scatter, you won't be able to capture that in your FEM.
Brian
www.espcomposites.com
RE: Part passing FEA but failing lab test
as for linear vs non-linear ... how much is the part deflecting (geometric non-linearity) and how close to yield (material non-linearity) ?
RE: Part passing FEA but failing lab test
Cheers
Greg Locock
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