I have a CEM3 printed circuit board (PCB) material with 1oz copper on top and bottom. Does anyone know of a web site that has average Young's Modulus of Elasticity for PCB materials?
The simply supported results were better than the cantilever. I tested brass and steel. I was 8 – 17% off for simply supported and 19 - 23% off for the cantilever.
That makes me feel better that someone else has experienced difficulty in getting theoretical to match bench testing. I’ve spent quite a bit of time on this, I’m ready to use a fudge factor of about 20% and move on.
Donkey Dude: The force applied is in the middle.
Hacksaw:
1) yes, jaws made of steel.
2) Hand calcs don’t match experimental values. Hand calcs match FEA. I assume you meant to say this.
3) Unit conversions are not an issue.
4) Dimensional tolerance is negligible and was checked with measurements.
Simply supported beam, tested 8/14.
Test Setup:
C260 Brass, 115mm long x 19 wide x .83 thick. Specimen was supported on two steel dowel pins and a point load applied in middle.
Measured results: deflection = 1mm, F=2.7N, deflection=3mm, F=8.1N
FEA:
2D, 4 elements though thickness, BC left end...
RPstress:
Please elaborate/rephrase on the following:
Re plate deformed shape, the FE predicts deflection at the free corners of the brass plate of 0.387", as opposed to 0.04" at the applied enforced deformation in the exact center, for both linear and non-linear results.
Is it...
I again verified the Instron pull tester with a dial force gauge (beam type) – Instron tensile/compression tester sanity check OK.
I did subtract out take up compliance. The measured curves are always linear.
I believe my original simply supported fixturing had some problems. I chose a thick...
Sorry for late reply, been traveling a lot. I’ll try to answer all questions.
The accuracy of the load cell was in the 20-80% scale range. I also did an accuracy/sanity check with dead weights and it checked out.
Unfortunately do not have the capability to find E with my pull tester other than...
The simply supported beam FEA results for force were 60% higher than the measured results. I have tried multiple materials with different geometries, 4 cantilevers and 1 simply supported and they all range from 30 – 60% off.
I shouldn’t have used the term exactly. The hand calculations were 7%...
It is good to here that rpstress thinks E values should be close to published values. It kind of defeats the advantages of FEA if I had to pay (to outsource) to get E values for every material. I work with many different materials.
Yes analysis should linear with reasons stated before.
I...
Thanks for the input. I have been checking the instrumentation and it is a calibrated, accurate Instron pull test machine. I will attempt to do more instrumentation verification studies.
Have either of you done a similar bending test and come up with accurate FEA results vs. actual measurements?
EnglishMuffin:
I have used several standard materials with published E values, (brass and steels). Could they all be this far off? I get my E values from Matweb.com, texts, and other sources and they all are about the same for each material. I have suspected this but have no way of varifing this...
8 node bricks for 3D, 4 node for 2 D. I don't think it is the elements because the FEA results agree perfectly with the hand calculated formula. Also, I used different elements, 2D vs. 3D, coarse and fine meshes, and the results don't change much.
