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Direct comparison to strain gage
Posted Oct 24, 2012, 5:59 p.m. EDT Version 4.3a 2 Replies
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I'm modeling a simple fixed-free beam to compare with a piezo strain gage with a foil strain gage that I have on an actual beam (aluminum, 20cm x 2cm x 2mm). I'm trying to decide which strain I should have Comsol give me that would directly compare with the physical strain gages. I have the foil strain gage mounted on top of the beam near the fixed end and the piezo gage directly underneath it as well as a force sensor on the free end where I have a shaker.
I apply a force similar to what my force sensor gives me (~41N) to the free end in the Comsol model and want to see the theoretical strain on top and bottom where the physical sensors are.
I was using the "First principal strain" for my results which looks alright on the top of the beam, but I don't see the negative of it on the bottom as I was expecting. Is this the wrong strain to look at?
I'm using solid mechanics in 4.3a
Thanks for any help
Jon
I apply a force similar to what my force sensor gives me (~41N) to the free end in the Comsol model and want to see the theoretical strain on top and bottom where the physical sensors are.
I was using the "First principal strain" for my results which looks alright on the top of the beam, but I don't see the negative of it on the bottom as I was expecting. Is this the wrong strain to look at?
I'm using solid mechanics in 4.3a
Thanks for any help
Jon
2 Replies Last Post Aug 20, 2014, 4:38 a.m. EDT
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Posted:
1 decade ago
Hi
interesting question,
Now I expect this is from a coordinate definition, as if you plot the principle stress or strain for directions 1,2,3 the symmetric one is ep2/sp2, and not ep1 nor ep3.
I expected to be able to find the definition back in the equation view but that is not the case, so you need to go back to the documentation and dig out the formulas (try a search) then to check how the principal directions are projected on your model, to sort this out ;)
But if you plot the principal Stress/strain arrows (under plot more) you will see that the arrows look rather logical in direction, and these are build upon the default coordinate and sp/ep values
--
Good luck
Ivar
interesting question,
Now I expect this is from a coordinate definition, as if you plot the principle stress or strain for directions 1,2,3 the symmetric one is ep2/sp2, and not ep1 nor ep3.
I expected to be able to find the definition back in the equation view but that is not the case, so you need to go back to the documentation and dig out the formulas (try a search) then to check how the principal directions are projected on your model, to sort this out ;)
But if you plot the principal Stress/strain arrows (under plot more) you will see that the arrows look rather logical in direction, and these are build upon the default coordinate and sp/ep values
--
Good luck
Ivar
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Posted:
1 decade ago
hi, i would like to know how do u modelled the strain gage on your model
tq in advance
tq in advance