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Visual representation of thermal expansion not making sense

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Hi all.

To communicate my problem I made a simple bimetallic strip (library Materials Values for Copper and Iron) which is fixed to a surface where a temperature T is introduced - no thermal dissipation is assumed here. So as I change the applied T, the bimetallic strip bends one way or another depending on the applied temperature and the CTEs of the metals.

Fine - easy right? My understanding fades, however, when I notice the relative positions of the vector drawing depicting the "original" (T = T(ref)) condition vs the colorized 'Stress (solid)' plot depicting the strained condition of the strip --- these drawings don't seem to progress as a function of the specified temperature, rather they just "jump" to some final value. See images below to understand what I mean: images are for temperatures 500K 1000K 3000K and 294K and T(ref) From Multiphysics>Thermal Expansion is 293.15K . In reality, that strip should be bending continuously depending on what the temperature of the assembly is - but what I observe in the model is a physical bending of the object which "snaps" to one degree of bending or the other, even if deviation from T(ref) is a fraction of a kelvin. This is clearly not correct.

So, am I missing a setting in 'Solid Mechanics' or something so that this bending be described properly? Surely there is a way to accurately report these expansion values. The von Mises Strain gives numbers that are reasonable -- but the bending trend itself seems wrong.

Thank you for the help!



3 Replies Last Post 22 giu 2018, 17:16 GMT-4
Jeff Hiller COMSOL Employee

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Posted: 6 years ago 22 giu 2018, 16:27 GMT-4

Hello Peter,

The deformations you see on your screen are scaled - otherwise they would often not be visible to the naked eye.

The scaling factor is different in your different cases, giving the impression that the deformations are the same when in fact they are different. You can see that automatically-computed scaling factor in the GUI, and you can change it to a fixed value if you would like.

Jeff

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Jeff Hiller
Hello Peter, The deformations you see on your screen are scaled - otherwise they would often not be visible to the naked eye. The scaling factor is different in your different cases, giving the impression that the deformations are the same when in fact they are different. You can see that automatically-computed scaling factor in the GUI, and you can change it to a fixed value if you would like. Jeff

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Posted: 6 years ago 22 giu 2018, 16:54 GMT-4

Hello Jeff,

Thank you very much for your response. Seems like you've hit on the right issue. A couple of googles haven't helped me - is the relevant setting you are referring to the Solid Mechanics > Linear Elastic Material > Geometric Nonlinearity> "Force linear strains" radio button setting? It would be less confusing for us in our application to see the actual geometric deflection of our system, not the scaled version.

Thanks again for the rapid help. -Peter

Hello Jeff, Thank you very much for your response. Seems like you've hit on the right issue. A couple of googles haven't helped me - is the relevant setting you are referring to the Solid Mechanics > Linear Elastic Material > Geometric Nonlinearity> "Force linear strains" radio button setting? It would be less confusing for us in our application to see the actual geometric deflection of our system, not the scaled version. Thanks again for the rapid help. -Peter

Jeff Hiller COMSOL Employee

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Posted: 6 years ago 22 giu 2018, 17:16 GMT-4
Updated: 6 years ago 22 giu 2018, 17:17 GMT-4

See https://www.comsol.com/forum/thread/95741/boundary-load-change-having-no-effect?last=2015-11-24T19:25:19Z

Jeff

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Jeff Hiller
See https://www.comsol.com/forum/thread/95741/boundary-load-change-having-no-effect?last=2015-11-24T19:25:19Z Jeff

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