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Poisson’s ratio and thermal expansion

Posted 16 nov 2016, 11:20 GMT-5 Structural Mechanics Version 5.2a 4 Replies

Reza V
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I have problem calculating strain due to thermal expansion. Consider a large rectangular plate under uniform temperature increase. The strain should be simply the value of thermal expansion multiply by value of temperature increase. However the result from modeling shows an added value to strain due Poisson’s ratio. This part of strain changes with Poisson’s ratio. I figured out this is due to very small value of stress (in the order of e-6) created by numerical errors. These very small values of stress are negligible. But they should not influence the result by activating Poisson’s ratio effect for thermal strain values. Is there any tolerance or limit in the software to avoid this problem? I appreciate any help or advise in this regard.
4 Replies Last Post 18 nov 2016, 20:20 GMT-5
Reza V
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Posted: 8 years ago 16 nov 2016, 13:21 GMT-5
From the numerical point of view, calculation shows that the Poisson’s ratio should be multiply to that portion of strain in another direction which is caused by mechanical load and not total strain in another direction.
From the numerical point of view, calculation shows that the Poisson’s ratio should be multiply to that portion of strain in another direction which is caused by mechanical load and not total strain in another direction.
Reza V
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Posted: 8 years ago 17 nov 2016, 18:06 GMT-5
Does any one know whether there is any solution for this problem?
Does any one know whether there is any solution for this problem?
Henrik Sönnerlind COMSOL Employee

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Posted: 8 years ago 18 nov 2016, 01:34 GMT-5
Hi,

I guess that you are running the simulation under plane strain conditions. Then the zero out-of-plane strain will cause an extra expansion in the other two directions, since a compressive out-of-plane stress is induced.

Your assumption of what will happen is relevant for only for plane stress.

Regards,
Henrik
Hi, I guess that you are running the simulation under plane strain conditions. Then the zero out-of-plane strain will cause an extra expansion in the other two directions, since a compressive out-of-plane stress is induced. Your assumption of what will happen is relevant for only for plane stress. Regards, Henrik
Reza V
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Posted: 8 years ago 18 nov 2016, 20:20 GMT-5
Dear Henrik,
You are right. It was great help. My calculation for plane stress and plane strain conditions confirms what you said and also the result of the software.
Thank you very much.
Best regards,
Reza
Dear Henrik, You are right. It was great help. My calculation for plane stress and plane strain conditions confirms what you said and also the result of the software. Thank you very much. Best regards, Reza

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