Ivar KJELBERG
COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted:
1 decade ago
04.10.2011, 14:20 GMT-4
Hi
if you use linear material models I do not believe you have "relaxation" that is a different non-linear phenomena, you need to model using another physics settings and material properties. The linear model is correct for "small" temperature changes (even if these can be for a human quite "large"
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Good luck
Ivar
Hi
if you use linear material models I do not believe you have "relaxation" that is a different non-linear phenomena, you need to model using another physics settings and material properties. The linear model is correct for "small" temperature changes (even if these can be for a human quite "large"
--
Good luck
Ivar
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Posted:
1 decade ago
06.10.2011, 12:40 GMT-4
Hi Ivar,
Thank you so much for your reply. I've changed my physics setting to thermal viscoelastic now. The linear model seems to be fairly simple, however, I'm still having the same problem.i.e the stress never relaxes to zero, even at very short relaxation time (1 s) . According to Maxwell model, you would expect the stress to decrease exponentially with time. so why comsol still asks for a strain reference temperature which in my opinion is the reason why the stresses in my test case never relax. Apologies if I'm asking naive questions, it's just I've just started looking at this sort of problems.
Many thanks,
Ali
Hi Ivar,
Thank you so much for your reply. I've changed my physics setting to thermal viscoelastic now. The linear model seems to be fairly simple, however, I'm still having the same problem.i.e the stress never relaxes to zero, even at very short relaxation time (1 s) . According to Maxwell model, you would expect the stress to decrease exponentially with time. so why comsol still asks for a strain reference temperature which in my opinion is the reason why the stresses in my test case never relax. Apologies if I'm asking naive questions, it's just I've just started looking at this sort of problems.
Many thanks,
Ali
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Posted:
1 decade ago
09.10.2011, 07:26 GMT-4
Ali,
You are correct in your description of the phenomenon of thermal stress relaxation with time, temperature, and stress. The physics you describe needs to be represented in your model. The relaxation arises from time dependent deformation due to the material behavior of creep, which can be incorporated by adding a general form PDE to your model. To do this, you need to know the creep behavior of your material. See the example model and documentation at the link below.
www.comsol.com/showroom/documentation/model/207/
Regards,
K. Funke
Ali,
You are correct in your description of the phenomenon of thermal stress relaxation with time, temperature, and stress. The physics you describe needs to be represented in your model. The relaxation arises from time dependent deformation due to the material behavior of creep, which can be incorporated by adding a general form PDE to your model. To do this, you need to know the creep behavior of your material. See the example model and documentation at the link below.
http://www.comsol.com/showroom/documentation/model/207/
Regards,
K. Funke
Nagi Elabbasi
Facebook Reality Labs
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Posted:
1 decade ago
10.10.2011, 01:12 GMT-4
Check your viscoelastic constants. To approach a basic Maxwell model the long term shear modulus in the Generalized Maxwell Model must be zero. That should get the stresses relaxing to zero regardless of the reference temperature.
Nagi Elabbasi
Veryst Engineering
Check your viscoelastic constants. To approach a basic Maxwell model the long term shear modulus in the Generalized Maxwell Model must be zero. That should get the stresses relaxing to zero regardless of the reference temperature.
Nagi Elabbasi
Veryst Engineering
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Posted:
1 decade ago
12.10.2011, 04:58 GMT-4
Many thanks, it works well now by adding a creep physics as you suggested.
Best,
Ali
Many thanks, it works well now by adding a creep physics as you suggested.
Best,
Ali
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Posted:
1 decade ago
13.10.2011, 10:20 GMT-4