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Unrealistic results in Elasto-Plastic analysis: Thermal Stress Problem

Posted 25.02.2014, 00:41 GMT-5 Heat Transfer & Phase Change, Geometry, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization, Studies & Solvers, Structural Mechanics 3 Replies

Deemi Qaiser
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I am modeling a Thermal stress analysis of 3D wire wherein Temperature field (x,y,z) was imposed by using Interpolation function (imported a .txt file). It is simply an Elastic-Plastic analysis. Because of higher values of imposed temperatures, specimen goes into plastic region. I set the Linear elastic-Perfectly Plastic model (i.e. The plastic region starts when induced stress exceeds the Yield strength of the material).
However, the result are unrealistic i.e. Elastic strain are very low, a zero plastic strain and only thermal strain is very high. I think the total strain is mainly showing up as Thermal strain and contribution of other strains are almost zero.

I have attached the report file. Need help. Any comments or suggestions are appreciated.
3 Replies Last Post 26.02.2014, 09:16 GMT-5
Suresh Seetharam
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Posted: 1 decade ago 25.02.2014, 16:44 GMT-5
Hi,


I am not sure I have an answer.

I suspect some problem in your boundary condition, because if you don't have appropriate constraints, the stresses may not develop? Did you check if von Mises exceeds initial yield stress, if not you will not have plastic strain.


Suresh
Hi, I am not sure I have an answer. I suspect some problem in your boundary condition, because if you don't have appropriate constraints, the stresses may not develop? Did you check if von Mises exceeds initial yield stress, if not you will not have plastic strain. Suresh
Deemi Qaiser
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Posted: 1 decade ago 25.02.2014, 23:27 GMT-5
Thanks Suresh. Yes, I have checked it again. Actually, my model is using symmetry boundary conditions so 3 surfaces have constraints. And, I guess symmetry is enough to make plastic strain happen.

Any method for manipulation of Results data ? I wonder, may I say that Thermal strain is actually plastic strain?
Thanks Suresh. Yes, I have checked it again. Actually, my model is using symmetry boundary conditions so 3 surfaces have constraints. And, I guess symmetry is enough to make plastic strain happen. Any method for manipulation of Results data ? I wonder, may I say that Thermal strain is actually plastic strain?
Josh Thomas Certified Consultant
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Posted: 1 decade ago 26.02.2014, 09:16 GMT-5
Deemi,

Your specified yield strength is much higher than the stress you are seeing. The results seem realistic to me because stress is below yield. You should have zero plastic strain. Volumetric expansion isn't going to give stress unless you have a displacement constraint somewhere. The relatively small stresses you do see I believe are coming from the temperature distribution being non-uniform. Try increasing the temperature gradients in the temperature distribution. Otherwise, it seems that you won't get plasticity.

--
Best regards,
Josh Thomas
AltaSim Technologies
Deemi, Your specified yield strength is much higher than the stress you are seeing. The results seem realistic to me because stress is below yield. You should have zero plastic strain. Volumetric expansion isn't going to give stress unless you have a displacement constraint somewhere. The relatively small stresses you do see I believe are coming from the temperature distribution being non-uniform. Try increasing the temperature gradients in the temperature distribution. Otherwise, it seems that you won't get plasticity. -- Best regards, Josh Thomas AltaSim Technologies

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