How to disregard thermal stresses?

marlon · September 27, 2015, 11:11

Hi,

When I simulate a simple block, 2D, free, and I apply an uniform thermal condition (cooling in my case), It starts to shrink (as we expected) and we can see a displacement in the result. Ok.

However, Ansys also shows a stress happening. One can say there's stress since Sigma = E*Epsilon (Hook's Law), however, since the body is free in all directions, it shouldn't show any stress. It's just a shrinkage. What can we do to disconsider this stress in the result?

For example:
A material has yield strength = X at 295K and yield strength = Y at 80K (Y use to be >X). So, if I aply a load < Y at 80K, this material will be ok.

But, when I simulate the cooling, Ansys shows me there's a stress = Y-10 MPa acting. Therefore, just applying 10MPa would be enought to damage the body, and it's not true.

Now, why is it a big problem (a bug?): imagine we have two bodies, of different materials, conected side by side. Since they have different expansion coefficients, now we really expect a stress caused by this difference of shrinkage. I'm interessed in this values, disregarding that effect Ansys shows about just cool a body.

Pauli · October 2, 2015, 13:17

If you are using ANSYS Mechanical go under the Geometry section select the part then set Thermal Strain Effects to no.

marlon · October 2, 2015, 21:23

Hi,

Actually, check the thermal stress is important, the problem was they should not exist when a body of just one material is cooled without fixed points.

One said to me change from "Plane Strain" to "Plane Stress" at that analysis and it worked.

September 27, 2015, 11:11	How to disregard thermal stresses?	#1
marlon New Member Marlon Saveri Join Date: Aug 2015 Posts: 8 Rep Power: 10	Hi, When I simulate a simple block, 2D, free, and I apply an uniform thermal condition (cooling in my case), It starts to shrink (as we expected) and we can see a displacement in the result. Ok. However, Ansys also shows a stress happening. One can say there's stress since Sigma = EEpsilon (Hook's Law), however, since the body is free in all directions, it shouldn't show any stress. It's just a shrinkage. What can we do to disconsider this stress in the result? For example: A material has yield strength = X at 295K and yield strength = Y at 80K (Y use to be >X). So, if I aply a load < Y at 80K, this material will be ok. But, when I simulate the cooling, Ansys shows me there's a stress = Y-10 MPa acting. Therefore, just applying 10MPa would be enought to damage the body, and it's not true. Now, why is it a big problem (a bug?): imagine we have two bodies, of different materials, conected side by side. Since they have different expansion coefficients, now we really expect a stress caused by this difference of shrinkage. I'm interessed in this values, disregarding that effect Ansys shows about just cool a body. Last edited by marlon; September 27, 2015 at 11:23. Reason: I'd changed Y by X at the explanation*

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October 2, 2015, 13:17		#2
Pauli Senior Member Pauli Join Date: Mar 2009 Posts: 189 Rep Power: 17	If you are using ANSYS Mechanical go under the Geometry section select the part then set Thermal Strain Effects to no.

October 2, 2015, 21:23		#3
marlon New Member Marlon Saveri Join Date: Aug 2015 Posts: 8 Rep Power: 10	Hi, Actually, check the thermal stress is important, the problem was they should not exist when a body of just one material is cooled without fixed points. One said to me change from "Plane Strain" to "Plane Stress" at that analysis and it worked.