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**oltreuomo****Member**- Registered: 2016-09-05
- Posts: 19

Hi,

Could someone give me some guidance on the proper way to retrieve thermally-induced stresses/strains of a structure in a free (mechanically unconstrained) state? I am simply trying to analyze a thick composite cylinder, modeled using solid elements with orthotropic properties.

I first perform a linear thermal analysis to apply the temperature distribution that I want. Then, to retrieve the thermally-induced stresses, I assign a reference temperature using AFFE_MATERIAU/VALE_REF and perform a linear static analysis using MECA_STATIQUE. The issue that I am having is that I am unable to come up with a set of boundary conditions for MECA_STATIQUE which allows the cylinder to change size freely with temperature (and not build stresses due to imposed displacement constraints), and also not fail due to encountering a singular matrix.

Does anyone have any advice for doing this? Thanks in advance.

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**stephaneberger****Member**- From: Strasbourg (France)
- Registered: 2012-10-15
- Posts: 68

Hi,

To run static calculation you must avoid any rigid body motion.

In your case, you have to lock your model, at least one node.

stephane

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**tianyikillua****Member**- From: Paris
- Registered: 2017-11-06
- Posts: 8

Hi,

I have exactly the same problem (thermal stresses induced by temperature dilataion on an unconstrained structure).

I end up by solving the mechanical problem via an iterative solver (GCPC in Code_Aster). This will give you a solution including a rigid body motion. Then I performed a least squares analysis in ParaView to remove this rigid body motion in order that the displacement field is orthogonal to rigid body motions.

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**RenatoLi****Member**- Registered: 2018-01-04
- Posts: 1

Same problem here, but unfortunately what Tiany suggested didn't work for me. Any other ideas would be much appreciated.

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**jeanpierreaubry****Guru**- From: nantes (france)
- Registered: 2009-03-12
- Posts: 3,041
- Website

many structure, particularly revolution one, can be given a set of boundary conditions that will not induce any mechanical stress

it would be a good idea to post a sketch o better the mesh to give an advice

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**tianyikillua****Member**- From: Paris
- Registered: 2017-11-06
- Posts: 8

RenatoLi wrote:

Same problem here, but unfortunately what Tiany suggested didn't work for me. Any other ideas would be much appreciated.

Hi, in which sense that the method doesn't work for you? You do not want to conduct an additional post processing step or you think the solution is not physically meaningful?

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