What is the best analysis to use for thermal expansion and sliding over surfaces

[Anonymous]

Hi all,

I have a 1m length of SHS which is welded to a block (block on the left in the first picture) (see pictures for arrangement) and allowed to slide over the remaining two blocks (in first picture). The blocks are fixed in all translations and rotations. I am wanting to see deformation/displacement, and stresses (of the SHS) when applying an internal temperature (700K) and external temperature (300K) to the SHS. I have attempted this problem before, however, I couldn't get the SHS to slide over two of the blocks. What is the best analysis type to use for this problem? Possibly Linear Steady State Heat Transfer then use results in Linear Static?

This is how I am thinking I should set up the analysis:

• Apply constraints (fixed in translation and rotation) to bottom surface of blocks.
• Apply internal and external temperatures to SHS.
• Surface contact of first block will remain as bonded.
• Surface contact of remaining two block will need to be sliding/no separation.

Obviously I will apply mesh, idealisations etc.

1. Is there anything I am missing?
2. Is there a better method to set up this analysis?
3. If I do not apply a friction value within the sliding surface contacts, what value is used?

Thanks in advance.

[John_Holtz · Accepted solution]

Hi @Anonymous

The answers to your questions are as follows:

1. Is there anything I am missing? Not really.
2. Is there a better method to set up this analysis?
   1. Were you planning on applying a convection load to the inside and outside, or a temperature load? I would suggest a convection load. Your SHS looks to be thin wall. Unless it is made from a very expensive insulating material, I doubt that it can have a temperature gradient of 400 K through the wall. Using convection loads would calculate that the average temperature is around 500 K with a small temperature gradient.
   2. Instead of sliding/no separation, you might want to use separation contact. If there is no mechanism that forces the bodies to remain in contact, the separation contact would be more realistic. In other words, if the temperature gradient wants to bow the beam, or if there are any loads that want to bend the beam, separation contact will allow it to lift off of the supports (again, assuming that is the real arrangement).
3. If I do not apply a friction value within the sliding surface contacts, what value is used? No friction is equivalent to 0.

[Anonymous]

Thanks John, much appreciated. I should have mentioned this problem described is only as a representation/simplification of a much larger problem thus, as you say, the temperature gradient is quite large for this case. I am going to apply a convection load - the ambient temperature is the external temperature described in my problem. I will trial the use of both contacts - the only force applied to the bodies is gravity thus, it should be allowed to bow as you suggested. 

Does the separation contact allow it to expand in length (-Z direction in this case)? As the expansion of length is a key output for this problem.

Cheers

[Anonymous]

John, please ignore my previous reply - forgot there were separation and separation/no sliding contacts. Getting the most realistic results using separation contact and applying gravity. 

Thanks for you help.