8 Replies Latest reply on Mar 18, 2015 11:43 AM by Doug Rawlings

Explanation for predefined Contact Resistance

Doug Rawlings Mar 4, 2015 9:19 AM

Hi,

I'm using SolidWorks Flow to do some thermal modelling and I'm a little wary of the predefined contact resistances. Basically I'm looking for a clear explanation of what the descriptions mean.

For example:

"Aluminum, ground, air (Roughness 0,25 micrometer)"

Does this mean aluminium in contact with aluminium, both surfaces having a ground finish to 0.25 micrometres, assembled in air and therefore has air trapped in the cavities formed between the two surfaces?

Or is it aluminium in contact with the ground? (OK, unlikely)

Or is it aluminium in contact with air?

Or is it...

I've looked through the Help and can't find anything that tries to explain these. I'm reasonably happy that my first explanation is the relevant one but I don't like uncertainty.

Thanks for your help,

Doug.

Re: Explanation for predefined Contact Resistance

Bill McEachern Mar 4, 2015 9:25 AM (in response to Doug Rawlings)

I would say its the first one. These things don't tend to make a huge difference as they tend to be quite thin. However, for some problems it does matter. In system level analysis I run without them as a first approximation. If things are close to being an issue I put them in and use something conservative.
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- Re: Explanation for predefined Contact Resistance
  
  Doug Rawlings Mar 4, 2015 9:51 AM (in response to Bill McEachern)
  
  Bill,
  
  Thanks for that. I also agree with your overall strategy but I'm working on something that is looking too close for that sort of simplification. And my customer seems to expect such things to be accounted for in any situation.
  
  Thanks for the help,
  
  Doug.
  
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  - Re: Explanation for predefined Contact Resistance
    
    Jared Conway Mar 5, 2015 2:11 AM (in response to Doug Rawlings)
    
    aluminum in contact with ground, 0,25 micrometer roughness, air filling the gaps
    
    if your customer wants this level of fidelity, i'd ask them for the contact resistance that they want you to apply
    
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    - Re: Explanation for predefined Contact Resistance
      
      Doug Rawlings Mar 16, 2015 2:30 PM (in response to Jared Conway)
      
      Jared,
      
      Thanks for the reply and I apologise for being so late in looking at it, I don't have ready access to the Internet at the moment.
      
      I'm afraid your answer has thrown me a bit. When you say "aluminum in contact with ground", what do you mean by ground? I would normally interpret that to be either a) ground, earth, dirt b) the floor or c) electrical ground. And that's kind of one of the interpretations I'd started with but didn't make sense to me.
      
      Unfortunately in this case the client doesn't have much more of a clue than me! Or at least I've not found that person yet. I work as a contractor and have been cornered into doing this (since I admitted to knowing a bit about SolidWorks Flow). The one person who does this sort of thing regularly said to use the pre-defined contact resistance for aluminium (without specifying which one) but I'm trying to understand things a bit better than that.
      
      If you can give a bit more detail on what you mean by ground then it would be appreciated,
      
      Regards,
      
      Doug.
      
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      - Re: Explanation for predefined Contact Resistance
        
        Jared Conway Mar 17, 2015 2:43 AM (in response to Doug Rawlings)
        
        now that I read it again, I think ground means ground surface finish
        
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        Re: Explanation for predefined Contact Resistance
        
        Doug Rawlings Mar 17, 2015 8:27 AM (in response to Jared Conway)
        
        Hi Jared,
        
        Ah, that's good that we all seem to have come to the same conclusion. Although the confusion shows how badly worded the original description is, especially when it's caused someone with your experience to have to look at it twice.
        
        Thanks Bill and Jared for your help, and to anyone else who looked at this question.
        
        Doug.
        
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        Re: Explanation for predefined Contact Resistance
        
        Jared Conway Mar 18, 2015 1:20 AM (in response to Doug Rawlings)
        
        what will probably really boggle your mind is what should you choose if you have 2 different materials?
        
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        Re: Explanation for predefined Contact Resistance
        
        Doug Rawlings Mar 18, 2015 11:43 AM (in response to Jared Conway)
        
        I'm trying not to think about that...
        
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