7 Replies Latest reply on Aug 21, 2009 3:55 PM by Jose Eduardo Fernandes de Camargo

singularity & "hot spots" , how to deal with it?

Paul Fichman Jul 28, 2009 2:00 AM

I checked a simple tube with variable cross section for bending .

hand calculation states a max. stress of 312 MPa. the simulation show a max. stress of 1100 MPa.

the high stress is a "hot spot" format. if I refine the mesh, the stress result will go higher. in fact , a very coarse mesh gives closer results to reality.

how do I tackle these "hot spots"? it makes the whole simulation useless.

Re: singularity & "hot spots" , how to deal with it?

Derek Bishop Jul 28, 2009 6:13 AM (in response to Paul Fichman)

I cannot see why you would get singularities on a supported tube. Need to get a better description of the geometry, the supports being used and where the problem is occuring.
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- Re: singularity & "hot spots" , how to deal with it?
  
  Paul Fichman Jul 28, 2009 9:35 AM (in response to Derek Bishop)
  
  this is the model. a remote load that creates bending at the top of the tube & fixed constrain at the bottom.
  
  test tube-Study 1-Results-Stress1.jpg 54.5 KB
  
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  - Re: singularity & "hot spots" , how to deal with it?
    
    Poovaiah Devenira Jul 28, 2009 10:17 AM (in response to Paul Fichman)
    
    Hi, I would need more data regarding the Load, The length of the moment arm, the radius of the fillet and Cross section.
    
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  - Re: singularity & "hot spots" , how to deal with it?
    
    Derek Bishop Jul 28, 2009 10:47 AM (in response to Paul Fichman)
    
    I would not ignore the area showing as red. The grooved section is an obvious stress raiser. Did you use a stress concentration factor when doing the calculations manually? Using a coarse mesh will cause the FEA simulation to overlook small irregularities.
    
    And by the way, a singularity occurs where you have a corner sharp corner that comes to a point. From what I can see you don't have that situation.
    
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    - Re: singularity & "hot spots" , how to deal with it?
      
      Paul Fichman Jul 29, 2009 2:02 AM (in response to Derek Bishop)
      
      Derek, I didn't used correction factor in my calculation.
      the high stress volume will remain even if I fillet all sharp edges to the max.
      you recommend not to ignore these areas, how should I interpret this high stress result? it's 3 times higher than manual calculation .
      should I assume that the part will deform or remain below the Yield point (350 MPa)?
      
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      - Re: singularity & "hot spots" , how to deal with it?
        
        Derek Bishop Jul 29, 2009 3:09 AM (in response to Paul Fichman)
        
        Hello Paul,
        Do you have an engineering background? If so, may I suggest you grab out the old text books and revise stress concentration. It seems to be the issue here. I am saying I would not ignore the high stresses. You are the designer and must take responsibility for how the design is altered to ensure that it avoids the problems the FEA has highlighted if you conclude they are correct. Sorry mate. Cannot help you much more.
        
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        Re: singularity & "hot spots" , how to deal with it?
        
        Jose Eduardo Fernandes de Camargo Aug 21, 2009 3:55 PM (in response to Derek Bishop)
        
        Paul,
        
        Could you plot a mesh and geometry image? This could help to find the better way to deal with this singularity. It seems to be a result from the narrow channel in your model.
        
        Best regards,
        Eduardo Camargo
        
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