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Modelling Compression of a rubber block

Question asked by Christopher Hardy on Sep 10, 2013
Latest reply on Jul 13, 2018 by Paul Millhouse

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Hi,

My names Chris, I am a beginner to SolidWorks simulation, my apologies if I use any incorrect terminology or assumptions.

But can someone please help me with a current project I am working on.

I am currently trying to model a rubber block being compressed by 2 metal plates (from top and bottom). I have attained raw stress-strain curve data from physical experimentation to

represent the material's non-linear elastic behavior.

So as of now, these are the things I have done to the model:

1) Draw the physical rubber block

2) Added forces of 1N @ the top and bottom of the rubber block, with a time dependancy using "Variation with Time" to represent the 2 blocks compressing the rubber. (force will be multiplied by the supplied time curve Y value)

3) Changed the Study time properties to match real life experimentation time

4) specified material properties with "Nonlinear Elastic", Poisson ratio 0.4995, Thermal Expansion 0.0002/K, Mass Density 358 kg/m^3, Tensile Strength 13789514 N/m^2

The only thing left which I do not quiet understand is the constraints I need to place on the mode, Can someone please help me with this ?

And please let me know if I left anything important out.

Thanks for your help

(Attached is the rubber block that needs to be compressed: Top/bottom face dimension = 150mm x 50mm)

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Small Rubber Sample.SLDPRT.zip40.6 KB

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Christopher Hardy Sep 10, 2013 1:42 AM

Here is an error image when i try to constrain the top and bottom surfaces usign Reference Geometry. I have only allowed movement along "Plane Dir 2"

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Jared Conway @ Christopher Hardy on Sep 10, 2013 11:20 AM

as a first crack at this, make it easy on yourself.

cut the model in a quarter, apply symmetry restraints on the cut faces and then apply your load. this artificially restrains your problem at the center point which will make it stable. then you can start removing symmetry restraints to learn what kind of restraints are needed to hold things in place.

regarding the tangent modulus error, it sounds like you have too many inputs for your material. either enter the E and Etan or the stress strain curve. not both. there are a bunch of articles on this in the solidworks KB and it is covered in the solidworks premium training. we also offer one-on-one training for this type of problem if you're interested.

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Christopher Hardy @ Jared Conway on Sep 17, 2013 9:44 PM

Hi Jared,

Thanks for the help. Just wondering, what do you mean by the E and Etan ? I do not think I have come across that function.

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Christopher Hardy @ Jared Conway on Sep 18, 2013 2:45 AM

The other thing I am worried and unsure about is the size of the load/displacement.

The step 1 error message states that it could either be:

Lack of adequate restraint (using symmetry on cut faces)
Material Properties not Defined (I believe this is defined, as i used for another analysis)
Load Increment to large or to small (what is large and what is small?)

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Jared Conway @ Christopher Hardy on Sep 18, 2013 3:32 AM

Might be worth posting your model at this point. Sounds like you're missing some steps on the setup.

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Christopher Hardy @ Jared Conway on Sep 18, 2013 6:57 AM

Jared I will create a new discussion, Sorry i couldn't find a link to upload a new attachment

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Jared Conway @ Christopher Hardy on Sep 18, 2013 11:31 AM

using the advanced editor in the top right you can post new models. just in case someone comes across this thread in the future, can you post a link in both threads pointing to the other

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Jerry Steiger Sep 10, 2013 11:23 PM

Christopher,

Rubber parts are usually quite hard to simulate accurately. Compression loads are particularly hard, as the results depend strongly on the friction coefficient between the faces of the part and the tester.

Rubber materials are strongly nonlinear in their response. Linear approximations only work for very small strains. You have to do a lot of testing to establish a good material model for each rubber material. There are laboratories that specialize in doing this type of testing.

Jerry S.

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Paul Millhouse @ Jerry Steiger on Jul 13, 2018 5:26 PM

Sorry to bring up an old post. Hey Jerry Steiger (and others), in your opinion, could this be more accurately modeled without the top and bottom plates? I have a similar problem where I simply need to simulate compression of a rubber part. I could fix the bottom surface and apply the compressive force on the top surface. That way there is no friction forces or other assembly components to deal with, just simple compression of the (rubber or similar) part. Would that help? Thanks

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10 Replies

Christopher Hardy Sep 10, 2013 1:42 AM
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Here is an error image when i try to constrain the top and bottom surfaces usign Reference Geometry. I have only allowed movement along "Plane Dir 2"
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- Jared Conway @ Christopher Hardy on Sep 10, 2013 11:20 AM
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  as a first crack at this, make it easy on yourself.
  
  cut the model in a quarter, apply symmetry restraints on the cut faces and then apply your load. this artificially restrains your problem at the center point which will make it stable. then you can start removing symmetry restraints to learn what kind of restraints are needed to hold things in place.
  
  regarding the tangent modulus error, it sounds like you have too many inputs for your material. either enter the E and Etan or the stress strain curve. not both. there are a bunch of articles on this in the solidworks KB and it is covered in the solidworks premium training. we also offer one-on-one training for this type of problem if you're interested.
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  - Christopher Hardy @ Jared Conway on Sep 17, 2013 9:44 PM
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    Hi Jared,
    
    Thanks for the help. Just wondering, what do you mean by the E and Etan ? I do not think I have come across that function.
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    - Jared Conway @ Christopher Hardy on Sep 18, 2013 1:58 AM
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      http://help.solidworks.com/2010/English/SolidWorks/cworks/legacyhelp/simulation/materials/material_models/von_mises_plasticity_model_(kinematic_isotropic).htm?format=P
      
      Etan and e are part of the bilinear material model
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      - Christopher Hardy @ Jared Conway on Sep 18, 2013 2:45 AM
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        The other thing I am worried and unsure about is the size of the load/displacement.
        
        The step 1 error message states that it could either be:
        Lack of adequate restraint (using symmetry on cut faces)
        Material Properties not Defined (I believe this is defined, as i used for another analysis)
        Load Increment to large or to small (what is large and what is small?)
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        Jared Conway @ Christopher Hardy on Sep 18, 2013 3:32 AM
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        Might be worth posting your model at this point. Sounds like you're missing some steps on the setup.
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        Christopher Hardy @ Jared Conway on Sep 18, 2013 6:57 AM
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        Jared I will create a new discussion, Sorry i couldn't find a link to upload a new attachment
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        Jared Conway @ Christopher Hardy on Sep 18, 2013 11:31 AM
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        using the advanced editor in the top right you can post new models. just in case someone comes across this thread in the future, can you post a link in both threads pointing to the other
        Like • Show 0 Likes0
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Jerry Steiger Sep 10, 2013 11:23 PM
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Christopher,

Rubber parts are usually quite hard to simulate accurately. Compression loads are particularly hard, as the results depend strongly on the friction coefficient between the faces of the part and the tester.

Rubber materials are strongly nonlinear in their response. Linear approximations only work for very small strains. You have to do a lot of testing to establish a good material model for each rubber material. There are laboratories that specialize in doing this type of testing.

Jerry S.
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- Paul Millhouse @ Jerry Steiger on Jul 13, 2018 5:26 PM
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  Sorry to bring up an old post. Hey Jerry Steiger (and others), in your opinion, could this be more accurately modeled without the top and bottom plates? I have a similar problem where I simply need to simulate compression of a rubber part. I could fix the bottom surface and apply the compressive force on the top surface. That way there is no friction forces or other assembly components to deal with, just simple compression of the (rubber or similar) part. Would that help? Thanks
  Like • Show 0 Likes0
  Actions

Modelling Compression of a rubber block

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