Modelling with a Rubber component 1

[WPM3022]

Hello Eng Tips.

I have a situation i'd like to model - it includes rubber as a cushion/ isolation between steel components. The application is a surface scraper: a blade connected to supporting steel via a rubber isolation cushion. I know the force at the blade, and want to check the supporting structure. The isolation cushion is a proprietary item (i'm not 'checking' that part of it), rather the supporting structure and the blade.

I'm having immense difficulty defining a hyperelastic material. I can find theory on the matter easily enough, but without performing my own testing, I cannot find any appropriate parameters for the material. The program I'm using can simulate the material, however i need a stress-strain/force-displacement curve for the material which i don't have (and cannot get).

Does any one have any stress-strain data resources (google isn't giving me much at all).

Anther related question: thought on if I assume that the cushion is a linear material (i.e. steel set to very low density) and use the simulation to . I'm not concerned with displacement of the blade, Would taking such an approach yield conservative results? Forgive the ignorance on this one please.

Thank you.

PS: Using either Strand 7 FEA or Nastran-in-CAD with Inventor.

 

[rickfischer51]

Check Matreality. They used to have some data on stuff they tested freely available on their website. Might still be there.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[btrueblood]

I've done some simple "proof of concept" modelling of rubber materials, and yes you can get an idea of what is going on using a linear modeller. For my device, I started with E = 3000 psi, and nu as close to 0.5 as I could get without the code bombing. I tweaked the E value to get the displacements closer to values supplied by the manufacturer of my parts, and once we had a design we were comfortable with, paid an outside company to do the testing and develop material model coefficients, and run non-linear models for us.

It sounds like you are planning to bond the rubber to other parts in your assembly. This gets tricky, you should be talking to a rubber molding shop, one with experience in bonding (hint: usually best done in the mold using bonding primers suited for your metals).

 

[WPM3022]

@rickfischer51

Thanks for the lead - can't find through a simple page 1 google search. If you have a link that'd be great.

 

[rickfischer51]

oops. Misspelled it. Matereality. cant spell to save my life. so I do FEA

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[rickfischer51]

"rubber Spring Design" by gobel has a plot youngs modulus vs IHRD, which is roughly the same as shore D.Might be useful for a first pass or if your deflections arent too high.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[marcopoloa]

@WPM3022

Hello there,

I was in the same situations for few months until few days ago I came across with the following website.

There is a lot of material, lot of plotted stress-strain diagram and the best of it you can download its data for free too!

https://www.campusplastics.com

Good diving

regards,
mark

 

[A-Run]

Hello WMP3022,

As isolation cushion is a proprietary item as you said, could you get Force/Displacement curves from the supplier/manufacturer for it? Then you can use a 6 DOF beam material (Beam element) with curves representing stiffness in all 6DOFs. This will let you evaluate your structure,

PS: I am writing this from experience of working in LS-Dyna environment. No idea about how to go about this with Strand 7 FEA or Nastran-in-CAD with Inventor

 

[WPM3022]

Thanks A-Run

i have requested and will keep you posted.

the text 'Rubber Springs Desing" by Goebel is most helpful too. I obtained a 1974 copy from my library.