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ashwini
2007-02-27, 23:46
Hi Group,

I am currently working on the rubber bushing in Ansys, purpose of the analysis is ,i need to find out the stiffness of the bushing.I am using Mooney Rivlin constants with d=0, this makes material incompressible. But i have a table of compression co-efficient Vs Mooney Rivlin constants.

I do not know how to use this cimpression-coefficient.........
Please Can any one help me in understanding the meaning of compression co-fficient? and also how can I use this in Ansys?

Ashwini

Jorgen
2007-03-05, 07:17
The traditional formulation of the Mooney-Rivlin model requires three material parameters: C10, C01, and D. The distortional response of the material is characterized by C10 and C01, and the volumetric response by D.

In your case you mention a table of "compresion coefficients vs. Mooney Rivlin constants". That does not make any sense to me. You only need 3 parameters for the MR model, not a table. Can you explain more about what the table contains?

- Jorgen

ashwini
2007-03-06, 00:02
Hi

This is the table I have, which gives the compression co-efficient value, Mooney rivlin constants with repsect to shore hardness.

Shore hardness E (Mpa) Shear G (Mpa) Compression Co-efficient C1 C2
10 0.4 0.13 1.04 0.05 0.013
20 0.7 0.23 0.97 0.09 0.023
30 1.2 0.4 0.88 0.16 0.04
40 1.7 0.57 0.8 0.23 0.057
50 2.5 0.83 0.7 0.33 0.083
60 3.8 1.27 0.6 0.51 0.127
70 6 2.00 0.54 0.8 0.2
80 11 3.67 0.5 1.47 0.367
90 23 7.67 0.5 3.07 0.767

Red color number shows thevalue compression co-efficient for each shore hardness.

I know only C1 and C2 and i do not know "D".
Is there any relation between compression co efficient value and D?
if so ,what is the relation?

Is it possible to attach any file in this forum along with the reply?
if yes means i can attach the file which shows the above table.

Thanks,
Ashwini

Jorgen
2007-03-07, 18:50
Oh, I see what you mean. Each line in the table is for a different material with a different shore hardness.

The term "Compression Co-efficient" is, as far as I know, not well-defined.
What I would do in your case is to take the given Mooney Rivlin constants as given in the table, and then simply pick a "D" value that corresponds to an almost incompressible material. I don't recall how ANSYS defines it, but ABAQUS defines D = 2 / kappa, where kappa is the bulk modulus. If you pick kappa = 500 * C1 (or so), then you will get an approximate bulk modulus.

If you really care about your results, however, I recommend that you perform actual experiments on your material.

- Jorgen