# Hyperelastic coefficient units

Are the units for the hyperelastic coefficients unitless? My projects are setup for English so I don’t know what to assume the units are because there are no units next to the coefficients.

Hi @cschmidt!

The constants are basically curve fitting constants for uniaxial tension (just one example) data from your experiment. A good discussion can be found here: Mooney-Rivlin Constants

Let me know if that helped! All the best and have a nice weekend!

Jousef

Hi Jousefm,

I am calculating my constants from the equations of Shear modolus and Bulk Modulus of my materials (Silicone Rubber and Nylon). But I am not sure what units should I express them on Simscale?

Thanks!

Hi @mpolo,
thanks for reminding us that the units are still missing! We’ll fix that asap.
As the coefficients C_{xy} for the hyperelastic materials are used to express the strain energy density, they are in the same unit as energy divided by volume. This means:

• SI: J/m³ = N/m² = Pa
• US: in*lbf/in³ = lbf/in² = psi

D_1 has obviously the inverse unit. You can also refer to our documentation for some details about the formulation we use.

Best,
Richard

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