# Yeoh (/MAT/LAW94)

LAW94 is a hyperelastic material model that can be used to describe incompressible materials.

- ${\overline{I}}_{1}={\overline{\lambda}}_{1}^{2}+{\overline{\lambda}}_{2}^{2}+{\overline{\lambda}}_{3}^{2}$
- First strain invariant
- ${\overline{\lambda}}_{i}={J}^{-\frac{1}{3}}{\lambda}_{i}$
- Deviatoric stretch

## Material Parameters

- ${C}_{10},{C}_{20},{C}_{30}$
- Material constants specify the deviatoric part (shape change) of the material
- ${D}_{1}$ , ${D}_{2}$ , ${D}_{3}$
- Parameters specify the volumetric change of the material

These six material constants need to be calculated by curve fitting material test data. RD-E: 5600 Hyperelastic Material with Curve Input includes a Yeoh fitting Compose script for uniaxial test data. The Yeoh material model has been shown to model all deformation models, even if the curve fit was obtained using only uniaxial test data.

## Poisson's Ratio and Material Incompressibility

LAW94 is available only as an incompressible material model.

## References

^{1}Yeoh, O. H. "Some forms of the strain energy function for rubber." Rubber Chemistry and technology 66, no. 5 (1993): 754-771