The Fung hyperelastic solid constitutive model.[^1]
**Parameters**
- The bulk modulus $`\kappa`$.
- The shear modulus $`\mu`$.
- The extra modulus $`\mu_m`$.
- The exponent $`c`$.
**External variables**
- The deformation gradient $`\mathbf{F}`$.
**Internal variables**
- None.
**Notes**
- The Fung model reduces to the [Neo-Hookean model](super::NeoHookean) when $`\mu_m\to 0`$ or $`c\to 0`$.