#[cfg(test)]
mod test;
use crate::{
constitutive::{
ConstitutiveError,
solid::{FIVE_THIRDS, Solid, TWO_THIRDS, elastic::Elastic, hyperelastic::Hyperelastic},
},
math::{IDENTITY, Rank2},
mechanics::{CauchyStress, CauchyTangentStiffness, Deformation, DeformationGradient, Scalar},
};
#[doc = include_str!("doc.md")]
#[derive(Clone, Debug)]
pub struct Fung {
pub bulk_modulus: Scalar,
pub shear_modulus: Scalar,
pub extra_modulus: Scalar,
pub exponent: Scalar,
}
impl Fung {
pub fn extra_modulus(&self) -> Scalar {
self.extra_modulus
}
pub fn exponent(&self) -> Scalar {
self.exponent
}
}
impl Solid for Fung {
fn bulk_modulus(&self) -> Scalar {
self.bulk_modulus
}
fn shear_modulus(&self) -> Scalar {
self.shear_modulus
}
}
impl Elastic for Fung {
#[doc = include_str!("cauchy_stress.md")]
fn cauchy_stress(
&self,
deformation_gradient: &DeformationGradient,
) -> Result<CauchyStress, ConstitutiveError> {
let jacobian = self.jacobian(deformation_gradient)?;
let isochoric_left_cauchy_green_deformation =
deformation_gradient.left_cauchy_green() / jacobian.powf(TWO_THIRDS);
let (
deviatoric_isochoric_left_cauchy_green_deformation,
isochoric_left_cauchy_green_deformation_trace,
) = isochoric_left_cauchy_green_deformation.deviatoric_and_trace();
Ok(deviatoric_isochoric_left_cauchy_green_deformation
* ((self.shear_modulus()
+ self.extra_modulus()
* ((self.exponent() * (isochoric_left_cauchy_green_deformation_trace - 3.0))
.exp()
- 1.0))
/ jacobian)
+ IDENTITY * self.bulk_modulus() * 0.5 * (jacobian - 1.0 / jacobian))
}
#[doc = include_str!("cauchy_tangent_stiffness.md")]
fn cauchy_tangent_stiffness(
&self,
deformation_gradient: &DeformationGradient,
) -> Result<CauchyTangentStiffness, ConstitutiveError> {
let jacobian = self.jacobian(deformation_gradient)?;
let inverse_transpose_deformation_gradient = deformation_gradient.inverse_transpose();
let isochoric_left_cauchy_green_deformation =
deformation_gradient.left_cauchy_green() / jacobian.powf(TWO_THIRDS);
let (
deviatoric_isochoric_left_cauchy_green_deformation,
isochoric_left_cauchy_green_deformation_trace,
) = isochoric_left_cauchy_green_deformation.deviatoric_and_trace();
let exponential =
(self.exponent() * (isochoric_left_cauchy_green_deformation_trace - 3.0)).exp();
let scaled_shear_modulus_0 = (self.shear_modulus()
+ self.extra_modulus() * (exponential - 1.0))
/ jacobian.powf(FIVE_THIRDS);
Ok(
(CauchyTangentStiffness::dyad_ik_jl(&IDENTITY, deformation_gradient)
+ CauchyTangentStiffness::dyad_il_jk(deformation_gradient, &IDENTITY)
- CauchyTangentStiffness::dyad_ij_kl(&IDENTITY, deformation_gradient)
* (TWO_THIRDS))
* scaled_shear_modulus_0
+ CauchyTangentStiffness::dyad_ij_kl(
&deviatoric_isochoric_left_cauchy_green_deformation,
&((&deviatoric_isochoric_left_cauchy_green_deformation
* &inverse_transpose_deformation_gradient)
* (2.0 * self.exponent() * self.extra_modulus() * exponential / jacobian)),
)
+ CauchyTangentStiffness::dyad_ij_kl(
&(IDENTITY * (0.5 * self.bulk_modulus() * (jacobian + 1.0 / jacobian))
- deformation_gradient.left_cauchy_green().deviatoric()
* (scaled_shear_modulus_0 * FIVE_THIRDS)),
&inverse_transpose_deformation_gradient,
),
)
}
}
impl Hyperelastic for Fung {
#[doc = include_str!("helmholtz_free_energy_density.md")]
fn helmholtz_free_energy_density(
&self,
deformation_gradient: &DeformationGradient,
) -> Result<Scalar, ConstitutiveError> {
let jacobian = self.jacobian(deformation_gradient)?;
let scalar_term =
deformation_gradient.left_cauchy_green().trace() / jacobian.powf(TWO_THIRDS) - 3.0;
Ok(0.5
* ((self.shear_modulus() - self.extra_modulus()) * scalar_term
+ self.extra_modulus() / self.exponent()
* ((self.exponent() * scalar_term).exp() - 1.0)
+ self.bulk_modulus() * (0.5 * (jacobian.powi(2) - 1.0) - jacobian.ln())))
}
}