$\newcommand{\Dev}{\operatorname{Dev}}$ $\newcommand{\dev}{\operatorname{dev}}$ $\newcommand{\grad}{\operatorname{grad}}$ $\newcommand{\Grad}{\operatorname{Grad}}$ $\newcommand{\divg}{\operatorname{div}}$ $\newcommand{\Ei}{\operatorname{Ei}}$ $\newcommand{\tr}{\operatorname{tr}}$ $\newcommand{\Divg}{\operatorname{Div}}$ $\newcommand{\cay}{\operatorname{cay}}$ $\newcommand{\rot}{\operatorname{rot}}$

This material uses a strain-dependent diffusivity tensor that is isotropic in the reference configuration and accommodates strain-induced anisotropy: $$\begin{equation} \mathbf{d}=\left(d_{0r}\mathbf{I}+\frac{d_{1r}}{J^{2}}\mathbf{b}+\frac{d_{2r}}{J^{4}}\mathbf{b}^{2}\right)\left(\frac{J-\varphi_{r}^{s}}{1-\varphi_{r}^{s}}\right)e^{M\left(J^{2}-1\right)/2},\label{eq512} \end{equation}$$ where $J$ is the jacobian of the deformation, i.e. $J=\det\mathbf{F}$ where $\mathbf{F}$ is the deformation gradient, and $\mathbf{b}=\mathbf{F}\cdot\mathbf{F}^{T}$ is the left Cauchy-Green tensor. Note that the diffusivity in the reference state ($\mathbf{F}=\mathbf{I}$ ) is isotropic and given by $\mathbf{d}=\left(d_{0r}+d_{1r}+d_{2r}\right)\mathbf{I}$ .