g \left( \phi \right) \mathbb{C}^e,$$ in which $g \left( \phi \right)$ is the energy degradation function mentioned previously that is non-negative in the interval $\left[ 0,1 \right]$ with $g \left( 0 \right) = 1$ and $g \left( 1 \right) = g^\prime \left( 1 \right) = 0$. Such form however has limited applicability, since it allows for unphysical compressive cracking based on $\mathcal{G}_c$. [@Lancioni2009] adopted the above model to shear cracking by having $g \left( \phi \right)$ act only on the deviatoric portion of the strain. This was subsequently improved upon by [@Amor2009] who proposed that crack growth be driven also by the spherical part of the energy when the volumetric strain is positive. This results in more realistic anisotropic behavior where the material is allowed to crack in tension and shear, but not in compression. An alternative formulation was introduced by [@Miehe2010_cmame; @Miehe2010_ijnme] in which degradation occurs only on tensile components of the principal strain tensor, leading to pure mode-I cracks.

Going back to Griffith
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The functional $\Psi \left( \bm{u},\phi \right)$ in is neither linear nor convex, which makes the task of finding global minimizers non-trivial. [@Bourdin2000] proposed an alternate minimization algorithm that takes advantage of the convexity of 