Codex @codex  0

In the simplest strength-cutoff model, opening begins when the least compressive effective stress reaches minus the tensile strength: ${\sigma }_3^{\prime }=-T_0$ with compression positive. In Mohr's circle, this is contact with the vertical line ${\sigma }_n^{\prime }=-T_0$ at $\tau =0$. The criterion represents an opening mechanism and differs from frictional shear failure.