Fig. 5: The tensile porosity algorithm.

Material originally at the reference state (a; \(\rho={\rho }_{0}\)) goes into a distended state, \(\frac{\rho }{{\rho }_{0}} < 1\) (A'), for which the negative pressure predicted by the equation of state (solid black line) for the material is below the minimum pressure permitted by the strength model, \({P}_{{\min }}\) (dashed line; shown here as 0.1 GPa for illustration). The physical state of such a material is a distended, fractured rock mass. In the original iSALE algorithm, no porosity is added and the solid (and bulk) density is left unchanged, whilst the (negative) pressure is capped at \({P}_{{\min }}\) (b). In the new tensile porosity method, the density of the solid is adjusted to be consistent with the minimum pressure \({P}_{{\min }}\) (c) and porosity (~2% in the example shown) is inserted to fill the remaining volume of the cell and ensure mass conservation.