Numerical simulation of experimental fracture in BD and CCNBD sandstone specimens using the Advanced Augmented-FEM

Soft rocks subject to experimental tests exhibit strain localization in strip zones where micro-cracks coalesce and interact, finally resulting in a physical fracture. The associated load–displacement diagram shows a softening branch typical of quasi-brittle materials, as which soft rocks are classified. This constitutive behavior and the evolution of localization bands can be numerically described using continuous, discrete or continuous/discontinuous models. In this work, the results of experimental tests performed on sandstone specimens extracted from a cantilever beam recently collapsed from a historic building in Palermo (Sicily) are reported. The Brazilian Disc (BD) test was used to evaluate the splitting tensile strength and the Cracked Chevron Notched Brazilian Disc (CCNBD) test was used to determine the Mode-I fracture toughness. Then, numerical simulations of the BD and CCNBD tests are run by applying the continuous-discontinuous AA-FEM modeling approach. The displacement jump is simulated through an InterPHase mechanical device, which could refer to the same constitutive model used for the bulk material. Crack propagation is simulated using a crack-tracking algorithm based on an isotropic damage constitutive model and concepts of substructure and critical damage. In addition to the experimental data contribution, this is the first simulation of BD and CCNBD tests using the AA-FEM strategy. A great deal of relevance is given to the calibration of constitutive parameters in light of experimental tests. Good agreement is obtained between AA-FEM and experimental results. It seems, however, that some differences exist between numerical parameters and the values directly or indirectly derived from experiments.