Comparison of FEM-based 3-D dynamic fracturing simulations using intrinsic and extrinsic cohesive zone models

Smeared crack approach coupled with cohesive zone model has been an attractive way for the realistic simulations of dynamic fracturing of rocks and frequently utilized in the framework of the Finite Element Method (FEM). In many cases, cohesive elements (CEs) with initially-zero-thickness are inserted at the onset of numerical simulations and these are used to express the dynamic fracturing, which is called “intrinsic cohesive zone model (ICZM)”. However, since the ICZM must introduce penalty terms to express the intact behavior of the CEs, this tends to render higher compliance of bulk rock, resulting in smaller wave propagation speed. In this paper, by introducing a so-called “extrinsic cohesive zone model (ECZM)”, which adaptively inserts the CEs, we compared the results of 3-D dynamic fracturing simulations by the ICZM and ECZM using the experimental data obtained from the dynamic spalling test for rocks. Using the same Young’s modulus, Poisson’s ratio, density and strengths estimated from the experiments, our results suggest that the outcome of the ICZM and experiment showed large discrepancy especially for the intact stress wave propagation while the ECZM showed good agreement with the experiment. Therefore, our results could have some implications on the current situation in which more and more simulations using the ICZM such as in hybrid FEM-DEM have been applied to rock fracture mechanics problems.