Numerical Simulation of Crack Growth and Coalescence in Rock-Like Materials Containing Multiple Pre-existing Flaws

Abstract

A novel meshless numerical method, called general particle dynamics (GPD), is proposed to simulate samples of rock-like brittle heterogeneous material containing four preexisting flaws under uniaxial compressive loads. Numerical simulations are conducted to investigate the initiation, growth, and coalescence of cracks using a GPD code. An elasto-brittle damage model based on an extension of the Hoek-Brown strength criterion is applied to reflect crack initiation, growth, and coalescence and the macrofailure of the rock-like material. The preexisting flaws are simulated by empty particles. The particle is killed when its stresses satisfy the Hoek-Brown strength criterion, and the growth path of cracks is captured through the sequence of such damaged particles. A statistical approach is applied to model the heterogeneity of the rocklike material. It is found from the numerical results that samples containing four preexisting flaws may produce five types of cracks at or near the tips of preexisting flaws including wing, coplanar or quasi-coplanar secondary, oblique secondary, out-of-plane tensile, and out-of-plane shear cracks. Four coalescence modes are observed from the numerical results: tensile (T), compression (C), shear (S), and mixed tension/shear (TS). A higher load is required to induce crack coalescence in the shear mode (S) than the tensile (T) or mixed (TS) mode. It is concluded from the numerical results that crack coalescence occurs following the weakest coalescence path among all possible paths between any two flaws. The numerical results are in good agreement with reported experimental observations.

Cracking process of a granite specimen that contains multiple pre‐existing holes under uniaxial compression

“…From the viewpoint of laboratory experiments, acoustic emission (AE), photographic monitoring, digital image correlation (DIC), and computed tomography (CT) scanning techniques are adopted to capture the crack evolution process in rock that contains pre-existing flaws under compression or tension. [12][13][14][15] From the view point of numerical simulation, crack initiation and coalescence process of rock is reproduced in RFPA3D, 16 FLAC, 17 AUTODYN, 18 FEMDEM, 19 NOSB-PD, 20 NMM, 21 GPD, 22 and particle flow code (PFC). 23 To simulate the loading-type failure of underground openings, Fakhimi et al 24 tested a sandstone specimen that contains a central hole under biaxial compression.…”

Simulation of cracking behaviours in interlayered rocks with flaws subjected to tension using a phase‐field method

“…Wu and Wong and Zhang et al adopted NMM to predict the propagation of tensile and shear fractures. Zhou et al investigated the crack initiation, growth, and coalescence in rock‐like materials containing multiple preexisting flaws using GPD. However, they have their inherent deficiencies in modelling fracture problems, including mesh dependency, when the crack path is uncertain before, or in considering both merging and branching of multiple cracks with no additional techniques.…”

Digital energy grade‐based approach for crack path prediction based on 2D X‐ray CT images of geomaterials

“…Therefore, crack path prediction is crucial in engineering practices. Various methods can be applied to study cracking characteristics and failure mechanisms and to simulate the evolution process of cracks, including the infrared imaging technique, the finite element method, the extended finite element method, the peridynamics, the general particle dynamics, the phase‐field method with the arc‐length method and level‐set techniques, and the burgeoning computed tomography techniques . For example, Miranda et al predicted the propagation life of cracks in generic 2D structural components using a cost‐effective two‐phase methodology; Geißler et al estimated discrete crack paths using the adaptive modified nodal coordinates and element boundary combined with a finite element framework; Haeri et al investigated the crack initiation, propagation, and coalescence process of brittle materials using the higher‐order displacement discontinuity method and Scanning electron microscope (SEM) images and studied the crack propagation mechanism of precracked rock‐like materials; Azevedo et al combined a natural neighbor radial point interpolation method with the meshless method to predict the crack path of materials and extended it to fracture mechanics; Wick et al proposed a rate‐dependent formulation to solve the crack propagation problems in elasticity and elastoplasticity conditions in the phase field framework; Zhao et al proposed a new data analysis method to investigate the morphological changes in a single fracture of rocks under different confining pressures based on transient pulse tests and 3D laser scanning; and Martínez et al discussed fretting fatigue crack trajectory using the extended finite element method (XFEM) method.…”