Crack Initiation Criteria and Fracture Simulation for Precracked Sandstones

Abstract

The friction coefficient, tip curvature, and different-width crack state influence the stress intensity factor (SIF). The maximum circumferential tensile stress (MTS) and minimum strain energy density criterion (S) face challenges in explaining the mode-II fracture propagation of cracks. The maximum radial shear stress (MSS) and modified twin shear stress factor (ITS) criteria are proposed as the brittle mode-II fracture criteria. The experiments and numerical analysis are also performed. The results indicate that the fracture angles of the MSS and ITS were similar and different from the results of MTS and S. The equivalent stress intensity factors (ESIFs) from the mixed mode I-II are proposed to determine the fracture mode. There are different fracture models for different cracks under tensile and compressive stresses. The ratio of the tensile strength to uniaxial compressive strength influenced the fracture angle of ITS. The lateral pressure coefficient (k) had a significant effect on the mode-II fracture angle when the angle between the crack and the vertical direction is less than 40° and the lateral pressure coefficient is more than 0. Because the same fracture mode k (k > 0) can inhibit mode-I fracturing, conversely, it can also promote mode-I fracturing. Experimental results and numerical simulations of fracture propagation under uniaxial compression confirmed that the theoretical results were correct.

Experimental Evaluation of the Influences of Water on the Fracture Toughness of Mudstones with Bedding

“…where r c is the fracture progress zone of the three types of SCB specimens with different soaking times (refer to Table 8). By substituting equations (1), (2), and (6) into equations (12) and (13), the mixture parameter M e and mixed-mode fracture toughness ratio K eff /K Ic are achieved for SCB specimens in terms of Y I , Y II , and T * as follows:…”

“…e critical value of SIF corresponding to crack propagation is referred to as the fracture toughness, which is a key mechanical parameter that characterizes rock resistance against crack propagation [9][10][11][12]. Experimental results have investigated the fracture toughness of synthetic rocks containing clay (which are regarded as isotropic materials) under the influence of water content [13,14].…”

Parallel Offset Crack Interactions in Rock under Unloading Conditions

“…According to the superposition principle, the stress state C 1 of the rock mass can be made equivalent to the (Figure 4). According to the stress circle theory, the vertical stress σ β and shear stress τ β acting on the crack surface in Figure 4 can be expressed as follows [22,23]:…”

Near Crack Line Elastic‐Plastic Field for Mode I Cracks under Plane Stress Condition in Rectangular Coordinates

“…In linear elastic fracture mechanics [1][2][3], the stress intensity factor is the most critical parameter for the analysis of the elastic stress field near the crack tip [4][5][6][7][8]. However, in elastic-plastic fracture mechanics [1,2,9], the conventional crack tip asymptotic analysis method is widely used for the elastic-plastic analysis near the crack tip region [10][11][12][13][14][15][16][17]; such a method is confined by the small-scale yielding conditions.…”