A thermodynamically consistent phase field model for mixed-mode fracture in rock-like materials

Natural flaws containing fillings strongly affect the mechanical properties and failure process of rocks in practical engineering. In this work, uniaxial compression tests are performed on filled and unfilled red sandstone specimens containing two parallel dentate flaws. Two monitoring technologies––acoustic emission (AE) and high-speed camera––are employed to record the cracking process of the flawed rocks. The effects of filling and ligament angles on the mechanical properties of the flawed rocks are analyzed. The relationship between AE parameters and stress–strain curves is established in order to evaluate the cracking process. The fracture behaviors between the filled and unfilled specimens are qualitatively compared. An intensity analysis method, based on the historic index and severity, is employed to assess the damage level of the flawed rocks. Simultaneously, a judgmental design criterion, including safety, early warning, and instability, is developed, which can be employed to evaluate the stability of rock structures. 

Cracking Characteristics and Damage Assessment of Filled Rocks Using Acoustic Emission Technology

Experimental investigation of the strain rate effect on crack initiation and crack damage thresholds of hard rock under quasi-static compression

Dynamic mechanical responses and crack evolution of burst-prone coal with a single prefabricated fissure

Failure mechanism of brittle rock with 3D parallel preset flaws based on the particle displacement trend method

Open flaws without any filling material are common fracture structures in real rock. To study the failure characteristics of this fracture structure, small-scale rock-like samples with single internal 3D open flaws are prepared, and uniaxial compression tests are conducted. Digital image correlation (for surface strain and failures) and acoustic emission (for internal microfracture behaviors) monitoring technologies are also employed to analyze the flaws. The test results are verified through numerical simulations. Different inclination angles of the internal preset flaws are found to have little influence on the strength of the samples, and the surface and internal secondary failures of the samples exhibit very different development processes and distributions. The particle displacement trend method is applied to explain the initiation mechanism of secondary cracks, but the corresponding analyses are only reasonable if particle information along the y-axis is considered. Therefore, the particle information in the y-axis is incorporated by defining new 2D sections (with y-axis) or partial 3D models. Based on these research methods, the initiation mechanism of secondary cracks is reasonably explained, and the influence of the preset flaw thickness on the particle displacement trend fields and secondary failures in surrounding rocks can be discussed. Finally, the simulation results prove that the Mode II and III failures are usually coupled, and direct Mode III failures (displacement of two parts of rock parallel to each other and in opposite directions) only occur in the front and rear surrounding rocks of the preset flaw.

Long Chen

Papers

Experimental and numerical study of failure characteristics of brittle rocks with single internal 3D open-type flaw

Failure mechanism of brittle rock with 3D parallel preset flaws based on the particle displacement trend method