Mechanical properties and charge signal characteristics in coal material failure under different loading paths

Abstract

Rock burst is a catastrophic dynamic disaster caused by sudden failure and instability of coal, loading paths play an important role in the failure of coal, the coal failure process is associated with charge exception information. Hence, violent coal failure mechanics and time-frequency domain distribution of charge signal such as rock burst under different loading paths should be studied in-depth. In this paper, grade and cyclic loading test were carried out for coal with impact tendency samples produced by blocks cored from 800 depth in Xiaoqing coal mine of the Tiefa coal group in northeast China. Theory discussion was carried out for the result of stress and strain, frequency-spectra analysis was conducted for the wavelet charge data, figures showing the evolution mechanism of mechanical properties and the relationship of timefrequency domain amplitude of charge signals in coal with different loading paths and stage were obtained. The failure process and characteristics of coal under different loading paths were summarized. It found that the loading path changed the manner of energy accelerate-release, there were more plastic strain generation in coal under cyclic loading than that under grade loading, the former was more likely to cause greater damage and failure, then the strength of coal under cyclic loading is generally lower than that under grade loading, an energy conversion mechanical model of stress, damage and deformation was developed and explained the effect of the loading path. Charge signal was primarily distributed in the strengthening and peak stages, where there was a high amplitude pulse at each stress drop. The charge pulse was a type of low frequency signal with a primary frequency distribution range of 1-100 Hz. Discussion on the charge generating mechanism from the perspective of friction slip, it demonstrated that the charge obtained during the coal failure process directly to stress loaded on and damage, the result verified it better. We propose that the research results in this study could be efficiently applied to daily mining activities, to provide an early warning and effectively avoid rock burst disaster.

Mechanical Properties of Bump‐Prone Coal with Different Porosities and Its Acoustic Emission‐Charge Induction Characteristics under Uniaxial Compression

“…e main part of the AE and charge is generated during the macrocrack extending stage, where the curves of accumulation manifest growth, according to the research [12,13] that acoustic emission re ects the stress wave of crack propagation. e self-potential anomalies in the loading and destruction processes of coal are observed caused by free charges generated, which is the comprehensive result of the piezoelectric e ect, the microcrack interface barrier dislocation, and the sliding frictional electricity generation e ect between the fracture surfaces, within existing knowledge [23,35,36]. To date, however, the primary and secondary nature of several bioelectricity mechanisms remains a key scienti c issue that requires a deep research, and our academic view is updated to the sliding friction which is the main electricity generation mechanism; thus, the following discussion suggests that the charge pulse is the free charge of crack friction.…”

Analysis of Similarities and Differences between Acoustic Emission and Charge Signal Based on Fractal Characteristics of Coal Fracture

“…Cylindrical specimens measuring φ 50 mm × 100 mm were prepared, and both ends of each specimen were polished to ensure that the flatness error was less than ±0.02 mm (Figure 1). Affected by the special occurrence state and material composition of coal, as well as the initial damage formed inside, the samples taken from the same block have different characteristics of color uniformity in the macro, which leads to the dispersion of the mechanical properties of coal samples [34,35].…”

Energy Distribution Law of Dynamic Failure of Coal-Rock Combined Body

“…With the deepening of coal mining depth and the increase of coal mining breadth, the frequency and intensity of geological dynamic disasters are gradually increasing; especially, the rock burst is the most serious [1][2][3][4]. On October 20, 2018, the "10•20" rock burst accident in Longyun Coal Mine of Shandong Province caused 21 deaths and 1 injury, which seriously affected the safe production of mines and caused huge economic losses and casualties.…”