A study on fractal characteristics of acoustic emission under multiple heating and loading damage conditions

Abstract

This study is aimed at revealing the fractal characteristics of acoustic emission (AE) under multiple heating and loading damage conditions and disclosing the evolution of fractal parameters during coal deformation and fracturing. To achieve this aim, an AE multi-parameter experimental system of coal under heating-constant pressure-loading multiple damage conditions was established to monitor the localizable geophysical signals, the mechanics and temperature parameters during the damage and failure of coal. The following research results were obtained: AE signals under multiple heating and loading damage conditions exhibit evident fractal characteristics. The values of correlation dimensions of coal samples under three conditions follow the order: Unrestrained heating > Uniaxial loading > Temperature-pressure conditions, while the intensities of AE signals follow the order: Unrestrained heating < Uniaxial loading < Temperature-pressure conditions. The coal sample under the heating condition has the smallest correlation dimension and the most disordered AE signals. The AE time series was analyzed with aid of the time-varying multifractal theory. The results show that the time-varying multifractal parameter Δαm increases with the rise of loading and temperature while parameter ΔF declines gradually, indicating that strong AE signals gradually become dominant with the rise of temperature and pressure. Besides, as the dynamic changes of Δαm and ΔF values can accurately reflect the environment of coal, they can be used to evaluate the deformation and fracturing process and failure stages of coal.