Effects of displacement rate on mechanical behaviors and failure mechanism of non-caking coal in Brazilian splitting tests

With the increasing coal mining depth, dynamic disasters are occurring more frequently in coal mines. The loading rate has a close relation to the mechanical properties, behaviors and failure mechanisms of both coal and rock. In order to examine the influence of loading rates on tensile properties, deformation characteristics, failure mode, and micro-failure mechanism of non-caking coal, acoustic emission (AE) tests were conducted under Brazilian splitting conditions with five different displacement rates. The experiment results indicate that the tensile strength of non-caking coal increases logarithmically with the increase in displacement rate, and the duration of the primary fracture compaction stage shortens with the displacement rates. The AE spatio-temporal evolution for coal with varying displacement rates shows similar trends, and the AE event reaches to a maximum at 0.8 σ_c (peak stress). The high amplitude AE events appear at different phases at varying displacement rates, and the concentration area of AE events coincides with the fracture surface. The spatial fractal dimensions of the AE events range from 1.1 to 1.9 under varying displacement rates and show a downward trend with the increase of stress. The fractal dimension of the fracture surface range from 2.14 to 2.25 and increases with the displacement rate. The micro-failure mechanism of non-caking coal discs under varying displacement rates is a mixture of tension-shear cracks (mainly tensile cracks), followed by shear cracks. The external load causes tensile and shear cracks at high displacement rates, while mainly tensile cracks at low displacement rates.