Mechanical responses and acoustic emission behaviors of coal under compressive differential cyclic loading (DCL): a numerical study via 3D heterogeneous particle model

Abstract

The stability of coal walls (pillars) can be seriously undermined by diverse in-situ dynamic disturbances. Based on a 3D particle model, this work strives to numerically replicate the major mechanical responses and acoustic emission (AE) behaviors of coal samples under multi-stage compressive cyclic loading with different loading and unloading rates, which is termed differential cyclic loading (DCL). A Weibull-distribution-based model with heterogeneous bond strengths is constructed by both considering the stress–strain relations and AE parameters. Six previously loaded samples were respectively grouped to indicate two DCL regimes, the damage mechanisms for the two groups are explicitly characterized via the time-stress-dependent variation of bond size multiplier, and it is found the two regimes correlate with distinct damage patterns, which involves the competition between stiffness hardening and softening. The numerical b-value is calculated based on the magnitudes of AE energy, the results show that both stress level and bond radius multiplier can impact the numerical b-value. The proposed numerical model succeeds in replicating the stress–strain relations of lab data as well as the elastic-after effect in DCL tests. The effect of damping on energy dissipation and phase shift in numerical model is summarized.

Precursors of Cyclic Loading and Unloading Sandstone Failure Based on “Acoustic-Thermal” Loading–Unloading Response Ratio

“…where DIECR is the change rate of differential infrared radiation energy, (∆AIRT) 2 i+1 and (∆AIRT) 2 i are the infrared radiation energy at the T i+1 and T i time, respectively. DIECR illustrates the trend of infrared radiation energy change over time.…”

“…Affected by the disturbance of loading and unloading, the mechanical performance of rock mass under cyclic loading is one of the important factors affecting the long-term stability of the projects. The mechanical behavior and catastrophic process of coal and rock under cyclic loading will become extremely complex [1][2][3][4]. Therefore, it is of great significance to analyze the mechanical characteristics of rocks in the process of cyclic loading and unloading and to study and capture the failure precursors of rocks in the process of cyclic loading and unloading for monitoring the stability of rocks in coal mining faces.…”