Dynamic characteristics and crack evolution laws of coal and rock under split Hopkinson pressure bar impact loading

Abstract

The aims of this paper are to comprehensively explore both the dynamic mechanical properties and crack evolution characteristics of coal and rock during impact failure. First, experimental specimens are prepared from coal seam, direct roof rock strata and direct floor rock strata in the same area to highlight the correlations between test pieces. Second, a dynamic strain gauge and high-speed (HS) camera are adopted to reflect the stress wave signal and crack evolution. Then, based on digital image correlation (DIC) technology and the mass screening method, the evolution laws of surface cracks during crushing and the distribution characteristics of sample fragments after crushing are studied from the perspective of fractal, and finally compared with those of the simulation analysis. The results are as follows. (1) The coal and rock samples from the same area have both consistency and differences. The dynamic mechanical properties of coal and rock are affected by the impact velocity and the physical properties of the specimen. Higher impact speeds and densities lead to the more obvious brittleness of the specimen when destroyed. Conversely, the sample shows more plasticity and ductile yield. (2) The self-similarity is significantly manifested in the evolution of surface cracks during impact and the distribution characteristics of fragments after impact. The box dimension and quality screening dimension are applicable to quantitatively characterize the evolution process and results of coal and rock fractures. (3) The simulation results based on the Holmquist–Johnson–Cook (HJC) and Riedel–Hiermaier–Thoma (RHT) constitutive models agree well with the experimental results, and the RHT constitutive model is more consistent. This study may contribute to a more comprehensive understanding of the dynamic characteristics and crack evolution laws of coal and rock under impact loading and provide references for further research and discussion.

Dynamic mechanical response and failure characteristics of coal and rock under saltwater immersion conditions

“…To capture the damage images of coal and rock during SHPB impacts, the data processing and video acquisition unit shown in Fig. 3b also included an ultrahigh-speed camera and a high-brightness flood light, which is convenient for effectively revealing the details of crack evolution during coal and rock damage 34 . The specific equipment parameters are shown in Table 2.…”

“…Notably, during the testing process, on the one hand, the distinction between coal and rock and cracks is low, and on the other hand, the original images are affected by artefacts, noise, and other noncrack elements recorded by the high-speed camera. In this experiment, Ratsnake software 71 was used for crack extraction and image annotation, and the FracLac plug-in in ImageJ software 34 was used to evaluate the box dimensions of the cracks.…”

“…Notably, the above research results were all obtained under static or quasistatic conditions. In fact, due to strong disturbances such as rapid excavation and coal blasting in coal mines 34 , analysing the dynamic damage and destruction of water-bearing coal and rock masses under impact loads is also highly important. The mechanical properties and failure characteristics of coal and rock masses under static and dynamic loads are completely different 35 .…”

An analysis of impact load and fragmentation dimension to explore energy dissipation patterns in coal crushing

“…Zhou 31 investigated persistent fractured granites, scrutinizing the loading rate effects on dynamic damage and energy evolution during the process. Wu 32 utilized SHPB to discern the dynamic tensile strength variations of pre-tensioned rocks, with Zhao 33 focusing on the fractal traits of coal-bearing seam crack extensions under similar conditions. Li 34 entailed introducing radial restraints in SHPB specimens to enhance the compressive strength of concrete-like samples, and Wang 35 explored the mechanical properties and progressive fracturing of concrete materials under biaxial confinement and repetitive dynamic loads.…”

Discrete characteristics of instantaneous frequency of EMR induced by coal and rock fracture

“…In recent years, with the increasing intensity and depth of coal mining, coal and rock dynamic disasters have become increasingly serious in China [1][2][3]. Effective monitoring and early warning of coal and rock dynamic disasters is the key to disaster prevention and control.…”