Acoustic emission characteristics of a fine-grained marble with different thermal damages and specimen sizes

Acoustic emission (AE) is a technique which has been widely used in geomechanics to study the progressive micro-cracking behavior of rocks in response to different loadings. However, the study of the combined effects of thermal damage and specimen size on the performance of rocks using the AE technique is still limited, which needs further investigation. This study experimentally investigated the AE characteristics of a fine-grained marble with different thermal damages and specimen sizes. The variation of AE counts in response to the rock deformation can divide the stress-strain relation into several stages. The AE activity is limited in the initial deformation stage and multiplies at a stress level about 0.7 to 0.8 times the peak stress. However, the AE signals in the initial stage become more prominent as the treatment temperature increases. The accumulated AE parameters (i.e., AE counts, AE hits, and AE energy) are found to decrease with the increase in the treatment temperature. The b-value, which generally decreases as the stress approaches the peak strength, correlates well with the stress-strain relation. It is also found that the b-value generally increases as the treatment temperature gradually increases, which is mainly attributed to the initially generated thermal micro-cracks in the rock specimen. The real-time spatial distribution of AE events is in considerable agreement with the failure mode observed in laboratory tests. Overall, the results in this study reveal that the AE technique is capable of studying the micro-cracking behavior involved in the deformation process of rocks possessing different degrees of thermal damage and with different specimen sizes.