Abstract
The Kaiser effect reflects the memory of the loaded rock to the irreversible damage and deformation. The stress level, loading rate and lithology are the main factors affecting the Kaiser effect of the rock. To identify the accurate stress point of the Kaiser effect, the MTS 816 rock mechanics testing system and the DS5-A acoustic emission testing and analysis system were adopted. The uniaxial cyclic loading–unloading and acoustic emission characteristic test of 90 rock specimens from three types of rocks under different stress level and loading rate was carried out. The evolution of acoustic emission under uniaxial compression of the rock corresponds to the compaction stage, elastic stage, yield stage and post-peak stress drop stage of the rock deformation and failure process and is divided into the quiet period, transition period, active period and decay period of the acoustic emission. The larger the hardness of rock is, the earlier the stress point of the Kaiser effect appears. The loading stress level (σA) has appreciable influence on the Kaiser effect of the rock. When σA ≥ 0.7σc, the Kaiser effect disappears. Usually, the dilatancy stress (crack initiation stress) does not exceed 70% of the uniaxial compressive strength (σc) of the rock, and the stress point can be the threshold to determine whether the Kaiser effect occurs. The influence of loading rate (lr) on Felicity rate (FR) is relatively large when lr < 0.01 mm/s, and FR rapidly grows with increase of the loading rate. When lr ≥ 0.01 mm/s, the influence of the loading rate on FR is relatively small. The findings facilitate the future application of the Kaiser effect and improvement of the accuracy of the acoustic emission data interpretation.
Highlights
The acoustic emission (AE) of rock refers to the phenomenon of radiation of acoustic waves due to the expansion of original fissures and defects and the initiation, evolution, expansion and fracturing of induced microcracks when a rock undergoes loading [1,2,3,4]
The experimental results indicate that the Kaiser effect of rocks disappears and the Felicity effect appears when the influencing factors such as stress level, loading path and loading rate vary [21,26,27]
The Felicity effect is called the anti-Kaiser effect, which means that during the cyclic testing, when the loading stress is less than the highest stress level in the loading history, the AE events loading testing, when the loading stress is less than the highest stress level in the loading history, the occur noticeably
Summary
The acoustic emission (AE) of rock refers to the phenomenon of radiation of acoustic (elastic) waves due to the expansion of original fissures and defects and the initiation, evolution, expansion and fracturing of induced microcracks when a rock undergoes loading [1,2,3,4]. The AE parameters can describe the degree of damage and failure of the rock. The rock damage and failure modes are assessed by acoustic emission parameters [10,11,12]. The relationship between the rock deformation and failure process and AE parameters is studied in the test to explore the evolution of AE under different stress paths and experimental environment.
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