## 5 Acoustic Emission Characteristics under Different Cyclic Loading and Unloading Conditions  
Acoustic Emission Ring Count and Energy Count Characteristics under Different Cyclic Loading and Unloading Conditions  
This study investigated the relationship between the initiation, development, and propagation of internal fractures in rocks during the process of loading and unloading, and the characteristics of acoustic emission. Acoustic emission ring count and energy count were used as parameters to reflect the internal damage of the rock. Based on experimental data, we plotted the curves of acoustic emission ring count, energy count, and stress variation over time during different cyclic loading and unloading processes (refer to Figures 11 and 12).  
Figure 11: Grading Cycle Loading and Unloading Acoustic Emission Ringing Count and Time.  
Figure 10: Relationship between rock damage and number of cycles under different cyclic loading and unloading paths.  
From Figures 11 and 12, it can be observed that during the first four cycles of loading and unloading, the influence of internal defects in the rock resulted in the gradual closure of its internal voids. As a result, both acoustic emission energy count and acoustic emission ring count exhibited subtle characteristics. From the fifth cycle to the ninth cycle, during the initial loading phase of each cycle, the internal portion of the rock was compacted, leading to an increase in the acoustic emission ring count. When the rock was in the elastic stage, the acoustic emission ring count entered a brief stable period. As the load increased beyond the previous target stress level, the acoustic emission ring count showed an increasing trend and exhibited a pronounced Kaiser effect [10]. When the rock reached its peak strength, the acoustic emission signals became dense, with a maximum ring count of 3745 and an acoustic emission energy of 3.0 \(\times\) 10\({}^{8}\). During the unloading process, the acoustic emission signals remained weak.  
The curves depicting the variation in acoustic emission ring count, energy count, and stress over time during the cyclic loading and unloading process with a lower limit are shown in Figures 13 and 14.  
Figure 12: Grading Cycle Loading and Unloading Energy Count and Time.  
Figure 13: Acoustic Emission Ringing Counts and Time Curve during Variable Lower Limit Cyclic Loading and Unloading Process.  
Based on Figures 13 and 14, it can be inferred that during the cyclic loading and unloading process with a decreasing lower limit, the acoustic emission ringdown count increases when the stress exceeds the previous target stress, exhibiting a significant Kaiser effect. Additionally, during the unloading process, there is a noticeable decrease in the acoustic emission ringdown count, indicating a transition into a weak state. Similar characteristics can be observed in the cyclic loading and unloading with the same stress level. When the rock reaches its peak strength, the acoustic emission ringdown count becomes more concentrated, reaching a maximum of 1755 counts, with an acoustic emission energy of 1.8 \(\times\) 10\({}^{9}\). This implies that damage occurs on the macroscopic surface of the rock, with penetrating fractures propagating from bottom to top.