Impacts of Cyclic Loading and Unloading Rates on Acoustic Emission Evolution and Felicity Effect of Instable Rock Mass

Mingwei Zhang,Nong Zhang,Deyu Qian,Shengdong Liu,Qingbin Meng

doi:10.1155/2018/8365396

Mingwei Zhang, Nong Zhang + Show 3 more

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https://doi.org/10.1155/2018/8365396

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Abstract

Uniaxial cyclic loading-unloading compression experiments with schemes of six loading rates and six unloading rates were carried out on the combined testing platform. Impact of loading and unloading rates on rock AE characteristics was revealed. Results show that increasing loading and unloading rates resulted in decreasing total AE rings in the entire rock deformation and failure process. Increasing loading rate decreased the AE rings at loading stages, and increasing unloading rate decreased the AE rings at unloading stages in the same cycle. Total AE counts had a negative linear relationship to the loading and unloading rates. The loading stage was the active period of the AE phenomena, and impacts of the loading rate on the AE characteristics were more apparent. Especially when the loading rate was greater than 2.0 kN/s, brittle failure of rock specimens became noticeable. After the cyclic load reached the uniaxial compressive strength of 1/3∼1/2 times, the rock Felicity effect became more obvious. With the increase of the loading rate, the Felicity ratio decreased in the elastic stage and increased a little in the plastic stage, whereas with the increase of the unloading rate, the Felicity ratio decreased gradually in the elastic stage and remained almost the same in the plastic stage.

Highlights

Acoustic emission (AE) is a physical phenomenon that occurs when materials release elastic waves during the deformation and failure caused by external forces [1, 2]
Lavrov [8] observed the Kaiser effect in a brittle limestone cyclically loaded with different loading rates and found that damage formed in rock at a high loading rate can hardly be revealed by reloading with slow rate, yet the damage formed during loading with slow rate can be successfully revealed by using fast reloading
Rock AE phenomena are unrepeatable under the influence of external loads. at is, one time of primary expansion of internal microcracks only induces one AE event with a certain amount of intensity. erefore, quantity and intensity of AE phenomena basically represent the development degree and expansion intensity of internal microcracks in the rock body

Summary

Introduction

Acoustic emission (AE) is a physical phenomenon that occurs when materials release elastic waves during the deformation and failure caused by external forces [1, 2]. Roughout the uniaxial cyclic loading-unloading compression deformation and failure process, the total AE rings released by rock specimens decrease gradually with the increase of loading rate (Figure 7(a)).

Results

Conclusion