Microcrack Growth Properties of Granite under Ultrasonic High-Frequency Excitation

Dajun Zhao,Meiyan Wang,Shulei Zhang

doi:10.1155/2019/3069029

Dajun Zhao, Meiyan Wang + Show 1 more

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https://doi.org/10.1155/2019/3069029

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Abstract

The failure of most rock materials is essentially a process of crack initiation and propagation. It is of great significance to study the microcrack growth characteristics of granite under ultrasonic high-frequency excitation for understanding the failure mechanism of rock under ultrasonic vibration. In this paper, the experimental and numerical simulation methods are used to study the propagation characteristics of rock cracks under ultrasonic vibration. Scanning electron microscopy (SEM) was used to observe the growth of microcracks in granite samples after ultrasonic vibration for 0 min, 2 min, and 4 min. A discrete element software PFC2D was used to simulate and solve the cracking mechanism of rock cracks under ultrasonic vibration. Also, it is found that the action of ultrasonic vibration can effectively promote the development of microcracks in the granite samples. The main three cracks causing the failure of quartz under the ultrasonic high frequency are intragranular cracks, transgranular cracks, and grain boundary cracks. The breakage of transgranular cracks usually contributes a shell-like fracture, that is, a regular curved surface with a concentric circular pattern appears on the fracture surface, which is a typical quartz brittle fracture mode. In addition, the feldspar grain failure is mainly caused by intragranular crack and transgranular crack. Microcracks are wavy expansion in feldspar grain. Mica failure is mainly caused by grain boundary crack, and the effect of lamellar cleavage on the failure of mica is significant. Moreover, it is also found that the mechanism of microcrack propagation is tensile failure. The failure of feldspar grains is mainly contributed to the failure of granite.

Highlights

Using ultrasonic vibration technology to break hard rock is a new method in the field of geological exploration [1]
Granite can be used as a representative of hard rock because it is a common rock in the field of geological exploration. erefore, understanding the microcrack propagation characteristics of granite under ultrasonic vibration is essential for understanding the mechanism of breaking hard rock under ultrasonic vibration
The propagation characteristics of cracks in granite under ultrasonic vibration are studied by combining experimental and numerical simulation methods. e growth of microcracks in rock samples after ultrasonic vibration for 0, 2, and 4 minutes was observed by scanning electron microscopy

Summary

Introduction

Using ultrasonic vibration technology to break hard rock is a new method in the field of geological exploration [1]. E instability and failure of rocks is closely related to the initiation and propagation of microcracks that are induced by cyclic vibration loads [2]. Propagation of microcracks inside the rock is determined by the external load and the internal mesostructure. Granite can be used as a representative of hard rock because it is a common rock in the field of geological exploration. Erefore, understanding the microcrack propagation characteristics of granite under ultrasonic vibration is essential for understanding the mechanism of breaking hard rock under ultrasonic vibration. Over the past few years, considerable efforts have been made to investigate the failure mechanics of intact rocks under low-frequency cyclic vibration loading. Ray et al [4] concluded that the failure strength and elastic modulus of Chunar sandstone under cyclic stress decrease with the increase of strain rate, and the uniaxial compressive strength decreases

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