# Feasibility Study and Prospects of Rock Fragmentation Using Ultrasonic Vibration Excitation
## 1 Introduction  
Rock breakage and fragmentation have played an increasing role in civil and mineral sectors, and one of the challenges is to improve the efficiency of rock fragmentation by reducing the material consumption [1]. There are a number of literatures available on the study of the optimised methodology used for rock breakage and fragmentation, based on various rock fragmentation mechanisms [2, 3]. The existing methods mainly include drilling and blasting, hydraulic fracturing, and thermal fracturing. However, these methods normally have the disadvantages of the serious wear of drill pipes, slow borehole drilling speed, large loss of machine tools and energy consumption, high costs, and unsatisfactory working efficiency in field application, especially when they are adapted to optimise hard rock breakage and fragmentation.  
Ultrasound has been successfully utilised in many different areas, such as medicine [4, 5] and petroleum engineering [6]. With regards to rock breakage and fragmentation, many scholars have carried out studies on ultrasonic drilling machines and lapping machines and achieved a series of results. [PERSON] et al. [7] and [PERSON] et al. [8] studied the influence of the vibration frequency of acoustic drilling machines on rock breakage by theoretical calculation and field monitoring, and found that the drilling speed of acoustic drilling machines is 5 times that of ordinary drilling machines. This provides a theoretical basis for improving the rock-crushing performance of acoustic drilling machines. [PERSON] et al. [9]tested the compressive strength of rock samples at different static load levels by changing the size of the upper static load when ultrasonic excitation was applied to coal samples and studied the dynamic process of fracture development of rock samples with the application of CT scanning. It was concluded that the strength of rock samples decreases with the increase of the static load applied to the upper part of the samples. [PERSON] and [PERSON] [10] performed laboratory experiments to analyze the fracture development characteristics of saturated porous rocks under ultrasonic excitation. The results revealed that ultrasonic excitation can effectively increase the porosity of samples and reduce rock strength, which proves the feasibility of the ultrasonic vibration excitation method in rock engineering. [PERSON] et al. [11; 12] and [PERSON] et al. [13] used nuclear magnetic resonance (NMR) and computed microtomography to study the three-dimensional morphology of fractures in fractured rock masses. This research method has important reference value for the study of the fracture morphology of rock samples after ultrasonic vibration. [PERSON] et al. [14] carried out experimental studies on ultrasonic cracking to increase the permeability of coal seams. They used ultrasonic waves to conduct vibration excitation on coal samples, combined with NMR observation technology and electron microscope scanning technology to understand the variation of pore sizes of coal samples against excitation time, and disclosed that ultrasonic high-frequency vibration can increase the porosity of coal samples.  
In this paper, the fracture development and fracture evolution characteristics of red sandstone, granite, marble and limestone specimens under ultrasonic vibration excitation are studied. It is proved that ultrasonic vibration excitation can effectively break these four kinds of hard rocks. It is found through statistical analysis of the compressive strength of the rocks that ultrasonic vibration excitation can effectively reduce the compressive strength of rock samples.