# Feasibility Study and Prospects of Rock Fragmentation Using Ultrasonic Vibration Excitation
## 4 Engineering Application and Progress of Ultrasonic Excitation of Coal and Rock Mass
### Rock Breakage Test Using Ultrasonic Excitation  
The effect of ultrasonic excitation on rock damage was experimentally studied. Excitation and crushing tests were carried out on rock specimens of different sizes using a custom-made ultrasonic excitation rock test device which was developed by us (see Figure 4). The rock specimens were collected from red sandstone, granite, marble, and limestone. Each specimen had dimensions of 50 mm (in diameter) \(\times\) 100 mm (in height). A compressive loading of 20 N was applied to the top of the specimen. The fracture length and the failure time of the specimen during ultrasonic excitation were observed and recorded. The ultrasonic power was 2.6 kW, with a frequency of 20 kHz. The physical experiment schemes are shown in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline
**Lithology** & **Size/mm** & **Static Pressure/N** & **Time/s** & **Group Count** \\ \hline Sandstone & \(\Phi 50\times 100\) & 20 & 60 & 4 \\ \hline Granite & \(\Phi 50\times 100\) & 20 & 60 & 4 \\ \hline Marble & \(\Phi 50\times 100\) & 20 & 60 & 4 \\ \hline Limestone & \(\Phi 50\times 100\) & 20 & 60 & 4 \\ \hline \end{tabular}
\end{table} 
Table 2: Physical experiment schemes. Figure 3: High-power ultrasonic equipment: (**a**) a 160 kW ultrasonic generator structure diagram; and (**b**) a 10 kW ultrasonic transducer. The authors conducted preliminary tests using ultrasonic excitation for rock breakage. Take the specimen with a size of \(\Phi\) 50 \(\times\) 100 mm, and carry out the ultrasonic excitation experiment under the additional static pressure of 20 N. Observe the expansion and the development of longitudinal and transverse cracks of the specimen every 10 s, including the number of cracks, the crack expansion speed, types of cracks, etc. The ultrasonic power is 2.6 kW, with a frequency of 20 kHz. The physical experiment schemes are shown in Table 2.  
The test process is shown in Figure 5.  
During the test, a certain loading was applied to the rock specimen. Under the ultrasonic excitation, the rock produced a large amount of dust within 1 min. After 3 min, the section contacted by the rock specimen and the tool head was obviously fractured. Localised fracturing into powder occurred at the upper half of the specimen. After 5 min, when the test was finished, the majority of the specimens had completely failed. The experimental results are listed in Table 3.  
Figure 4: Test setup for ultrasonic excitation loading test. Figure 5: The test process of ultrasonic vibration excitation: (**a**) at the start; (**b**) during the test; and (**c**) after finished. The representative limestone specimen that shows obvious fracture development in Section 4.1 is selected as an example. In order to study the fracture development characteristics of the specimen, high resolution 3D-X ray microimaging system (3D-XRM) scanning was performed; the specimen was loaded by a compressive loading of 20 N with an excitation time of 50 s. The specimen in the scanning experiment has dimensions of 50 mm (in diameter) \(\times\) 100 mm (in height). Since the maximum scanning \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Rock Type** & **Before Ultrasonic Excitation** & **After Ultrasonic Excitation** & **Maximum Fracture Length (mm)** & **Average Failure Time(s)** \\ \hline Red sandstone & & & & \\ \hline Granite & & & & \\ \hline Marble & & & & \\ \hline Limestone & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Failure of different rock types under ultrasonic excitation. height in each 3D-XRM scanning process is 50 mm, the height of the final scanning image if also 50 mm. The scanning results are provided in Figure 6.  
It can be seen from Figure 6 that with the increase of excitation time, the internal fractures of limestone specimens are continuously expanding and developing, the number of fractures is continuously increasing, and the internal longitudinal expansion depth is continuously increasing.