Abstract
Ultrasonic vibration rock breaking is a new type of rock breaking technology. By studying the mechanical properties of red sandstone under ultrasonic vibration, the mechanical behavior and damage mechanism of rock under the impact of high-frequency vibration can be revealed more comprehensively from macro- and microscopic standpoints. In this paper, the cylindrical red sandstone specimen is used as the study object subjected to vibration excitation via the ultrasonic vibration device. The change in the mechanical parameters of red sandstone specimens is analyzed via a single-axial compression test. The red sandstone specimens are vibrated to study the effects of high-frequency vibration on their natural frequency. The latter’s natural frequency is measured using the knocking method, while the micro-disruption characteristics of the red sandstone are observed via electron microscopy. The T2 spectrum, aperture distribution, porosity, and nuclear magnetic resonance image (MRI) evolution characteristics of red sandstone specimens are obtained via nuclear magnetic resonance technology. The results show that ultrasonic vibration deteriorates the red sandstone compressive strength and elastic modulus by 55.3% and 26.9%, respectively, after 120 s of excitation. Under ultrasonic vibration excitation, the rock specimen’s natural frequency is reduced by 2.4% due to its mass and elastic modulus variation. Many transgranular cracks are generated in the sandstone, splitting the crystal nucleus into smaller blocks. The generation of new micropores is observed in the T2 spectrum, and the maximum increase in the dimensions of micropores and mesopores at the two peaks is 58.7% and 4.67%, respectively. The variation trend of rock specimen porosity is completely consistent with the variation in micropores’ content. MRI images indicate that the microcrack aggregation occurs in the edge area of the contact surface between the exciter and rock.
Highlights
Most of the deep rock formations are hard rock formations, the efficient breaking of which has become one of the major problems in the field of geological exploration.1 Ultrasonic vibration is a new type of rock-breaking technology with a high application prospect
It can be seen that the compressive strength and elastic modulus of red sandstone decrease with the increase in excitation time, and the decreasing rate gradually decreases
This paper studied the mechanical properties and pore variation characteristics of red sandstone under ultrasonic highfrequency vibration excitation
Summary
Most of the deep rock formations are hard rock formations, the efficient breaking of which has become one of the major problems in the field of geological exploration. Ultrasonic vibration is a new type of rock-breaking technology with a high application prospect. Wiercigroch et al. experimentally tested the efficiencies of conventional rock drilling methods and the ultrasonic impact. They found that the material removal rate was increased by ten times under the impact of ultrasonic vibration. Many researchers performed an in-depth study of the rock failure mechanism under the impact of ultrasonic vibration. Zhou analyzed the deformation process and damage characteristics of granite under ultrasonic excitation Most of these studies are on granite, and there are few studies on brittle red sandstone. When the rock’s natural frequency is close to the ultrasonic vibration frequency, the rock will resonate At this time, the rock’s amplitude is the largest, and the rock is prone to damage. The rock specimens with natural frequencies between 11.600 and 11.700 kHz were selected for subsequent tests
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