A New Index of Energy Dissipation Considering Time Factor under the Impact Loads

et al. 2022

Geofluids

To promote the application of ultrasonic vibration rock crushing technology in underground rock-drilling engineering, it is necessary to investigate the damage and fracture characteristics of hard rock under the excitation of ultrasonic vibration. In this study, the brittle red sandstone was taken as the research object, the rock fracture experiments under the excitation of ultrasonic vibration were carried out, and the macrodeformation of rock samples was monitored by strain gauges. The experimental results show that the strain curve of rock samples under the excitation of ultrasonic vibration can be divided into the compaction stage, elastic deformation stage, and damage stage; with the increase in static load, the maximum intrusion depth and maximum failure depth of rock samples increase exponentially. To study the damage evolution and energy dissipation mechanism of rock samples under the excitation of ultrasonic vibration, a numerical model was established by using particle flow software PFC2D. The results show that the proposed model can effectively simulate the failure characteristics of rock samples under the excitation of ultrasonic vibration. Through the analysis of the displacement field, stress field, and dynamic fracture process of rock samples, the damage and fracture mechanism of rock samples under the excitation of ultrasonic vibration were revealed. In addition, the ultrasonic vibration simulation tests on rock samples were carried out under different static loads, and the number of rock cracks and energy dissipation process were monitored in real time. The results show that static loads can accelerate the initiation and propagation of cracks and improve the utilization rate of rock crushing energy.

Section: Particle Flow Simulation Of Ultrasonicmentioning

confidence: 99%

Research on Fracture Characteristics and Energy Dissipation of Hard Rock under the Excitation of Ultrasonic Vibration

Zhang

et al. 2022

Geofluids

“…Wang proposed a new index of energy dissipation of dynamic loading. 35 In the SHPB, the incident energy affects the dynamic characteristics of the specimen, and the energy magnitude has received widespread attention in previous studies. However, the action time of the energy also affects the dynamic characteristics of the specimen.…”

Section: Test Principlementioning

confidence: 99%

“…In the above description, the damage is caused by energy dissipation. 35 To study the mesodamage of red sandstone specimens, the nonimpacted rocks were investigated with NMR, and the detection was carried out again after every impact. Figure 10 shows the general trend of the resulting curves.…”

Section: Porosity Distributionmentioning

confidence: 99%

Dynamic response and damage evolution of red sandstone with confining pressure under cyclic impact loading

Fatigue Fract Eng Mat Struct

Guo

et al. 2022

Self Cite

Abundant mesoscale damage occurs prior to rock destruction, and the change in porosity can reflect the dynamic mechanical characteristics of the rock. In this study, red sandstone specimens were dynamically loaded by a split Hopkinson pressure bar (SHPB) with confining pressure. The change in porosity was reflected by the new index of porosity variation rate (Rv), and the relationships between the cyclic impact and the dynamic characteristics and porosity variation were analyzed. The average filtering algorithm was emphasized to remove the noise of grayscale NMR images. It was concluded that the number of impacts before crushing gradually decreases with increasing air pressure for the overall trend, there is no obvious rebound, and the energy dissipation increases before the crushing of the specimens. There is an abrupt difference in the dynamic characteristics between the third impact and the fourth impact. The pore space changes from medium and large pores to micropores with impact loading. The peak of the microporous porosity difference curve shifts to smaller micropores. The new index can describe pore closure and expansion. The image processing method used in this work obtained accurate statistical information that confirms the presence of a large number of microcracks before crushing.

Dynamic characteristics and energy evolution of granite subjected to coupled static–cyclic impact loading

Geomech. Geophys. Geo-energ. Geo-resour.

Liu

Gao

et al. 2023

In many underground rock projects, rock masses are subjected to coupled static–cyclic dynamic loading. In this paper, dynamic tests were carried out on granite specimens using a modified split Hopkinson pressure bar to study the dynamic characteristics and energy evolution of the rock under coupled static–cyclic impact loading. The results show that both the dynamic characteristics and the energy evolution of granite are sensitive to the number of repeated impacts and the confining pressure. Under the same confining pressure, the dynamic increase factor (DIF), dynamic elastic modulus, and transmitted energy ratio decreases, while the cumulative dissipated energy, cumulative specific energy dissipation and dissipated energy density tend to increase as more impact cycles are applied. The effect of confining pressure on enhancing the mechanical property of the rock is pronounced: the peak stress of rocks under confining pressure during cyclic impact is higher than their quasi-static compressive strength, and the DIF increase as the confining pressure increases. However, its effect on the dynamic elastic modulus is fairly insignificant. The confining pressure could change the crack propagation path of the specimens, and the failure mode is mainly a tensile failure, with no obvious axial splitting. By increasing the confining pressure, the energy dissipation capacity of the rock is significantly improved, and its increased rate of internal damage could be slowed down. Graphical abstract