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Ultrasonic velocity field imaging offers a robust tool for characterizing and analyzing damage and its evolution within fractured rock masses. The combined application of ultrasonic first arrival waves and coda waves can significantly enhance the accuracy and range of velocity field imaging. This manuscript introduces an improved imaging method that integrates the propagation probability distribution of the first arrival and coda waves to calculate the velocity field. The proposed method was applied to the velocity field imaging of a medium with multiple scatterers and varying degrees of fracturing. The overall error and calculation unit error of the proposed method were analyzed, and its improvement in calculation accuracy and applicable scope was verified. Additionally, this method was employed to image the velocity field during the damage process of fractured rock masses. The imaging results were compared against digital speckle patterns to confirm the method's suitability. Finally, we discussed the impact of measurement errors and sensor missing on the accuracy of the computational outcomes presented in this method. These two situations will affect the calculation results, and the influence of reducing the number of sensors is smaller than that of measuring time shifts with error. [ABSTRACT FROM AUTHOR]

The notched semicircular bending samples with different microwave irradiations were subjected to 3‐point bending fracture tests under mixed‐mode I/II loading to investigate the effects of microwave irradiation on the fracture characteristics of basalt. Influences of the irradiation duration on the temperature, P‐wave velocity, and mixed‐mode I/II fracture characteristics under 2 kW power were studied. The acoustic emission device was utilized to monitor the acoustic emission signals during the destruction process. The P‐wave velocity and equivalent fracture toughness are weakened by microwave irradiation, but the ductility of basalt is enhanced by microwave irradiation. The microscopic characteristics of the treated basalts were observed by scanning electron microscope. Microwave irradiation aggravated the creation and propagation of microcracks and pores. The study of the influence of microwave irradiation on mixed‐mode I/II fracture characteristics of rock provides effective theoretical support for microwave‐assisted rock fragmentation. Mixed‐mode I/II fracture toughness of basalt is weakened by microwave irradiation.The temperature of basalt increased roughly linearly with microwave irradiation time.Increasing the microwave irradiation duration enhanced the ductility of basalt.Variation of microcrack is caused by the heating of the rock by microwave. [ABSTRACT FROM AUTHOR]

In rock and mining engineering, it is essential to predict rock cuttability and drillability for estimating drilling costs, selecting suitable drilling/cutting machine and tools, and achieving high productivity. To predict the drillability and cuttability, many destructive methods have been developed. However, they are often expensive and time-consuming. To explore a non-destructive method, this paper builds a series of empirical relationships between rock characteristic impedance and its drillability and cuttability indices by using a large quantity of measured data from various laboratory and field tests in previous publications. The relationships between rock’s UCS (uniaxial compressive strength) and its drillability and cuttability indices are also built for comparison. The results indicate that: (1) the penetration rates of both percussive drilling and rotary drilling depend on rock characteristic impedance, and they decrease with increasing impedance. (2) The specific energies in percussive drilling, rotary drilling and cutting all increase with increasing rock impedance. (3) Most of current drillability indices such as alfa, DRI, CLI and Shore hardness have a certain relationship with rock impedance. (4) Characteristic impedance has a more confident relation with drillability and cuttability than the UCS. Since determination of rock impedance does not necessarily require a destructive method, characteristic impedance has a great potential to be taken as an index to predict rock drillability and cuttability. [ABSTRACT FROM AUTHOR]