Analysis of Microwave Thermal Stress Fracture Characteristics and Size Effect of Sandstone under Microwave Heating

Abstract

Microwave-induced rock fracture is one of the promising approaches of achieving non-blasting continuous mining and assisted mechanical rock breaking. It is of great theoretical and practical significance to study the temperature effect and fracture characteristics of rocks of different sizes under microwave heating; however, there are few studies in this field. Microwave heating of φ 50 × 100 mm, φ 50 × 50 mm, and φ 50 × 25 mm sandstone samples with different heating powers and times was performed to measure the temperature of the sample, the microwave energy absorbed, the mass, and the P-wave velocity before and after heating. The results show suppress that (i) under the same heating conditions, the mass difference and the temperature increase range of φ 50 × 100 mm and φ 50 × 50 mm samples are larger than that of the φ 50 × 25 mm samples; (ii) the wave velocity change rate and the damage factor of samples increase with the increase of heating power and time; (iii) different size specimens have different crack- propagation modes. The main crack of φ 50 × 100 mm specimens usually starts from the middle of the height of the specimen; for the φ 50 × 50 mm specimens, it usually starts from the middle or bottom-end surface of the specimen height; the main crack of φ 50 × 25 mm specimens starts from the vertical surface of the specimen. With an increase in the heating time, the length and width of the main crack continuously increase and secondary cracks are generated. The fracture mode of the sample is also related to the size of the sample. The fracture mode can be divided into three parts: melt fracture, thermal-expansion fracture, and secondary thermal-expansion fracture. The relationship between the sample temperature and the absorbed microwave energy is approximately linear.

Numerical Modelling of Microwave Heating Assisted Rock Fracture

“…The energy absorbed by rock through the exposure to microwave radiation is converted to heat. The amount of heat produced by microwaves in a particular rock depends in general on water content, size (Gao et al 2011), mineral composition (Nicco et al 2020), andschistosity (He et al 2019) of the rock. Moreover, microwave radiation conditions such as power level, exposure time and distance from rock have an influence on temperature intensity and distribution (Wang and Forssberg 2005).…”

Effect of strong dielectric substances on the damage characteristics of rocks exposed to microwave radiation: Insight from experiments and mechanisms

“…Rock specimens of various sizes underwent microwave heating tests by Gao Feng et al. (Gao et al., 2020) And the results showed that these rocks have different temperature responses and crack expansion patterns. Thermocouples were implanted into the granite specimens to further investigate the variation in interior temperature.…”

Damage Evolution of Granite under Ultrasonic Vibration with Different Amplitudes

“…ere is always a strong demand for e cient and rapid drilling in hard rock strata. Based on this, numerous scholars begin to search for new methods of rock crushing [1]. It is widely recognized that cyclic impact loading can cause fatigue failure inside the rock [2][3][4].…”