Mechanical behavior and fracture characteristics of granite under microwave treatment based on continuous-discrete method

Microwave⁃assisted rock⁃breaking has the advantages of green,and low energy consumption,which is a promising method to achieve an efficient excavation of hard rock strata in deep coal resources development. Therefore,the mechanism of microwave⁃assisted rock⁃breaking has attracted the attention from engineering and aca⁃ demic fields. In this study, based on the difference of microwave absorption capacity of granite minerals, by using the continuum analysis of microwave electromagnetic and discrete element mechanics model,the micro miner⁃ al temperature discrete assignment was implemented. And a method for calculating and analyzing the mechanical prop⁃ erties of granite under microwave treatment was proposed and verified as a reliable approach in terms of temperature field,mechanical properties,and failure pattern. Then,the fracture evolution,mechanical behavior and fracture mecha⁃ nism of the microwave treated granite specimen under the uniaxial / triaxial loading conditions were revealed by numeri⁃ cal simulation. The results show that: ① Under microwave treatment, two relatively low⁃temperature regions and one hot spot appear in the specimen. When the specimen is treated under relatively low microwave power (≤2 kW),the internal crack is nearly negligible. The crack development is dominated by the tensile failure of grain boundaries if the specimen is treated under a relatively high microwave power(≥3 kW) . In the latter case,the crack is centered on the hot spot and extends to the surrounding area, and finally forms a crack network. ② For uniaxi⁃ al compression, the peak stress, elastic modulus, and damage threshold of the specimen decrease with the increase of microwave power,and this drop is more obvious at relatively high microwave power(≥3 kW) . When the microwave power is relatively high(≥3 kW),the initial crack generated by microwave treatment dominates the crack evolution of the specimen,and the specimen exhibits a trend of initial crack growth as well as significant local failure.③ For tri⁃ axial compression,with the increase of microwave power,the effect of initial confining pressure on the strength of the specimen is continuously strengthened. When the specimen is under relatively low microwave power (≤ 2 kW), the change of elastic modulus with confining pressure is not obvious, but when microwave power increases (≥3 kW),the initial confining pressure significantly improves the elastic modulus of the specimen. With the increase of microwave power,confining pressure promotes the continued bearing capacity and stress transfer of fractured parti⁃ cles,and the failure of the specimen is transformed from intergranular failure to intragranular failure,which leads to the full development of crack network and inhibits the concentrated failure of local structures caused by high power heating(≥3 kW) . © 2023 China Coal Society. All rights reserved.