Abstract: In view of the low crushing efficiency of traditional hard rock and the unknown influence mechanism of cooling path in microwave-assisted rock breaking,this study systematically explored the influence of different cooling methods on rock damage after microwave irradiation with basalt as the object. By comparing the wave velocity,tensile strength,fractal dimension and strain field characteristics of rock under natural cooling,real-time high temperature and water impact cycle cooling paths, it is found that water impact cycle cooling significantly aggravates the difference of thermal stress inside and outside the specimen through rapid cooling,thus maximizing the damage effect. The experimental results show that the cooling strategy of shortterm radiation combined with intermittent water flow impact can effectively drive multi-scale crack propagation. Among them, the cycle path effect of water flow impact for 30 s after 45 s of radiation is the best,resulting in a decrease of wave velocity by 19%,a decrease of tensile strength by nearly 50%,and a significant increase of fractal dimension. The microscopic analysis further reveals the crack propagation mechanism dominated by thermal stress gradient. The results show that under the same energy consumption,the greater the temperature difference,the better the damage effect. The circulating cooling strategy of shortterm radiation combined with intermittent water flow impact can significantly improve the efficiency of microwave-assisted rock breaking. It can provide reference for the application of microwave-assisted rock breaking in subsequent experiments and engineering practice. 

Key words: microwave radiation,basalt,cooling type,fractal dimension,damage effect