# The Law and Mechanism of the Effect of Surface Roughness on Microwave-Assisted Rock Breaking
## 5 Conclusions  
In this study, microwave-irradiation tests were carried out on basalt samples (from Chifeng, Inner Mongolia) with surfaces of different roughness, and the influences of rough rock surfaces on the effect of microwave irradiation were explored through numerical simulation. The main conclusions are presented subsequently.  
1. After microwave irradiation, the distribution of the high-temperature region of the flat surface sample is mainly concentrated in the central area, whereas the high-temperature area of the rough surface sample is unevenly distributed with the main high-temperature region appearing in the convex surface area. The temperature peaks  
Figure 18: Shear stress distribution (The red area represents the high stress area, and the blue area represents the low stress area, maximum stress point temperature of 100 \({}^{\circ}\)C). (**a**) Flat surface. (**b**) Non-flat surface.  
of all rough rock surfaces were much larger than those of flat surfaces; the temperature peak increased with the increase in roughness. (2) When microwaves irradiate rocks, thermal stress is generated, and when the stress is greater than the strength of the rock, the rock is damaged. After microwave irradiation, no macroscopic cracks were observed on the flat surface, whereas crack propagation on the rough surface was obvious: New cracks were generated on the surface, and existing cracks continued to propagate. The P-wave velocities of the rough surface specimens were significantly reduced. (3) Through numerical simulation, it was determined that the average surface electric field strength and average surface temperature of the rough surface samples were greater than those of the specimen with the flat surface. The distribution of the plastic zone is related to the distribution of the electromagnetic field and temperature; the total volume of the plastic zone increased first and then decreased with the increase in roughness. (4) The comprehensive experimental and theoretical analysis shows that the influencing factors of rough rock surfaces on the effect of microwave irradiation are mainly the refraction and reflection of electromagnetic waves on the rock surface, heat conduction, and stress concentration.  
Conceptualization, F.C., G.L. and Z.Z.; methodology, F.C.; software, G.L. and Z.W.; formal analysis, F.C., G.L. and Z.Z.; investigation, Z.Z.; resources, Z.Z.; data curation, G.L.; writing--original draft preparation, G.L.; writing--review and editing, F.C., G.L. and Z.Z.; supervision, Z.W.; project administration, Z.Z.; funding acquisition, F.C. and Z.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by The National Natural Science Foundation of China (11872301) and The Natural Science Basic Research Program of Shaanxi Province (2020)M-453.  
Not applicable.  
The data presented in this study are available upon request from the corresponding author. The data are not publicly available due to the conduct of further research based on some of the data in this article.  
The authors thank the Xi'an University of Science and Technology for their experimental and technical support.  
The authors declare no conflict of interest.