Thermal Stress Evolution and Microstructural Development in Simulated Lunar Regolith During Microwave Sintering and Cooling

Microwave sintering technology is widely regarded as one of the most promising construction techniques for in situ resource utilization in lunar bases due to its high energy efficiency and unique heating mechanism. However, the extremely low-temperature environment on the lunar surface creates a transient temperature gradient of over a thousand degrees Celsius between the sintered body’s surface and its interior. This temperature difference induces significant thermal stress during the cooling process, leading to macroscopic surface cracks and even structural failure, which severely limits the engineering feasibility of this technology. To evaluate the surface integrity of lunar in situ sintered bodies and determine the safe processing window for microwave sintering, this study develops a multiphysics computational model that couples electromagnetic, thermal, and stress fields. The results show that when the cooling rate is below 15 °C/min, the surface stress remains below the material’s tensile strength threshold, effectively preventing crack formation. However, at a cooling rate of 16 °C/min, the surface stress exceeds this threshold, leading to crack initiation. Further analysis reveals that the cooling rate significantly affects the microstructure, with slow cooling maintaining a dense structure, while fast cooling promotes the formation of microcracks, particularly in regions with low Si/Al content. This study provides a reference for the microwave sintering process of lunar regolith and proposes a strategy of controlling the cooling rate below 15 °C/min.