The Influences of Microwave Irradiation and Heat Treatment on the Dynamic Tensile Response of Granite

The paramount significance of temperature’s influence on rock engineering endeavors underscores its profound capacity to alter the physical and mechanical attributes of rocks. Among the most crucial techniques utilized to thermally induce damage and diminish the tensile resilience of rock materials are microwave irradiation and heat treatment. This research examines and compares the effects of these two modalities on the dynamic tensile characteristics of Fangshan granite (FG), including their implications under conditions of overload and dependencies on loading rate, utilizing the sophisticated Split Hopkinson Pressure Bar (SHPB) apparatus. In particular, the dynamic real tensile strength (RST) of Brazilian disc (BD) specimens was meticulously gauged and contrasted after subjecting them to microwave irradiation at a potent 6 kW for varying durations (1.5, 3.0, and 4.5 min) and heat treatment across distinct temperature thresholds (178 °C, 345 °C, and 473 °C). To enhance the precision of the measurements, an overload correction was implemented by affixing a strain gauge in close proximity to the core of the BD specimen. The conventional dynamic tensile strength exhibited a reduction of approximately 20 to 30% with the prolongation of microwave radiation time. Furthermore, an additional decrease in tensile strength was observed with the elevation of heat treatment temperatures, reaching a maximum reduction of up to 40%. This phenomenon can be attributed to the proliferation and expansion of microcracks within the rock matrix. It was noteworthy that the RTS, corrected for overloading effects, exhibited a comparable trend to the dynamic traditional tensile strength (TTS). Both were significantly correlated with the loading rate, with the dynamic tensile strength demonstrating an average decrease of approximately 25% when the loading rate was increased. Interpolation and fitting analyses were employed to investigate the effects of microwave radiation duration, heat treatment temperature, and loading rate on the dynamic tensile strength of FG samples. Furthermore, it was established that the overload ratio increased in conjunction with an increase in microwave radiation duration, heat treatment temperature, and loading rate, reaching a maximum value of 1.5.