Progressive fracture and energy response of granite subjected to rapid localized flame heating

Abstract

The progressive fracture and energy responses of granite following rapid localized flame heating were investigated using three-point bending tests on untreated single-edge-notched beams and specimens heated to target surface temperatures of 200–600 °C and naturally cooled to room temperature. Acoustic emission (AE) and digital image correlation (DIC) measurements were combined with fracture-surface SEM observations and main-crack-path analysis. The results showed that the mean peak nominal stress decreased from 15.17 to 5.39 MPa with increasing target surface temperature, a reduction of approximately 64.5%, while mean failure CMOD and LPD increased monotonically and reached their maxima at 600 °C. Post-peak load degradation and crack propagation occupied most of the loading history, with 97.27–99.87% of the final cumulative AE absolute energy recorded after peak load. Representative post-peak b-values were lower than pre-peak values, indicating a greater relative contribution from high-amplitude events, while tensile-type AE events dominated the RA–AF classification. DIC showed upward strain localization from the notch tip and macroscopic failure dominated by opening. Crack paths varied non-monotonically with temperature, with the greatest deflection and tortuosity at 400 °C, where path correction reduced the calculated fracture energy by approximately 11.2%. Among the representative specimens, path-corrected fracture energy peaked at 180.51 N/m at 500 °C, whereas cumulative AE absolute energy peaked at 300 °C. These findings provide an experimental basis for evaluating granite fracture following localized thermal disturbance and for thermally assisted rock breaking.