Experimental study on mode I fracture characteristics of heated Flossenbürger granite with different cooling methods using DIC and AE

A systematic understanding of microcracking behavior and fracture properties in granite is essential for rational design and long-term stability assessment in deep underground engineering applications, including high-level radioactive nuclear waste geological disposal and geothermal energy exploitation. Among the three fundamental fracture modes, Mode I fracture is the most prevalent. To investigate the influence of thermal treatment on the Mode I fracture behavior of brittle rocks, notched semi-circular bend (SCB) specimens of Flossenbürger granite are thermally treated at seven target temperatures (25–350 °C) and subjected to two cooling methods (air cooling and water cooling), followed by semi-circular bend tests. Acoustic emission (AE) counts and cumulative energy are adopted to track internal microcrack evolution, while full-field displacement/strain measurements from digital image correlation (DIC) are used to identify fracture initiation, fracture process zone (FPZ) development, and the critical crack opening displacement. The combined AE–DIC approach provides multi-source cross-validation and supports quantitative interpretation of damage evolution and fracture mechanisms. Microscopic observations of granite thin sections are further performed to assess thermally induced microcracks under different scenarios and to relate microscale damage to the macroscopic response.

Keywords: Thermal treatment; Digital image correlation; Acoustic emission; Mode I fracture characteristics.