Femtosecond laser micro-machining for accurate determination of fracture toughness of glass

A fundamental issue in solid matter is how to accurately determine the fracture toughness. Glass is a brittle material that typically exhibits failure through brittle fracture, making it significant to know the accurate fracture toughness. The classic methods, including single-edge notched beam (SENB), single-edge V-notched beam (SEVNB), chevron notched beam (CNB), and single-edge precracked beam (SEPB), have been widely explored while suffering from limitations such as low efficiency, low preparation success rate, or large notch root radius (rho) leading to overestimation. In this paper, we propose an effective strategy for the determination of fracture toughness of glass by employing the ultrashort pulse laser micro-machining (FSL-SEVNB). The ultrashort pulse laser is featured by exceptionally high peak power and rather short pulse widths that are on the order of femtoseconds, showing great potential for ultra-fine machining. By using the protype BK7 glass, the relation between the laser parameters and the induced microstructure is systematically studied. Importantly, the submicron-level crack with rho similar to 0.85 mu m can be induced. This enables the achievement of high stress concentration, and as a result, the accurate determination of K-Ic. In addition, it is necessary to note that the method exhibits high comparability to SEPB. Furthermore, the strategy can reach similar to 100% success rate with high efficiency (several minutes for sample preparation). The progress about ultrashort pulse laser-assisted micro-machining is believed to offer a novel perspective for extreme field applications in material characterization.