Testing Method for Determination of Microscopic Fracture Toughness for Rock Materials

The fracture behavior of rocks is known to depend on the microstructures of the rocks: the distribution and orientation of the microcracks, and the type, size, and shape of mineral grains. To explain quantitatively the effect of the microstructures on the fracture of rocks, the determination of the fracture toughness of grain and grain boundaries, namely, the microscopic fracture toughness (MFT), is necessary. The authors developed a testing method for determination of MFT for rock materials. A microsized specimen of a cantilever beam type with dimensions of 10 by 10 by 50 μm was used in this testing method, and we built a special testing machine for this specimen. Microsized specimens were made within grains of Iksan granite by Focused Ion Beam machining, and the MFT of its constituents—plagioclase, alkali feldspar, and quartz—was determined using this testing method at room temperature. The MFT varied widely and the results are discussed based on the mineralogical knowledge. This testing method will be helpful to more accurately interpret the fracture behavior