Fracture Toughness of Granite Measured Using Micro to Macro Scale Specimens

The objective of this study is to examine any variation from micro to macro scale mode-I fracture toughness of granite using micro-sized specimen and semi-circular specimen. The rock used in the tests is Iksan granite (Korea) which is composed of minerals, such as plagioclase and alkali feldspar, quartz. In order to investigate micro scale fracture toughness, a mechanical testing machine was used. This machine is an original one and developed by ourselves. In the test, a micro-sized cantilever beam type specimen was used. Its dimension is 10 × 10 × 50 μm. On the other hand, in order to examine macro scale fracture toughness, Semi-Circular Bend (SCB) test is adopted. This is one of ISRM-suggested methods for estimation of the mode-I fracture toughness of rocks. The semi-circular specimens are prepared with a radius of 12.5 mm to 50 mm. Based on the fracture toughness obtained from both tests, the size effect of granite is discussed in the range from micro to macroscale.