Abstract
This article is the summary for the paper receiving the frontier award from the Japanese Society for Rock Mechanic (JSRM) in the fiscal year of 2018. In order to evaluate the fracture toughness of rock, until now, the proposed test methods assumes that the rock specimen is isotropic homogeneous material. Also, the specimen size of several centimeters is recommended. However, rock is a natural material and is composed of millimeter-sized mineral particles, ground mass and substrates, etc. In addition, rocks are said as heterogeneous at microscopic viewpoints because it includes weak planes such as pores and preexisting micro cracks. Numerous studies have been conducted on the effect of microstructure characteristics on the fracture toughness of rocks. It is discussed that the fracture toughness of granite, which is a crystalline rock, is influenced by micro cracks, orientation of mineral grains, kind of mineral grains within the rock and grain boundary characteristics.
In this study, a micro material testing device for rock was developed based on the microscopic strength test method used in the field of metal material mechanics, and the microscopic fracture toughness test method was constructed at the same time. In addition, microscopic fracture toughness of mineral grains within granite was evaluated using a micro material testing device.
