Review of the Relationships between Crack Initiation Stress, Mode I Fracture Toughness and Tensile Strength of Geo-Materials

Abstract

It has been accepted that, in geo-materials, almost all the cracks forming at final failure in the tension test and those occurring at the crack initiation (CI) and crack propagation stages in the compression test are tensile cracks. Because of this, tensile strength is attracting more attention. Compared with the experiment for obtaining tensile strength, the results obtained from a CI stress experiment are inaccurate for the subjective judgments of the user, and the results obtained from the fracture toughness test show a rather large variation of 30–50%. A review was conducted to determine the relationships among CI stress, Mode I fracture toughness, and tensile strength from the view of the failure mechanism and the data gathered from the available literature. It was found that CI stress has a linear relationship with Brazilian tensile strength with the linear coefficient of 0.075, and the linear coefficient between Mode I fracture toughness and tensile strength is in the range of 0.1–0.15, although both correlation coefficients are at a low level. The relationships can be the basis for preliminary design purposes and for rock classification and characterization. It is suggested that the shape of the sample for testing should be consistent and the methods for obtaining each property should be standardized, and more data are needed for further study.