The Effect of Rock Type and Test Method on the Relationship Between MODE I Fracture Toughness and Rock Tensile Strength

Mode I fracture toughness is an important rock property in fracture mechanics. Due to its challenging test procedures, empirical formulas, in terms of different rock properties, have been suggested for its rapid prediction. Due to similarities between K_IC and rock Tensile Strength tests in their failure’s nature and morphology, many K_IC–TS relationships have been proposed in literature. Recently the topic of rock fracture toughness has become more popular. So, it is vital to revisit existing K_IC–TS relationships such that the influence of other parameters related to rock type and test method can be studied. In this paper, the effects of rock type, i.e. Igneous, Sedimentary and Metamorphic, and test method on K_IC–TS relationship were investigated. K_IC–TS relationships were deduced based on regression analysis of literature data using linear, power, exponential, and logarithmic mathematical models. It was found that rock type has a more significant effect on K_IC–TS relationship than test method. Moreover, power model was found to be the best to represent K_IC–TS relationship. Eight power relationships were proposed for the prediction of K_IC under level I and static testing conditions. When compared with previously suggested relationships in literature, the proposed relationships showed similar trends and comparable K_IC values particularly at tensile strength values lower than 10 MPa. It was concluded that the proposed relationships can be used to predict K_IC considering test method and rock type with reasonable accuracy.