Mode I and mixed mode fracture studies in brittle materials using the Brazilian disc specimen

High Strength Cement Mortar (HSCM) with very fine sand exhibits a typical brittle behavior. In the present work, a linear elastic fracture mechanics based model is used for the fracture studies conducted on this material. The experimental testing program is based on the diametral compression test of disc specimens containing an internal slant crack. Under the Mode I loading condition, the test method which has been previously used is applied to determine the critical value of the stress intensity factor, K_IC, for HSCM. The same disc specimen is also tested under combined Mode I and Mode II loading conditions. By changing the notch orientation angle with respect to the loading direction, the mode of fracture is varied from pure Mode I to Mixed-Mode. Based on the Mixed-Mode fracture envelope, it is shown that the disc specimen which is currently used for several brittle materials provides a wide range of |K_II| / K_I ratios. In pure Mode I loading case, after determining K_IC, it is possible to obtain the graph of normalized critical load versus normalized crack length. For the purpose of comparison, some available experimental data on Mode I and/or Mixed Mode fracture of some other brittle materials such as glass, sintered carbide, and polymethyl methacrylate (PMMA) were also evaluated. It can be concluded that there is a good fit between the experimental results and the theory.