Evaluation Method for Determination of Fracture Toughness of Brittle Materials by the Use of Small Sized Specimens

Recently, core based specimens have been proposed for standard fracture toughness testing of rock, in a draft of the testing standard of the International Society for Rock Mechanics (ISRM), which recommends two chevron-notched specimens. In this study, fracture toughness tests, according to the recommended testing procedure, were conducted on chevron-notched core based specimens of granite. In addition to these specimens, straight-notched core specimens with three different geometries were also tested, where the J-integral approach and AE technique were used to determine fracture toughness and the effect of specimen geometry on fracture toughness was examined. As a result it was found that the ISRM test method yields inconsistent fracture toughness values depending on the specimen geometry. Finally it was shown that the J-integral/AE method as applied to straight-notched specimens provides a suitable evaluation procedure for the fracture toughness testing of rock. Furthermore, the test method developed in this study was applied to other brittle materials which were nuclear grade graphites and mortar.