Effect of specimen dimensions on fracture toughness of Harsin marble rock

The determination of fracture toughness of a rock material requires a standard specimen with specific geometry dimensions. If the dimensions of specimen are lower than special values, the obtained fracture toughness may not be accurate. In order to attain the fracture toughness of rock materials correctly, several criteria have been proposed for the required minimum dimensions. In this study, some tests were conducted on the semi-circular specimen containing an edge crack and subjected to three-point-bend loading (SCB specimen) and the suggested criteria for the required minimum crack length and thickness were assessed. The specimens were made of Harsin marble rock. The results obtained from the fracture tests showed that these criteria are not comprehensive and are not consistent with the experimental results. Therefore, by using the necessary correction factors in equations related to the minimum crack length and thickness, these equations were revised such that they can estimate the experimentally observed results for the Harsin rock.