Experimental verification of a fracture mechanics model for tensile strength prediction of Indiana Limestone

A model is proposed that enables the direct use of apparent fracture toughness values, KQ, as measured from fracture specimens with dimensions too small to produce a valid measure of KIC. The approach is not intended to predict KIC from KQ values measured on subsized specimens as has been previously attempted by others, but rather to use KQ values directly for applications in which the geometry dictates that the use of KIC would be inappropriate. The assumption made is that KQ depends only on crack length with parameters such as thickness, remaining ligament, and stress gradient having a second-order effect. This assumption is supported by considerable experimental data for Indiana limestone. These data are used with a model for the intrinsic flaw geometry to predict the tensile strength of this rock. The predicted value is within 30% of the measured values which compares to a previous prediction that is 6 times too high. 20 references.