A new method to compute size independent fracture toughness values for brittle materials

Abstract

Generally, linear elastic fracture mechanics (LEFM) is inadequate for fracture toughness ( K Ic ) characterizations of brittle or quasi-brittle materials such as ceramics, concretes, and rocks, because large process zones exist. In order to obtain a valid, size independent K Ic value (or to satisfy the small scale yielding criterion), huge specimen sizes are required. For this reason, a testing method based on the nonlinear tension-softening behavior has been proposed. A new computational scheme for determining size independent fracture toughness of brittle materials is presented in detail. This scheme is direct, accurate and it eliminates several numerical steps (including curve fitting and taking derivatives of fitted curves) and the associated errors from the original experimental technique. All theoretical concepts and the experimental technique of this new and more efficient method of deducing the tension-softening curve for brittle and quasi-brittle materials are presented. Results and comparisons of a fracture toughness investigation of sandstone and basalt using both tension-softening and LEFM concepts are also presented.