NONLINEAR FRACTURE PARAMETERS FOR CEMENT BASED COMPOSITES: THEORY AND EXPERIMENTS.

Many have attempted to apply linear elastic fracture mechanics (LEFM) to quantitatively express the fracture toughness of concrete. For example, by testing notched beams one can calculate, using the formulas developed from LEFM, fracture toughness in terms of K//I//C, the critical stress intensity factor for Mode I opening. Unfortunately, it has been observed that when K//I//C is calculated from the measured values of the maximum load and the initial notch length, its value is dependent on the dimensions of the beams. This size dependency of the single parameter LEFM based fracture criterion can be attributed primarily to the non-linear effects associated with crack propagation in concrete. In this paper, a simple method is suggested to calculate a size-independent fracture toughness parameter.