Effetto di scala nella propagazione a fatica di fessure frattali

Several experimental tests have shown that the material strength under static or fatigue loading decreases by increasing structural size, and some theoretical arguments have been proposed to interpret such a phenomenon. As far as fatigue crack growth is concerned, limited information on size effect is available in the literature. In the present paper, by exploiting some concepts of fractal geometry, new definitions of fracture energy and stress-intensity factor based on physical dimensions different from the classical ones are discussed. Then, a size-dependent crack growth law (expressing crack growth rate against stress intensity factor range) is proposed and used to interpret relevant experimental data related to concrete.