Fatigue fracture criterion of composite materials

The first investigations on the fatigue strength of composite materials were carried out on cyclic tension of plastics reinforced by fiberglass. Since that time, intensive studies of fatigue strength of composite materials were begin. The experimental data obtained for different types of composite materials shown, that the fatigue fracture processes are governed by the accumulation of defects of different nature. The main mechanisms that determine the durability of composites is the kinetics of the damaged state development until the final fracture. At the same time, according to the experimental results, the damage accumulation curve of the total damage is defined by increased function of the time (number of loading cycles) until to the moment of macro fracture. In this paper, based on these studies and the conception of scattered damage and fracture, fatigue strength criterion is formulated. Fatigue criterion coefficients are concretized and damage accumulation curves are plotted, which depends on the number cycles and stress level. The comparison with experimental results on fatigue of glass-reinforced plastics and carbon fiber reinforced plastics is given.