Features of development of nonuniform microscopic strains and fatigue damage accumulation in carbon steels

1. Direct measurement of local strains in fixed microvolumes of a metal undergoing alternating cyclic loading (symmetrical) established the existence of an extremely inhomogeneous strain state in structural elements of the alloy. An increase in the number of load cycles is accompanied by an increase in the inhomogeneous nature of the accumulation of unidirectional microplastic strains: while plastic strain reaches exceptionally large values (several percent) in some individual microvolumes, it remains equal to zero in other places. 2. It was shown that the mechanism of development of plastic strain in carbon steels with cyclic loading at stresses below the yield point is based on the local character of the initiation of plastic strain in the weakest elements of the metal structure. 3. The micromechanism of the fatigue fracture of a true polycrystalline alloy is based on microinhomogeneous strain and is characterized by the stable fixing of “sources” of increased or reduced strain from the very first load cycles. This is evidence of the large role of the alloy microstructure and grain-boundary properties in determining the kinetics of development of local microstrains. Here the distribution of microstrains by alloy structural element is satisfactorily described by a normal distribution law.