REVIEW OF MODELS OF FATIGUE FRACTURE UNDER CYCLIC LOADING
The failure under cyclic loading is the result of repetitive elastic and plastic deformations, distributed unevenly throughout the volume. Modern diesel engines have a high level of boost and it causes considerable thermal and mechanical loads acting on the piston. The failure from fatigue occurs in repeated elastic and plastic deformations in the individual parts or sections throughout its volume, that is the precursor of cracks. However, a piston with a crack can work practically all the resource if there is no crack propagation. The crack creates its own stress field, which is determined by the stress intensity factor. It characterizes the stress concentration at the crack tip and depends of the load, form of geometry detail, crack size, and in the case of anisotropic material. Crack growth analytically described by scientists more than 60 dependencies and all are based on the fact that that occur at the crack tip, as well as the rate of development of cracks depends on the number of cycles and from the stress concentration factor. The magnitude of the stress intensity factor determines the stability or instability of the crack development. The crack is called stable if it does not increase or increases linearly with increasing load. The crack on the edge of the combustoг piston can not develop if the corresponding mode is selected, and then we can ensure that the crack will not increase its size. The crack be unstable if it is not development from the load. We appraised fatigue models used in the presence of cracks and recommendations for calculation of longevity.