Models of Fatigue Fracture Under Cyclic Loading Pistons of Internal Combustion Engines

摘要

The crack on the piston under cyclic loading is the result of repetitive elastic and plastic deformations distributed unevenly throughout the volume. The microcracks from fatigue occur in repeated elastic and plastic deformations in the individual parts or sections throughout the volume of piston, that is, the precursor of cracks. However, a piston with a microcrack 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 characterizing the stress concentration at the crack tip and depends on the load, forms of a detail, crack size, and the anisotropy of the material. For the analytical description of the crack growth rate, it has been proposed more than 60 formulas and they are all based on the fact that all processes occurring at the crack tip and the rate of crack growth of the number of cycles depend on the stress concentration factor. The magnitude of the stress intensity factor allows one to judge about the stability or instability of cracks. The crack is called stable if it is not growing or its growth is linearly dependent on the load. When you select the corresponding operating mode of the engine, the crack on the edge of the combustion chamber of the piston may not develop and this way you can ensure that the crack has not increased its size. The crack would be unstable if its distribution only slightly depends on the load.