FATIGUE PROCESS OF AUTOMOBILE MATERIALS

Abstract

During operation, the structural elements of cars are exposed to temperatures and vibrations. Overwhelming majority of the destruction of metal structures is caused by their fatigue. It causes economic losses and often human casualties from accidents. Therefore, the task of ensuring the operability of parts and components of automobiles is one of the most relevant in the modern automotive industry. So it is necessary to know the patterns of behavior of metallic materials, obtained by different technologies, when they are exposed to vibration. Destruction of the metal structure directly affects the behavior of the samples deflection, reflecting the competition of two mutually oppositephenomena – hardening and softening. It directly influences structural damageability of the metal. The article is devoted to the study of kinetics of fatigue failure of automotive materials using the calibration of structural damage to their surface with behavior of the curves of changes in current deflection under alternating loading. The paper considers automotive materials (steel grades 20KhI3, 14Kh17N2, 35KhGSА) and model metals and alloys (Copper M1, Brass L63T, aluminum alloy V95pchT2) in different structural state under cyclic loading for low, room and high temperatures with fixation of the sample deflection and structural damage corresponding to it. It is possible to study kinetics of fatigue destruction of the sample material by the deflection curves, which is an integral characteristic of destructive processes occurring under alternating loading. Using these processes, one can track the stages of damage during fatigue of metallic materials – damage to the structure at the initial stage, moment of the macroscopic crack appearance, its subsequent advancement up to complete separation of the structural material. It is probable to identify ratio of the period duration before the appearance of a fatigue crack and its subsequent growth, as well as to determine the average rate at which the fatigue crack moves through the body of the metal sample. It is important that it is also possible to estimate the kinetics of materials destruction under the conditions when direct study of the structural state of the sample surface is impossible, for example, in conditions of cryogenic and high temperatures, and also, for example, in the presence of corrosive media. In combination with fractographic and metallographic analysis of the fatigue process, the deflection curves allow, based on the evaluation of the stages of materials destruction, to carry out selection of the latter for the structural elements of a car taking into account its operating conditions and optimizing the technology of parts manufacturing to increase serviceability and maintainability.