Fatigue Process in Materials for Automotive Industry

Structural parts of automobiles in operation are exposed to the influence of temperature and vibration. The overwhelming majority of metal destruction cases is caused by metal fatigue. It results in economic losses and often leads to accident-induced human casualties. This is why one of the most relevant tasks for the modern automotive industry is to ensure the operability of automobile parts and components. Thus, it is necessary to know the behavioral patterns of metal materials obtained by different technologies and exposed to vibration. The destruction of metal structure directly affects the behavior of sample deflection that reflects the competition between hardening and softening as two mutually opposite phenomena. They directly affect the structural damageability of metals. This article is about the study of the kinetics of fatigue failures of materials for the automotive industry by the calibration of structural damage to their surface with the behavior of the curves of changes in current deflection at alternating loads. The paper considers automotive materials (20KhI3, 14Kh17N2, 35KhGSA steel grades) and model metals and alloys (M1 copper, L63T brass, V95pchT2 aluminum alloy) in various structural states under cyclic loads at low, room, and elevated temperatures, including the registration of the samples deflection and the related structural damage. The article also reveals the possibility to study the fatigue failure kinetics of the sample materials by deflection curves that provide an integral characteristic of destructive processes observed at alternating loads. These processes can be used to monitor the phases of fatigue damage to metal materials, including structural damage in the initial phase, occurrence of a microscopic crack and its subsequent propagation to the complete separation of the structural material. These phases can be used to find out the correlation between the period before the fatigue crack nucleation and the subsequent crack propagation, and also determine the average rate with which the fatigue crack spreads across the metal sample body. It is also important that deflection curves can be used to evaluate the destruction kinetics of materials when the structural state of sample surfaces cannot be examined directly, for example, at cryogenic and elevated temperatures or in corrosive media. Deflection curves used together with fractographic and metallographic analysis of fatigue allow evaluating destruction phases of materials and using this evaluation to choose the latter for structural automobile parts, considering vehicle operation conditions, and optimizing the parts fabrication technology to enhance the service life of automobiles and improve their repairability.