Executive Summary : | Fretting fatigue is a wear phenomenon that reduces the fatigue strength of a component when two components are in contact under load, with a small relative displacement of a few microns between them. This can occur in various applications such as dovetail assembly turbine blades, steam generators, hip joints in human implants, railway axles, and bolted joints. Fretting can cause surface microcrack initiation within the first few thousand cycles, significantly reducing component lifetimes. In normal fatigue, crack initiation accounts for approximately 90% of the fatigue life, but under fretting fatigue, the initiation phase could be curtailed to 5% or less of the total cyclic life. Cracks due to fretting are usually hidden by the contacting components and are not easily detected. Catastrophic failure can occur if conditions are favorable for the continued propagation of cracks initiated by fretting. The complex nature of this phenomenon involves several variables, including contact force between mating parts, cyclic frequency, temperature, environment, slip amplitude, frictional forces, and more. The current design codes used in power plants, jet engines, and high-speed railways do not consider damage due to fretting, which is crucial for ensuring structural integrity and preventing catastrophic failures. Ferritic-Martensitic steels are considered potential candidates for next-generation ultra-supercritical power plants due to their excellent microstructure stability, swelling resistance, and adequate mechanical properties in irradiation environments. Understanding the fretting fatigue behavior of these materials under high temperatures is essential for safety standards. |