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Fretting, which can occur when two bodies in contact undergo a low amplitude relative slip, can drastically reduce the fatigue performance of a material. The extent of fretting damage is dependent on the material combination and is affected by many parameters, making it difficult to design against fretting. Some of these parameters include contact force, displacement amplitude, and contacting materials. This work develops a method for quantifying the extent of damage from fretting as a function of these parameters for a thin sheet of AISI 301 stainless steel in the full hard condition in contact with both ANSI A356 aluminum and AISI 52100 steel contacting bodies. Fretting experiments were conducted on a Phoenix Tribology DN55 Fretting Machine using a fixture which was developed for holding thin specimens. The displacement amplitude and normal force were systematically varied in order to cover a range that could typically be experienced during service. The tribological behavior was studied by analyzing friction force during cycling and inspecting the resulting surface characteristics. Fretting damaged specimens were cycled in tension in a servohydraulic test system to failure. The decrease in fatigue life caused by fretting damage was determined by comparing the stress-life (S-N) response of the fretted specimens to the S-N response of the virgin material, thus characterizing the severity of the fretting damage. The conditions that lead to the greatest reduction in life were identified in this way. Using the fracture mechanics based NASGRO model, an Equivalent Initial Flaw Size (EIFS) was used to quantify the level of fretting damage, thus separating the life of the component into crack nucleation and subsequent propagation. This method and data will allow engineers to design more robust components that resist fretting damage, thus increasing the safety and reliability of the system.

Fatigue-crack growth data for the lower arm of the Apache helicopter’s scissor assembly is presented from an Army alternate source qualification test. The lower arm model is imported to finite element analysis software to obtain the stress state at a crack location. The stress state and geometry are used in seven fatigue-crack growth cases in NASGRO and AFGROW, with an additional four cases discussed briefly. The results from the fatigue-crack growth routines are compared to the fatigue-crack growth data from the Army’s test. One case reproduces the crack growth data prior to breakthrough. Some cases are shown to be more applicable to this configuration than others are. The process of performing fatigue life estimates is discussed. Suggestions are made on the viability of this approach and possible future avenues for development.