DigitalClone Fretting Fatigue Life Prediction

The U.S. Navy is seeking an advanced fretting fatigue life prediction method for naval aerospace applications that advances the science, physics-based modeling & simulation (M&S), and mitigation techniques for fretting fatigue damage to improve durability, reliability, and performance in naval aero-structural applications. Fretting is a wear phenomenon that occurs when two surfaces in contact undergo small oscillatory motions with respect to one another. This small relative motion results in slippage in the outer regions of two contacting surfaces, where the shear force is sufficient to overcome frictional resistance. High points or asperities of the mating surfaces in the slip zone adhere to each other, resulting in the formation of shallow pits and a powdery debris (fretting wear). Microcracks can be initiated by the shear stress present in the slip zone within the first several thousand cycles. Since these cracks are usually not observable during operation, the need for a strategy for predicting their formation and propagation becomes apparent. Fretting fatigue is particularly detrimental in gearbox housing and assemblies and in various structural joints, where the combination of high cyclic loads, harsh environmental conditions (e.g., vibrations, thermal cycling), and material properties lead to accelerated degradation. In response to U.S. Navy SBIR Topic N25B-T032, Sentient proposes to utilize its DigitalClone for EngineeringTM (DCE) modeling technology for fretting fatigue applications. It is well recognized that initiation of fatigue failure generally occurs by nucleation and propagation of critical micro-cracks with sizes ranging from several micrometers to a few hundred micrometers. The growth of these cracks does not follow the conventional linear elastic fracture mechanics (LEFM) approach. Therefore, in order to obtain a reliable life prediction model, a physics-based model is needed to analyze the fatigue crack nucleation and short crack growth. During Phase I, Sentient is proposing to further develop our DCE modeling software to include the features required for fretting fatigue analysis including debris (captured in contact zone) modeling, corrosion effects, and microstructure modeling relevant to fretting fatigue applications. This model not only accounts for the effect of microstructure on the fretting fatigue crack creation and early growth, but also predicts the effect of presence of debris and corrosion on the fatigue life of the structure. In Phase I, material selection will be done through communication with Navy TPOCs and Aerospace OEMs for fretting fatigue in aerospace applications. Specimen manufacturing and coupon testing will be performed as part of Phase II. In Phase II, we will implement coupon and component physical testing for validation of our improved DCE modeling tool through collaboration with aerospace OEMs.