Crack nucleation, first spall generation, and spall growth in rolling contact fatigue (RCF) are known to be highly sensitive to the heterogeneity of the microstructure. Yet the current state-of-the-art in the design of high performance bearing materials and microstructures is highly empirical requiring substantial lengthy experimental testing to validate the reliability and performance of these new materials and processes. We have laid the groundwork necessary to determine the influence of microstructure in RCF to aid in the development and processing of bearing steels. Microstructure attributes that may control the fatigue behavior are explicitly modeled in a 41xxx steel. The methodology is demonstrated by studying the role of an aluminum oxide inclusion embedded in a matrix of tempered martensite and retained austenite. The matrix is represented by crystal plasticity, which provides more realistic accumulations of localized plastic strains with cycling compare to homogenized J2 plasticity. As a demonstration of the approach, the relative influence of the volume fraction of retained austenite on RCF is evaluated.
Both experimental and numerical studies were conducted to investigate the effectiveness of composite patch repair on underwater structures, especially aluminum alloy structures. Physical samples were prepared using 5XXX aluminum plates with a premachined hole and E-glass woven fabric layers. The epoxy resin was selected such that it could be cured underwater. Test samples were prepared under different curing conditions such as dry curing and wet curing with different durations of in-water exposure. Strain gages were attached to all samples. The samples were tested for both tensile and four-point bending loads. Furthermore, numerical modeling and simulations were conducted, and the numerical models were validated against the experimental measurements. Then, the interface normal and shear stresses were determined from the numerical models so as to understand the delamination failure at the interface between the aluminum and composite patches. Underwater composite patching showed good interface strength and potential for successful usage in repairs.
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