A Methodology for Designing Fatigue Resistant Materials

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This research project is centered around novel sets of in-situ mechanical loading / synchrotron x-ray diffraction experiments aimed at understanding evolving micromechanical states associated with microcrack initiation in multiphase metallic alloys. In these tests, lattice strains will be measured during cyclic loading and a methodology will be developed for attaining strains over a vast expanse of x-ray scattering directions for many different families of lattice planes. These data are crucial to the development of a simulation environment referred to as the Digital Material Through a collaboration with researchers working at the forefront of x-ray detection technology (Professor Sol Gruner's group at Cornell), a unique set of highly time resolved in-situ experiments will be conducted that will have exposures on the order of microseconds. By taking exposures over several cycles out of several thousand cycles, it will be possible to produce lattice strain "snapshots" during cyclic loading, which will create a "real time" link to the evolving mechanical state on the size scale of a metallic grain - exactly what we need to begin to understand microcrack initiation. The project will begin by examining model iron / copper alloys - ideal for this study due to their mutual insolubility and distinct property differences, but will eventually center on several Aluminum/Beryllium alloys - which are also virtually insoluble. In addition, the attenuation lengths for these materials are much smaller than the Fe/Cu so a thicker specimen - crucial for cyclic experiments - and lower x-ray energies will be possible. The educational goals of this project are based on enabling mechanical engineers to employ their design training within the materials engineering arena. This project will also greatly expand the conventional experimental repertoire that most engineering students possess. The students working on this project will learn to think of facilities like synchrotron beam lines as a place to conduct standard characterization experiments. The Brush Wellman company and Los Alamos National labs will partner with Cornell in the fabrication of the Al/Be specimens. Alloys at several phase fractions will be produced. The experimental program is one aspect of the material representation system referred to as the Cornell Digital Material. This project will initiate the creation of a Digital Material representation aimed at accelerating the design and implementation of fatigue resistant materials.