Research Highlights: Garrison Hommer
Garrison’s research interests lie in the experimental study of multiscale and multiaxial behaviors in structural alloys. These behaviors include phenomena such as asymmetry and anisotropy, and experimental study focuses on how they can give rise to stress and strain path dependence. Macroscopically, these phenomena can be seen as stress–strain curve dependence on loading directionality and path, while they originate at the meso and microscopic levels. Material texture and grain shape contribute at the mesoscale, while crystal symmetry and associated deformation mechanisms (e.g., slip, twinning, phase transformation) contribute at the microscale. Understanding how meso- and microscale behaviors give rise to macroscopic behavior is paramount to a broad range of fields, including sheet metal formability, component life management, and material modeling. These multiscale data are collected by combining a custom planar biaxial load frame with the far-field high-energy diffraction (ff-HEDM) technique and digital image correlation (DIC). The ff-HEDM technique uses X-rays to probe the material and give nondestructive 3D data at the micro- and mesoscales, while DIC provides macroscopic strain data.
Garrison is currently studying the micromechanics of tension–tension biaxial dwell fatigue in titanium aerospace alloys used in turbine compressor discs of jet engines. Dwell fatigue is the cycling of sustained load, where each flight is a single cycle in the case of a jet engine. Dwell fatigue is known to reduce the lifetime of a component relative to fatigue without dwell periods because of titanium’s low symmetry (i.e., anisotropic) crystal structure (hexagonal close packed) and its propensity for texture regardless of processing method. This phenomenon has primarily been studied under uniaxial loading; however, turbine compressor discs experience biaxial loading during service.
G. M. Hommer, J. S. Park, P. C. Collins, A. L. Pilchak, and A. P. Stebner, “A New In Situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment,” in Advancement of Optical Methods in Experimental Mechanics, Volume 3, S. Yoshida, L. Lamberti, and C. Sciammarella, Eds. Cham: Springer International Publishing, 2017, pp. 61–70.