GARRISON HOMMER, PHD

RESEARCH FOCUS

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.

In his PhD work, Garrison studied 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. His PhD research was funded by the Center for Advanced Non-Ferrous Structural Alloys (CANFSA). Collaborators included Adam Pilchak of the Air Force Research Laboratory and Peter Collins of Iowa State University.

PUBLICATIONS

1. G.M. Hommer, A.L. Pilchak, A.P. Stebner (2018) Normalized Resolved Shear Stress Calculations for Single Crystals Subjected to Multiaxial Loading. Materialia, https://doi.org/10.1016/j.mtla.2018.06.009.
2. L. Casalena, A.N. Bucsek, D.C. Pagan, G.M. Hommer, G.S. Bigelow, M. Obstalecki, R.D. Noebe, M.J. Mills, A.P. Stebner (2018) Structure-Property Relationships of a High-Strength Superelastic NiTi–1Hf Alloy. Advanced Engineering Materials, https://doi.org/10.1002/adem.201800046.
3. G.M. Hommer, J.S. Park, P.C. Collins, A.L. Pilchak, A.P. Stebner (2017) A New In Situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment. In: Yoshida S., Lamberti L., Sciammarella C. (eds) Advancement of Optical Methods in Experimental Mechanics, Volume 3. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham.
4. R.W. Wheeler, O. Benafan, X. Gao, F.T. Calkins, Z. Ghanbari, G.M. Hommer, D. Lagoudas, A. Petersen, J.M. Pless, A.P. Stebner, and T.L. Turner (2016) Engineering Design Tools for Shape Memory Alloy Acutators: CASMART Collaborative Best Practics and Case Studies. Volume 1: Multifunctional Materials; Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Structural Health MonitoringASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Stowe, Vermont, USA, Sept. 28–30, 2016.
5.  G.M. Hommer, A.P. Stebner (2016) Development of a Specimen for In-Situ Diffraction Planar Biaxial Experiments. In: Beese A., Zehnder A., Xia S. (eds) Fracture, Fatigue, Failure and Damage Evolution, Volume 8. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham.

PRESENTATIONS

1. G.M. Hommer, J.S. Park, P.C. Collins, A.L. Pilchak, A.P. Stebner, “Micromechanics of Biaxial Cold Dwell Fatigue in Ti-7Al Using Far-Field High-Energy Diffraction Microscopy,” July 2018, The 18th International Conference on the Strength of Materials (ICSMA), Columbus, OH.
2. G.M. Hommer, A.P. Stebner, A.L. Pilchak, “Micromechanical study of biaxial dwell fatigue in Ti-7Al using in situ far-field high energy diffraction microscopy (ff-HEDM),” July 2017, The Advanced Photon Source User Science Seminar, Lemont, IL. Invited
3. G.M. Hommer, A.P. Stebner, A.L. Pilchak, “A New in situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment: Application to Micromechanics of Biaxial Dwell Fatigue in Ti-7Al,” June 2017, CHESS Users’ Meeting, Ithaca, NY. Keynote
4. G.M. Hommer, J.S. Park, P.C. Collins, A.L. Pilchak, A.P. Stebner, “A New in situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment,” Oct. 2016, Society of Engineering Science 53rd Annual Technical Meeting, College Park, MD.
5. G.M. Hommer, A.P. Stebner, A.L. Pilchak, “A New in situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment,” Aug. 2016, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH. Invited
6. G.M. Hommer, A.P. Stebner, A.L. Pilchak, J.S. Park, J.D. Almer, P.C. Collins, J. Vignes, S. Lemmer, “A New In-Situ Far-Field High Energy Diffraction Microscopy Planar Biaxial Experiment,” July 2016, 3rd International Congress on 3D Materials Science, St. Charles, IL. Awarded 2nd Place, Student Poster Competition
7. G.M. Hommer, J.S. Park, P.C. Collins, A.L. Pilchak, A.P. Stebner, “A New in situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment,” June 2016, The Advanced Photon Source User Science Seminar, Lemont, IL. Invited
8. G.M. Hommer, J.S. Park, P.C. Collins, A.L. Pilchak, A.P. Stebner, “A New in situ Planar Biaxial Far-Field High Energy Diffraction Microscopy Experiment,” June 2016, Conference and Exposition on Experimental and Applied Mechanics, Orlando, FL.
9. G.M. Hommer, J. Baca, E. Graves, D. Kirk, A. Petersen, L. Shade, A.P. Stebner, “CASMART Design Challenge: Team SPB Solar Array,” Sept. 2015, ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Colorado Springs, CO. Consortium for the Advancement of Shape Memory Alloy Research and Technology Student Design Challenge Award
10. G.M. Hommer, A.P. Stebner, “Planar Biaxial Specimen Design for In Situ Diffraction Experiments,” June 2015, Conference and Exposition on Experimental and Applied Mechanics, Costa Mesa, CA.
11. G.M. Hommer, A.P. Stebner, “Planar Biaxial Specimen Design for In Situ Diffraction Experiments,” Apr. 2015, Colorado School of Mines Mechanical Engineering Student Seminar Competition, Golden, CO. Awarded Best Presentation