Sam Luther, Ph.D. - Associate - Materials and Corrosion Engineering

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Academic Credentials

Ph.D., Welding Engineering, The Ohio State University, 2022
M.S., Welding Engineering, The Ohio State University, 2020
B.S., Welding Engineering, The Ohio State University, 2016

Professional Honors

University Nuclear Leadership Program Research and Development Grant, U.S. Nuclear Regulatory Commission, 2022-2025
1st Place, International Metallographic Contest, 2019
Graduate Research Fellowship, American Welding Society Foundation, 2018-2021
Distinguished University Fellowship, The Ohio State University, 2016-2017, 2021-2022

Professional Affiliations

American Welding Society – AWS
ASM International
The Association for Materials Protection and Performance – AMPP

Dr. Luther's expertise is in metallurgy, welding, and integrated computational and materials engineering. He has experience and knowledge with a range of alloy systems critical to petrochemical, nuclear, and renewable energy industries.

Dr. Luther received his Ph.D. degree in Welding Engineering from The Ohio State University. He has expertise in failure analysis, advanced materials characterization, and electron microscopy. Dr. Luther's knowledge is applied in failure analysis and development of mechanistic models for failure phenomena. His research interests are in metallurgical data analysis and the development of machine learning and artificial intelligence models in materials science.

Before joining Exponent, Dr. Luther's dissertation research at OSU focused on quantification of the susceptibility to ductility-dip cracking (DDC) in nickel-based alloys for the nuclear energy industry. This self-proposed research was funded by the American Welding Society's Graduate Research Fellowship and OSU's Distinguished University Fellowship. Experimental work included automated robotic welding, high-temperature mechanical testing, and metallographic analysis via visible light and electron microscopy techniques including EDS and EBSD. Data analysis of the mechanical testing led to his development of a new computational method involving the correlation of imposed mechanical energy to DDC in highly restrained welds. Dr. Luther also characterized thermal faceting on DDC fracture surfaces to an unprecedented level of detail, which included atomic-scale TEM imaging, and provided key steppingstones for the future of studying and mitigating a failure mechanism which has been challenging scientists for over 100 years.

In addition, while at OSU, Dr. Luther contributed his expertise to projects involving hydrogen-induced cracking in duplex stainless steels, dilatometry analysis of advanced high strength steels, and characterization of liquation cracking/DDC in low alloy steel-to-nickel-based alloy dissimilar welds.

Aside from research experience, Dr. Luther has also served as a graduate teaching assistant for both undergraduate and graduate level materials science and welding engineering courses at OSU.

Dr. Luther has utilized materials science and engineering knowledge combined with programming and data analysis to develop novel and modern solutions to longstanding weldability challenges in high-chromium nickel-based alloys. This project began with an FEA model of a highly-restrained weld combined with a real-world weld mockup developed by collaborating researchers in a past study. The model was re-visited and stress/strain data from the weld cross-section were extracted for further calculations. The principle of imposed mechanical energy (IME), or integration of the stress-strain curve, was applied at each node in the weld cross-section and data were classified by temperature range to isolate the activity of key mechanisms contributing to DDC. The results support the hypothesis that DDC temperature range IME nucleates voids, low temperature IME grows voids into cracks, and high temperature IME mitigates cracking via inducing recrystallization.

In another project in his dissertation research, Dr. Luther designed a thermomechanical testing procedure which induces DDC in materials using methods more similar to production conditions than past work. Through these experiments, fracture surfaces were obtained which exhibit thermal faceting. This was a novel discovery in relation to DDC and provoked an in-depth characterization analysis via TEM. Dr. Luther collaborated with a team of experts at OSU's Center for Electron Microscopy and Analysis (CEMAS) to measure nanoscale crystallographic and compositional features of this thermal faceting. Highlights of the findings include near defect-free microstructure and atomically sharp corners in the nanoscale thermal facets. These findings are the next step in understanding the DDC mechanism and have attracted the interest of the Nuclear Regulatory Commission, who will be funding a $500,000 research grant awarded to OSU for the continuation of Dr. Luther's research.
Luther S, Alexandrov B, McCracken S, Tatman J. "Correlation of imposed mechanical energy with ductility-dip cracking in a highly restrained weld of Alloy 52." Journal of Manufacturing Processes 2022, 79:767 — 88.
Luther S, Alexandrov B. "Recreating Ductility-Dip Cracking via Gleeble-Based Welding Simulation." Welding Journal 2021, 100:27 — 39.
Presentations
Luther S, Bott J, Kirchhofer R, Smith L, Templeton B. Failure Investigations of Three Unique Brittle Failure Mechanisms in Steel Timber Fasteners. Presentation, International Materials Applications and Technologies Conference, Detroit, MI, 2023.
Luther S., Alexandrov B. Thermal Faceting on the Ductility-Dip Cracking Fracture Surfaces of Nickel-Based Alloys — Occurrence, Characterization, and Implications for the Cracking Mechanism. Presentation (Invited), Fabtech Professional Program, Chicago, IL, 2023.
Luther S, Alexandrov B. Effect of Sulfur on Microstructural Evolution Prior to Ductility-Dip Crack Nucleation in Inconel Alloy 690. Presentation, Advances in Welding and Additive Manufacturing Research, Online, 2022.
Luther S, Alexandrov B. Mapping Imposed Mechanical Energy in a Multipass Weld to Correlate with Ductility-Dip Cracking. Presentation and Poster, Fabtech Professional Program, Online, 2021.
Luther S, Alexandrov B. Using Imposed Mechanical Energy as a Metric to Correlate Sysweld Model of Multipass Welding to Gleeble Simulation. Presentation and Poster, Fabtech Professional Program, Online, 2020.
Luther S, Alexandrov B. Using Fixed-Displacement Thermal Cycling to Simulate Welding Thermo-Mechanical Histories Leading to Ductility-Dip Cracking. Presentation and Poster, Fabtech Professional Program, Chicago, IL, 2019.
Luther S, Alexandrov B. Thermal Faceting in Austenitic Weld Metal During Multipass Welding. Presentation and Poster, Fabtech Professional Program, Atlanta, GA, 2018.
Luther S, Alexandrov B. Quantification of the Susceptibility to Ductility-Dip Cracking in Welds of Ni-Based Alloys. Presentation, Materials Science & Technology, Columbus, OH, 2018.
Luther S, Alexandrov B. Quantification of the Susceptibility to Ductility-Dip Cracking in Welds of Ni-Based Alloys. Presentation, International Conference on the Strength of Materials, Columbus, OH, 2018.
Luther S, Alexandrov B. Quantification of the Susceptibility to Ductility Dip Cracking in Weld overlays of Ni-Based Alloys. Presentation, Fabtech Professional Program, Chicago, IL, 2017.
Luther S, Alexandrov B. Characterization of Cracking in Nickel-Based Alloy Overlays. Presentation, Materials Science & Technology, Pittsburgh, PA, 2017.
Luther S, Alexandrov B. Quantification of the Susceptibility to Ductility Dip Cracking in Weld overlays of Ni-Based Alloys. Presentation, EPRI Welding and Repair Technology Conference, Orlando, FL, 2017.

Sam Luther

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