Plenary Sessions
Welcome to RSTC & Plenary Session
Tuesday, September 29, 2026 | 9:00 – 10:20 a.m. | 303A
Dr. Thomas M Holden, Northern Stress Technologies
From String and Sealing Wax to an ISO Standard: The Development of Techniques to Determine Residual Stress by Neutron Diffraction
Neutron diffraction measurements of strain in order to deduce residual stresses at depth have been made for nearly half a century on many kinds of components and materials often with great success. Given that the cost of getting it wrong can be very expensive it is useful to ask the question “What can go wrong with a neutron diffraction measurement?” The answers to this question can usefully mark the progress of the method. The lecture will deal with errors that can arise in the course of a measurement: some are quite obvious and some are more subtle. The author is qualified to answer this question since he has made many of these mistakes and sometimes even recognized trouble ahead of time. The problems of the nearly-filled gauge volume, large-grained samples and the accuracy of the method will be addressed with examples taken from experience. Both constant-wavelength and time of flight methods will be considered.
Professor Gary Schajer, University of British Columbia
Improved Spatial Resolution Within Deep-Hole Drilling Residual Stress Measurements
The deep-hole drilling method provides a very effective technique for measuring residual stress profiles through the thickness of large metallic specimens ranging in size up to several hundred mm. This capability is challenging to achieve by any other method. The method involves drilling a small diameter pilot hole through the specimen and then measuring the change in the internal diameter caused by a subsequent overcoring of the material around the hole. Classical Kirsch equations are used to calculate the residual stresses from the measured diameter changes at the various depths within the pilot hole. In this calculation, it is typically assumed that the response of the material at each depth depends only on the material at that depth, without any influence from the adjacent material. This approach works satisfactorily when the residual stresses vary smoothly with depth. However, it gives rather poor spatial resolution when detailed features are present. The present work considers the interactions between the material at each hole depth and the adjacent material and presents a practical computational method for accounting for those interactions. Example calculations demonstrate a much-enhanced ability to resolve local residual stress details.
Wednesday Plenary Session
Wednesday, September 30, 2026 | 8:30 – 10:30 a.m. | 303A
Professor Albrecht Conle, University of Waterloo
Using Cyclic Mean Stress Relaxation Data to Predict Residual Stress Changes Due to Fatigue Loading
A method for predicting the cyclic fatigue induced residual stress(RS) relaxation is proposed. Specifically, with reference to a new on-line data base for cyclic mean stress relaxation results, the key variable of fatigue “hot-spot” stress-strain hysteresis loop width (plastic strain) is estimated and used to predict the rate of expected residual stress relaxation. In the paper the similarities of the stress-strain state denoted by a measured RS, when compared to the residuals induced and followed during a cyclic mean stress relaxation fatigue test, are discussed. Examples of the expected behavior of RS states during primarily elastic fatigue loading and during plasticity at the fatigue hot spot are depicted for cold work induced RS. Finally the RS behavior of both a carburized steel case induced RS and a welded steel induced RS are documented.
Dr. Michael B. Prime, Los Alamos National Laboratory
Hidden biases and insufficient uncertainties in residual stress measurements, and clever ways to beat them
“Ignorance is not probabilistic [1].” So how can we put true uncertainty bars on measurements when we don’t know all the biases? This talk presents two recent but very different examples tackling this vexing issue for residual stress measurements.
First, incremental slitting and hole drilling require an inverse solution that suffers from a bias-variance tradeoff. Frustratingly, the significant bias is mathematically unknowable. Beghini and Grossi recently proposed an ingenious method: start with a low-bias inverse solution but plagued by high variance, then spatially average it to obtain accurate uncertainties with reduced variance (noise). We show this approach works even better than expected and then discuss the implications of spatially averaging stress measurements.
Second, neutron diffraction measurements often show insufficient uncertainties when based solely on peak-fit statistics. Fortunately, neutron measurements have a little-used physical constraint that can be exploited to test whether uncertainties are adequate. Strain measurements at different orientations must obey the strain transformation equation. In measurements on an additive friction-stir deposition component, we show that peak-fit uncertainties had to be approximately doubled to achieve agreement across strains measured at 36 orientations. We discuss how to apply this justified approach to get true uncertainties in practice using a minimal number of additional orientations.
Because residual stress measurements are used to make life-critical structural integrity assessments, applying large enough uncertainties to our measurements is essential.
1. Yakov Ben-Haim on Info-Gap theory.
Dr. Stefanus Harjo, J-PARC Center, Japan Atomic Energy Agency
Low-Temperature Deformation Mechanisms in Ultrafine-Grained Stainless Steel: Operando Neutron Diffraction
Hydrogen is attracting considerable attention as a clean energy carrier for a sustainable society. Efficient hydrogen transportation and storage often require liquid hydrogen, necessitating structural materials with excellent cryogenic performance.
FCC stainless steels are promising candidates because of their high resistance to hydrogen embrittlement; however, their yield strength at low temperatures remains insufficient. Grain refinement into the ultrafine-grained regime is an effective approach to improve the strength of metastable austenitic stainless steels, although their low-temperature deformation behavior is still not fully understood.
In this study, operando neutron diffraction combined with digital image correlation was employed to investigate the deformation mechanisms of ultrafine-grained metastable austenitic stainless steel under cryogenic conditions. Detailed results and the associated strengthening mechanisms will be presented.
IMAT Keynote
Tuesday, September 29, 2026 | 10:30 – 11:30 AM
Exhibit Hall 400ABC – Industry Forum
Moon to Mars – Artemis II Mission… Next Steps
Tyler Nester, Chief Engineer, Artemis II, NASA
Abstract: NASA’s Moon to Mars program has entered a transformative new phase. Following the March 2026 “Ignition” initiative, the Artemis architecture has been revised to work towards an accelerated mission cadence, a permanent lunar surface presence, and a parallel push towards future Mars missions. Presented from the perspective of NASA’s Artemis II Chief Engineer, this talk provides a program-level overview of the revised Artemis and Moon to Mars plans, highlights from the recently completed Artemis II flight, key lessons learned, and the next steps now underway.
On April 1, 2026, Artemis II launched four astronauts on the maiden crewed flight of the Space Launch System (SLS) and the Orion spacecraft Integrity, completing a 695,081-mile lunar flyby — farther than any humans have ever traveled — before splashing down on April 10. The mission validated Orion life support and crew operations in deep space, demonstrated manual piloting in support of future rendezvous and docking, and executed the first crewed reentry from lunar-return velocities in over fifty years. Highlights from post-flight assessments will be shared at an overview level, with a particular focus on items relevant to the IMAT community.
The talk closes with information on NASA’s path forward: the Ignition initiative; revised Artemis III objectives; the Artemis IV lunar landing and subsequent mission cadence; and longer-horizon Mars precursor activities, including the Space Reactor-1 Freedom nuclear-electric propulsion demonstration. Each of these milestones depends on materials and manufacturing advances that the IMAT community is central to delivering.
Biography: Tyler Nester is the acting Moon-to Mars Chief Engineer on the Artemis Program. He served as the technical authority for NASA’s Artemis II mission. Prior to this role, Mr. Nester served as a Senior Advisor for Production at NASA Headquarters. As part of this role, he assisted with overall programmatic and technical planning, coordination, management, and integration activities. Mr. Nester previously served as the chief of staff for NASA’s SLS (Space Launch System) Program office assisting with overall programmatic and technical planning, coordination, management and integration activities. Since joining NASA in 2010 and prior to becoming the chief of staff, Mr. Nester worked in several roles in the SLS program including serving as the manager of the SLS Integrated Flight Certification Team. Before that, he served as the associate chief engineer for the SLS Program for seven years. Prior to his civil service career at NASA, Mr. Nester worked as an analyst, a systems engineer, and a chief engineer at a NASA contractor and as a project engineer in the automotive industry. Mr. Nester earned a bachelor’s degree in mechanical engineering from the University of Illinois at Urbana-Champaign, a master’s degree in mechanical engineering from Michigan State University, and a master’s degree in business administration from Indiana University’s Kelley School of Business. He has received numerous honors and awards during his NASA career, including NASA’s Space Flight Awareness Management award, the NASA Exceptional Service Medal, and numerous special service and group awards.
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