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

Abandoning the Notion of Measured Stress as a Point Quantity to Remove “Unknowable” Bias in Residual Stress Inverse Solutions

Although it is not always recognized, almost all residuals stress measurement methods require an inverse solution to analyze the data, and inverse solutions suffer from a bias-variance tradeoff. The bias is mathematically “unknowable” and often at least the same magnitude as the variance. Therefore, and unfortunately, just the variance is often reported as the total uncertainty, but it significantly underestimates the true total uncertainty. Beghini and Grossi recently proposed an ingenious method to spatially average a low-bias high-variance inverse solution to get an accurate uncertainty without noisy results. In this talk, their method is checked on the incremental slitting method using various data sets to show that, indeed, the bias is avoided and the uncertainty is accurate. The implications of stress measurements being averaged over some volume, rather than defined at a point, are examined. In most cases, the effects of residual stress are an integral effect over some volume anyways, so the implications are minimal. The payoff of an accurate uncertainty is extremely beneficial.

 

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.