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.