Neutron diffraction methods for the study of residual stress fields

TLDR

The study presents a technique to measure the residual stress tensor averaged over a specified volume within a component. The method uses high‑resolution neutron diffraction to detect minute lattice‑spacing changes, infers stress from strain via anisotropy‑aware theory, and details suitable diffractometer types. Experimental validation on bent, plastically strained, and torsionally strained mild steel specimens, along with practical demonstrations on fatigue, weld, and tube‑to‑plate joints, confirms the method’s accuracy and reveals anisotropic strain responses.

Abstract

Abstract A technique is described for the measurement of the residual stress tensor averaged over a specified volume within a component. The method involves measurement of small changes in lattice spacing using high resolution neutron diffraction. The stress is inferred from these measurements of the strain, and the theory of the relationship between the two quantities is described, including the effects of crystalline anisotropy. The various types of high resolution neutron diffractometer suitable for the work are described. Experimental results validating the method are given for a simple bent bar of mild steel of known strain, a plastically strained mild steel bar, and a mild steel tube of known torsional strain. Examples of the method in practical use are given by a cracked fatigue test specimen, a double-V test weld and a weld joining a tube to a plate. A more detailed example is the anisotropic response of a polycrystalline sample under elastic and plastic strain; this is illustrated by measurements on many different Bragg reflections from a plastically strained mild steel bar.