Residual Stress Measurement
Equipment for residual stress measurement encompasses a range of measurement techniques, including X-ray diffraction, incremental hole drilling, the contour method, neutron diffraction and synchrotron X-ray diffraction.
A comprehensive materials characterisation service is now provided by StressMap.
The Contour Method
The Contour Method for measuring residual stress was first published in 2000. It involves cutting a body into two parts, measuring the deformed shape (contour) of the cut surface, and using a virtual model to infer the residual stress present prior to cutting. The current method can be readily applied to determine the direct component of the stress tensor acting normal to the cut in simple components (such as welded plates). However, the accuracy and reliability of the method is currently undefined.
Our research aims to develop and apply the Contour Method to engineering components having complex geometry, and find new ways for obtaining more than one component of the stress tensor from measurements. In addition, we are undertaking fundamental studies to determine how to restrain specimens during sectioning, how to avoid plasticity and artefacts arising from cutting, how best to measure the cut surface and how to automate analysis of the results in a reliable way.
Map of hoop residual stress in a welded pipe (25mm thick) measured by the Contour Method
Analysis of the diffraction spectra produced by the interaction of X-rays or neutrons with crystallographic materials provides a powerful non-destructive means of measuring the residual stress in engineering components at multiple length-scales. Our group led the design of one of the worlds first dedicated neutron strain scanning instruments based at the ISIS neutron facility near Oxford in the UK and we continue to have a particularly close relationship with this facility. We are also intensive users of large-scale neutron and synchrotron facilities throughout the world as well as in-house laboratory X-rays.
Our research focuses on:
- Technique development: the development, in collaboration with ISIS, of novel experimental techniques such as the use of neutron tomography imaging data to guide ND strain measurements
- Instrument development: Collaboration with ISIS on new instrument paradigms such as the proposed joint imaging and diffraction instrument (IMAT)
- Applications: The reliable extension of ND residual stress measurement to difficult critical and complex welds, such as the dissimilar metal welds common to nuclear power plant.
Codes and Standards.