Determination and mitigation of the uncertainty of neutron diffraction measurements of residual strain in large-grained polycrystalline material

For large-grained samples it is advantageous to perform pairs of neutron diffraction measurements at the same spatial location but rotated 180° around the geometric centre of the gauge volume as a means of minimizing the scatter coming from the random positioning of grains within the gauge volume

Plasticity in the contour method of residual stress measurement

The contour method is a powerful measurement technique that can provide two-dimensional maps of residual stress in engineering components. However, like most strain relief techniques, it can lose accuracy owing to plasticity when residual stresses have high magnitude relative to the yield strength of the material being measured. Finite element analysis is utilised to provide an insight into how plasticity introduced by material removal can influence the accuracy of the contour method. In addition the effect of component restraint during the cut is investigated and the results discussed with respect to published experimental measurements

A novel cutting strategy for reducing plasticity induced errors in residual stress measurements made with the contour method

The contour method (CM) has emerged as a valuable technique for the measurement of residual stresses (RS). The method involves cutting the sample in which residual stresses are to be measured, using wire electric discharge machining (EDM), and measuring the deformation that occurs on the newly created surface, which can be related to the residual stresses that existed beforehand. The contour method provides a full 2-D map of the stresses acting in a direction normal to the plane of the cut. It is ideally suited to measurements in power plant welds since, unlike diffraction-based techniques, it is not affected by microstructure gradients, and it is well suited to thick section components. However, as with other mechanical strain relief techniques, it is prone to errors arising from plasticity when residual stresses close to the yield strength of material are encountered. This paper describes contour method measurements in an AISI Type 316L austenitic steel three-pass. A novel cutting and restraint strategy is applied in an attempt to reduce plasticity errors following optimisation studies simulating the cutting process using the finite element (FE) method