Residual stresses in welded joints may have significant effects on structural performance, and residual stress measurement supports the understanding of weld joint behavior. This paper describes two methods for measurement of weld residual stress and presents detailed descriptions of their application. Examples include a comparison of residual stress in joints made by conventional electric arc and electron beam methods as well as residual stress mitigation by thermal stress relief and laser peening surface treatment.
Although measurement of subsurface residual stress in thick sections may help to assess the structural integrity of pressure systems, there have been few methods reported in the literature capable of such measurements in a range of geometry. Neutron diffraction is one available method, but that is difficult to arrange because it requires access to a neutron source. In what follows, we discuss mechanical methods for residual stress measurement, which may be conducted using common industrial facilities.
The little data available in the literature for thick welds suggest that several characteristics of the residual stresses make their determination difficult. Perhaps the foremost challenge with such welds is the presence of high stress gradients with respect to geometry. Also, the residual stress field is always triaxial, with possibly all six components of residual stress being nonzero. Thick welded joints, therefore, present one of the most difficult residual stress distributions to measure.
The most common method of residual stress measurement is x-ray diffraction (XRD), and it has been used extensively in metallic material. The method is typically used to determine the average residual stress within a millimeter-scale round spot at the surface of a component. XRD is limited to materials with a regular periodic (crystalline) atomic structure. XRD is well understood and is supported by industrial practice standards (Noyan, 1987).
