An evaluation of residual stress distribution in welded compact tension specimens using neutron diffraction

Abstract

The neutron diffraction technique was used to determine the residual stress field in welded compact tension specimens of the aluminium-lithium alloy AA 2095. The deep penetrating characteristic of neutrons was exploited to evaluate the through-thickness variation in residual stress. Moreover, insight into the redistribution of these stresses was gained by extending a fatigue crack through the residual stress field and re-examining the stress distribution. The specimen without a crack was found to have a high compressive stress (of the order of - 135MPa) ahead of the notch. This rose to a maximum tensile stress of about 50MPa, 22 mm from the notch, followed by a drop to negative values further ahead of the notch. It was observed that the magnitude of the stresses changed on moving into the thickness of the specimen. However, the form of the graph showing stress versus distance ahead of the notch remained unchanged. When fatigue cracks of different lengths were introduced, the magnitude of the stress close to the tip first increased with crack length, before decreasing and then rising again. Nevertheless, the form of the graph remained unchanged and the stress at the crack tip remained compressive. The paper concludes that any study of the response of a component to mechanical loading involving a residual stress field must take these factors (i.e. through-thickness stress variation and stress redistribution) into consideration.

Fatigue crack propagation behaviour in thick steel weldments

“…Rading (2005) presents residual stress measurements for a different welded steel CT specimen, with different thickness, using neutron diffraction. No full field measurement is given in that work; nevertheless, in the regions where a comparison can be made, the trend of the residual stress data of Rading (2005) is similar to the present one. Mochizuki (2007) presents the through thickness variation of residual stress, obtained with the inherent strain method, for a X-shaped Crack propagation in steel weldments groove with a lower thickness and a different welding sequence.…”

“…Details concerning this residual stress measurement are available in Richter-Trummer and de Castro (2011). Rading (2005) presents residual stress measurements for a different welded steel CT specimen, with different thickness, using neutron diffraction. No full field measurement is given in that work; nevertheless, in the regions where a comparison can be made, the trend of the residual stress data of Rading ( 2005) is similar to the present one.…”

The through-the-thickness measurement of residual stress in a thick welded steel compact tension specimen by the contour method

“…An attempt at the measurement of through-thethickness data was presented in 2005 by Rading [11], which showed the residual stress distribution in smaller and thinner welded aluminium CT specimens. Neutron diffraction was used, and data for two situations was acquired: near surface and midthickness, although the technique used by Rading could, in principle, provide full field data.…”

“…Data on residual stress fields in welded CT specimens include early results obtained by the sectioning technique [6], the cut-compliance method [7], XRD [8][9][10], and more recently by the neutron diffraction technique [11]. Rading [11], dealing specifically with the through-the-thickness variation provides data only for two situations: near surface and mid-thickness; this is most likely related to the beam time necessary for the acquisition of each data point. Other measurement results are available for multi-pass welds, but with plate geometries different from CT specimens.…”