Digital Repository, CONVEGNO IGF XXII ROMA 2013

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Numerical-experimental analysis for residual stress determination in a welded joint
G. Marannano, S. Allenza, A. Pasta, L. Fratini

Last modified: 2013-06-27


The life of a mechanical component depends on the interaction between mechanical characteristics of the
material of which it is made and to the stresses to which it is subjected.
In order to determine the total stress acting in a mechanical component, in addition to the stresses caused by external
loads imposed during the use, it is necessary to know the residual stress field resulting from manufacturing process and
often associated with non-uniform plastic deformation.
Typically, the residual stresses are not uniform throughout the deformed metallic material: these are detrimental because,
very commonly, they reduce the elastic limit of the material and cause the tendency of the component to deform during
subsequent processing.
The particularly insidious aspect of residual stress is that its presence generally goes unrecognized until after malfunction
or failure occurs.
However, even if tensile residual stress fields reduce the mechanical performance of the material by causing the onset of
brittle fracture and wear phenomena, the compressive residual stresses generally have a beneficial effect and cause a delay
of the onset and the subsequent propagation of the fatigue crack.
Experimental methods for measurement of residual stress in a mechanical component are very different, and each of them
is based on a different physical principle.
Among them, the cut-compliance (CC) is a technique introduced by W. Cheng and I. Finnie [1, 2] (and independently
from T. Fett [3] and K. J. Kang [4]) and recently it was developed by H. J. Schindler [5, 6].
The basic idea is related to create, progressively, a size increment of a small notch in order to relieve the residual stresses.
From the variation of the deformation values caused by notch growth, it is possible to calculate the residual stress
The potential of this technique have been described extensively by several authors. Prime et al. [7] have evaluated the
residual stresses in aluminum alloy sheets; Pasta et al. [8] have employed the CC technique to determine the stress intensity
factor and to study its influence on the fatigue crack propagation in Ti-6-4 joints machined by friction stir welding (FSW);
Dalle Donne et al. [9] have used the CC technique in order to determine the residual stress field in a compact tension
specimen made by FSW, obtaining good correspondence between the experimental results and literature data; Fratini et al.
[10, 11] determine the residual stress field in FSW welded joints on complex geometry components.
The accuracy of the results obtained in several applications has amply demonstrated the simplicity and effectiveness of the
cut-compliance technique. The only factor that limit the field of application of this technique is related to determine the
weight functions h(x, a) and the influence function Z(a) on the considered component.
For simple geometry components, analytical expressions of these functions can be easily found in the literature [5, 12-15],
while for components of complex geometry must be properly determined.
In the paper, a numerical and experimental study for the determination of residual stresses in a welded joint is carried out.
The specimen is made by welding together an Al 6082-T6 aluminum alloy plate and a profiled sheet with complex section. In particular, the experimental study allows to determine the trend of residual stresses in the longitudinal direction, in the
middle section perpendicular to the weld line.

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