Engineering model for the quantitative consideration of residual
stresses in fatigue design of welded components
Received: 3 November 2016 /Accepted: 29 March 2017 / Published online: 25 April 2017
International Institute of Welding 2017
Abstract Residual stresses are one of the major factors
influencing the fatigue strength of welded components.
However, the current IIW bonus factor concept for the mean
stress correction is limited to a qualitative evaluation of resid-
ual stress effects. By combining residual stress measurements
and fatigue testing, the authors derive an improved bonus
factor concept that considers residual stresses quantitatively.
The proposed concept considers the combined effect of load
mean stresses and cyclically stabilized residual stresses. It is
pointed out that the yield strength is not a capable measure to
determine whether residual stresses have Blow^ or Bextreme^
impact on the fatigue strength of welded steels. It is rather
recommended to evaluate residual stress effects based on the
effective stress ratio reflecting local loading conditions.
Keywords (IIW Thesaurus) Welded joints
Residual stresses may have severe influence on the fatigue
strength of welded components. The current IIW recommen-
dations for fatigue design of welded structures assume high
tensile residual stresses conservatively . This accounts for
unknown residual stress conditions from manufacturing such
as welding and on-site mounting. The fatigue design S-N
curves within this IIW recommendation are provided for high
tensile mean stresses accordingly. Thus, local mean stresses
present in real stresses and its effects are normally neglected.
However, this guideline provides a bonus factor concept for
the consideration of mean stress effects if more detailed infor-
mation on the real residual stress condition is available. The
bonus factor for the enhancement of the design reference fa-
tigue strength (FAT) ranges from 1 to 1.6 depending on the
residual stress conditions (Blow^, Bmoderate^,extreme^). This
concept works well in theory, but in practice it is very hard to
classify the present residual stress state in one of these groups.
Consequently, residual stresses may be overestimated and this
concept may result in overconservative fatigue designs.
Another problem with classifications of residual stress con-
ditions in Blow^, Bmoderate^ and Bextreme^ is that these groups
are most often related to the yield strength of the construction
material. It was shown earlier that the yield strength is not a
capable measure for residual stress generation or residual stress
effects . The magnitude of residual stresses is not as impor-
tant as their stability under service loading conditions.
Nowadays, the mechanisms of residual stress generation from
welding are well understood [3–6]. Residual stresses can be con-
trolled to some extent through the manufacturing chain by con-
trolling heat input, shrinkage constraints and adaption of weld
procedures. Alternatively, post-weld heat treatment methods are
available to reduce tensile residual stresses or to generate com-
pressive residual stresses . Further residual stresses from
manufacturing can be examined by structural designers by means
of experimental or numerical methods efficiently. Consequently,
structural designers demand for a design concept that allows to
consider real residual stress states within the design process rather
than to use vague residual stress classifications.
Recommended for publication by Commission XIII - Fatigue of Welded
Components and Structures
* Jonas Hensel
Institute of Joining and Welding, TU Braunschweig,
Weld World (2017) 61:997–1002