A Literature review for the state of the art: Fatigue life extension of welded structures by peening and TIG dressing

Rapport, 2019

Fatigue is one of the most detrimental phenomena that endangers
the life expectancy of welded steel structures. weld is susceptible to
fatigue more than other parts because of the high stress concentration,
the existing weld defects and the residual stress induced by welding.
If the structure is in service, the structure might be already cracked.
Different techniques were developed to extend the fatigue life of the
structure and retrofit any existing crack, Peening and TIG remelting
are just examples. A literature study is conducted to establish
better understand on the effect of these two treatment methods their
efficiency in crack retrofitting.
The crack retrofitting experiments consist of two stages, pre-fatigue
loading and loading after treatment. The first stage requires crack
detection, different methods were investigated and the most efficient
among them is the use of local strain drop measured by strain gauges.
Peening treatment is found to be a function of the crack depth.
Retrofitting the crack when it’s still shallow results in longer fatigue
life. The treatment is found to be mainly relying on two effects: the
crack orientation and the introduced residual stress. Peening causes
a change in crack orientation which elongate the fatigue life. The
higher and deeper compressive residual stress causes retardation of
crack growth and deceleration of crack propagation.
TIG remelting is another effecitve method which can retrofit crack
deeper than peening. Its efficiency is a function of the crack depth and
the fusion depth. Usually, the fusion depth is greater than 2mm which
is greater than the peening indentation depth which hardly can reach
0.6 mm. In short, TIG is more appropriate to retrofit cracks deeper
than 1mm while Peening results in longer life if the largest crack is
shallower than 1mm.