Research has been initiated on the application of weld improvement methods to increase the fatigue life of offshore wind energy plants and other fatigue loaded structures. The effect of the application of Ultrasonic Peening (UP) and Ultrasonic Impact Treatment (UIT) has been compared to the effect of shot peening. Further investigations focussed on the improvement effect of UP on preloaded details whereas preloading has been defined as the application of the full design fatigue loading. The fatigue tests prove that the three analysed improvement methods lift the fatigue strength of virgin and also of preloaded welded notch details strongly.
In offshore engineering often the fatigue of welded details is relevant for the design. Due to their exposure to wind and wave loads they are highly fatigue loaded structures so that the fatigue design is decisive. Therefore, the need of new methods to increase the fatigue strength of those details increases.
Off- and onshore wind energy plants are designed for a service life of 20 years. The first wind energy boom started in the 80s so that a large number of wind energy plants will reach their designed service life in the coming years. Due to economical reasons a lot of those plants should remain in service despite of a certain amount of repowering. Both, builders and operators, are interested in the increase of the life time, on the one hand to increase the return of invest, and on the other hand to improve the competitiveness of this form of alternative energy. This leads to the need of methods to increase their service life in the next years.
The most critical notch details of those cyclic loaded structures are welded joints. Therefore the use of weld improvement methods seem to have promising benefits.
