LETS Global continuously participates in projects where the application of ultrasonic peening is further investigated and documented.
Here we present a selection of some of the latest projects where LETS Global has contributed with the application of the ultrasonic peening to different types of fatigue test specimens. The results shows constantly an improvement in fatigue life of four times.
Fatigue behavior of high-strength steel welded joints in offshore and marine systems (FATHOMS)
Fatigue test results of ultrasonic peening treated FCAW welds (FATHOMS)
In Figure 50 the effect of ultrasonic peening applied on FCAW welds is shown. Fatigue tests were performed mainly at high stress ratio, R=0.5, in order to investigate the beneficial effect of the postwelding treatment on fatigue performances in more strict conditions close to the in service ones. It is noticeable that the treatment improves fatigue behavior for both X100 and X70 welds. This was expected, as the residual stresses after the treatment, as shown in WP2, results strongly compressive. In Figure 51 the results in post-welded specimens are compared with the promising results obtained on LH joints. According to the number of tests performed in the frame of the current project it seems that the use of ultrasonic peening (UP) leads to better fatigue performance of the joints with respect to the Laser Hybrid welding technique applied in the root pass. Nevertheless it should be underlined that the performance of the post welding treatment requires additional time before laying the joint in the sea bed and this should be taken into account when considering the potential benefits achievable.
Fatigue life assessment of bridge details using finite element method
Fatigue test results of ultrasonic peening treated cope-hole specimens
The UP treated specimens also show a good performance. The statistical evaluation of the UP treated specimens, with a fixed slope of 3, reveals a characteristic fatigue strength of 133.6MPa accompanied by a standard deviation of 0.150. This indicates a fatigue life extension of approximately 4.2 times compared to the as-welded specimen. Finally, it should be noted that, the nominal stress for the specimens is defined as the total calculated force in main-plate at the midsection of cope-hole using a 3D solid FEM model divided by its area.