Papers by Keyword: Ultrasonic Peening

Abstract: Fatigue cracks mostly initiate at areas subjected to high tensile residual stress and stress concentration. Ultrasonic peening is a mechanical method to increase fatigue life by imparting compressive residual stress. In this study residual stresses are characterized in fillet welded ship structural steel plates with longitudinal attachments. As-welded, ultrasonically peened, and specimens peened then subjected to accelerated corrosion testing were measured. Residual stress characterization was performed by the contour method and neutron diffraction.

Abstract: TIG dressing combined with ultrasonic peening was conducted on low-strength steel Q235B in this paper, the fatigue strength of which was compared with original welding state, TIG dressing and ultrasonic peening respectively. The results indicate that fatigue strength of welded joints treated by TIG dressing is increased by 36%, composite processing method 57% and ultrasonic peening 56%, with little difference between composite processing method and ultrasonic peening in loading condition R=0.1. Stress concentration factor at weld toe treated by composite processing method is less than that by ultrasonic peening and with less residual compressive stress relief, the former is more effective in improving fatigue life at high stress level. Residual compressive stress at weld toe treated by composite processing is close to ultrasonic peening method and the effect of stress concentration is weakened, the two methods don’t appear to be much different.

Abstract: Undercuts often exists in the surface at weld toe. Undercuts affects the capability of weld subjected to dynamic loading greatly and fatigue cracks usually initiate from these zones with undercuts. Combining with low-alloy middle strength steel 16Mn，study of increasing the fatigue strength and the fatigue life was carried out. Compared with specimen without defects, the fatigue strength of specimen with undercuts has been increased by 10~20%. Study also shows that comparing with as-welded specimen with defects, with TIG dressing treatment, fatigue strength of cruciform weld joint of steel 16Mn has been increased by 70%, fatigue life by 5~8 times. Compared with as-welded specimen without defects, fatigue strength has been increased by 34%, fatigue life by 3~4 times. Undercuts have no adverse effects on fatigue property of welded joints under TIG dressing.

Abstract: The fatigue tests of Q235B steel unload longitudinal fillet welded joints containing high welding residual stress were carried out. And the effect of welding residual stress on fatigue performance of the welded joints treated by ultrasonic peening has been studied. Specimens were divided into four groups: as welded, specimens treated by ultrasonic peening(UP), specimens treated by stress relief treatment(SRT) and specimens treated by both ultrasonic peening and stress relief treatment(UP+SRT). Test results show that the effect on fatigue performance of the welded joints treated by ultrasonic peening from welding residual stress is small. It is safe that using the small specimens treated by ultrasonic peening and not containing high welding residual stress to appraise the fatigue performance improvement on large-scale welded structures which are as the same junction style and thickness as the small.

Abstract: The surface of U70 rails was treated by ultrasonic peening method. Keeping the electric current 1.5 A, the amplitude 24 µm and the frequency 10000 HZ during the treatment, the peening duration was 10 min, 20 min, 40 min and 60 min respectively. The wear property, wear appearance, and structural appearance of specimens have been studied by M-2000 wear tester and 6360LA scanning electron microscope. Results show that ultrasonic peening treatment can significantly improve the wear resistance of U70 rails, and the longer the peening duration, the stronger the wear resistance. The wear mass loss of the specimen with 60 min treatment is only 27 % of the one untreated. The reason is that ultrasonic peening can form plastic deformation zones. The depth of plastic deformation zones increases with the peening duration. The depth of plastic deformation zones of the specimen with 60 min treatment is nearly 100 µm. Longer peening duration means severer plastic deformation. In the plastic deformation zone, ferrite is refined to smaller grains so that the matrix is strengthened.