Fatigue Strength of Fillet Welded Joints in 80kg/mm² High Strength Steel (Report 1)

Fatigue Strength of Plate with Transverse Fillet Welded Attachments

Abstract

Fatigue tests on plates with transverse fillet welded attachments were performed to confirm the fatigue strength of fillet welds joining the web plate and stiffener of a box girder of a bridge fabricated of 80 kg/mm² high strength steel.
Pulsating tension fatigue tests have revealed the following facts:
(1) In the present test range of leg length (h) (h=8-20mm, h/T=0.34-0.82, T being the thickness of main plate), the fatigue strength of plates with transverse fillet welded attachments, is little affected by the leg length of fillet. Even beyond the present test range of leg length the effect of leg length will not be great. The 2×10⁶ cycles fatigue strength of plates with transverse fillet welded attachment, if statistically treated assuming it to be independent of the leg length, will be 13.2 kg/mm² (in terms of joint factor, βj=3.33) and 11.6kg/mm² with non-failure probability of respectively 50% and 90%.
(2) As a method for improving the fatigue strength of plates with transverse fillet welded attachments, machine-finishing of the toe of fillet weld has proved effective. Though the effect was minor for a notch radius at the toe of fillet weld p=2 mm R, the improvement amounted to 5-6 kg/mm² in fatigue strength and 3-6 times in fatigue life, at p=5 mm R.
(3) The critical fillet size (hcr) in a fillet welded tee-joint has been found to be 1.8<2hcr/T< 1.9; and thereby the 2×10⁶ cycles fatigue strength (plate stress) of it is estimated at about 10.4 kg/mm², which is lower than the fatigue strength of plates with transverse fillet welded attachments.