Fatigue properties of FS welds with a kissing bond (bonded welds) were studied by comparing the test results of bonded welds with those of sound welds. The fatigue life of bonded welds is 21 similar to 43 times shorter than that of sound welds under the stress ratio R = 0.1, and the fatigue characteristic values of each welds have decreased from 100.24 MPa for sound welds to 65.57 MPa for bonded welds at 2 x 10(6) cycles. At the macroscopic level there is no evidence of failure by shear. The fatigue fracture revealed cracks initiated from the root tip of kissing bond. (c) 2006 Springer Science + Business Media, Inc.