Abstract
The influence of weld-improving method on fatigue strength enhancement and thickness effect was studied through the experiments on fillet-welded Tee joints under bending stress. To clarify the thickness effect of improved joints, fatigue tests for three kinds of improving methods such as toe grinding, TIG dressing, shot peening were carried out on the joints with thicknesses of 10, 22, 40 and 80 mm. Furthermore, five kinds of weld treatments were applied on 40 mm thick joints to investigate enhancement in fatigue strength. These results were compared with that of as-welded joints. In addition to the experiment, finite element analyses (FEA) were conducted on both Tee and cruciform joints to study the effect of stress distribution.Main results of the study are summarized as follows ;(1) The thickness effect for toe grinding is smaller than that of the as-welded joints. TIG dressing and shot peening have almost the same thickness effect as that of the as-welded joints.(2) The thickness effect exponent of effective stress concentration factor by FEA well corresponds to that of experiments, and explains the difference between the as-welded and toe-ground joints. The thickness effect for fatigue crack propagation life by analysis is rather small.(3) Not only the main plate thickness but the rib plate thickness should be considered in the evaluation of thickness effect. This combined effect can be expressed by a multiplication form of thickness effects for main plate and rib plate.(4) The fatigue strength of the toe-ground joints is highest among all the test series. The enhancement in fatigue strength by weld improvement is mainly due to the increase of fatigue strength for crack initiation.
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