Effect of Upset Burr on Torsional Fatigue Strength of Friction Welded Carbon Steel Joints

Carbon steel was friction welded and torsion fatigue tests were conducted on weld joints having an upset burr in order to reveal the effect of an upset burr on fatigue strength. It was found that the fatigue strength of joints having a constant toe radius decreased with a decrease in hardness ratio (hardness of toe/hardness of base material). Softened joints (hardness ratio≤1) and hardened joints (hardness ratio>1) fractured at the toe of the upset burr and in the base material, respectively. On the other hand, the fatigue strength of joints having constant hardness ratio increased with toe radius. Using correlation analysis, a reasonable multiple regression equation was obtained between torsional fatigue strength and the fatigue factors, that is, the hardness ratio and toe radius of the upset burr. Thus, using this regression equation, the torsional fatigue strength of friction welded joints having an upset burr could be estimated.