Eliminating the Hook of the Lap Joint by Double-Side Friction Stir Welding

Hook is a typical defect of lap joint. It can induce stress concentration and is detrimental to joint strength. Thus, hook should be eliminated. In this work, by using the vertical squeezing force of the plastic material near the lap interface, we have successfully eliminated the hook by a double-size friction stir welding process. The results show that the double-side welding method can eliminate the hook in a wide parameter range. The rotating speeds ranging from 800 to 2000 rpm can effectively depress the bending of the lap interface, thereby eliminating the hook. The joint shows high strengths after the hook is eliminated. The maximum failure load of 15.195 kN is obtained when using the rotating speed of 1200 rpm. The joints show shear fracture mode when using rotating speed lower than 1200 rpm, and tensile fracture when the rotating speed is higher than 1600 rpm.