Design of Dog-Bone-Shaped Ultrasonic Vibrational Fatigue Specimen and its Application in Study on VHCF Behavior of 6063 Aluminium Alloy

Based on the design of specimen with standard hourglass shape, a modified dog-bone-shaped ultrasonic vibrational fatigue specimen was proposed and studied in this paper. The resonance length and the distribution functions of axial displacement and stress of such specimen were obtained analytically. A comparison of the very high cycle fatigue (VHCF) life of 6061 aluminium alloy with dog-bone-shaped specimen and hourglass-shaped specimen was done and it indicate that the forer is obviously lower than the latter and the data obtained by specimen with proposed shape are conservative. Then, the ultrasonic vibrational fatigue test of 6063 aluminium alloy specimen with dog-bone-shape was done, showing that the fatigue failure occured at the middle of the specimen with invariable section where has predicted maximum stress; the S-N curve descends continuously and there is no fatigue limit as the traditional fatigue conception describes; the fatigue crack grows in the form of shearing.