Effect of ultrasonic fatigue testing method on fatigue properties and crack initiation mechanism of S06 steel

To research the effect of ultrasonic fatigue method on fatigue properties and initiation mechanism, fatigue properties of S06 steel were tested by using ultrasonic fatigue testing machine and high-cycle fatigue testing machine. Fatigue life of ultrasonic fatigue specimens is longer than high-cycle fatigue specimens, and it may be attributed to b. c. c. crystals structure of S06 steel and chemical reaction at crack tip. Fatigue cracks of ultrasonic fatigue specimens originate from surface and cracks of high-cycle fatigue specimens originate from both surface and interior. The effect of ultrasonic fatigue method on initiation mechanism may be attributed to looseness of surface residual stress during ultrasonic fatigue testing.