Ultrasonic detection of fretting fatigue damage at bolt joints of aluminum alloy plates

The fatigue failure evaluation was carried out to determine the effect of the tightening torque of the bolt on the failure mode and the fatigue life of bolted joints of aluminum alloy plates 2024-T3 at different levels of the stress amplitude. These results were shown in the tightening torque and fatigue life diagram. Regardless the stress amplitude, when the tightening torque is relatively lower the mechanical fatigue failure occurred at the edge of the bolt hole, and the fatigue life increased with the tightening torque. When the tightening torque is increased further, the fretting wear failure occurred near the bolt hole due to the gross sliding of the specimen surface, and the fatigue life increased with the increase in tightening torque. At a higher range of tightening torque, the fatigue life decreased with the increasing tightening torque, and the fretting fatigue failure occurred near the bolt hole. A tightening torque boundary between the fretting failure and the mechanical fatigue increased with increasing stress amplitude. The ultrasonic measurement with surface acoustic wave was also carried out during the fatigue testing, and the echo reflected from the fretting fatigue crack was detected at a position 1.8–2.1 mm ahead of the bolt hole in the fastened condition.