Ultrasonic evaluation of fatigue crack appearing at bolt joint of aluminum alloy plate

摘要

Bolted specimens of the aluminum alloy plate (A2024-T3) were subjected to fatigue testing to evaluate effects of the tightening torque on the fatigue life and the failure mode at different levels of the stress amplitude. Two modes of failure were observed, i.e. mechanical fatigue failure from the bolt hole edge in the range of small tightening torque, and fretting fatigue near the bolt hole edge in the range of higher torque regardless the stress amplitude. Then the in-process ultrasonic measurement was carried out with the surface acoustic wave to detect initiation and propagation of a fretting crack of the bolted specimen during the fatigue testing. During the fatigue process, the intensity of the scattering wave gradually increased at the fretted region ahead of a bolt hole with the number of fatigue cycles. It was assumed that the fretting crack appeared at the edge of the fretted area when the average intensity of the scattered wave reached a critical value.