Online remaining fatigue life estimation of curved steel connection using nonlinear ultrasonic modulation

An online monitoring technique was developed to continuously estimate the remaining fatigue life of a padeye. Piezoceramic ultrasonic transducers were surface-mounted on the padeye for ultrasound generation and sensing. A fatigue index is defined and calculated from the experimentally measured nonlinear ultrasonic modulation components. The fatigue index is also derived as a simple power function of the loading cycles based on the Nazarov–Sutin and Paris–Erdogan theories. Then, the remaining fatigue life is estimated and continuously updated by fitting the power function to the ultrasonic modulation data accumulated up to the present time.