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Gerges Dib,Surajit Roy,Pradeep Ramuhalli,채장범 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.3
Second harmonic generation using nonlinear ultrasonic waves have been shown to be an early indicatorof possible fatigue damage in nuclear power plant components. This technique relies on measuringamplitudes, making it highly susceptible to variations in transducer coupling and instrumentation. Thispaper proposes an experimental procedure for in-situ surface wave nonlinear ultrasound measurementson specimen with permanently mounted transducers under high cycle fatigue loading without interruptingthe experiment. It allows continuous monitoring and minimizes variation due to transducercoupling. Moreover, relations describing the effects of the measurement system nonlinearity includingthe effects of the material transfer function on the measured nonlinearity parameter are derived. An insituhigh cycle fatigue test was conducted using two 304 stainless steel specimens with two differentexcitation frequencies. A comprehensive analysis of the nonlinear sources, which result in variations inthe measured nonlinearity parameters, was performed and the effects of the system nonlinearities areexplained and identified. In both specimens, monotonic trend was observed in nonlinear parameterwhen the value of fundamental amplitude was not changing.