抄録
In this study, we applied non-contacting NRUS (Nonlinear resonant ultrasound spectroscopy), and nonlinear three-wave interaction methods with non-contacting transducer, EMAT (Electromagnetic acoustic transducer) to evaluation of fatigue damage in pure copper plates subjected to zero-to-tension fatigue loading. They are resonance-based techniques exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. In nonlinear three-wave interaction method, two intersecting ultrasonic waves produce a scattered wave when the resonance condition is satisfied. The wave amplitude is measured. NRUS and nonlinear three-wave interaction methods exhibit high sensitivity to micro-structural change of the damaged material. They rapidly increase from 60 % of fatigue life to the fracture. The change of the nonlinear acoustics in three-wave interaction methods sensitivity is higher than that in NRUS. These noncontact resonance-EMAT measurements can monitor the evolution of the nonlinear acoustics throughout the fatigue life and has a potential to assess the damage advance and to predict the fatigue life of metals.
