J042042 非線形三波相互作用法による金属材料の疲労過程中の非線形超音波挙動の変化

Abstract

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.