Nonlinear Resonant Ultrasound Spectroscopy (NRUS) applied to fatigue damage evaluation in a pure copper

Abstract

We studied a monitoring technique of fatigue damage in 3N polycrystalline copper under a cyclic zero-to-tension loading by the nonlinear resonant ultrasound spectroscopy (NRUS). 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. We used an electromagnetic acoustic transducer (EMAT) to monitor NRUS of bulk-shear-wave propagating in the thickness direction of the plate sample. NRUS exhibits much larger sensitivity to the damage accumulation than the velocity. It rapidly increases from 70% of fatigue life to the fracture. The attenuation shows the peak at 80% of the life. This NRUS novel phenomenon is interpreted in terms of dislocation mobility. This technique has potential to assess the damage advance and to predict the fatigue life of metals.