Noncontact nonlinear resonant ultrasound spectroscopy to evaluate creep damage in an austenitic stainless steel

In this paper, we described an evaluating technique of creep damage in an austenitic stainless steel by the combination with an electromagnetic acoustic transducer (EMAT) and the nonlinear resonant ultrasound spectroscopy (NRUS), which was a resonance-based technique 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 was manifest by a shift in the resonance frequency. The nonlinearity with NRUS showed a peak at 50 % and a minimum at 70 % of the total creep life. This nonlinearity measurement has a potential to assess creep damage advance and predict the creep remaining life of metals.