SHMThe mechanical damage of centrifugally cast austenitic stainless steel (CCASS) under tensile stress was quantitatively evaluated by the electro-mechanical impedance (EMI) technique. The influence of loading profiles on the impedance results was investigated. Two frequency bands, 25-65 kHz and 72-112 kHz, were selected and scanned during the intervals of mechanical testing. The resonance frequency shift Δf and root-mean-square deviation (RMSD) of electrical impedance signatures under different damage states were extracted as damage identification indexes. Results show that Δf and RMSD had a good correspondence with the evolution of mechanical damage. In other words, they had small values at the elastic deformation stage, which increased rapidly after the transition to plastic deformation. Δf had an approximately linear relationship to the nominal tensile stress, increasing from about 0.05 to 1.65 kHz until the final failure. The evolution of RMSD values, however, depended on the testing frequency band. The reason for this difference was discussed comprehensively. The impedance results under different loading conditions demonstrated that holding the load in the plastic deformation stage would lower the resonance frequency and thus conceal the genuine damage evolution if the impedance testing was conducted simultaneously. Nevertheless, the influence of elastic deformation under tensile stress was small for the 3 mm-thick CCASS plate.

The mechanical damage evaluation of Z2CN18.12N welding joint with Lamb wave was concerned in this study. The excitation parameters were optimized from the aspects of number of cycles, central excitation frequency, and the electric fields excitation profiles of the piezoelectric transducers. Moreover, the influence of the mechanical clamping was also analyzed. Results show that the enhanced anti-symmetric wave mode under the anti-symmetric electric fields excitation was better regarded as the excitation signal and the optimum excitation parameters had a strong dependence on the mechanical clamping, which should be carefully considered. The corresponding waveforms under the optimum parameters could be clearly defined and separated with each other very well. This would provide a basis for the future study of online monitoring and evaluation.