Quantitative electro-mechanical impedance evaluation of tensile damage to austenitic stainless steel
The 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.
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Document Type: Research Article
Publication date: January 1, 2013
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- Official Journal of The British Institute of Non-Destructive Testing - includes original research and devlopment papers, technical and scientific reviews and case studies in the fields of NDT and CM.
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