Noncontact nonlinear resonance ultrasound spectroscopy for small metallic samples
Maier, Steffen Georg
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The aim of this research is to evaluate the influence of microscopic material damage to the hysteretic nonlinearity parameter, α. Therefore, this study applies contact and noncontact setup combinations of the nonlinear resonance ultrasound spectroscopy (NRUS) technique to small metallic specimen and analyzes their validity and signifi- cance. The various resonance modes of small plates (20mm x 1mm) and slender bars (10mm x 10mm x 100mm) are excited by contact-coupled and noncontact air-coupled piezoelectric transducers and a laser vibrometer detects the out-of-plane velocity of the vibrating specimen surfaces. The amount of the shift of the resonance frequency for increasing excitation levels represents the nonlinear behavior of the material. The experimental setups together with the measuring and data processing protocols are optimized and analyzed for measurement accuracy and system nonlinearity and eval- uated with the results of a thermally aged 17-PH stainless steel measurement series. The results show the advantages of noncontact over contact excitation and demon- strate the sensitivity of this NRUS technique to microstructural changes in stainless steel.