Ultrasonic resonance spectroscopy (URS) utilizes information in the frequency domain obtained due to the constructive and destructive interference of elastic waves for nondestructive evaluation of inspected objects. In a resonance test an ultrasonic tone-burst with sweeping frequency is applied to an ultrasonic transducer and a resonance spectrum of the inspected structure is acquired. The method based on tracing resonance frequency of a resonant transducer using a PLL circuit was developed and examined. It appeared that its sensitivity in more demanding applications was unsatisfactory. An alternative method based on sensing probes electrical impedance was developed and verified using CFRP specimens with artificial and natural defects. NBS tests of layered structures performed using a narrowband transducer require proper choice of transducer and its resonance frequency. Today, this choice is performed ad hoc, based on operators experience and some recommendations from the instrument manufacturer. The theoretical model of the multi-layered structure including the piezoelectric transducer presented in the paper makes this choice much easier and enables maximization of the transducer indication with respect to the parameters of the inspected structure. The model enables accounting for the effects of natural variations in dimensions and material properties as well as optimizing sensitivity of the NBS transducer to defects. Simulation results obtained using the presented model were used to explain the principle of narrowband inspection of multilayered structures. The simulation results were verified by measurements performed using a network analyzer. Preliminary mechanized tests performed on selected specimens yielded very promising results; the proposed method was capable of detecting artificial delaminations in CFRP of different thicknesses as well as natural impact defects.
Narrowband ultrasonic spectroscopy for NDE of layered structures
Schmalbandige Ultraschallspektroskopie zur ZfP von Schichtstrukturen
2004
8 Seiten, 8 Bilder, 7 Quellen
(Nicht paginiert)
Conference paper
Storage medium
English
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