Nonlinear vibro-ultrasonics for detection of damage and weak bonds in composites

Dunn, Mitchell

doi:10.14264/uql.2018.209

Cited by 3 publications

(22 citation statements)

References 81 publications

(174 reference statements)

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“…However, this could be simply explained if 250 kHz corresponded to a system resonance, therefore resulting in a higher excitation amplitude and hence detection. When beam deflection, as opposed to applied voltage, is used as the independent variable (Dunn et al, 2017b) these effects tend to disappear (Dunn, 2017a). Based on experimental results Klepka, Pieczonka, W.J.…”

Section: An Interesting Results Comes Frommentioning

confidence: 99%

“…Therefore, it is possible that the point at which nonlinearity becomes detectable simply coincides with the point at which defects become macroscopic. While a good argument, it appears that experimental evidence disagrees and relationships between applied excitation and sidebands is typically linear (Carcione, Blanloeuil, Rose, et al, 2019;Dunn, 2017a), at least for the excitation domain that has been used. In any case, the 'turning-on' of nonlinearity at certain combinations of excitation parameters is likely a result of experimental measurement limits.…”

Section: An Interesting Results Comes Frommentioning

confidence: 99%

“…In any case, the 'turning-on' of nonlinearity at certain combinations of excitation parameters is likely a result of experimental measurement limits. Therefore, while experimental evidence suggests that there might exist a minimum threshold for the detection of nonlinearity, care should be taken not to confuse experimental detectability limits with the fundamental limitations of Figure 2.20: Modulation index versus (a) applied excitation amplitude and (b) beam deflection amplitude (Dunn, 2017a), beam ω n ≈ 52 Hz (Figure 2.13) nonlinear methods.…”

Section: An Interesting Results Comes Frommentioning

confidence: 99%

“…Staszewski, 2006;Croxford et al, 2009;, and ultimately nonlinear methods also seek to allow the detection of weak and kissing bonds. While substantial progress has been made (Zaitsev and Sas, 2000;Alston et al, 2018;Dunn, 2017a) reliable detection of these types of defects has been a substantial challenge.…”

Section: Vibro-acoustic Methodsmentioning

confidence: 99%

“…. 2.20 Modulation index versus (a) applied excitation amplitude and (b) beam deflection amplitude (Dunn, 2017a), beam ω n ≈ 52 Hz (Figure 2.13…”

Section: 19mentioning

confidence: 99%

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An investigation into novel techniques for nonlinear NDT measurements and their applications

Carcione¹

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Non-Destructive Testing (NDT) encompasses a diverse field of techniques that can be used to detect the presence of damage in mechanical components and parts. Among these techniques, ultrasonic pulse echo NDT is the most common method used to detect damage. Conventional ultrasonic NDT utilizes piezoelectric transducers to send and receive pulses of acoustic energy into a part. The interaction of these elastic waves with material defects can be measured as small amounts of reflected energy. However, current methods have significant limitations when it comes to defects such as micro-cracks, closed cracks or weak bonds. It is recognized that nonlinear acoustics methods can be used for the detection of early stage damage and material defects that are generally undetectable with traditional methods. One of these methods is nonlinear wave modulation also referred to as nonlinear vibro-acoustics. In this technique a sample is excited at two distinct frequencies, known as pumping and probing waves. The pumping wave is normally between 10-1000 Hz and the probing wave is in the ultrasonic range. Interactions with defects, such as cracks or weak bonds, causes intermodulation of these two frequencies due to nonlinear effects. These effects include nonlinear contact dynamics, hysteresis and contact acoustic nonlinearity (CAN). This intermodulation results in additional frequencies being present in the frequency domain that were not part of the original excitation. These new frequencies are known as sidebands or harmonics and can be directly observed by taking an FFT of the system response. This work attempts to address the disadvantages of conventional nonlinear NDT methods while also expanding the understanding of nonlinear phenomena through novel processing methods and apparatuses. In this research three novel methods have been developed. The first method utilizes nonlinear frequency mixing without requiring the use of a low frequency pumping wave. The sample is excited at several distinct but similar frequencies in the ultrasonic range using only one piezoelectric transducer. This eliminates the need of a shaker for low frequency excitation, greatly simplifying experimental design. The second technique is a novel data processing method. It is based on the down-conversion of the probing wave to recover a low frequency distorted wave, this provides a more direct and meaningful analysis of nonlinear wave modulation compared to conventional methods. This technique uses all of the sideband spectra around the probing frequency. This is in contrast to existing methods that typically only consider the first or second pair of sidebands in their analysis. Lastly, an entirely non-contact, air-coupled nonlinear vibro-acoustic measurement technique and apparatus has been developed and demonstrated. This apparatus uses non-contact ultrasonic transducers for probing wave excitation and a loudspeaker inside a resonant cavity to provide a pumping excitation. The technique is demonstrated for the detection of near surface defects for thin pl...

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Section: An Interesting Results Comes Frommentioning

confidence: 99%

Section: An Interesting Results Comes Frommentioning

confidence: 99%

Section: An Interesting Results Comes Frommentioning

confidence: 99%