Non-linear methods based on ultrasonic waves to analyse disbonds in single lap joints

Scarselli, Gianfranco; Ciampa, Francesco; Nicassio, Francesco; Meo, Michele

doi:10.1177/0954406217704222

Cited by 18 publications

(10 citation statements)

References 25 publications

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“…Differences between experimental and numerical signal amplitudes were due to the need of limiting the computational time using particular mesh sizing and contact parameters (not affecting indeed the correlation with the experimental results). As done in [30][31][32], the specimen was excited by harmonic voltage imposed at sensor A and the dynamic response was picked up at receivers B and D. The signal frequency was varied from 2.1 kHz to 138 kHz corresponding to the resonance frequency of sensors with C.L. respectively of 7.5 and 1 mm calculated analytically by Equation (1).…”

Section: Resultsmentioning

confidence: 99%

“…In this way, it was possible to evaluate the state of each PZT and then to distinguish the fully bonded sensors from those impaired. The identified undamaged sensor was then used to excite the others with harmonic signal sweeping up to high frequencies to find subharmonics induced by LDR ( [31,32]). The presence of subharmonic at f D = f e /2 in the acquired signals allowed to detect and to characterise possible debondings of the sensors mounted on the structure.…”

Section: Discussionmentioning

confidence: 99%

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Nonlinearities Associated with Impaired Sensors in a Typical SHM Experimental Set-Up

2018

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Structural Health Monitoring (SHM) gives a diagnosis of a structure assessing the structural integrity and predicting the residual life through appropriate data processing and interpretation. A structure must remain in the design domain, although it can be subjected to normal aging due to usage, action of the environment, and accidental events. SHM involves the integration of electronic devices in the inspected structure that sometimes are Piezoelectric Transducers (PZT). These are lightweight and small and can be produced in different geometries. They are used both in guided wave-based and electromechanical impedance-based methods. The PZT bonding requires essential steps such as preparation of the surfaces, application of the adhesive, and assembly that make the bonding process not so easy to be realised. Furthermore, adhesives are susceptible to environmental degradation. Transducer debonding or non-uniform distributed glue underneath the sensor causes the reduction of the performance and can affect the reliability of the SHM system. In this paper, a sensor diagnostic method for the monitoring of the PZT operational status is proposed in order to detect bonding defect/damage between a PZT patch and a host structure. The authors propose a method based on the nonlinear behaviour of the contact PZT/structure that allows the identification of the damaged PZT and the geometrical characterization of the debonding. The feasibility of the diagnostic procedure is demonstrated by numerical studies and experiments, where disbonds were created by inhibiting the adhesive action on a part of the interface through Teflon film. The proposed method can be used to evaluate the sensor functionality after an extreme loading event or over a long period of service time.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Nonlinearities Associated with Impaired Sensors in a Typical SHM Experimental Set-Up

2018

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“…In standard thermosonics tests, the frequency bandwidth is generally chosen from experience of the operator. However, nonlinear ultrasonic tests from literature (see for instance [6,27,28]) showed that harmonics of the LDR frequency in damaged metal and composite samples of different geometries with mm-size defects were generated by exciting the material at frequencies ranging between 30 kHz and 70 kHz. Hence, such a frequency range was used in this project to excite fatigue micro-cracks with air-coupled transducers.…”

Section: Ldr Frequency-selection Using Narrowband Sweep Excitationmentioning

confidence: 99%

Nonlinear air-coupled thermosonics for fatigue micro-damage detection and localisation

Dyrwal

Meo

Ciampa

2018

NDT & E International

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Over the years, traditional active infrared thermography has played a pivotal role in ensuring that a component is free of any damage. However, whilst optical thermography is still not sufficiently sensitive to the presence of material micro-flaws, current vibro-thermography requires inspection solutions that are not always feasible, such as the use of coupling materials between the sensing probe and the monitored structure. This paper presents a valid alternative to current thermographic systems by developing and experimentally validating nonlinear aircoupled thermosonics for a contactless, rapid and accurate detection of fatigue micro-cracks in an aero-engine turbine blade. The proposed thermographic method combines the high sensitivity to micro-damage of nonlinear ultrasonic techniques with non-contact air-coupled ultrasonic transducers and thermographic equipment. Narrowband frequency sweeps were performed to identify local damage resonance frequencies in order to generate large vibrational amplitudes at the damage location and compensate for signal losses caused by the high acoustic impedance mismatch between the air and the sample. An infrared camera was then used to acquire the thermal response generated by frictional heat at the crack interfaces. Moreover, an image processing method based on a combination of morphological opening and a Savitzky-Golay smoothing filter was employed to enhance the quality of thermal images affected by anisotropic heating and thermal noise effects. Nonlinear aircoupled thermosonics experiments were validated with laser Doppler vibrometry scan measurements and compared with both flash and pulsed phase thermography. Thermal imaging results showed that the proposed nonlinear air-coupled thermosonics was the only thermographic technique able to detect fatigue micro-cracks, thus demonstrating its potential as an efficient and sensitive inspection tool for micro-damage detection in geometrically complex components.

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“…In the recent years, adhesive bonding defects have been defined as kissing bond in which adherend and adhesive are in some way connected through a layer that exhibits an altered normal or shear stiffness (Yan et al, 2009). Several authors have numerically and experimentally shown that kissing-bond such as damage in SLJs can be detected using Nonlinear Elastic Wave Spectroscopy (NEWS) methods as in Scarselli et al (2017b) and Nicassio et al (2019). These approaches are based on detection of acoustic Non-linearities due to Non-linear behavior of damages that is broadly defined as Contact Acoustic Non-linearity (CAN) (Drewry and Wilcox, 2014).…”

Section: Introductionmentioning

confidence: 99%

Non-linear Lamb Waves for Locating Defects in Single-Lap Joints

Nicassio

Carrino

Scarselli

2020

Front. Built Environ.

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A novel method based on Non-linear Lamb waves behavior and Local Defect Resonance (LDR) is proposed for locating and evaluating disbonds in Single-Lap Joints (SLJ) typically used in aerospace industry. The presence of damages/defects such as disbonds leads to the presence of sub-and super-harmonics components in the frequency response. The maximum acoustic wave-damage interaction is reached by particular excitation frequencies that enhance the Non-linear response causing LDR. The LDR frequency is experimentally evaluated through the appearance of a single subharmonic component in the frequency spectrum of signals received by piezoelectric transducer (PZT) bonded on the structure. The Non-linear properties of Lamb waves are exploited to make defects generate subharmonic waves at LDR frequency. An algorithm is implemented for damage/defect localization that is accurately obtained by knowing PZTs positions, Time of Flight (ToF) and propagation properties of subharmonics packet. Several disbonds with different dimensions are artificially reproduced on an aluminum SLJ: experimental and FE results show good accordance both in usual (single damage) and critical (multi-damage) scenario. The paper proposes a baseline-free method for the disbonds detection, characterization and localization in SLJs that uses the PZT signals without affecting adhesive interface, thus allowing for an active health monitoring.

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Non-linear methods based on ultrasonic waves to analyse disbonds in single lap joints

Cited by 18 publications

References 25 publications

Nonlinearities Associated with Impaired Sensors in a Typical SHM Experimental Set-Up

Nonlinearities Associated with Impaired Sensors in a Typical SHM Experimental Set-Up

Nonlinear air-coupled thermosonics for fatigue micro-damage detection and localisation

Non-linear Lamb Waves for Locating Defects in Single-Lap Joints

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