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(a) Photograph of experimental setup for low-frequency vibration acquisition, (b) electromechanical responses of the printed sensor to vibration at representative frequencies from 200 to 1000 Hz, (c) response of the printed sensor at 200 Hz compared with metal foil strain sensor, and (d) relationship between response of the printed sensor against driven voltage at 500 Hz.
Source publication
A nanocomposite-based sensor ink made from carbon black and polyvinyl pyrrolidone was developed for fabricating a new breed of sensor by an inkjet printing approach, to accommodate the general purposes of structural health monitoring. This ink can be directly deposited onto the surface of various substrates or engineering structures such as polyimi...
Contexts in source publication
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... cantilevered beam (280 mm in length, 30 mm in width, and 1 mm in thickness), trimmed from the glass fiber epoxy plate prepared in section ''Development of printable sensor networks,'' was adhered to a force transducer (8200; B&K Ò , Denmark) installed on an electromechanical shaker (4809; B&K Ò , Denmark) for low-frequency vibration testing, as presented in Figure 3(a). A sinusoidal signal generated by the low- frequency waveform generator was transmitted to the beam under different frequencies through the adhesion point 200 mm from the clamped end via the shaker. ...
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... sinusoidal signal generated by the low- frequency waveform generator was transmitted to the beam under different frequencies through the adhesion point 200 mm from the clamped end via the shaker. Good consistency and reversibility of the vibration signal can be observed at each cycle of the response signals acquired by the nanocomposite sensor in the low-frequency range from 200 to 1000 Hz with slight fluctuations, as indicated in Figure 3(b). The response signals, acquired by the nanocomposite sensor and by a metal foil strain gauge that was adhered to the back of the beam, show good consistency without any obvious hysteresis, upon processed with a fast Fourier transformation-based filter, as shown in Figure 3(c). ...
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... consistency and reversibility of the vibration signal can be observed at each cycle of the response signals acquired by the nanocomposite sensor in the low-frequency range from 200 to 1000 Hz with slight fluctuations, as indicated in Figure 3(b). The response signals, acquired by the nanocomposite sensor and by a metal foil strain gauge that was adhered to the back of the beam, show good consistency without any obvious hysteresis, upon processed with a fast Fourier transformation-based filter, as shown in Figure 3(c). A half-cycle delay is noted, which is owing to the fact that the two types of sensors were placed at the front and back surfaces of the beam, respectively. ...
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... half-cycle delay is noted, which is owing to the fact that the two types of sensors were placed at the front and back surfaces of the beam, respectively. From Figure 3(d), the intensity of the signal increases proportionally with the rise in excitation voltage, a result validating the applicability of the response signal for quantitatively reflecting the strain values. ...
Citations
... Structural health monitoring (SHM) can be used to automate the task of fatigue crack discovery by strategically designing and deploying dedicated sensor networks. Largearea electronics (LAE) [19,20] is a particularly promising technology by enabling sensing skin-type applications through the deployment of dense sensor networks covering large surfaces and capable of local measurements, thus facilitating fatigue crack detection over full-scale components [21,22]. Specific examples of dense sensor networks include an eddy current sensor array fabricated by integrating an actuating coil and a sensing coil into a flexible printed circuit board [23] applied to welds, ultrasonic guided wave-based piezoelectric lead zirconate titanate disks supported by a thin flexible dielectric film used for diagnosis and assessment of fatigue cracks in the weld of a T-shape bogie frame [24], a mechanoluminescent sensor fabricated by coating SrAl 2 O 4 :Eu ceramic powder on an aluminum foil through screen-printing to detect cracks on welding points located on the outside surface of a pressurized pipe [25], fiber Bragg grating sensors used for discovering and localizing cold cracks in welded areas of steel plates [26], and commercial piezoelectric sensor networks applied to monitor weld cracks on T-type joints in steel offshore oil and gas jacket platforms [27] and metro train bogie frames [28]. ...
Load-induced fatigue cracking in welds is a critical safety concern for steel transportation infrastructure, and the automation of their detection using commercial sensing technologies remains challenging due to the randomness in crack initiation and propagation. The authors have previously proposed a corrugated soft elastomeric capacitor (cSEC), which is a flexible and ultra-compliant thin-film strain gauge that transduces strain into a measurable change in capacitance. The cSEC technology has been successfully demonstrated for measuring bending strain as well as angular rotation in a folded configuration. This study builds on prior discoveries to characterize the sensor’s capability at monitoring fatigue cracks in corner welds, for which the sensor needs to be installed in a folded configuration. A crack monitoring algorithm is developed to fuse the cSEC data into actionable information. Experimental work is conducted on an orthogonal welded connection, mimicking a plate-to-web joint in steel bridges, with cSECs folded over the fillet welds. The sensor’s electromechanical behavior is characterized, and results confirm that the cSEC is capable of fatigue crack detection and quantification. In particular, results show that the cSEC can detect a minimum crack length of 0.48 mm and that its overall sensing performance, including signal linearity, resolution, and accuracy, is adequate under no damage, yet decreases with increasing crack size, likely attributable to the simplification of the electromechanical model and higher noise produced by the loading equipment under smaller applied displacement.
... Under acousto-ultrasonic wave-induced strains, quantum tunneling effect generated in the formed nanofiller conductive network induces a dynamic alteration in the electrical conductivity and thus the piezoresistivity of the sensors, endowing the sensors with capacity in perceiving acousto-ultrasonic wave signals. This type of thin film-like sensors can be sprayable [5,17] and printable [18,19] to various structural surfaces, and tailor-made to resonate a specific frequency of the signal to be acquired by fine-tuning the degree of sensor conductivity [18]. The developed sensors feature values such as rapid prototyping, flexibility, lightweight and broadband response, blazing a new trail in developing in-situ SHM for aircraft and spacecraft. ...
Small‐scale and flexible acoustic probes are more desirable for exquisite objects like human bodies and complex‐shaped components than conventional rigid ones. Herein, a thin‐film flexible acoustic sensor (FA‐TES) that can detect ultra‐broadband acoustic signals in multiple applications is proposed. The device consists of two thin copper‐coated polyvinyl chloride films, which are stimulated by acoustic waves and contact each other to generate the triboelectric signal. Interlocking nanocolumn arrays fabricated on the friction surfaces are regarded as a highly adaptive spacer enabling this device to respond to ultra‐broadband acoustic signals (100 Hz–4 MHz) and enhance sensor sensitivity for film weak vibration. Benefiting from the characteristics of high shape adaptability and ultrawide response range, the FA‐TES can precisely sense human physiological sounds and voice (≤10 kHz) for laryngeal health monitoring and interaction in real‐time. Moreover, the FA‐TES flexibly arranged on a 3D‐printed vertebra model can effectively and accurately diagnose the inner defect by ultrasonic testing (≥1 MHz). It envisions that this work can provide new ideas for flexible acoustic sensor designs and optimize real‐time acoustic detections of human bodies and complex components.
There has been considerable interest in piezoresistive nanocarbon-loaded polymer films for structural health monitoring, including damage detection and strain monitoring. While good performance has been demonstrated, issues related to practical implementation have received less attention. Here we present sensors made from exfoliated graphite nanoplatelets (xGnP) incorporated into a commercial paint that is applied to Sikorsky aircraft. A formulation and a fabrication method are developed that deliver high piezoresistive strain sensitivity alongside mechanical integrity. At approximately 7 wt% xGnP, the gauge factor in tension is in the range of 30–55, and the effectiveness of the sensors for damage monitoring is demonstrated by the detection of perforations. To obtain a paintable solution, key considerations in choosing the solvent employed for introducing the nanocarbon are compatibility and the ability to keep the nanocarbon suspended, which is achieved using ethyl acetate. The ability to form sensors in situ on aircraft structures requires an uncomplicated method of making robust electrical connections, which is demonstrated here using embedded copper mesh. The strong, often nonlinear, environmental sensitivity of polymer-nanocarbon materials must also be considered in applications; here, increasing temperature and humidity both raise sensor resistance. This work shows that a second, unstrained reference sensor would work well for automatic compensation. Lastly, a method for effecting a repair that employs standard processes and maintains the high gauge factor is demonstrated. With these advances, the paint-xGnP sensors are ready for in-the-field testing on aircraft.
Guided waves-based structural health monitoring (SHM) methods have potential for practical applications, since they are sensitive to small damages and are able to realize large area monitoring. Among these methods, the Reconstruction Algorithm for Probabilistic Inspection (RAPID), using a Piezoelectric transducer (PZT) sensor array, is one of the most widely used imaging algorithms to perform active damage monitoring and localization. However, since the sensing paths are distributed inside the sensor array with the non-uniform density, the RAPID algorithm can only localize damage when it is occurring inside of the array. If the damage occurs outside of the array or both inside and outside of the array, that is, multi-type damage, the performance of RAPID algorithm would not be satisfactory. In this paper, a scattering coefficient-based RAPID algorithm with damage indexes separation and imaging fusion is proposed. The amplitude of damage scattered signal at the corresponding time of fight is adopted as the weight in the probability distribution function, and damage indexes are then classified into two categories in the RAPID algorithm for the inside and outside damage localization respectively. Finally, an experiment on the complex composite plate, with the center large hole and surrounding bolt holes, is carried out to verify this proposed method. Experimental results show that this method can realize multi-type damage localization with errors less than 40 mm.
Structural health monitoring (SHM) is widely used to examine the structural integrity of a structure to improve safety considerations, minimize maintenance cost, and avoid sudden breakdowns that might occur under various loadings under service conditions. Fiber reinforced polymer (FRP) composites are widely used in aerospace, automotive, marine, energy, infrastructure, armor, and biomedical applications due to their high specific stiffness and strength, high degree of dimensional and thermal stability, and good resistance to corrosion. Thus, SHM of the damages developed in FRPs during service conditions is very crucial. However, traditionally used sensors for SHM in composites provide limited sensitivity and might negatively affect the structural integrity. Therefore, a self-sensing approach by evaluating the electrical resistance change (ERC) of FRPs has been successfully used by many researchers. The purpose of this chapter is to describe the ERC techniques using various nanoparticles such as graphene, carbon nanotube, expanded graphite, and carbon black.
Recent quantum leap in far-field laser techniques has advanced noncontact implementation of nondestructive ultrasonic imaging, in pursuit of enhanced accessibility, detectability and practicability. Nevertheless, when laser-generated thermoelastic waves are extended to thick waveguides, they manifest fairly low signal-to-noise ratios (SNRs), along with severe wave diffusion, consequently lowering image resolution and contrast. With these motivations, a laser-ultrasonics imaging approach is developed, in conjunction with i) entropy-polarized bilateral filtering (Entropy-P-BF) for signal denoising, and ii) minimum variance (MV) beamforming for defect imaging, targeting at precise characterization of a submillimeter defect (with its characteristic dimension being smaller than the wave diffraction limit) in a thick waveguide. The entropy-polarized bilateral filtering denoises laser-induced ultrasonic wave signals via a two-dimensional convolution, the weight matrices of which are continuously updated according to local noise and uncertainty. With an elevated SNR, MV beamforming subsequently conducts an apodized beamforming to image the defect. Experimental validation is conducted by imaging a void-type defect, 0.7 mm only in its diameter, in a jet aero-engine turbine disk. Results prove that the developed approach is capable of characterizing a submillimeter defect accurately in a thick waveguide with thickness ∼25 times the wavelength of laser-induced shear wave, regardless of a fairly low SNR (<1dB).
