This paper presents guided waves based damage detection by using a hybrid PZT actuator and optic fiber Bragg grating (FBG) sensors. In the hybrid sensing, a piezoelectric wafer (PZT) is used to generate incident guided waves based on the piezoelectric principle. Meanwhile, multiple fiber Bragg grating sensors (FBG) are adopted as receivers to measure the high-frequency small-strain guided waves base on the full width half maximum (FWHM) principle. If the inspected structure has damage such as hole, crack and notch, the incident guided waves will be reflected or scattered by the damage. Through multiple FBG sensors at different locations, the damage induced waves can be acquired and further processed for damage detection. In this research, two configurations are explored, the rosette and line arrangements of multiple sensors. The sensing and wave source localization on aluminum plate are demonstrated. The results show that wave source can be successfully detected by using both the FBG rosette and the FBG array.
This paper presents the phased array beamforming and imaging using guided waves in anisotropic composite laminates. A generic phased array beamforming formula is presented, based on the classic delay-and-sum principle. The generic formula considers direction-dependent guided wave properties induced by the anisotropic material properties of composites. Moreover, the array beamforming and imaging are performed in frequency domain where the guided wave dispersion effect has been considered. The presented phased array method is implemented with a non-contact scanning laser Doppler vibrometer (SLDV) to detect multiple simulated defects at different locations in an anisotropic composite plate. The array is constructed of scan points in a small area rapidly scanned by the SLDV. Using the phased array method, multiple simulated defects at different locations are successfully detected. Our study shows that the guided wave phased array method is a potential effective method for rapid inspection of large composite structures.
This paper studies impact induced delamination detection and quantification methods via guided wavefield data and spatial wavenumber imaging. In this study, the complex geometry impact-like delamination damage in a composite laminate is created through the quasi-static indention technique. To detect and quantify the delamination damage, the guided ultrasonic waves are excited through a piezoelectric actuator, and the guided wavefields are measured by a scanning laser Doppler vibrometer. The acquired guided wavefields contain a wealth of information regarding the wave propagation in the composite plate and complex wave interaction at the delamination region. To process the wavefield data and evaluate the delamination damage, the measured wavefields are analyzed through the spatial wavenumber imaging method which can generate an image containing the dominant local wavenumber at each spatial location. For a proof of concept, the approach is first applied to a single Teflon insert simulating a delamination, and then to the complex geometry impact-like delamination damage. The results show that the spatial wavenumber imaging can not only determine the delamination location, but also provide quantitative information regarding the delamination size and shape. The detection results for the impact induced delamination are compared to an ultrasonic C-scan image and wavenumber images are studied for two different excitation frequencies. Fairly good agreement is observed for portions of the delamination, and differences in wavenumber are observed at the two different frequencies. Results demonstrate that the spatial wavenumber imaging is a promising technique for yielding delamination location and size information.
In this paper, the fundamentals of guided waves in honeycomb sandwich structures are investigated through
wavefield and wavenumber analyses. The guided wavefields are obtained through finite element modeling (FEM) as
well as laser vibrometry experiments. The FEM and laser vibrometry results agree well with each other. At low
frequencies, the guided wavefields show global guided waves which propagate in the entire sandwich with elliptical
wave fronts. With the increase of wave frequency, the global guided waves gradually disappear. At high frequencies,
guided waves propagate in the single skin plate instead of the entire sandwich, and strong wave interactions with the
honeycomb core are observed. To further investigate the wave propagation fundamentals in the honeycomb sandwich,
the guided wavefields are transformed to the wavenumber spectra by using three-dimensional Fourier transform. In the
wavenumber domain, the wavenumber spectra unveil the wavenumber information of the wavefields. At the low
frequencies, the wavenumber spectra of honeycomb sandwich are elliptical ring-shaped. With the increase of frequency,
the elliptical ring-shaped wavenumber band is gradually asymptotic to a circular ring. Moreover, with the increase of
frequency, the wavenumber values of the honeycomb sandwich are gradually getting closer to the wavenumbers of A0
mode in a single skin plate.
This paper presents a single Lamb mode phased array beamforming by using a hybrid piezoelectric transducer
(PZT)-scanning laser Doppler vibrometer (SLDV) system. The array system consists of a surface mounted PZT to
generate Lamb waves and a non-contact SLDV to acquire high spatial resolution time-space wavefield remotely. The
time-space wavefield contains Lamb waves which can be generated from the PZT excitation, damage scattering, mode
conversion, etc. A frequency-wavenumber (f-k) decomposition technique is used to decompose the miscellaneous Lamb
waves into individual wave mode components and wave propagations in different directions. The f-k decomposition
allows using a single wave component as the phased array input for beamforming. The single mode array beamforming
methodology was verified through PZT-SLDV experimental tests on an aluminum plate with a bonded quartz rod as a
Toward the goal of delamination detection and quantification in laminated composites, this paper examines guided wave propagation and wave interaction with delamination damage in laminated carbon fiber reinforced polymer (CFRP) composites using frequency-wavenumber (f-k) analysis. Three-dimensional elastodynamic finite integration technique (EFIT) is used to acquire simulated time-space wavefields for a CFRP composite. The time-space wavefields show trapped waves in the delamination region. To unveil the wave propagation physics, the time-space wavefields are further analyzed by using two-dimensional (2D) Fourier transforms (FT). In the analysis results, new f-k components are observed when the incident guided waves interact with the delamination damage. These new f-k components in the simulations are experimentally verified through data obtained from scanning laser Doppler vibrometer (SLDV) tests. By filtering the new f-k components, delamination damage is detected and quantified.
Due to the heterogeneous nature of the cement-based materials, the ultrasonic waves in concrete exhibit highly scattering and attenuation, leading to the difficulty of concrete damaged detection. This paper presents a dual mode ultrasonic array imaging methodology that can map damage using Rayleigh surface waves and permanently installed piezoelectric sensors. The dual mode sensing integrates passive acoustic emission and active ultrasonic wave inspection. When a crack is developing, acoustic emission (AE) occurs and the disturbance can propagate outwards along the structure surface. A novel AE source imaging algorithm has been developed to detect and locate the AE source. Once the AE source is located, the sensor array switches to its active mode. For active sensing, one sensor in the array is used to generate Rayleigh wave for interrogation, while all the others are used as the wave receivers. All the sensory data are processed by the active ultrasonic array imaging algorithm. The proof-of-concept testing was performed on a grout specimen with representative dimensions. The passive array imaging algorithm was able to locate the AE source simulated by pencil lead break while active sensing imaging was able to detect the damage simulated by a hole. The duel mode imaging method is promising and economically beneficial for solving a key source localization problem in damage detection on large concrete structures.
In this work, we present our study of Lamb wave crack detection using wavenumber analysis. The aim is to demonstrate the application of wavenumber analysis to 3D Lamb wave data to enable damage detection. The 3D wavefields (including vx, vy and vz components) in time-space domain contain a wealth of information regarding the propagating waves in a damaged plate. For crack detection, three wavenumber analysis techniques are used: (i) time-space Fourier transform which can transform the time-space wavefield into frequency-wavenumber representation while losing the spatial information; (ii) short space Fourier transform which can obtain the frequency-wavenumber spectra at various spatial locations, resulting in a space-frequency-wavenumber representation; (iii) local wavenumber analysis which can provide the distribution of the effective wavenumbers at different locations. All of these concepts are demonstrated through a numerical simulation example of an aluminum plate with a crack. The 3D elastodynamic finite integration technique (EFIT) was used to obtain the 3D wavefields, of which the vz (out-of-plane) wave component is compared with the experimental measurement obtained from a scanning laser Doppler vibrometer (SLDV) for verification purpose. The experimental and simulated results are found to be in close agreement. The application of wavenumber analysis on 3D EFIT simulation data shows the effectiveness of the analysis for crack detection.
This paper presents a novel ultrasonic guided wave based inspection methodology for detecting and evaluating gas
accumulation in nuclear cooling pipe system. The sensing is in-situ by means of low-profile permanently installed
piezoelectric wafer sensors to excite interrogating guided waves and to receive the propagating waves in the pipe
structure. Detection and evaluation is established through advanced cross time-frequency analysis to extract the phase
change in the sensed signal when the gas is accumulating. A correlation between the phase change and the gas amount
has been established to provide regulatory prediction capability based on measured sensory data.