Showing papers on "Guided wave testing published in 2020"

A scalable data-driven approach to temperature baseline reconstruction for guided wave structural health monitoring of anisotropic carbon-fibre-reinforced polymer structures:

Abstract: To account for the temperature effect on guided wave signals in complex structures, a significant amount of baseline measurements typically need to be collected over a large temperature range to se...

An Improved Method for Pipeline Leakage Localization With a Single Sensor Based on Modal Acoustic Emission and Empirical Mode Decomposition With Hilbert Transform

Abstract: Due to its great convenience for inspection of pipelines under special conditions, leakage localization with a single acoustic emission (AE) sensor has attracted increasing attention. However, the reported study achieves a good accuracy of leakage localization only for short source-to-sensor distance. In this work, an improved method for pipeline leakage localization with a single sensor is proposed based on modal acoustic emission and empirical mode decomposition with Hilbert transform (EMD-HT). The pipeline is considered as a cylindrical shell to compute the velocity dispersion curves of different guided wave modes. A criterion to select the specific wave modes for leakage localization is presented with the consideration of frequency matching, dispersive properties, and the modes’ confusing possibilities. Integrating the empirical mode decomposition (EMD) with wavelet transform (WT), the framework of the proposed method is developed. A number of field experiments were performed on a steel pipe with a continuous leakage source. The results show that using the proposed method, a maximum relative leakage localization error of 7.32% for the source-to-sensor distances from 0 to 33 meters (m) can be achieved, which is much improved than those of the reported method. With the capacity of precisely locating the leakage source within the range of 33m for each side of the sensor, the proposed method provides a promising way to make the AE technique more suitable for in-situ inspection of pipelines.

Pure S0 and SH0 detections of various damage types in aerospace composites

Abstract: This paper proposes a new single-mode guided wave-based method to detect various types of damage in aerospace composites. In this method, single-mode guided wave excitation was achieved using adjustable angle beam transducers (ABT). The ABT tuning angles of various pure-mode guided waves were calculated based on Snell's law applied to the composite dispersion curves. A finite element (FE) simulation of pure S0 mode excitation in a crossply composite plate was conducted and the simulation results were validated by the experiment. For the first time, angle beam transducers were applied to generate pure shear horizontal (SH0) wave in a thick quasi-isotropic composite plate. The pure SH0 wave excitation was successfully verified by a three-dimensional (3D) FE simulation. SH0-mode wave propagation and interaction with delaminations were further conducted and strong trapped waves within the delamination regions were observed. Experiments using S0 or SH0 pure-mode guided waves were conducted to detect various types of composite damage, such as wrinkle damage in the crossply composite plate, multilayer delaminations by Teflon inserts, and actual impact damage in the thick quasi-isotropic composite plate. A significant amplitude drop was observed due to the presence of different composite damage types. In addition, a linear scanning method using pure SH0 wave was also developed to estimate the sizes of delaminations and impact damage. Both numerical and experimental results demonstrated the validity and usefulness of the proposed method for the detection of various damage types in composites.

Impact damage detection in composites using a guided wave mixing technique

Abstract: Combined harmonics at sum or difference frequencies can be generated by the cross-interactions of guided wave mixing in tested sample with material nonlinearity. However, it is also observed that there are multi-combined harmonic modes generated at various mixing frequencies during guided waves mixing process. It is still obscure to select certain combined harmonic mode to identify damage for the reason that acoustic nonlinear response is much more complicated than damage itself. Considering multiple mixing frequency components can be generated during guided wave mixing, this paper investigates a feasibility to detect impact damage in composite laminates by the combination of guided wave mixing technique and mixing frequency peaks count approach. Experimental observation of the combined harmonics at mixing frequency generated by guided wave mixing clearly identifies the existences of material nonlinearity in the specimen. The present results show a monotonic increase of the correlation of the value of mixing frequency spectral peak count with respect to impact energy induced into the specimens. The technique developed provides an alternative for practical application of guided wave mixing for nondestructive test in a quantizable manner.

Conformal gradient-index phononic crystal lens for ultrasonic wave focusing in pipe-like structures

Abstract: We explore a conformal gradient-index phononic crystal lens integrated within a pipe to amplify guided wave modes toward improved ultrasonic inspection of pipelines. The proposed conformal lens is composed of an array of cylindrical steel stubs attached to the outer surface of a steel pipe, which are tailored according to the hyperbolic secant profile of refractive index in the circumferential direction of the pipe. Hence, the ultrasonic guided wave energy is focused in the axial direction of the pipe and amplified at the focal point of the lens. Refractive indices are calculated using dispersion curves obtained from the finite element simulations of the stubbed unit cells, and the curved lens is designed for the second longitudinal wave mode of the pipe, which is commonly used in guided wave testing. The proposed lens design is implemented on a steel pipe, which is typically used in the distribution networks utilized in cities, and simultaneous focusing of longitudinal wave modes in a broad frequency range is verified through both numerical models and experimental measurements.

Location Specific Temperature Compensation of Guided Wave Signals in Structural Health Monitoring

Abstract: In guided wave structural health monitoring, defects are typically detected by identifying high residuals obtained through the baseline subtraction method, where an earlier measurement is subtracted from the “current” signal. Unfortunately, varying environmental and operational conditions (EOCs), such as temperature, also produce signal changes and hence, potentially, high residuals. While the majority of the temperature compensation methods that have been developed target the changed wave speed induced by varying temperature, a number of other effects are not addressed, such as the changes in attenuation, the relative amplitudes of different modes excited by the transducer, and the transducer frequency response. A temperature compensation procedure is developed, whose goal is to correct any spatially dependent signal change that is a systematic function of temperature. At each structural position, a calibration function that models the signal variation with temperature is computed and is used to correct the measurements, so that in the absence of a defect the residual is reduced to close to zero. This new method was applied to a set of guided wave signals collected in a blind trial of a guided wave pipe monitoring system using the T(0, 1) mode, yielding residuals de-coupled from temperature and reduced by at least 50% as compared with those obtained using the standard approach at positions away from structural features, and by more than 90% at features such as the pipe end. The method, therefore, promises a substantial improvement in the detectability of small defects, particularly at the existing pipe features.

Compressed Sensing Method for Health Monitoring of Pipelines Based on Guided Wave Inspection

Abstract: The pipeline in-service needs to be inspected in a certain period to master its structural health status. An ultrasonic guided wave, which can propagate along pipelines with less energy loss, provides an efficient method for long-term in situ inspection. The guided waves can detect both corrosion and cracks existing in structures. To overcome the problem of huge amounts of data and to maintain defect identification accuracy, the compressed sensing method for guided wave inspection is proposed. The compression process is essentially a scheme of analog to information conversion to compress the signal. It is accomplished by random demodulation and the equivalent sampling rate below the Nyquist rate helps to save most of the storage. Compressed data are recovered to the sparse spatial domain based on the constructed dictionary from a guided wave propagation model. To verify the effectiveness of the proposed method, both numerical simulations and experimental investigations are conducted. The results indicate the availability of compression and high accuracy of defect location after recovery. The influences of different compression schemes and compression ratios are further analyzed. In addition, the comparisons with direct recovery without compression and traditional analysis methods demonstrate the advantageous performance of the proposed method.

Hierarchical approach for uncertainty quantification and reliability assessment of guided wave-based structural health monitoring:

Abstract: In this article, a hierarchical approach is proposed for the design and assessment of a guided wave-based structural health monitoring system for the detection and localisation of barely visible im...

Super-resolution visualization of subwavelength defects via deep learning-enhanced ultrasonic beamforming: A proof-of-principle study

Abstract: Detecting small, subwavelength defect has known to be a challenging task mainly due to the diffraction limit, according to which the minimum resolvable size is in the order of the wavelength of a propagating wave. In this proof-of-concept study, we present a deep learning-enhanced super-resolution ultrasonic beamforming approach that computationally exceeds the diffraction limit and visualizes subwavelength defects. The proposed super-resolution approach is a novel subwavelength beamforming methodology enabled by a hierarchical deep neural network architecture. The first network (the detection network) globally detects defective regions from an ultrasonic beamforming image. Subsequently, the second network (the super-resolution network) locally resolves subwavelength-scale fine details of the detected defects. We validate the proposed approach using two independent datasets: a bulk wave array dataset generated by numerical simulations and guided wave array dataset generated by laboratory experiments. The results demonstrate that our deep learning super-resolution ultrasonic beamforming approach not only enables visualization of fine structural features of subwavelength defects, but also outperforms the existing widely-accepted super-resolution algorithm (time-reversal MUSIC). We also study key factors of the performance of our approach and discuss its applicability and limitations.

Multimode Guided Wave Detection for Various Composite Damage Types

Abstract: This paper presents a new methodology for detecting various types of composite damage, such as delamination and impact damage, through the application of multimode guided waves. The basic idea is that various wave modes have different interactions with various types of composite damage. Using this method, selective excitations of pure-mode guided waves were achieved using adjustable angle beam transducers (ABTs). The tuning angles of various wave modes were calculated using Snell’s law applied to the theoretical dispersion curves of composite plates. Pitch–catch experiments were conducted on a 2-mm quasi-isotropic carbon fiber-reinforced polymer (CFRP) composite plate to validate the excitations of pure fundamental symmetric mode (S0) and shear horizontal mode (SH0). The generated pure S0 mode and SH0 mode were used to detect and separate the simulated delamination and actual impact damage. It was observed that S0 mode was only sensitive to the impact damage, while SH0 mode was sensitive to both simulated delamination and impact damage. The use of pure S0 and SH0 modes allowed for damage separation. In addition, the proposed method was applied to a 3-mm-thick quasi-isotropic CFRP composite plate using multimode guided wave detection to distinguish between delamination and impact damage. The experimental results demonstrated that the proposed method has a good capability to detect and separate various damage types in composite structures.

Artificial Intelligence-Based Bolt Loosening Diagnosis Using Deep Learning Algorithms for Laser Ultrasonic Wave Propagation Data

Abstract: The application of deep learning (DL) algorithms to non-destructive evaluation (NDE) is now becoming one of the most attractive topics in this field. As a contribution to such research, this study aims to investigate the application of DL algorithms for detecting and estimating the looseness in bolted joints using a laser ultrasonic technique. This research was conducted based on a hypothesis regarding the relationship between the true contact area of the bolt head-plate and the guided wave energy lost while the ultrasonic waves pass through it. First, a Q-switched Nd:YAG pulsed laser and an acoustic emission sensor were used as exciting and sensing ultrasonic signals, respectively. Then, a 3D full-field ultrasonic data set was created using an ultrasonic wave propagation imaging (UWPI) process, after which several signal processing techniques were applied to generate the processed data. By using a deep convolutional neural network (DCNN) with a VGG-like architecture based regression model, the estimated error was calculated to compare the performance of a DCNN on different processed data set. The proposed approach was also compared with a K-nearest neighbor, support vector regression, and deep artificial neural network for regression to demonstrate its robustness. Consequently, it was found that the proposed approach shows potential for the incorporation of laser-generated ultrasound and DL algorithms. In addition, the signal processing technique has been shown to have an important impact on the DL performance for automatic looseness estimation.

Guided wave tomography based on least-squares reverse-time migration:

Abstract: A key to successful damage diagnostics and quantification is damage imaging through ultrasonic guided wave tomography. We propose the implementation of least-squares reverse-time migration in a cir...

Infrared properties of high-purity silicon

Abstract: High-purity silicon is a readily available material of utility in realizing a variety of long-wavelength optical and guided wave components. The transmittance of uncompensated for silicon is measured in the far- and mid-infrared regimes at room and cryogenic temperatures. The experimental and analysis techniques used to extract the refractive index from 100-1000cm-1 (100-10 µm) are presented, and the results are compared to the literature. An average refractive index below 300cm-1, n^(300K)=3.417+i8.9×10-5, which transitions in cooling to n^(10K)=3.389+i4.9×10-6, is observed.

A review on ultrasonic guided wave technology

Abstract: This paper will provide some understanding on the Guided Wave Technology (GWT). Prior to the review of GWT, the authors will be providing some introduction on brief history of guided wave, basic physics on ultrasonic including on modes of wave propagation, operation principle of piezoelectric, Magnetostrictive, Electromagnetic Acoustic Transducer, general theory of elasticity, Short-Time Fourier Transform and Wigner-Ville distribution to enable new readers to follow the entire flow. Some selected research in the area of Structural Health Monitoring, Nondestructive Testing and flow properties determination will be summarised in detail.

Detection of interfacial weakness in a lap-shear joint using shear horizontal guided waves

Abstract: This study aims to develop a shear horizontal guided wave based technique to evaluate the interfacial adhesion of aluminium-epoxy-aluminium tri-layer in a lap shear joint. A 3-D Multi-physics finite element model was developed to investigate the physics of the interaction of SH modes with a tri-layer structure. By employing the boundary stiffness approach, different cases of interfacial adhesion-ranging from perfect bond, intermediate and weak bond, were simulated. Frequency-wavenumber analysis reveals that at the bond overlap region, the incident SH0 wave mode-converts to fundamental (SH0-like) and first-order(SH1-like) modes. The dispersion characteristics of first-order mode (SH1-like) was found to be dependent on the adhesion level, and this influences the time responses collected on a receiver plate in guided wave through-transmission configuration. Experiments were carried out on aluminium-epoxy-aluminium lap shear joints using PPM-EMAT transducers. The analysis shows that this technique can detect and quantify different levels of adhesion, rather than merely classifying as good or bad bonds.

Air-Coupled, Contact, and Immersion Ultrasonic Non-Destructive Testing: Comparison for Bonding Quality Evaluation

Abstract: The objective of this study is to compare the performance of different ultrasonic non-destructive testing (NDT) techniques for bonding quality evaluation. Aluminium-epoxy-aluminium single lap joints containing debonding in the form of release film inclusions have been investigated using three types of ultrasonic NDT methods: contact testing, immersion testing, and air-coupled testing. Apart from the traditional bulk wave ultrasound, guided wave testing was also performed using air coupled and contact transducers for the excitation of guided waves. Guided wave propagation within adhesive bond was numerically simulated. A wide range of inspection frequencies causing different ultrasonic wavelengths has been investigated. Average errors in defect sizing per ultrasonic wavelength have been used as a feature to determine the performance of each ultrasonic NDT technique. The best performance is observed with bulk wave investigations. Particularly, the higher frequencies (10–50 MHz) in the immersion testing performed significantly better than air-coupled testing (300 kHz); however, air coupled investigations have other advantages as contactless inspection. Whereas guided wave inspections show relatively lower accuracy in defect sizing, they are good enough to detect the presence of the debonding and enable to inspect long range. Even though each technique has its advantages and limitations, guided wave techniques can be practical for the preliminary in-situ inspection of adhesively bonded specimens.