Guided Wave Non-destructive Testing Research Articles

Optimizing focal resolution imaging in Lamb wave time-reversal through periodic plate-column structures: Simulation and experimental study

Ultrasonic guided wave non-destructive testing technology, as one of the most widely used techniques in non-destructive testing, has encountered challenges in breaking the diffraction limit to achieve finer super-resolution imaging during its development. As a type of wave accompanying ultrasonic guided wave damage detection, the transient wave has had the potential to achieve super-resolution imaging in recent years due to its high wave number and sub-wavelength characteristics. In order to overcome its spatial attenuation characteristics, this study constructs a periodic plate-column structure metamaterial. By utilizing its resonance with sub-wavelength Bloch modes at specific frequencies and the interaction with transient waves carrying sub-wavelength information, the wave carrying sub-wavelength signals is amplified, transformed, and transmitted to the far field, thereby achieving super-resolution imaging. The dispersion characteristics of the periodic plate-column structure were simulated and experimentally investigated. The super-resolution imaging effect of the periodic plate-column structure metamaterial was simulated using the time-reversal imaging method and experimentally validated, providing a basis for achieving damage super-resolution imaging with periodic plate-column structures.

Guided waves in long range nondestructive testing and structural health monitoring: Principles, history of applications and prospects

The early work on long range guided wave nondestructive testing (NDT) was largely done in industry, and multiple applications were developed before a surge in academic interest starting in the early 1990s. This paper reviews the history of the field, covering the topics that must be addressed in the design of a test procedure, as well as applications in both NDT and Structural Health Monitoring (SHM). The use of guided waves in long range NDT is relatively mature, and largely limited to simple structures in applications that are difficult or impossible to address by conventional point inspection methods. Point methods are impractical in most large area SHM applications where it is necessary to detect isolated defects since it is not possible to cover the whole area of interest with transducers. Guided waves therefore have great potential in SHM as they enable a large area of structure to be monitored from a limited number of transduction locations, so reducing the added weight, cost and complexity of the attachment to the structure. It is also possible to improve the sensitivity of the test relative to that obtained in one-off inspection by monitoring the change in signals with time using baseline subtraction. Current SHM deployments are largely in the same types of structure as those where guided wave NDT is used, but there is substantial potential for increasing the range of applications. The paper concludes with a review of the research and development needs for this potential to be realised.

On the use of a linear array EMAT for remote thickness gauging using the reflected modes on a steel pipe

Guided wave nondestructive testing refers to a set of fast and reliable techniques used to scan structures such as plates or pipes over medium to long range distances. The structural filtering method uses high-order modes and their cutoff frequency-thickness products to estimate the thickness along an inspection line. A corroded region, which can be approximated by a local loss of thickness, will act as a filter on the propagating modes. Because of their cutoff frequency-thickness product, some modes will not be able to propagate and will be either reflected or converted. Shear horizontal guided waves are the main candidate for structural filtering due to the simplicity of interpretation of their dispersion curves and their low sensitivity to non-viscous surface fluid loading. Electromagnetic acoustic transducers (EMAT) provide fast and efficient SH wave transduction but the most common designs, namely, periodic and permanent magnet EMAT is a mono element probe allowing modes to be excited only around a fixed wavelength. Recent work has shown that a linear array EMAT can be combined with a phase velocity excitation to allow almost complete control of the emitted waves in the frequency wavenumber space. In this paper, the linear array EMAT developed is used to estimate the minimum thickness of a defect machined on a 10.2 mm thick steel pipe with an external diameter of 323.8 mm. The measurements and finite element simulations carried out enabled us to estimate the thickness in several positions, with a maximum error of 0.4 mm and locate the defect with an error of 10 mm over a propagation distance of 600 mm.

Microcrack Defect Quantification Using a Focusing High-Order SH Guided Wave EMAT: The Physics-Informed Deep Neural Network GuwNet

It is challenging to apply deep learning in professional fields that lack big data support, especially in industrial structure health assessments using ultrasonic guided wave nondestructive testing (NDT) method. To solve this problem, one feasible solution is to introduce the concept of NDT physics into a deep neural network to compensate for the network's poor predictive abilities when trained on small datasets. Therefore, we propose a physics-informed deep neural network, named GuwNet, based on a unidirectional oblique-focusing (UOF) high-frequency, high-order shear horizontal guided wave electromagnetic acoustic transducer (EMAT) to quantify microcrack defects more accurately. First, the designed focused-transmission omnidirectional-reception UOF-EMAT can produce pure high-frequency, high-order guided waves. Through a circumferential arrangement of multiple receiving transducers, the maximum amount of information can be obtained regarding the reflected waves of the defect. This method solves the inherent problems of an EMAT (i.e., low energy conversion efficiency) and achieves effective detection of microcrack defects. Second, we study the quantification principle of microcrack defects suitable for UOF-EMAT, and propose a deep neural network using physical knowledge regarding this theory. We rationally design the network structure based on the quantitative principles and logic obtained from this article. In addition, feedback and feedforward loss functions suitable for evaluating different forms of variables are proposed to integrate the physical concepts of ultrasonic guided wave testing into the neural network training. Finally, we verify the performance of the proposed GuwNet based on the UOF-EMAT. Compared with traditional nonphysics-informed methods, the length, depth, and direction of the quantification errors are reduced to 0.127 mm, 0.279% <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d_t</i> , and 1.843°, respectively, and the average quantification error is reduced by more than 80%.

Guided Wave Propagation in Functionally Graded One-Dimensional Hexagonal Quasi-Crystal Plates

ABSTRACTDue to the high brittleness, cracks, holes, and other defects that are easily generated in quasi-crystal structures can affect safe applications in serious cases. For guided wave non-destructive testing, the propagation of Lamb and SH waves in functionally graded one-dimensional hexagonal quasi-crystal plates are investigated. Governing equations of wave motion in the context of Bak’s model are deduced and solved by the Legendre orthogonal polynomial method. Dispersion curves, phonon and phason displacement, and stress distributions are illustrated. The convergence of the present method applied to functionally graded quasi-crystal plates is verified. Moreover, the influences of the phonon-phason coupling effect and graded fields on wave characteristics are analyzed. Some new results are obtained: angular frequencies of phason modes always decrease as phonon-phason coupling coefficients, Ri, increase; and phonon and phason displacements of Lamb and SH waves at high frequencies are mainly distributed in the region that contains more quasi-crystal material with a smaller elasticity modulus and less rigidity. The obtained results establish the theoretical foundation of guided wave non-destructive testing for functionally graded quasi-crystal plates.

Sensitivity analysis of radial defect detection of gun barrel based on ultrasonic guided wave

In this paper, aiming at the low efficiency of defect detection of weapon equipment, ultrasonic guided wave non-destructive testing technology is proposed to detect the radial wear defects in gun barrel which have a great impact on its combat effectiveness. At the same time, the sensitivity of different modes of L0,2 and t0,1 ultrasonic guided waves to the detection of such defects is analyzed in this paper, so as to provide theoretical guidance for the mode selection of ultrasonic guided waves in the next practical detection of gun barrel.

Ultrasonic Guided Wave Inspection of Anchor Rods Embedded in Soil

Ultrasonic guided wave nondestructive testing for small-diameter cylindrical steel anchor rods embedded in soil was experimentally studied by using piezoelectric probes attached to the sides of the rods. The 60-kHz longitudinal [L(0,1)] mode was chosen as the guided wave for pulse-echo measurements on anchor rods with a diameter of around fifteen millimeters mainly because of its low attenuation due to energy leakage into the surrounding soil. Pulse-echo measurements were performed by using four transmitting and four receiving probes attached to the sides of anchor rods protruding above ground. Appropriate procedures for the transmission and reception can selectively generate the L(0,1) mode going in only the downward direction and can selectively extract the signal of the L(0,1) mode coming from only the lower direction, which considerably improves the signal-to-noise ratio (SNR). An experimental study for detecting defects of artificial cross-sectional loss on embedded anchor rods was conducted to examine the fundamental performance of the measurements by means of evaluating the SNRs. An on-site field experiment on actually used equipment was carried out to examine the potential of estimating degrees of real corrosion wastage on embedded anchor rods. The results show that the attenuation rate of the L(0,1) mode in the buried part of the rod and distance amplitude correction (DAC) curves taking account of the attenuation rate are effective in estimating the degrees of corrosion wastage on embedded anchor rods.

Global-Local model for guided wave scattering problems with application to defect characterization in built-up composite structures

Predicting scattering of elastic guided waves in multi-layered solid plates with geometrical and/or material discontinuities is of great interest to many fields, including ultrasonic-based Non-Destructive Testing (NDT) and health monitoring of critical structural components (SHM). The problem is complicated by the multimode and dispersive behaviour of the guided waves. This paper describes a unified Global-Local (GL) approach that is computationally efficient in cases that can be very complex in terms of geometry and/or material properties. One example of this is a composite built-up structure. The proposed GL procedure discretizes the “local” region with the scattering discontinuity by regular finite elements, and utilizes the efficient Semi-Analytical Finite Element solutions in the “global” region away from the scatterer. The GL formulation that is presented includes the dispersive unforced solutions for each applicable mode, the mode tracking, the scattered spectra (reflection and transmission), and the energy balance calculations. The algorithm is applied to the case of a composite skin-to-stringer assembly used in modern aircraft construction. Various representative defects in this assembly are modelled, and transmission spectra are calculated for both axial or flexural guided wave modes used in excitation. The resulting scattered spectra (which are the broadband transfer functions of the structure) can be useful to either select suitable wave mode-frequency combinations or to identify specific defects in guided-wave NDT or SHM tests of these components.

Guided waves in layered cylindrical structures with sectorial cross-section under axial initial stress

Due to mechanical loads, thermal fields and the limitation of the manufacturing technology, initial stresses in layered cylindrical structures are ineluctable. Accordingly, for the purpose of the guided wave nondestructive testing for the layered cylindrical structure with a sectorial cross-section, an analytical approach, the double-orthogonal polynomial method is utilized to investigate the influence of axial initial stress on wave characteristics. Based on Biot’s “Mechanics of Incremental Deformations”, the dynamic equations for the sectorial cylindrical structures in terms of displacements and axial initial stress are deduced. By virtual of the Heaviside function, the boundary conditions are automatically incorporated into constitutive equations and then into wave equations. The corresponding dispersion curves and displacement distributions of various sectorial cylindrical structures are calculated. Numerical results indicate that the influence of the initial stress applied on the outer layer is much significant at low frequencies, and the influence of the initial stress applied on the inner layer is much significant at high frequencies; the cut-off frequencies have negative relation with the area of the cross-section; the displacements at high frequencies are mainly distributed in the layer with smaller elasticity modulus, especially the layer simultaneously with bigger initial stress.

Experimental Study on Cable Guided Wave Non-Destructive Testing of Long Span Bridge

Present status of NDT technology for cables and suspender of long span bridges is introduced in this paper. The principles, advantages and disadvantages of various testing technologies for parallel wire stayed cables are described. An experimental study was carried out for non-destructive testing using guided wave technology. It is clear that the feasibility of guided wave technology be applied to cable detection. A clear proportional relationship between detection defects and signal response is defined.

Guided wave propagation in functionally graded cylindrical structures with sector cross-sections

The differential equations governing guided waves in functionally graded cylindrical structures with sector cross-sections are solved by introducing the double orthogonal polynomial series method into the cylindrical coordinate system, and the wave characteristics are subsequently investigated. The validity of the present method is confirmed by way of the comparison with available references, and the convergence is discussed. The corresponding phase velocity dispersion curves, displacement distributions and Poynting vectors are illustrated. The influences of the variation in the radius to thickness ratio, angular measure and gradient index on the guided wave characteristics are discussed, which can be used as significant guidance on ultrasonic guided wave non-destructive testing for functionally graded cylindrical structures with sector cross-sections.

Guided wave propagation in cylindrical structures with sector cross-sections

By introducing the double orthogonal polynomial method from the Cartesian coordinate system into the cylindrical coordinate system, this paper investigates the guided wave propagation in cylindrical structures with sector cross-sections. Comparison with available reference results, the validity of the presented method is verified. The corresponding phase velocity dispersion curves, displacement distributions, stress curves and the Poynting vectors are illustrated. The influences of the radius-to-thickness ratio and angular measure on the characteristics of the guided wave are discussed, which gives significant guidance on ultrasonic guided wave nondestructive testing for cylindrical structures with sector cross-sections.

A method of recognition and elimination to the pseudo defect signals by ultrasonic guided wave NDT for pipes

The detected signals using ultrasonic guided wave non-destructive testing (NDT) for pipes with the method of excited and received to one end of pipe, which run with come-and-go many times of reflection and transmission between the two ends of pipe and the defect location in pipe until its energy dissipation over. The multiple reflection and transmission process lead to the appearance of the pseudo defect signals which seriously affect the judgement of the defect numbers and its locations in pipes. Aiming at the difficulty problem of the pseudo defect signal identification, the sketch map of the propagation path of ultrasonic guided wave in pipeline is drawn. The position characteristic of the pseudo defect signal is summarized. Namely: the pseudo defect signal does not appear in the first reflection cycle of the detected signals or its amplitude of the signal is negligible; meanwhile, the larger amplitude of the pseudo defect signal appear from the the second reflection cycle of the detected signals, and which is symmetric with the real defect signal about the time domain midpoint of the signal period in the second reflection cycle. The correctness of this characteristic law is verified by using numerical simulation and experimental results. According to the characteristic law of the pseudo defect signal, the defect wave packet signals in the ultrasonic guided wave detected signals were identified and extracted, and the matching pursuit method and the numerical comparison assignment method were used to eliminate the pseudo defect signal. The conclusion are shown that the proposed method of the pseudo defect signal recognition and elimination in the ultrasonic guided wave NDT for pipes is practical and effective, which achieves the goal of discarding the false and retain the true detected signals, and solve the the detected signals recognition difficulty problem in ultrasonic guided wave NDT for pipes, and also greatly promotes the application of the ultrasonic guided wave NDT technology.

Phase-delayed laser diode array allows ultrasonic guided wave mode selection and tuning

Selecting and tuning modes are useful in ultrasonic guided wave non-destructive testing (NDT) since certain modes at various center frequencies are sensitive to specific types of defects. Ideally one should be able to select both the mode and the center frequency of the launched waves. We demonstrated that an affordable laser diode array can selectively launch either the S0 or A0 ultrasonic wave mode at a chosen center frequency into a polymer plate. A fiber-coupled diode array (4 elements) illuminated a 2 mm thick acrylic plate. A predetermined time delay matching the selected mode and frequency was employed between the output of the elements. The generated ultrasound was detected by a 215 kHz piezo receiver. Our results imply that this array permits non-contacting guided wave ultrasonic NDT. The solution is small, affordable, and robust in comparison to conventional pulsed lasers. In addition, it does not require experienced operators.

Relationship between Frequency Selection and Pipe Characteristics for Guided Waves NDT

Selecting proper guided wave exciting frequency is of important practical significance in the engineering application of guided wave non-destructive testing(NDT).The characteristic of guided wave propagation in pipes that L(0, 1) and L(0, 2) have a cutoff frequency are respectively discussed, and the calculation formulas of their cutoff frequency are given.The varied relationship between the cutoff frequency of L(0, 1) and L(0, 2) mode guide waves, the outer diameter and wall thickness of pipes are discussed respectively.For a given steel pipe, experiments are carried out by selection of different exciting frequency.The results show that the"low-pass"type cutoff frequency of L(0, 1) and"high-pass"type cutoff frequency of L(0, 2) are reduced with the increase of outer diameter of pipes, and the"low-pass"type cutoff frequency of L(0, 1) and"high-pass"type cutoff frequency of L(0, 2) initially increase with the increase of wall thickness of pipes, but the increased amplitude decreases slowly.When the outer diameter of pipes attains a certain value, both of the cutoff frequencies are irrelevant to wall thickness of pipes.The experimental results are in agreement with theoretical computation of selected exciting frequency for guided wave NDT of pipes.