Non-contact Ultrasonic Testing Research Articles

Debonding inspection with an enhanced miniature EMAT based on multiple pulse echoes

The present paper proposes a non-contact ultrasonic testing method for the debonding inspection of metal-based composite structures, utilizing an improved electromagnetic acoustic transducer (EMAT). The enhanced EMAT incorporates a carbonyl iron powder coil backplate and a small butterfly coil to enhance the detecting ability for interfacial bonding. A two-dimensional finite element model is developed to quantify the effectiveness of the carbonyl iron powder coil backplate on increasing the eddy current density and the magnetic flux density in the specimen. An experimental setup was designed using the Ritec SNAP 5000 and the improved EMATs to examine an aluminium-epoxy resin composite structure. Ultrasonic C-scan images of the specimen's bonding interface were obtained from the experiment. Both simulation and experimental results show that carbonyl iron powder coil backplates can increase the efficiency of the EMATs. By investigating the influence of echo number on debonding detection, it was revealed that employing higher-order echoes and utilizing carbonyl iron powder as the coil backplate can enhance the debonding detection capability. The C-scan imaging results indicate that the utilization of high-order echoes enhances imaging quality, and the employment of high-quality miniaturized EMATs enhances the capability for quantitative analysis of debonding defects.

Deep Learning–Based Time-Series Classification for Robotic Inspection of Pipe Condition Using Non-Contact Ultrasonic Testing

Abstract This journal paper explores the application of Deep Learning (DL)-based Time-Series Classification (TSC) algorithms in ultrasonic testing for pipeline inspection. The utility of Electromagnetic Acoustic Transducers (EMAT) as a non-contact ultrasonic testing technique for compact robotic platforms is emphasized, prioritizing computational efficiency in defect detection over pinpoint accuracy. To address limited sample availability, the study conducts benchmarking of four methods to enable comparative evaluation of classification times. The core of the DL-based TSC approach involves training DL models using varied proportions (60%, 80%, and 100%) of the available training dataset. This investigation demonstrates the adaptability of DL-enabled anomaly detection with shifting data sizes, showcasing the AI-driven process's robustness in identifying pipeline irregularities. The outcomes underscore the pivotal role of artificial intelligence (AI) in facilitating semi-accurate but swift anomaly detection, thereby streamlining subsequent focused inspections on pipeline areas of concern. By synergistically integrating EMAT technology and DL-driven TSC, this research contributes to enhancing the precision and near real-time inspection capabilities of pipeline assessment. This investigation collectively highlights the potential of DL networks to revolutionize pipeline inspection by rapidly and accurately analyzing ultrasound waveform data.

Noncontact nondestructive ultrasonic techniques for manufacturing defects monitoring in composites: a review

Composite materials are widely used in most industries due to their high specific strength, specific stiffness, and their relatively lighter weight compared to other traditional materials. However, the presence of defects arising from manufacturing processes or during service loads can make these structures more susceptible to a diminished performance. Furthermore, the former defects are inevitable in composite structures, but they can be reduced. Each type of defect requires specific inspection techniques and configurations. In this work, a review of the different types of composites manufacturing processes and their corresponding resultant defects is presented with the various nondestructive evaluation techniques employed for these defects’ characterization. The emphasis of this paper is on ultrasonic inspection and detection techniques for they present high sensitivity to surface/subsurface discontinuities, superior depth of ultrasonic penetration for flaw detection, feasibility on large scales, and instantaneous and detailed images production. Notably, noncontact ultrasonic testing techniques are also reviewed, air-coupled techniques in specific, and highlighted as a fine alternative to conventional contact inspection systems as they reduce the restrictions that coexist with the use of couplants. Moreover, these ultrasonic testing techniques are summarized to show the latest research progress achieved in the field of air-coupled ultrasonic inspection systems for manufacturing defects’ monitoring in composite structures including delamination, porosity, dryness, waviness, and resin lack/excess. Finally, we highlight the type and central frequency of the transducers and experimental results present in literature and obtained in terms of both detection and size of the defects.

In-Motion Railroad Tie Deflection Measurement via Ultrasonic Airborne Sonar and Computer Vision Techniques

ABSTRACT It is known in the railroad maintenance engineering community that the deflection of railroad ties is an indicator of the quality of the tie–ballast interface, whose deterioration may cause dangerous train derailments. A new technology is proposed to reconstruct the full-field deflection profile of railroad ties in-motion by means of non-contact ultrasonic testing and computer vision techniques. The sensing layout consists of an array of air-coupled capacitive transducers (operated in pulse-echo sonar-based ranging mode) and a high frame-rate camera, rigidly connected to the main frame of a moving train car. The acquisition system is programmed such that the synchronized waveforms and images are collected and saved as train car moves. In the processing stage, a supervised machine learning-based image classification approach is developed to demarcate the tie boundaries. For this purpose, the Speeded-Up Robust Features (SURF) and Bag of Visual Words (BOVW) algorithms are employed to encode images into condensed feature vectors, which are subsequently fed into the Support Vector Machine (SVM) to train a classifier. The relative deflections of the identified ties are eventually computed by tracking the time-of-flight of the reflected waves from the surfaces flagged as tie. An image processing technique is also developed to estimate the spatial resolution of the tracking system, required to reconstruct the full-field deflection profile of the scanned ties. The importance of such a technique is stressed if the test run is performed without any dedicated positioning system. The proposed ‘tie sonar’ system was prototyped and used to reconstruct the deflection profile of the ties scanned during a series of test runs conducted at slow (walking) speed at the Rail Defect Testing Facility (RDTF) of UC San Diego as well as a BNSF yard in San Diego, CA, with a realistic train load. Further developments of this system should include a performance evaluation at higher speeds (e.g., revenue speed).

Assessment of degradation index in freeze-thaw damaged concrete using multi-channel contactless ultrasound

• Efficient data acquisition framework for contactless ultrasonic testing utilizing multi-channel MEMS array. • Introduction of Degradation Index based on leaky Rayleigh waves with increasing freeze-thaw damage in concrete. • Numerical and experimental Validations with data obtained from freeze-thaw damaged concrete. • Improvement of surface damage detection with ultrasound scanning compared to the point measurement-based methods. Concrete is among the most widely used construction materials, especially in national infrastructure such as bridges, dams, and ports. This material fulfills an important role in ensuring the durability of structures that incorporate it. With recent climate change, issues related to degradation of concrete resulting from combined deterioration, e.g., freeze-thaw damage and chloride attack, have been increasingly reported, and, accordingly, there have been many studies focusing on the assessment of concrete durability using non-destructive testing. Non-contact ultrasonic testing measures leaky Rayleigh waves propagating through concrete, where the measurement procedure is a fully non-contact manner with the help of advanced sophisticated MEMS (Microelectromechanical systems) hardware technology. In the present study, a 64-channel non-contact ultrasonic system was developed to assess freeze-thaw damage of concrete elements, and an algorithm to assess concrete damage based on the velocities of leaky ultrasonic waves, the degradation index (DI), was proposed. The proposed system and algorithm were verified through a numerical analysis and experiments with varying degrees of freeze-thaw damage. The numerical analysis results showed that the velocity of ultrasonic waves, along with the degree of degradation, decreased with an increasing simulated damage ratio. The experimental freeze-thaw test results also confirmed that the DI was more sensitive to damage from the initial freeze-thaw cycles compared to the existing evaluation indexes, such as the relative dynamic elastic modulus.

The effect of copper grain size on laser ultrasonic backscattered signal

Grain size has an essential influence on the serviceability of metallic materials. In this paper, a noncontact laser ultrasonic testing platform is built to study the effect of copper grain size on the laser ultrasonic backscattered signal. According to the correlation between grain size and ultrasonic wavelength, the ultrasonic scattering by copper grains in the experiment contains not only Rayleigh scattering but also the transition region from Rayleigh scattering to stochastic scattering. Using time–frequency analysis, the influence of copper grain size on the characteristic parameters of backscattering was explored, and a prediction model of grain size was established, which was compared with the prediction model based on the attenuation method to verify the accuracy of the backscattering model. The results show that the backscattered signal can adequately characterize the grain size information and laser ultrasonics is a method that can realize on-line detection of grain size.

All-optical laser ultrasonic technique for imaging of subsurface defects in carbon fiber reinforced polymer (CFRP) using an optical microphone

Defects, such as delamination and debonding, are critical to the performance of carbon fiber-reinforced polymer (CFRP) composites. In recent years, non-destructive testing techniques have been improved for the inspection of these defects among CFRPs. In this study, an all-optical and non-destructive laser ultrasonic technique with an optical microphone detection module has been presented to detect the artificial subsurface defects among the CFRP composites. A finite element simulation based on the thermo-mechanical coupling model was used to study the process of nanosecond pulsed laser excitation of the CFRP laminate to produce ultrasound and the propagation behavior of ultrasound among the CFRP laminate. A series of non-contact laser ultrasonic testing experiments were carried out to study the flat bottom holes of different sizes via a laser ultrasonic detection system. The artificial subsurface defects were reliably identified by the presented all-optical laser ultrasonic system imbedded in the optical microphone using four feature images.

Автоматизована система безконтактного ультразвукового неруйнівного контролю якості корпусів ракетних двигунів твердого палива з композиційних матеріалів

Currently, in various industries (engineering, aircraft, energy, etc.) the issue of product quality assurance and control is particularly acute. This is due primarily to the ever-increasing requirements for increasing reliability with increasing loads on products, which entails the strengthening of technical standards. The issue of quality control for rocket and space technology products is especially relevant. Modern power structures of rocket and spacecraft made of polymer composite materials, and especially the body of solid fuel rocket engines (SFRЕ), are multilayer packages of various polymer-composite materials (PKM), obtained and interconnected in the process of manufacturing the body. The efficiency of SFRЕ depends on the quality of the formation of PKM in production conditions. The most important issues are the implementation of production quality control of composite structures, the reliability of control results and the ability to automate the control process. The article presents an automated system of non-contact ultrasonic non-destructive testing, which allows to control the stability of the technological process of forming the composite material of the wall of the SFRЕ body and, if necessary, to adjust it. The probability of detecting zones of anomalous violation of the integrity of the wall material of the SFRЕ housing is carried out due to adaptive algorithms, digital systems of multilevel matrix processing and optimal filtering of the received signals. The automated system of contactless ultrasonic non-destructive quality control of SFRЕ cases allows to register conditions of scanning and control for more visual representation of the defectogram in the expanded look of the case of a product in the course of control and at documentation of its results. The presented results of work on the development of an automated system of non-destructive testing of the integrity of the buildings of the SFRЕ type "cocoon" confirm the possibilities of practical implementation in production.

Fully noncontact inspection of closed surface crack with nonlinear laser ultrasonic testing method

Nonlinear ultrasonic testing method is one of few techniques that are effective for evaluating early material degradation and micro-crack initiation by analysing the nonlinear effects of ultrasonic waves. This study presents a noncontact nonlinear ultrasonic testing method based on lasers for closed surface crack inspection. A pulsed laser grating source by grating mask is applied to generate narrowband surface acoustic wave of a chosen frequency. A nonlinear numerical simulation based on Finite Element Method (FEM) is developed to simulate the generation of higher harmonics by closed surface crack. The simulation results show that the acoustic nonlinearity parameter increases with the micro closed crack length, while decreases with the micro closed crack buried depth. Moreover, the detection capability of this method is verified by an experiment. The experimental results show that the proposed laser-based nonlinear ultrasonic testing method can provide a fully noncontact and coupling-free measurement method for closed surface crack inspection.

Visual quantitative detection of rail surface crack based on laser ultrasonic technology

The surface rolling contact fatigue crack is a common crack on the rail surface. When it extends to a certain length, it will lead to rail fracture and affect the safety of railway operation. Therefore, it is necessary to carry out quantitative detection of RCF cracks to ensure the safety of railway operation. The state-of-the-art shows that the visualization method has advantages for quantitative crack detection. In this study, a quantitative detection method combining non-contact laser ultrasonic testing technology and variational mode decomposition (VMD) is proposed to realize the visual detection of the oblique crack on the railhead surface. Wigner time-frequency distribution and fir1 filtering are used to preliminarily filter all scanning signals. Further, VMD is utilized to decompose the signal into multiple intrinsic mode function (IMF) component signals and improve signal-to-noise ratio (SNR). According to the correlation coefficient (C) and SNR characteristics between different IMF components and the original signal, the optimal IMF component is selected. Finally, visual crack-induced surface wave energy from the ultrasonic propagation images is realized according to the time-domain and time characteristics of signals. The visual quantitative detection of RCF cracks in different lengths is realized clearly and intuitively, and the quantitative error is less than 5%. This method lays a foundation for the visual detection of laser ultrasonic rail surface defects.

Nondestructive assessment of cross-laminated timber using non-contact transverse vibration and ultrasonic testing

Cross-laminated timber (CLT) is a new generation of engineered wood product developed initially in Europe and has been used in North America for various applications. CLT is composed of at least three layers of lumber boards stacked crosswise in orthogonally alternating orientation to the adjacent layers. CLT has been gaining popularity and increasing application areas in the construction industry, such as building systems, mats for construction and temporary road applications as well as temporary bridges. It is especially identified as the prevailing material in modular construction for the future building industry. However, CLT as a relatively new structural material has limited studies related to their durability and long-term performance. Moreover, nondestructive evaluation methods to understand their mechanical behavior after exposure to harsh environment are lacking. This paper contributes to the development of a rapid nondestructive evaluation method to assess the mechanical properties using transverse vibration method and ultrasonic testing. The free vibration response triggered by the impulse excitation is captured using contact accelerometer and non-contact laser Doppler vibrometer (LDV). The LDV measurement is proven to respond similar to conventional accelerometers but more convenient as a rapid assessment method. While the longitudinal wave speed is measured by ultrasonic testing (UT) in a through-transmission mode, the modulus of elasticity was calculated in terms of measured wave speed. By investigating the different structural states and dimensions of CLT samples, the laboratory and the manufacturing facility, the influences of aging on effective dynamic modulus of elasticity (MOE) and damping are shown. The numerical and experimental results indicate the increase in moisture content decreases the fundamental frequency. Therefore, moisture content should be measured in order to examine the coupled effects of moisture content and aging on the fundamental frequency. The damping ratio extracted using half-power bandwidth method is shown as an additional information related to the moisture content. The non-contact transverse vibration method and UT are shown as an efficient nondestructive evaluation method for assessing the CLT structural state right after the manufacturing as a quality assurance method or after their service in field as a diagnostic tool.

Fully noncontact measurement of inner cracks in thick specimen with fiber-phased-array laser ultrasonic technique

To realize a fully noncontact ultrasonic testing method for inner cracks inspection in thick metal specimen, a phased array laser ultrasonic testing system with using a compact optic fiber array bundle and a laser interferometer is developed in this study. The focusing and steering of the shear wave and longitudinal wave generated with seven fiber-phased-array laser sources in thermoelastic regime is investigated by a numerical simulation and validated by the experiment. A non-contact measurement of the inner-surface cracks by both the angle-beam testing method and time-of-flight diffraction method with the fiber-phased-array laser ultrasonic technique have been studied.

A New Ultrasonic Testing Method for Residual Strain Measurement With Laser Grating

Abstract In this paper, a new and noncontact ultrasonic testing (UT) method using laser grating is proposed for the residual strain measurement. In this method, the laser grating technique is utilized to generate coherent surface waves with a specific wavelength in the narrow frequency band. A numerical method based on the finite element model is established to simulate the coherent surface waves generated by the laser grating in prestrained media to determine the capability and sensitivity of this method. The relationship between the strain and frequency spectrum of the coherent surface wave is studied. Finally, an experiment validation of the laser grating-based UT of residual strain is carried out using specimen with different plastic strains by the tensile test.

Measurement of Adhesive Bonding Strength With an EMAT in the Resonant Mode

Abstract The electromagnetic acoustic resonance (EMAR) method with shear wave is sensitive to boundary conditions and plate thickness. In this paper, a new noncontact ultrasonic testing method based on the electromagnetic acoustic transducer (EMAT) in the resonant mode is proposed for the bonding strength evaluation in metal-based adhesive structures. Different from the conventional pulse-echo method using short-burst excitation for bonding inspection, the attenuation coefficient feature of the resonant ultrasonic signal with long-burst excitation is applied to increase the signal-to-noise ratio (SNR) and detecting sensitivity of the EMAT for adhesive bonding strength evaluation. A theoretical model for adhesive bonding testing with EMAT signals in the resonant mode is established. To extract the signal feature representing the reflection coefficient, the time-domain signal was processed by Hilbert transformation and exponential curve fitting. Through the simulation on the received signal, the correlation between the attenuation coefficient of the exponent fitted curve and the strength on the adhesive imperfect interface were confirmed. Finally, the proposed correlation is verified by an experiment on stainless steel plates bonded with polymethyl methacrylate plates by epoxy adhesion via a permanent magnetic EMAT.

Progress on the ultrasonic testing and laser thermography techniques for NDT of tokamak plasma-facing components

ABSTRACT During manufacturing and operation, different kinds of defects, e.g., delamination or surface cracks, may be generated in the plasma-facing components (PFCs) of a Tokamak device. To ensure the safety of the PFCs, various kinds of nondestructive testing (NDT) techniques are needed for different defect and failure mode. This paper gives a review of the recently developed ultrasonic testing (UT) and laser thermography methods for inspection of the delamination and surface cracks in PFCs. For monoblock W/Cu PFCs of divertor, the bonding quality at both W-Cu and Cu-CuCrZr interfaces was qualified by using UT with a focus probe during manufacturing. A noncontact, coupling-free and flexible ultrasonic scanning testing system with use of an electromagnetic acoustic transducer and a robotic inspection manipulator was introduced then for the in-vessel inspection of delamination defect in first wall (FW). A laser infrared thermography testing method is highlighted for the on-line inspection of delamination defect in FW through the vacuum vessel window of the Tokamak reactor. Finally, a new laser spot thermography method using laser spot array source was described for the online inspection of the surface cracks in FW.

Detection and Characterization of Debonding Defects in Aeronautical Honeycomb Sandwich Composites Using Noncontact Air-Coupled Ultrasonic Testing Technique

The finite models of honeycomb sandwich composite with intact and embedded debonding defects are constructed. The sound pressure in fluid domain and the stress strain problem in solid domain are related by acoustic-structure coupling method, which visually shows the propagation process and modal characteristics of the acoustic wave inside the honeycomb sandwich composite. The simulation results show that the transmission longitudinal wave T1 (transmission initial wave) can effectively characterize debonding defects of honeycomb sandwich composite. However, in the actual detection of honeycomb sandwich composite, there are some problems, such as poor Signal-to-noise ratio (SNR) of received signal, incognizable transmission initial wave. In order to solve these problems, this paper proposes to apply polyphase coded pulse compression technique to air-coupled ultrasonic testing system. The actual test results show that the SNR of received signal is effectively improved, the transmission initial wave can be effectively identified, and the compressed signal has a good response to debonding defect. The air-coupled ultrasonic testing C scan result of honeycomb sandwich composite verifies the rationality and correctness of the theoretical simulation and signal processing technique, which promotes industrial application of air-coupled ultrasonic testing technique in the aerospace field.

Adhesive debonding inspection with a small EMAT in resonant mode

In this paper, a noncontact ultrasonic testing method with using a small electromagnetic acoustic transducer (EMAT) in resonant mode is proposed for metal-based adhesive debonding inspection. The small EMAT with a new magnet configuration and a small coil is developed firstly to improve the spatial resolution and detecting ability for minute defects. Different from conventional pulse echo method using short pulse excitation for debonding inspection, a new method based on power spectrum estimation of the resonant ultrasonic signal with long burst excitation is applied to increase the signal-to-noise ratio (SNR) and detecting ability of the small EMAT. Finally, ultrasonic C-scan images of specimens with various adhesive bonding are obtained to demonstrate the capability of this technique.

Refinement of defect detection in the contact and non-contact ultrasonic non-destructive testing of wind turbine blade using guided waves

The guided waves are widely used for the inspection of many composite structures as they can travel up to long distance along the thickness of the structure. Most of the times, the experimental investigations standalone is not able to locate and size the damages or defects due to dispersive, superimposed and scattered guided wave modes. Hence signal refinement of ultrasonic guided wave signals is required for identifying and characterizing the defects. In this work, disbond type defects presented on different locations of the segment of the wind turbine blade are estimated by applying the signal refinement techniques after experimental analysis. The experiment was carried out on a 1005 x 870 mm segment of wind turbine blade manufactured using a composite glass fiber reinforced plastic material. Two defects on the trailing edge (with diameter 15 and 25 mm) and three defects on the main spar (with diameters 25, 51 and 81 mm) of the WTB segment were investigated. The combination of macro fiber composite transducer, contact type and air-coupled transducers were used to transmit and receive the ultrasonic guided waves. The signal processing techniques are applied to the experimental signals for the estimation and characterization of defects.

Detection of small-flaw in carbon brake disc (C-C) using air-coupled ultrasonic C-scan technique

The purpose of this paper is to conduct the study on detection identification and assessment of internal defects for the C-C brake disc composite for aircrafts by applying non-contact air-coupled ultrasonic testing. The Non-contact Air-coupled Ultrasonic Testing (NAUT) used in this paper is the most advanced ultrasonic testing technique. It is a nondestructive testing that complements the energy loss occurred due to the acoustic impedance difference in the air with two transmitting/receiving non-contact ultrasonic probes and enables the non-contact ultrasonic testing through high-powered ultrasonic focusing by using high-frequency band ultrasonic Pulser- Receiver. In this paper, non-contact air-coupled ultrasonic detection experiment applied the Transmission Method and Reflection Method was conducted as follows; When detecting an internal defect of the carbon brake disc, we compared the C-scan results according to whether masking was applied to the side of the object to be detected, measured at the ultrasonic transmission frequencies of 340 kHz and 400 kHz respectively, to detect internal defects of the carbon brake disc through the measured C-scan images. In this way, we confirmed that there is a significant difference in the internal defect detection performance depending on the masking and the change in the ultrasonic transmission frequency value.

Development of a flexible film electromagnetic acoustic transducer for nondestructive testing

Electromagnetic acoustic transducers (EMATs) have been widely applied for non-contact and coupling-free ultrasonic testing (UT) of metal structures. In this paper, a new EMAT of flexible film type with thickness less than 1mm, which uses dual coil configuration but without a permanent magnet, is proposed for both ultrasound generation and detection. Instead of using permanent magnet, a planar magnetic coil fed with a rectangular-pulsed current with duration about 1.5ms is used to generate magnetic flux in the test objects. The obvious advantages of the proposed flexible film EMAT are that it can be easily applied for non-contact and coupling-free UT of curved structures and objects with very narrow inspection space. Pulsed electromagnetic fields and the induced ultrasound waves are studied by simulation and experiment. The results show that the flexible film EMAT has a good performance for generating and receiving ultrasonic waves and can be easily applied for testing of curved structural component with narrow inspection space.