Real-time Non-destructive Testing Research Articles

Mid-infrared optical coherence tomography with MHz axial line rate for real-time non-destructive testing

Non-destructive testing (NDT) is crucial for ensuring product quality and safety across various industries. Conventional methods, such as ultrasonic, terahertz, and x-ray imaging, have limitations in terms of probe-contact requirement, depth resolution, or radiation risks. Optical coherence tomography (OCT) is a promising alternative to solve these limitations, but it suffers from strong scattering, limiting its penetration depth. Recently, OCT in the mid-infrared (MIR) spectral region has attracted attention with a significantly lower scattering rate than in the near-infrared region. However, the highest reported A-scan rate of MIR-OCT has been 3 kHz, which requires long data acquisition time to take an image, unsatisfying industrial demands for real-time diagnosis. Here, we present a high-speed MIR-OCT system operating in the 3–4 µm region that employs the frequency-swept spectrum detection in OCT technique based on time-stretch infrared spectroscopy. By integrating a broadband femtosecond MIR pulsed laser operating at a repetition rate of 50 MHz, we achieved an A-scan rate of 1 MHz with an axial resolution of 11.6 µm, a 10 dB roll-off depth of about 700 µm, and a sensitivity of 55 dB. As a proof-of-concept demonstration, we imaged the surface of substrates covered by highly scattering paint coatings. The demonstrated A-scan rate surpasses previous state of the art by more than two orders of magnitude, paving the way for real-time NDT of industrial products, cultural assets, and structures.

Single-frame temporal phase-shifting shearography for real-time nondestructive testing

Shearography, which is an effective nondestructive testing (NDT) tool, can detect internal defects of composites materials. Temporal phase-shifting (TPS) shearography has a simple setup and high accuracy. It is suitable for quasi-static detection because it requires the acquisition of a sequence of speckle patterns before and after specimen deformation. To achieve dynamic shearographic NDT, this study adopted high-frequency synchronous driving mode of camera and piezoelectric transducer (PZT) phase shifter to generate and acquire phase-shifted patterns. Subsequently, a single frame TPS shearography requiring one phase-shifted pattern in the deformed state was proposed. Finally, using parallel computing technology and efficient approximations of arctangent function, a real-time four-step TPS shearographic NDT technique with high-quality phase imaging was developed. The experimental results demonstrate the effectiveness and robustness of the proposed method. The results show that the proposed method could reach a rate of approximately 24 fps (frames per second) at the spatial resolution of megapixels for defect detecting.

Ensemble learning based compressive strength prediction of concrete structures through real-time non-destructive testing

This study conducts an extensive comparative analysis of computational intelligence approaches aimed at predicting the compressive strength (CS) of concrete, utilizing two non-destructive testing (NDT) methods: the rebound hammer (RH) and the ultrasonic pulse velocity (UPV) test. In the ensemble learning approach, the six most popular algorithms (Adaboost, CatBoost, gradient boosting tree (GBT), random forest (RF), stacking, and extreme gradient boosting (XGB)) have been used to develop the prediction models of CS of concrete based on NDT. The ML models have been developed using a total of 721 samples, of which 111 were cast in the laboratory, 134 were obtained from in-situ testing, and the other samples were gathered from the literature. Among the three categories of analytical models—RH models, UPV models, and combined RH and UPV models; seven, ten, and thirteen models have been used respectively. AdaBoost, CatBoost, GBT, RF, Stacking, and XGB models have been used to improve the accuracy and dependability of the analytical models. The RH-M5, UPV-M6, and C-M6 (combined UPV and RH model) models were found with highest performance level amongst all the analytical models. The MAPE value of XGB was observed to be 84.37%, 83.24%, 77.33%, 59.46%, and 81.08% lower than AdaBoost, CatBoost, GBT, RF, and stacking, respectively. The performance of XGB model has been found best than other soft computing techniques and existing traditional predictive models.

Chloride ion permeation and electrochemical impedance response of red mud-coal metakaolin geopolymer concrete

In geopolymer concrete, chloride ions largely contribute to the surface passivation of steel reinforcement and accelerate its corrosion. However, real-time nondestructive testing of chloride ion diffusion has not been widely conducted. Therefore, this study determined the distribution of chloride ions in red mud-coal metakaolin geopolymer concrete with different water-binding ratios under natural immersion conditions. The electrochemical properties of geopolymer concrete in a sodium chloride environment were examined by electrochemical impedance spectroscopy (EIS) and the relationship between these properties and the chloride ion diffusion coefficient was established. The experimental results showed that the contents of free chloride ions, total chloride ions, and bound chloride ions gradually decreased with increasing penetration depth; total chloride ions and free chloride ions increased at the same depth with increasing water-binder ratio; and bound chloride ions decreased with increasing ratio. In addition, the contents of free chloride ions, total chloride ions, and bound chloride ions gradually increased with the increase of the immersion age. The EIS results showed that there was a significant correlation between the diffusion coefficient and the electrochemical parameters. Therefore, EIS is suitable for detecting the diffusion of chloride ions in geopolymer concrete.

Durability study and mechanism analysis of red mud-coal metakaolin geopolymer concrete under a sulfate environment

The durability of construction materials in sulfate environments is extremely important for their service life. Geopolymer concrete, as a new type of construction material, has been subjected to very little research in sulfate environments and lacks real-time nondestructive testing methods. For this reason, in this study, the physical and mechanical properties of geopolymer concrete synthesized from red mud and coal metakaolin were tested and compared with ordinary silicate cement concrete. The physical phase composition, micro-morphology, porosity and functional group composition of the red mud-coal metakaolin geopolymer concrete were further analyzed using XRD, SEM-EDS, FT-IR and NMR. In addition, the electrochemical properties of the geopolymer were tested by electrochemical impedance spectroscopy and correlated with the diffusion coefficient of the material. The results show that the stability and compressive strength of geopolymer concrete is significantly better than that of ordinary silicate cement concrete in sulfate environment. Ettringite and gypsum type expansion damage were present in ordinary silicate cement concrete. In contrast, only sodium sulfate crystals were found in geopolymer concrete and no expansion products were found. This nearly indicates that the inert interaction between sulfate and hydration products is the main reason for its superior sulfate resistance. There is a significant correlation between the diffusion coefficient of red mud-coal metakaolin polymer concrete and the electrochemical parameter RCP/t and RDCP/t. Therefore, electrochemical impedance spectroscopy testing can be used as a real-time, non-destructive means of monitoring the performance of geopolymer concrete in sulfate environments.

Quantitative Investigation of Acoustic Emission Waveform Parameters from Crack Opening in a Rail Section Using Clustering Algorithms and Advanced Signal Processing.

Acoustic emission (AE) is an emerging technology for real-time non-destructive testing of structures. While research on a simulated AE source in rail and testing on rail material using small beam samples have been conducted, a study is required in lab environment to investigate AE waveform characteristics generated by crack in rail. In this paper, a three-point bending test is conducted on an actual rail section of 1500 mm with transverse damage of 38% head area to simulate AE source due to crack opening in the rail. AE signals are recorded for three different loads. For data analysis, unsupervised machine learning algorithms such as k-means, fuzzy-C mean and gaussian mixture model are used to cluster and filter out usable signals from the whole dataset corrupted by noisy signals from various sources. k-mean with principal component was observed to be best technique based on silhouette score. The frequency and amplitude of waveform have been discussed in relation to load and crack opening displacement. This study establishes a baseline for linking load, crack opening, and AE wave characteristics. This work can ultimately aid in the development of robust denoising, and damage analysis algorithms based on the frequency content and dispersion of the AE waveform.

Development of on-line nondestructive testing device for welding cracks based on piezoelectric ceramic excitation

Perform real-time non-destructive testing of weld damage in various welded structures of steel to determine the degree of weld damage in order to make timely safety warnings to protect human life and property safety. In this paper, piezoelectric ceramics are arranged on both sides of the weld to find the best frequency of the excitation system. The sine signal of this frequency excites the piezoelectric ceramics on one side, and receives and analyzes the response signals of the piezoelectric ceramics on the other side. This paper uses direct digital frequency synthesis technology (DDS), power management circuit, differential amplifier circuit, band-pass filter circuit, phase detection circuit, amplitude detection circuit, etc. to design a system that can perform real-time nondestructive testing. The whole system can measure the changes of these signals in real time, and send the signals to the upper computer remotely. Analysis of these signals can initially determine the size and location of weld damage. The research results show that when the weld in the steel is damaged, the amplitude of the sinusoidal signal propagating through the weld will be attenuated, and the phase difference between the transmitted signal and the received signal will increase. This change is positively correlated with the degree of damage.

A Real-Time NDT Method Based on FBG Sensor Spectrums to Detect the Transverse Matrix Cracks in Composite Materials

Transverse matrix cracking is probably the first and most dominant mode of damage in composite materials. In this paper, a real-time Non-Destructive Testing (NDT) method was proposed to detect the transverse cracks by Fiber Bragg Grating (FBG) sensors. The experiment of observing the crack growth and recording FBG’s reflection spectrums as well as Finite Element Method (FEM) methods were conducted to help verifying the regularities of the reflection spectrum distortions in the cracking angle-ply [0n/ ± θm/0n] laminates. The results showed that the shape of the spectrum was highly correlated to the crack density of composites. From undamaged state to high crack density conditions, the shape of the spectrum experienced an ‘original-splitting-regressive’ process. Under the assumed ideal periodic strain distribution conditions, the peak width w of the reconstructed spectrums and crack density $$\rho$$ showed very good linearity which provided the possibility for quantitative detection of the crack density of composites.

Experimental Study of Microstructures in Bias Weld of Coiled Tubing Steel Strip With Multi-Frequency Eddy Current Testing

Coiled tubing technology is widely used in drilling and repairing operations, and the quality of bias weld directly determines the fatigue life of the coiled tubing. The microstructures consistency between the bias weld and the base metal determines that whether the fatigue resistance of the weld reaches the level of the base metal. In this paper, multi-frequency eddy current testing technique is used to detect the reactance of the bias weld zone and the base material zone within coiled tubing steel strip, which can be used to determine the microstructure consistency between the base metal area and the weld area, and in turn to improve the welding technology and heat treatment process. In this work, CT100 and CT90 materials with the bias weld for coiled tubing were used as the test samples, and the on-line real-time non-destructive testing technology was used to judge whether welding technology and heat treatment technology have been improved. The basis for determination is whether the mechanical properties and fatigue properties of the welding site reach the base material level. The weld zone and base metal zone can be identified by analyzing the characteristic cloud map of the detection signal, and then the quality of partial weld can be evaluated according to the difference of microstructure between them, which is of guiding significance for quality control and improvement of coiled tubing production process.

A nonlinear Kernel-based adaptive learning-by-examples method for robust NDT/NDE of conductive tubes

ABSTRACTIn this work, the real-time non-destructive testing and evaluation (NDT/NDE) of faulty conductive tubes from eddy current (EC) measurements is addressed and solved in a computationally efficient way by means of an innovative learning-by-examples (LBE) methodology. More specifically, the estimation of the descriptors of a defect embedded within the cylindrical structure under test (SUT) is yielded by combining a non-linear feature extraction technique with an adaptive sampling strategy able to uniformly explore the arising feature space. Predictions are then performed during the on-line testing phase by means of a support vector regression (SVR). Representative results from a numerical/experimental validation are reported to assess the effectiveness of the proposed approach also in comparison with competitive state-of-the-art approaches.

Real-time high-resolution mid-infrared optical coherence tomography

The potential for improving the penetration depth of optical coherence tomography systems by using light sources with longer wavelengths has been known since the inception of the technique in the early 1990s. Nevertheless, the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region, resulting in slow acquisition, low sensitivity, and poor axial resolution. In this work, a mid-infrared spectral-domain optical coherence tomography system operating at a central wavelength of 4 µm and an axial resolution of 8.6 µm is demonstrated. The system produces two-dimensional cross-sectional images in real time enabled by a high-brightness 0.9- to 4.7-µm mid-infrared supercontinuum source with a pulse repetition rate of 1 MHz for illumination and broadband upconversion of more than 1-µm bandwidth from 3.58–4.63 µm to 820–865 nm, where a standard 800-nm spectrometer can be used for fast detection. The images produced by the mid-infrared system are compared with those delivered by a state-of-the-art ultra-high-resolution near-infrared optical coherence tomography system operating at 1.3 μm, and the potential applications and samples suited for this technology are discussed. In doing so, the first practical mid-infrared optical coherence tomography system is demonstrated, with immediate applications in real-time non-destructive testing for the inspection of defects and thickness measurements in samples that exhibit strong scattering at shorter wavelengths.

Advanced statistical learning method for multi-physics NDT-NDE

This work presents an innovative multi-physics (MP) Learning-by-Examples (LBE) inversion methodology for real-time non-destructive testing (NDT). Eddy Current Testing (ECT) and Ultrasonic Testing (UT) data are effectively combined to deal with the localization and characterization of a crack inside a conductive structure. An adaptive sampling strategy is applied on ECT-UT data in order to build an optimal (i.e., having minimum cardinality and highly informative) training set. Support vector regression (SVR) is exploited to obtain a computationally-efficient and accurate surrogate model of the inverse operator and, subsequently, to perform real-time inversions on previously-unseen measurements provided by simulations. The robustness of the proposed MP-LBE approach is numerically assessed in presence of synthetic noisy test set and compared to single-physic (i.e., ECT or UT) inversion.

Imaging of spatial distributions of the millimeter wave intensity by using the Visible Continuum Radiation from a discharge in a Cs–Xe mixture. Part II: Demonstration of application capabilities of the technique

The paper presents the second part of the review on a high-sensitive technique for time-resolved imaging and measurements of the 2D intensity profiles of millimeter-wave radiation by means of Visible Continuum Radiation emitted by the positive column of a medium-pressure Cs-Xe DC Discharge (VCRD method). The first part of the review was focused on the operating principles and fundamentals of this new technique [Plasma Phys. Rep. 43, 253 (2017)]. The second part of the review focuses on experiments demonstrating application of this imaging technique to measure the parameters of radiation at the output of moderate-power millimeter-wave sources. In particular, the output waveguide mode of a moderate-power W-band gyrotron with a pulsed magnetic field was identified and the relative powers of some spurious modes at the outputs of this gyrotron and a pulsed D-band orotron were evaluated. The paper also reviews applications of the VCRD technique for real-time imaging and nondestructive testing with a frame rate of higher than 10 fps by using millimeter waves. Shadow projection images of objects opaque and transparent for millimeter waves have been obtained using pulsed watt-scale millimeter waves for object illumination. Near video frame rate millimeter-wave shadowgraphy has been demonstrated. It is shown that this technique can be used for single-shot screening (including detection of concealed objects) and time-resolved imaging of time-dependent processes.

FBG-based real-time evaluation of transverse cracking in cross-ply laminates

Transverse cracking is one of the most common initial failure modes of composites and has detrimental effects on the structural integrity. In this paper a novel real-time non-destructive testing method is proposed to evaluate the transverse cracking in cross-ply laminates. The FBG sensors were embedded in the cross-ply specimens [02/90n]s and [90n/02]s, n=2,3,4, at the interface along the fiber direction. The Digital Image Correlation measurement was applied in the tensile testing to determine the density of the transverse cracks. The FBG spectrum was distorted as the crack density increased and its width at a quarter of the peak w1/4 showed a high correlation with the crack density. A numerical method based on spectrum reconstruction using the Transfer Matrix Method was then introduced to investigate the relations between spectrum distortion and transverse cracking. The reconstructed spectrum has an accurate reproduction of the reflective spectrum of FBG. The results demonstrate that the spectrum distortion attributes to the non-uniform distributions of the longitudinal strain due to the transverse cracks and w1/4 can be applied as an effective indicator to evaluate the transverse crack density. The demodulation method using the FBG spectrum can be used to real-time detect the internal transverse cracks of composites.

Magnetic Camera and its Applications in Aging Aircraft, Express Train and Pipelines for Green Technology

Operation of the corresponding large machine is not allowed during the regular NDT period. Therefore, reducing the test period and extending the test frequency, i.e., lowering the machine stoppage time due to an inspection is a very important technique for efficient energy usage. For this reason, IT-based real-time non-destructive testing (IT-NDT) technology has been being developed. This presentation reports on a magnetic camera, which is one IT-NDT technology, including the up-to-date experiences.

High-speed high-precision and ultralong-range complex spectral domain dimensional metrology.

A precise, nondestructive dimensional metrological system is crucial to manufacturing and packaging of multi-component optical system. To this end, an orthogonal dispersive spectrometer based complex spectral domain interferometric system for high-speed high-precision and ultralong-range dimensional metrology is developed. An improved complex method based on actual spectral phase shift is proposed to achieve ultrahigh suppression of artifacts. Suppression ratios of 80 dB for DC and 60 dB for mirror images are realized, the highest ratios among existing complex methods. To ensure high-precision in distance determination, an averaged spectral phase measurement algorithm is adopted. A precision of 60 nm within a measurement range of 200 mm without axial movement of the sample is demonstrated. The measurement range is readily extendable if axial movement of the sample and range cascading are involved. The system holds potential applications in various areas for real-time nondestructive testing and evaluation.

Real-time quantitative phase reconstruction in off-axis digital holography using multiplexing.

We present a new approach for obtaining significant speedup in the digital processing of extracting unwrapped phase profiles from off-axis digital holograms. The new technique digitally multiplexes two orthogonal off-axis holograms, where the digital reconstruction, including spatial filtering and two-dimensional phase unwrapping on a decreased number of pixels, can be performed on both holograms together, without redundant operations. Using this technique, we were able to reconstruct, for the first time to our knowledge, unwrapped phase profiles from off-axis holograms with 1 megapixel in more than 30 frames per second using a standard single-core personal computer on a MATLAB platform, without using graphic-processing-unit programming or parallel computing. This new technique is important for real-time quantitative visualization and measurements of highly dynamic samples and is applicable for a wide range of applications, including rapid biological cell imaging and real-time nondestructive testing. After comparing the speedups obtained by the new technique for holograms of various sizes, we present experimental results of real-time quantitative phase visualization of cells flowing rapidly through a microchannel.

Real-time nondestructive testing of composite aeronautical structures with a self-adaptive ultrasonic technique

In the aeronautical industry, composite structures under testing often have complex and variable geometries. In such cases, an optimal use of ultrasonic transducer arrays requires specific algorithms in electronic systems in order to achieve rapid and reliable inspections. To fulfil such requirements, a new real-time and adaptive technique is presented. The surface adaptive ultrasound (SAUL) technique is based on an iterative algorithm that does not require a prior knowledge of the geometrical properties of the inspected domain. All different parts of a given component can be controlled using the same transducer array, such as a conventional linear array with a flat shape. In this paper, the adaptive processing is demonstrated through acquisitions performed with different typical aircraft composite structures. In addition, we present a new surface reconstruction algorithm. This fast algorithm is efficient and can be coupled with the real-time adaptive processing to reconstruct SAUL images and, then, to improve the characterization of flaws in composite materials.

A Soft Computing Approach to Crack Detection and Impact Source Identification with Field-Programmable Gate Array Implementation

The real-time nondestructive testing (NDT) for crack detection and impact source identification (CDISI) has attracted the researchers from diverse areas. This is apparent from the current work in the literature. CDISI has usually been performed by visual assessment of waveforms generated by a standard data acquisition system. In this paper we suggest an automation of CDISI for metal armor plates using a soft computing approach by developing a fuzzy inference system to effectively deal with this problem. It is also advantageous to develop a chip that can contribute towards real time CDISI. The objective of this paper is to report on efforts to develop an automated CDISI procedure and to formulate a technique such that the proposed method can be easily implemented on a chip. The CDISI fuzzy inference system is developed using MATLAB’s fuzzy logic toolbox. A VLSI circuit for CDISI is developed on basis of fuzzy logic model using Verilog, a hardware description language (HDL). The Xilinx ISE WebPACK9.1i is used for design, synthesis, implementation, and verification. The CDISI field-programmable gate array (FPGA) implementation is done using Xilinx’s Spartan 3 FPGA. SynaptiCAD’s Verilog Simulators—VeriLogger PRO and ModelSim—are used as the software simulation and debug environment.

A GMR–ECT based embedded solution for applications on PCB inspections

Abstract Real-time non-destructive testing and evaluation (NDT/E) of conducting materials using eddy current techniques (ECTs) has gained significance in the last few years. This paper proposes a real-time application of ECT–NDT system exploiting giant magneto-resistive (GMR) sensors for inspection of printed circuit boards (PCBs). Probe design aims to crack inspection over flat surface, especially suitable for micro-defect detection on high density bare PCB. We propose a system based on a GMR sensor able to detect the magnetic field resulting from the interaction between a planar coil exciter and PCBs. The EC signals, detected by the GMR sensor, have been acquired by a high speed analog-to-digital (A/D) converter, for a subsequent application of signal processing based on digital techniques. The achieved results have highlighted the efficient design of the system. The advantages of the proposed models and some possible improvements of the system are also discussed.