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Novel Approaches for Nondestructive Testing and Evaluation

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (10 August 2021) | Viewed by 32592

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Special Issue Editors

Prof. Dr. Jinyi Lee

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Guest Editor

Department of Electronic Engineering, Chosun University, Gwangju 61452, Korea
Interests: corrosion; crack; nondestructive testing; NDT; magnetization; Hall sensor, GMR sensor; magnetic field; eddy current; magnetic camera; steel manufacturing; express train; nuclear power generation; heat exchanger; aerospace; NDE; ultrasonic non destructive
Special Issues, Collections and Topics in MDPI journals

Dr. Hoyong Lee

E-Mail Website
Guest Editor

Department of Defense & Science Technology, Gwangju University, Gwangju 61743, Korea
Interests: failure analysis; magnetic sensors; nondestructive testing and evaluation; mechanical reliability of electronics system
Special Issues, Collections and Topics in MDPI journals

Dr. Azouaou Berkache

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Guest Editor

IT-based Real-Time NDT Center, Chosun University, Gwangju 61452, Korea
Interests: nondestructive testing; nondestructive evaluation; electromagnetic; numerical simulation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Nondestructive testing and evaluation (NDT&E) is one of the most important techniques for determining the quality and safety of materials, components, devices, and structures. NDT&E technologies include ultrasonic testing (UT), magnetic particle testing (MT), magnetic flux leakage testing (MFLT), eddy current testing (ECT), radiation testing (RT), penetrant testing (PT), and visual testing (VT), and these are widely used throughout modern industry.

However, some NDT processes, such as cleaning specimens and removing paint, cause environmental pollution, and must be inspected in limited environments (time, space, and sensor selection). Thus, NDT&E is classified as a typical 3D (dirty, dangerous, and difficult) job. In addition, the NDT operator judges the presence of damage by experience and subjective judgment, so in some cases a flaw that exists may not be detected during the test. Therefore, to obtain clearer test results, a means for the operator to determine the flaw more easily should be provided. In addition, the test results should be organized systemically in order to identify the cause of the abnormality in the test specimen and to identify the progress of the damage quantitatively.

Due to the necessity of technical advancement in NDT&E, many efforts are being made in the following areas:

(1) Integration of test methods using conventional NDT&E methods.

(2) Ultra-precise sensor (sensitivity and resolution) development using advanced technology in electrical and electronic fields.

(3) Ultra-fast inspection (real-time NDT and high-speed flaw recognition).

(4) Automation of the inspection process (applying robot technology).

(5) Visualization of test results (2-D or 3-D visualization).

(6) Preservation and management of test results.

(7) Application of artificial intelligence.

Applied Sciences has planned a Special Issue, “Novel Approaches for Nondestructive Testing and Evaluation,” which has gathered the results of many researchers and engineers to meet the needs of technological advances in NDT&E.

We invite researchers and engineers with novel technologies for visualizing NDT signals such as those of visible, static/time-varying magnetic flux densities, radiation (infrared, ultraviolet, nuclear), electromagnetic waves, acoustics, and stresses using various physical and electrical and electronic methods. We also welcome related technologies such as those pertaining to the quantitative evaluation of test results. Case studies in all fields, including aerospace, electric power generation, petrochemicals, automobiles, and parts and materials, would also be valuable contributions to our Issue.

Papers published in Applied Sciences require the author or authors to bear the financial burden of open access, but the journal has a high Impact Factor (2.217). Moreover, we are confident that this Special Issue will provide a great opportunity to contribute to the future development of the NDT&E industry.

We look forward to your participation.

Prof. Dr. Jinyi Lee
Dr. Hoyong Lee
Dr. Azouaou Berkache
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

nondestructive testing
visible inspection
infrared radiation
X-ray and X-ray backscatter
electromagnetic imaging
phase array UT
artificial intelligence
evaluation
reliability
probability of detection

Published Papers (14 papers)

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Editorial

Jump to: Research

6 pages, 198 KiB

Open AccessEditorial

Special Issue: Novel Approaches for Nondestructive Testing and Evaluation

by Jinyi Lee, Hoyong Lee and Azouaou Berkache

Appl. Sci. 2022, 12(2), 565; https://0-doi-org.brum.beds.ac.uk/10.3390/app12020565 - 07 Jan 2022

Cited by 2 | Viewed by 1167

Abstract

Nondestructive testing and evaluation (NDT&E) is one of the most important techniques for determining the quality and safety of materials, components, devices, and structures [...] Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

Research

Jump to: Editorial

9 pages, 1926 KiB

Open AccessArticle

Time-Resolved Neutron Bragg-Edge Imaging: A Case Study by Observing Martensitic Phase Formation in Low Temperature Transformation (LTT) Steel during GTAW

by Axel Griesche, Beate Pfretzschner, Ugur Alp Taparli and Nikolay Kardjilov

Appl. Sci. 2021, 11(22), 10886; https://0-doi-org.brum.beds.ac.uk/10.3390/app112210886 - 18 Nov 2021

Cited by 2 | Viewed by 1448

Abstract

Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW). The in situ visualization of austenitization upon welding and subsequent α’-martensite formation during cooling could be achieved with a temporal resolution of 2 s for monochromatic imaging using a single neutron wavelength and of 0.5 s for polychromatic imaging using the full spectrum of the beam (white beam). The spatial resolution achieved in the experiments was approximately 200 µm. The transmitted monochromatic neutron beam intensity at a wavelength of λ = 0.395 nm was significantly reduced during cooling below the martensitic start temperature M_s since the emerging martensitic phase has a ~10% higher attenuation coefficient than the austenitic phase. Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye–Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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12 pages, 2609 KiB

Open AccessArticle

THz-TDS Techniques of Thickness Measurements in Thin Shim Stock Films and Composite Materials

by Kwang-Hee Im, Sun-Kyu Kim, Young-Tae Cho, Yong-Deuck Woo and Chien-Ping Chiou

Appl. Sci. 2021, 11(19), 8889; https://0-doi-org.brum.beds.ac.uk/10.3390/app11198889 - 24 Sep 2021

Cited by 5 | Viewed by 1528

Abstract

Terahertz wave (T-ray) scanning applications are one of the most promising tools for nondestructive evaluation. T-ray scanning applications use a T-ray technique to measure the thickness of both thin Shim stock films and GFRP (glass fiber-reinforced plastics) composites, of which the samples were selected because the T-ray method could penetrate the non-conducting samples. Notably, this method is nondestructive, making it useful for analyzing the characteristics of the materials. Thus, the T-ray thickness measurement can be found for both non-conducting Shim stock films and GFRP composites. In this work, a characterization procedure was conducted to analyze electromagnetic properties, such as the refractive index. The obtained estimates of the properties are in good agreement with the known data for poly methyl methacrylate (PMMA) for acquiring the refractive index. The T-ray technique was developed to measure the thickness of the thin Shim stock films and the GFRP composites. Our tests obtained good results on the thickness of the standard film samples, with the different thicknesses ranging from around 120 μm to 500 μm. In this study, the T-ray method was based on the reflection mode measurement, and the time-of-flight (TOF) and resonance frequencies were utilized to acquire the thickness measurements of the films and GFRP composites. The results showed that the thickness of the samples of frequency matched those obtained directly by time-of-flight (TOF) methods. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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16 pages, 8769 KiB

Open AccessFeature PaperArticle

Three-Dimensional Imaging of Metallic Grain by Stacking the Microscopic Images

by Jinyi Lee, Azouaou Berkache, Dabin Wang and Young-Ha Hwang

Appl. Sci. 2021, 11(17), 7787; https://0-doi-org.brum.beds.ac.uk/10.3390/app11177787 - 24 Aug 2021

Cited by 5 | Viewed by 1447

Abstract

Three-dimensional observation of metal grains (MG) has a wide potential application serving the interdisciplinary community. It can be used for industrial applications and basic research to overcome the limitations of non-destructive testing methods, such as ultrasonic testing, magnetic particle testing, and eddy current testing. This study proposes a method and its implementation algorithm to observe (MG) metal grains in three dimensions in a general laboratory environment equipped with a polishing machine and a metal microscope. An image was taken by a metal microscope while polishing the mounted object to be measured. Then, the metal grains (MGs) were reconstructed into three dimensions through local positioning, binarization, boundary extraction, (MG) selection, and stacking. The goal is to reconstruct the 3D MG in a virtual form that reflects the real shape of the MG. The usefulness of the proposed method was verified using the carbon steel (SA106) specimen. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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18 pages, 4713 KiB

Open AccessArticle

Micromagnetic Characterization of Operation-Induced Damage in Charpy Specimens of RPV Steels

by Madalina Rabung, Melanie Kopp, Antal Gasparics, Gábor Vértesy, Ildikó Szenthe, Inge Uytdenhouwen and Klaus Szielasko

Appl. Sci. 2021, 11(7), 2917; https://0-doi-org.brum.beds.ac.uk/10.3390/app11072917 - 24 Mar 2021

Cited by 12 | Viewed by 1780

Abstract

The embrittlement of two types of nuclear pressure vessel steel, 15Kh2NMFA and A508 Cl.2, was studied using two different methods of magnetic nondestructive testing: micromagnetic multiparameter microstructure and stress analysis (3MA-X8) and magnetic adaptive testing (MAT). The microstructure and mechanical properties of reactor pressure vessel (RPV) materials are modified due to neutron irradiation; this material degradation can be characterized using magnetic methods. For the first time, the progressive change in material properties due to neutron irradiation was investigated on the same specimens, before and after neutron irradiation. A correlation was found between magnetic characteristics and neutron-irradiation-induced damage, regardless of the type of material or the applied measurement technique. The results of the individual micromagnetic measurements proved their suitability for characterizing the degradation of RPV steel caused by simulated operating conditions. A calibration/training procedure was applied on the merged outcome of both testing methods, producing excellent results in predicting transition temperature, yield strength, and mechanical hardness for both materials. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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17 pages, 10806 KiB

Open AccessArticle

Measurement of Thinned Water-Cooled Wall in a Circulating Fluidized Bed Boiler Using Ultrasonic and Magnetic Methods

by Jinyi Lee, Eunho Choe, Cong-Thuong Pham and Minhhuy Le

Appl. Sci. 2021, 11(6), 2498; https://0-doi-org.brum.beds.ac.uk/10.3390/app11062498 - 11 Mar 2021

Cited by 2 | Viewed by 1724

Abstract

In this paper, a nondestructive inspection system is proposed to detect and quantitatively evaluate the size of the near- and far-side damages on the tube, membrane, and weld of the water-cooled wall in the fluidized bed boiler. The shape and size of the surface damages can be evaluated from the magnetic flux density distribution measured by the magnetic sensor array on one side from the center of the magnetizer. The magnetic sensors were arrayed on a curved shape probe according to the tube’s cross-sectional shape, membrane, and weld. On the other hand, the couplant was doped to the water-cooled wall, and a thin film was formed thereon by polyethylene terephthalate. Then, the measured signal of the flexible ultrasonic probe was used to detect and evaluate the depth of the damages. The combination of the magnetic and ultrasonic methods helps to detect and evaluate both near and far-side damages. Near-side damages with a minimum depth of 0.3 mm were detected, and the depth from the surface of the far-side damage was evaluated with a standard deviation of 0.089 mm. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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12 pages, 5115 KiB

Open AccessArticle

Evaluation of Cracks on the Welding of Austenitic Stainless Steel Using Experimental and Numerical Techniques

by Azouaou Berkache, Jinyi Lee and Eunho Choe

Appl. Sci. 2021, 11(5), 2182; https://0-doi-org.brum.beds.ac.uk/10.3390/app11052182 - 02 Mar 2021

Cited by 8 | Viewed by 2732

Abstract

This paper deals with investigation and characterization of weld circumferential thin cracks in austenitic stainless steel (AISI 304) pipe with eddy current nondestructive testing technique (EC-NDT). During welding process, the heat source applied to the AISI 304 was not uniform, accompanied by a change of the physical property. To take into consideration this change, the relative magnetic permeability was considered as a gradiently changed variable in the weld and the heat affected zone (HAZ), which was generated by the Monte Carlo Method based on pseudo random number generation (PRNG). Numerical simulations were performed by means of MATLAB software using 2D finite element method to solve the problem. To verify, results from the modeling works were conducted and contrasted with findings from experimental ones. Indeed, the results of comparison agreed well. In addition, they show that considering this changing of this magnetic property allows distinguishing the thin cracks in the weld area. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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17 pages, 6766 KiB

Open AccessArticle

Leaky Lamb Wave Radiation from a Waveguide Plate with Finite Width

by Sang-Jin Park, Hoe-Woong Kim and Young-Sang Joo

Appl. Sci. 2020, 10(22), 8104; https://0-doi-org.brum.beds.ac.uk/10.3390/app10228104 - 16 Nov 2020

Cited by 4 | Viewed by 2642

Abstract

In this paper, leaky Lamb wave radiation from a waveguide plate with finite width is investigated to gain a basic understanding of the radiation characteristics of the plate-type waveguide sensor. Although the leaky Lamb wave behavior has already been theoretically revealed, most studies have only dealt with two dimensional radiations of a single leaky Lamb wave mode in an infinitely wide plate, and the effect of the width modes (that are additionally formed by the lateral sides of the plate) on leaky Lamb wave radiation has not been fully addressed. This work aimed to explain the propagation behavior and characteristics of the Lamb waves induced by the existence of the width modes and to reveal their effects on leaky Lamb wave radiation for the performance improvement of the waveguide sensor. To investigate the effect of the width modes in a waveguide plate with finite width, propagation characteristics of the Lamb waves were analyzed by the semi-analytical finite element (SAFE) method. Then, the Lamb wave radiation was computationally modeled on the basis of the analyzed propagation characteristics and was also experimentally measured for comparison. From the modeled and measured results of the leaky radiation beam, it was found that the width modes could affect leaky Lamb wave radiation with the mode superposition and radiation characteristics were significantly changed depending on the wave phase of the superposed modes on the radiation surface. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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22 pages, 2901 KiB

Open AccessFeature PaperArticle

A Comparison of Power Quality Disturbance Detection and Classification Methods Using CNN, LSTM and CNN-LSTM

by Carlos Iturrino Garcia, Francesco Grasso, Antonio Luchetta, Maria Cristina Piccirilli, Libero Paolucci and Giacomo Talluri

Appl. Sci. 2020, 10(19), 6755; https://0-doi-org.brum.beds.ac.uk/10.3390/app10196755 - 27 Sep 2020

Cited by 61 | Viewed by 4956

Abstract

The use of electronic loads has improved many aspects of everyday life, permitting more efficient, precise and automated process. As a drawback, the nonlinear behavior of these systems entails the injection of electrical disturbances on the power grid that can cause distortion of voltage and current. In order to adopt countermeasures, it is important to detect and classify these disturbances. To do this, several Machine Learning Algorithms are currently exploited. Among them, for the present work, the Long Short Term Memory (LSTM), the Convolutional Neural Networks (CNN), the Convolutional Neural Networks Long Short Term Memory (CNN-LSTM) and the CNN-LSTM with adjusted hyperparameters are compared. As a preliminary stage of the research, the voltage and current time signals are simulated using MATLAB Simulink. Thanks to the simulation results, it is possible to acquire a current and voltage dataset with which the identification algorithms are trained, validated and tested. These datasets include simulations of several disturbances such as Sag, Swell, Harmonics, Transient, Notch and Interruption. Data Augmentation techniques are used in order to increase the variability of the training and validation dataset in order to obtain a generalized result. After that, the networks are fed with an experimental dataset of voltage and current field measurements containing the disturbances mentioned above. The networks have been compared, resulting in a 79.14% correct classification rate with the LSTM network versus a 84.58% for the CNN, 84.76% for the CNN-LSTM and a 83.66% for the CNN-LSTM with adjusted hyperparameters. All of these networks are tested using real measurements. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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10 pages, 4479 KiB

Open AccessArticle

An Attention-Based Network for Textured Surface Anomaly Detection

by Gaokai Liu, Ning Yang and Lei Guo

Appl. Sci. 2020, 10(18), 6215; https://0-doi-org.brum.beds.ac.uk/10.3390/app10186215 - 08 Sep 2020

Cited by 5 | Viewed by 1742

Abstract

Textured surface anomaly detection is a significant task in industrial scenarios. In order to further improve the detection performance, we proposed a novel two-stage approach with an attention mechanism. Firstly, in the segmentation network, the feature extraction and anomaly attention modules are designed to capture the detail information as much as possible and focus on the anomalies, respectively. To strike dynamic balances between these two parts, an adaptive scheme where learnable parameters are gradually optimized is introduced. Subsequently, the weights of the segmentation network are frozen, and the outputs are fed into the classification network, which is trained independently in this stage. Finally, we evaluate the proposed approach on DAGM 2007 dataset which consists of diverse textured surfaces with weakly-labeled anomalies, and the experiments demonstrate that our method can achieve 100% detection rates in terms of TPR (True Positive Rate) and TNR (True Negative Rate). Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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18 pages, 1218 KiB

Open AccessArticle

Proposal of UWB-PPM with Additional Time Shift for Positioning Technique in Nondestructive Environments

by Nguyen Thi Huyen, Nguyen Le Cuong and Pham Thanh Hiep

Appl. Sci. 2020, 10(17), 6011; https://0-doi-org.brum.beds.ac.uk/10.3390/app10176011 - 30 Aug 2020

Cited by 3 | Viewed by 2123

Abstract

The ultra-wide band (UWB) technology has many advantages in positioning and measuring systems; however, powers of UWB signals rapidly reduce while traveling in propagation environments, hence detecting UWB signals are difficult. Various modulation techniques are applied for UWB signals to increase the ability for detecting the reflected signal from transmission mediums, such as pulse amplitude modulation (PAM), pulse position modulation (PPM), and so on. In this paper, we propose an ultra-wide band pulse position modulation technique with optimized additional time shift (UWB-PPM-ATS) to enhance the accuracy in locating buried object in nondestructive environments. Moreover, the Levenberg–Marquardt Fletcher algorithm (LMFA) is applied to determine the medium parameters and buried object location simultaneously. The influences of proposed modulation technique on determining system’s parameters, such as a propagation time, distance, and properties of the medium are analyzed. Calculation results indicate that the proposed UWB-PPM-ATS gives higher accuracy than the conventional one such as UWB-OOK and UWB-PPM in both homogeneous and heterogeneous environments. Furthermore, the LMFA with the proposed UWB-PPM-ATS outperforms the LMFA with the traditional modulation method, especially for unknown propagation environment. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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9 pages, 1191 KiB

Open AccessArticle

Indirect Method for Measuring Absolute Acoustic Nonlinearity Parameter Using Surface Acoustic Waves with a Fully Non-Contact Laser-Ultrasonic Technique

by Jihyun Jun and Kyung-Young Jhang

Appl. Sci. 2020, 10(17), 5911; https://0-doi-org.brum.beds.ac.uk/10.3390/app10175911 - 26 Aug 2020

Cited by 2 | Viewed by 1930

Abstract

This paper proposes an indirect method to measure absolute acoustic nonlinearity parameters using surface acoustic waves by employing a fully non-contact laser-ultrasonic technique. For this purpose, the relationship between the ratio of relative acoustic nonlinearity parameters measured using the proposed method in two different materials (a test material and a reference material) and the ratio of absolute acoustic nonlinearity parameters in these two materials was theoretically derived. Using this relationship, when the absolute nonlinearity parameter of the reference material is known, the absolute nonlinearity parameter of the test material can be obtained using the ratio of the measured relative parameters of the two materials. For experimental verification, aluminum and copper specimens were used as reference and test materials, respectively. The relative acoustic nonlinearity parameters of the two materials were measured from surface waves generated and received using lasers. Additionally, the absolute parameters of aluminum and copper were measured using a conventional direct measurement method, with the former being used as a reference value and the latter being used for comparison with the estimation result. The absolute parameter of copper estimated by the proposed method showed good agreement with the directly measured result. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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12 pages, 2237 KiB

Open AccessArticle

Fast Terahertz Coded-Aperture Imaging Based on Convolutional Neural Network

by Fengjiao Gan, Chenggao Luo, Xingyue Liu, Hongqiang Wang and Long Peng

Appl. Sci. 2020, 10(8), 2661; https://0-doi-org.brum.beds.ac.uk/10.3390/app10082661 - 12 Apr 2020

Cited by 7 | Viewed by 2346

Abstract

Terahertz coded-aperture imaging (TCAI) has many advantages such as forward-looking imaging, staring imaging and low cost and so forth. However, it is difficult to resolve the target under low signal-to-noise ratio (SNR) and the imaging process is time-consuming. Here, we provide an efficient solution to tackle this problem. A convolution neural network (CNN) is leveraged to develop an off-line end to end imaging network whose structure is highly parallel and free of iterations. And it can just act as a general and powerful mapping function. Once the network is well trained and adopted for TCAI signal processing, the target of interest can be recovered immediately from echo signal. Also, the method to generate training data is shown, and we find that the imaging network trained with simulation data is of good robustness against noise and model errors. The feasibility of the proposed approach is verified by simulation experiments and the results show that it has a competitive performance with the state-of-the-art algorithms. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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12 pages, 3161 KiB

Open AccessArticle

Ultrahigh Resolution Pulsed Laser-Induced Photoacoustic Detection of Multi-Scale Damage in CFRP Composites

by Siqi Wang, Jesse Echeverry, Luis Trevisi, Kiana Prather, Liangzhong Xiang and Yingtao Liu

Appl. Sci. 2020, 10(6), 2106; https://0-doi-org.brum.beds.ac.uk/10.3390/app10062106 - 20 Mar 2020

Cited by 17 | Viewed by 3533

Abstract

This paper presents a photoacoustic non-destructive evaluation (pNDE) system with an ultrahigh resolution for the detection of multi-scale damage in carbon fiber-reinforced plastic (CFRP) composites. The pNDE system consists of three main components: a picosecond pulsed laser-based ultrasonic actuator, an ultrasound receiver, and a data acquisition/computing subsystem. During the operation, high-frequency ultrasound is generated by pulsed laser and recorded by an ultrasound receiver. By implementing a two-dimensional back projection algorithm, pNDE images can be reconstructed from the recorded ultrasound signals to represent the embedded damage. Both potential macroscopic and microscopic damages, such as surface notches and delamination in CFRP, can be identified by examining the reconstructed pNDE images. Three ultrasonic presentation modes including A-scan, B-scan, and C-scan are employed to analyze the recorded signals for the representation of the detected micro-scale damage in two-dimensional and three-dimensional images with a high spatial resolution of up to 60 µm. Macro-scale delamination and transverse ply cracks are clearly visualized, identifying the edges of the damaged area. The results of the study demonstrate that the developed pNDE system provides a non-destructive and robust approach for multi-scale damage detection in composite materials. Full article

(This article belongs to the Special Issue Novel Approaches for Nondestructive Testing and Evaluation)

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