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Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Materials Characterization".

Deadline for manuscript submissions: closed (10 March 2025) | Viewed by 11478

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Prof. Dr. Luís Miguel Pereira Durão

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Department of Mechanical Engineering, ISEP, Polytechnic of Porto, Porto, Portugal
Interests: composites; machining; damage onset and propagation; damage assessment; image processing; non-destructive testing; mechanical testing
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Prof. Dr. Nuno Calçada Loureiro

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Department of Industrial Production Engineering, Instituto Superior de entre Douro e Vouga, Santa Maria da Feira, Portugal
Interests: biodegradable composites; green composites; mechanical characterization; production technologies; damage assessment; non-destructive techniques
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Dear Colleagues,

Non-destructive testing (NDT) is the application of scientific principles of physics, chemistry, and mathematics for the development of adequate procedures and specific equipment that can be used to study a part, object, or complex structure, like a car, airplane, or railway bridge, without causing any harm to the object under examination.

NDT is also used in many other industries, as well as in other non-industrial applications; for example, NDT is used to make sure that parts do not have defects that would make the customer unhappy or that passengers and luggage in an airport comply with the strict safety regulations. Some of the equipment and procedures used in NDT can also be found in the medical field, like with the use of X-rays in dental work or ultrasound in echography.

Presently, there is no doubt about the importance of NDT, as it leads to a considerable amount of savings by not destroying parts, some of them expensive, as it replaces the still too present destructive testing technique. Nowadays, there are many NDT techniques available. The field of quality control works to perfect these technologies year after year, allowing us to effectively replace destructive testing.

This Special Issue intends to act as a forum for the presentation of the latest developments in the field of research and development, as well as the demonstration of practical cases of the application of NDT in all industrial areas that can help foster future developments on this interesting theme. The most recent breakthroughs in the development of equipment and instruments by the NDT machine manufacturers will play an important role, allowing the NDT community to be in contact with some cutting-edge techniques and enabling new possibilities for their usage in new areas.

As Editors of this Special Issue, it is our pleasure to invite you to submit a manuscript, whether in the form of research articles or review articles. All submissions will be peer reviewed, and a first decision will be provided to authors approximately 14 days after submission. Once accepted, papers will be published continuously in the journal and listed together on the Special Issue webpage.

It is our pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Dr. Luís Miguel Pereira Durão
Prof. Dr. Nuno Calçada Loureiro
Guest Editors

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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. Materials 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 2600 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

NDT techniques
image processing
damage assessment
damage modelling
reliability
safety
mechanical strength
standardization

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Related Special Issue

Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications—2nd Edition in Materials

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Research

16 pages, 2167 KiB

Open AccessArticle

A Statistical Study on the Influence of Drilling Process in Delamination Observed in Composite Plates

by Hugo R. C. Cerqueira, João E. Matos, José L. Esteves, Susana C. F. Fernandes and Luis M. P. Durão

Materials 2025, 18(7), 1595; https://doi.org/10.3390/ma18071595 - 1 Apr 2025

Viewed by 346

Abstract

Composite materials are increasingly being implemented in various solutions, ranging from conventional applications, like furniture, to more advanced ones, such as aerospace, based on their excellent properties, such as high mechanical strength and low weight. There are applications in which these materials are coupled to other parts. To achieve this connection, drilling processes are commonly used. Drilling causes irreversible damage to the material, which influences the mechanical strength of the plates. This study was conducted on 48 carbon/epoxy plates, each with two drilled holes, based on DOE (design of experiments) and the Taguchi method to design the experimental plan and to validate the results. Three control factors were considered for drilling: drill bit type, cutting speed, and feed rate, as it is expected that a low feed rate and a high cutting speed is the drilling configuration that inflicts the least damage. Subsequently, these specimens were subjected to enhanced radiography and an image analysis processing tool based on MatLab^® to assess the data collected and compute damage results. At the end, in analyzing the results of the Taguchi method, it is possible to validate the assumptions on the influence of the drilling process in delamination extension. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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18 pages, 10317 KiB

Open AccessArticle

Advanced Thermal Imaging Processing and Deep Learning Integration for Enhanced Defect Detection in Carbon Fiber-Reinforced Polymer Laminates

by Renan Garcia Rosa, Bruno Pereira Barella, Iago Garcia Vargas, José Ricardo Tarpani, Hans-Georg Herrmann and Henrique Fernandes

Materials 2025, 18(7), 1448; https://doi.org/10.3390/ma18071448 - 25 Mar 2025

Viewed by 562

Abstract

Carbon fiber-reinforced polymer (CFRP) laminates are widely used in aerospace, automotive, and infrastructure industries due to their high strength-to-weight ratio. However, defect detection in CFRP remains challenging, particularly in low signal-to-noise ratio (SNR) conditions. Conventional segmentation methods often struggle with noise interference and signal variations, leading to reduced detection accuracy. In this study, we evaluate the impact of thermal image preprocessing on improving defect segmentation in CFRP laminates inspected via pulsed thermography. Polynomial approximations and first- and second-order derivatives were applied to refine thermographic signals, enhancing defect visibility and SNR. The U-Net architecture was used to assess segmentation performance on datasets with and without preprocessing. The results demonstrated that preprocessing significantly improved defect detection, achieving an Intersection over Union (IoU) of 95% and an F1-Score of 99%, outperforming approaches without preprocessing. These findings emphasize the importance of preprocessing in enhancing segmentation accuracy and reliability, highlighting its potential for advancing non-destructive testing techniques across various industries. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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25 pages, 5749 KiB

Open AccessEditor’s ChoiceArticle

A Statistical Assessment of Drilling Effects on Glass Fiber-Reinforced Polymeric Composites

by Ana Martins, Alda Carvalho, Ivo M. F. Bragança, Inês C. J. Barbosa, Joaquim Infante Barbosa and Maria A. R. Loja

Materials 2024, 17(22), 5631; https://doi.org/10.3390/ma17225631 - 18 Nov 2024

Cited by 1 | Viewed by 901

Abstract

Fiber-reinforced composites are extensively used in many components and structures in various industry sectors, and the need to connect and assemble such types of components may require drilling operations. Although drilling is a common machining process; when dealing with fiber-reinforced composite materials, additional and specific problems may arise that can com-promise mechanical integrity. So, the main goal of this work is to assess how various input variables impact two main outcomes in the drilling process: the exit-adjusted delamination factor and the maximum temperature on the bottom surface where the drilling tool exits. The input variables include the type of drilling tools used, the operating speeds, and the thickness of the plates being drilled. By using Analysis of Variance (ANOVA), the analysis aims to identify which factors significantly influence damage and exit temperature. The results demonstrate that the influence of tools and drilling parameters is critical, and those selections impact the quality of the hole and the extent of the induced damage to the surrounding area. In concrete, considering the initially selected set of tools, the BZT03 tool does not lead to high-quality holes when drilling medium- and high-thickness plates. In contrast, the Dagger tool shows potential to reduce exit hole damage while also lowering temperature. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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13 pages, 5081 KiB

Open AccessEditor’s ChoiceArticle

Low-Power Field-Deployable Interdigital Transducer-Based Scanning Laser Doppler Vibrometer for Wall-Thinning Detection in Plates

by To Kang, Soonwoo Han, Yun-Taek Yeom and Ho-Yong Lee

Materials 2024, 17(20), 5098; https://doi.org/10.3390/ma17205098 - 18 Oct 2024

Viewed by 718

Abstract

Lamb waves have become a focal point in ultrasonic testing owing to their potential for long-range and inaccessible detection. However, accurately estimating the flaws in plates using Lamb waves remains challenging because of scattering, mode conversion, and dispersion effects. Recent advances in laser ultrasonic wave techniques have introduced innovative visualization methods that exploit the dispersion effect of Lamb waves to visualize defects via, for example, acoustic wavenumber spectroscopy. In this study, we developed an interdigital transducer (IDT)-based scanning laser Doppler vibrometer (SLDV) system without a power amplifier using a low-power IDT fabricated from lead magnesium niobate–lead zirconate titanate single crystals. To validate the proposed low-power IDT-based SLDV, four different defective plates were measured for defects. A comparison between a conventional IDT-based SLDV, a dry-coupled IDT-based SLDV, and the proposed method demonstrated that the latter is highly reliable for measuring thin plate defects. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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17 pages, 6700 KiB

Open AccessEditor’s ChoiceArticle

Detecting the Sigma Phase in Duplex Stainless Steel by Magnetic Noise and First Harmonic Analysis

by João Silva, Edgard Silva, Augusto Sampaio, Rayssa Lins, Josinaldo Leite, Victor Albuquerque Silva and João Manuel R. S. Tavares

Materials 2024, 17(18), 4561; https://doi.org/10.3390/ma17184561 - 17 Sep 2024

Viewed by 1058

Abstract

Non-destructive electromagnetic tests based on magnetic noise analysis have been developed to study, among others, residual stress, heat treatment outcomes, and harmful microstructures in terms of toughness. When subjected to thermal cycles above 550 °C, duplex stainless steels form an extremely hard and chromium-rich constituent that, if it is superior to 5%, compromises the steel’s corrosion resistance and toughness. In the present work, a study was carried out concerning the interaction of excitation waves with duplex stainless steel. Hence, by analyzing the magnetic noise and variations in the amplitude of the first harmonic of the excitation waves, the detection of the deleterious sigma phase in SAF 2205 steel is studied. To simplify the test, a Hall effect sensor replaced the pick-up coil placed on the opposite surface of the excitation coil. Sinusoidal excitation waves of 5 Hz and 25 Hz with amplitudes ranging from 0.25 V to 9 V were applied to samples with different amounts of the sigma phase, and the microstructures were characterized by scanning electron microscopy. The results show that the best testing condition consists of applying waves with amplitudes from 1 V to 2 V and using the first harmonic amplitude. Thus, the test proved effective for detecting the formation of the deleterious sigma phase and can follow the ability to absorb energy by impact and, thus, the material embrittlement. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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14 pages, 6637 KiB

Open AccessArticle

Monitoring Fatigue Damage of Orthotropic Steel Decks Using Nonlinear Ultrasonic Waves

by Jiahe Liu, Fangtong Zheng, Wei Shen and Dongsheng Li

Materials 2024, 17(12), 2792; https://doi.org/10.3390/ma17122792 - 7 Jun 2024

Cited by 1 | Viewed by 1158

Abstract

Orthotropic steel decks (OSDs) are commonly used in the construction of bridges due to their load-bearing capabilities. However, they are prone to fatigue damage over time due to the cyclic loads from vehicles. Therefore, the early structural health monitoring of fatigue damage in OSDs is crucial for ensuring bridge safety. Moreover, Lamb waves, as elastic waves propagating in OSD plate-like structures, are characterized by their long propagation distances and minimal attenuation. This paper introduces a method of emitting high-energy ultrasonic waves onto the OSD surface to capture the nonlinear Lamb waves formed, thereby calculating the nonlinear parameters. These parameters are then correlated with the fatigue damage endured, forming a damage index (DI) for monitoring the fatigue life of OSDs. Experimental results indicate that as fatigue damage increases, the nonlinear parameters exhibit a significant initial increase followed by a decrease. The behavior is distinct from the characteristic parameters of linear ultrasound (velocity and energy), which also exhibit changes but to a relatively smaller extent. The proposed DI and fatigue life based on nonlinear parameters can be fitted with a Gaussian curve, with the R-squared value of the fitting curve being close to 1. Additionally, this paper discusses the influence of rib welds within the OSDs on the DI, whereby as fatigue damage increases, it enlarges the value of the nonlinear parameters without altering their trend. The proposed method provides a more effective approach for monitoring early fatigue damage in OSDs. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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25 pages, 5683 KiB

Open AccessArticle

Effects of Seawater on Mechanical Performance of Composite Sandwich Structures: A Machine Learning Framework

by Norman Osa-uwagboe, Amadi Gabriel Udu, Vadim V. Silberschmidt, Konstantinos P. Baxevanakis and Emrah Demirci

Materials 2024, 17(11), 2549; https://doi.org/10.3390/ma17112549 - 25 May 2024

Cited by 6 | Viewed by 981

Abstract

Sandwich structures made with fibre-reinforced plastics are commonly used in maritime vessels thanks to their high strength-to-weight ratios, corrosion resistance, and buoyancy. Understanding their mechanical performance after moisture uptake and the implications of moisture uptake for their structural integrity and safety within out-of-plane loading regimes is vital for material optimisation. The use of modern methods such as acoustic emission (AE) and machine learning (ML) could provide effective techniques for the assessment of mechanical behaviour and structural health monitoring. In this study, the AE features obtained from quasi-static indentation tests on sandwich structures made from E-glass fibre face sheets with polyvinyl chloride foam cores were employed. Time- and frequency-domain features were then used to capture the relevant information and patterns within the AE data. A k-means++ algorithm was utilized for clustering analysis, providing insights into the principal damage modes of the studied structures. Three ensemble learning algorithms were employed to develop a damage-prediction model for samples exposed and unexposed to seawater and were loaded with indenters of different geometries. The developed models effectively identified all damage modes for the various indenter geometries under different loading conditions with accuracy scores between 86.4 and 95.9%. This illustrates the significant potential of ML for the prediction of damage evolution in composite structures for marine applications. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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11 pages, 5228 KiB

Open AccessArticle

High-Resolution Ultrasound to Quantify Sub-Surface Wrinkles in a Woven CFRP Laminate

by Md Admay Amif and David A. Jack

Materials 2024, 17(9), 2002; https://doi.org/10.3390/ma17092002 - 25 Apr 2024

Cited by 3 | Viewed by 1467

Abstract

Carbon fiber reinforced polymer (CFRP) composites are popular materials in the aerospace and automotive industries because of their low weight, high strength, and corrosion resistance. However, wrinkles or geometric distortions in the composite layers significantly reduce their mechanical performance and structural integrity. This paper presents a method for non-destructively extracting the three-dimensional geometry, lamina by lamina, of a laminated composite. A method is introduced for fabricating consistent out-of-plane wrinkled CFRP laminate panels, simulating the in-service wrinkle observed in industries that utilize thick structure composites such as the vertical lift or wind power industries. The individual lamina geometries are extracted from the fabricated coupon with an embedded wrinkle from captured ultrasonic waveforms generated from single-element conventional ultrasonic (UT) scan data. From the extracted waveforms, a method is presented to characterize the wrinkle features within each individual lamina, specifically the spatially varying wrinkle height and intensity for the wrinkle. Parts were fabricated with visibly undetectable wrinkles using a wet layup process and a hot press for curing. Scans were performed in a conventional immersion tank scanning system, and the scan data were analyzed for wrinkle detection and characterization. Extraction of the layers was performed based on tracking the voltage peaks from A-scans in the time domain. Spatial Gaussian averaging was performed to smooth the A-scans, from which the surfaces were extracted for each individual lamina. The extracted winkle surface aligned with the anticipated wrinkle geometry, and a single parameter for quantification of the wrinkle intensity for each lamina is presented. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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22 pages, 5428 KiB

Open AccessArticle

Generation of Mechanical Characteristics in Workpiece Subsurface Layers through Milling

by Michael Storchak, Larysa Hlembotska and Oleksandr Melnyk

Materials 2024, 17(7), 1552; https://doi.org/10.3390/ma17071552 - 28 Mar 2024

Cited by 1 | Viewed by 978

Abstract

The generation of mechanical characteristics in workpiece subsurface layers as a result of the cutting process has a predominant influence on the performance properties of machined parts. The effect of the end milling process on the mechanical characteristics of the machined subsurface layers was evaluated using nondestructive methods: instrumented nanoindentation and sclerometry (scratching). In this paper, the influence of one of the common processes of materials processing by cutting—the process of end tool milling—on the generation of mechanical characteristics of workpiece machined subsurface layers is studied. The effect of the end milling process on the character of mechanical property formation was evaluated through the coincidence of the cutting process energy characteristics with the mechanical characteristics of the machined subsurface layers. The total cutting power and cutting work in the tertiary cutting zone area were used as energy characteristics of the end milling process. The modes of the end milling process are considered as the main parameters affecting these energy characteristics. The mechanical characteristics of the workpiece machined subsurface layers were the microhardness of the subsurface layers and the total work of indenter penetration, determined by instrumental nanoindentation, and the maximum depth of indenter penetration, determined by sclerometry. Titanium alloy Ti10V2Fe3Al (Ti-1023) was used as the machining material. Based on the evaluation of the coincidence of the cutting process energy characteristics with the specified mechanical characteristics of the machined subsurface layers, the milling mode effect of the studied titanium alloy, in particular the cutter feed and cutting speed, on the generated mechanical characteristics was established. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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22 pages, 6900 KiB

Open AccessArticle

Damage Detection in FRP-Reinforced Concrete Elements

by Pranit Malla, Seyed Saman Khedmatgozar Dolati, Jesus D. Ortiz, Armin B. Mehrabi, Antonio Nanni and Jiayi Ding

Materials 2024, 17(5), 1171; https://doi.org/10.3390/ma17051171 - 2 Mar 2024

Cited by 6 | Viewed by 2004

Abstract

Fiber-Reinforced Polymer (FRP) composites have emerged as a promising alternative to conventional steel reinforcements in concrete structures owing to their benefits of corrosion resistance, higher strength-to-weight ratio, reduced maintenance cost, extended service life, and superior durability. However, there has been limited research on non-destructive testing (NDT) methods applicable for identifying damage in FRP-reinforced concrete (FRP-RC) elements. This knowledge gap has often limited its application in the construction industry. Engineers and owners often lack confidence in utilizing this relatively new construction material due to the challenge of assessing its condition. Thus, the main objective of this study is to determine the applicability of two of the most common NDT methods: the Ground-Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU) methods for the detection of damage in FRP-RC elements. Three slab specimens with variations in FRP type (glass-, carbon- and basalt-FRP, i.e., GFRP, CFRP, and BFRP, respectively), bar diameter, bar depths, and defect types were investigated to determine the limitations and detection capabilities of these two NDT methods. The results show that GPR could detect damage in GFRP bars and CFRP strands, but PAU was limited to damage detection in CFRP strands. The findings of this study show the applicability of conventional NDT methods to FRP-RC and at the same time identify the areas with a need for further research. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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