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Nondestructive Testing (NDT)
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Nondestructive Testing (NDT)

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: closed (27 February 2020) | Viewed by 44029

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Prof. Dr. Giuseppe Lacidogna

E-Mail Website
Guest Editor
Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin, Italy
Interests: nondestructive testing (NDT); acoustic emission; electromagnetic emission; critical phenomena in structural mechanics; critical phenomena in geophysics; fracture mechanics; static and dynamic analysis of high-rise buildings
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Because of the unavoidable aging and deterioration of materials, the efficient maintenance of civil structures and infrastructures is becoming a major issue for public and private institutions. As a matter of fact, the structural conditions of built heritage affect both safety and economic aspects. In this context, structural health monitoring (SHM) is emerging as a crucial research field, able to provide vital information regarding the damage levels of structures and materials. In particular, by exploiting the most advanced technologies and techniques, nondestructive testing (NDT) is the ideal candidate in detecting defects and structural issues, both at the laboratory and full-scale levels, in a non-invasive way. Among others, acoustic emission, vibration-based identification methods, digital image correlation, tomography techniques, sonic-ultrasonic tests, Raman and terahertz spectroscopy, electromagnetic analysis, etc. allow to evaluate the state of damage and its evolution during time. The aim of this Special Issue is, thus, to bring together researchers working in the field of NDT-SHM, both at the material and structure scale. It expects to provide novel insights on the application of NDT to a wide variety of materials (concrete, steel, masonry, composites, etc.) in the field of Civil Engineering and Architecture. Both experimental and numerical studies are welcome. 

Prof. Giuseppe Lacidogna
Guest Editor

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Keywords

  • structural health monitoring
  • nondestructive testing
  • acoustic emission
  • vibration-based identification methods
  • digital image correlation
  • tomography
  • Raman spectroscopy
  • Terahertz spectroscopy
  • electromagnetic tests

Related Special Issues

Published Papers (15 papers)

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Research

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16 pages, 4317 KiB  
Article
Nondestructive Monitoring Techniques for Crack Detection and Localization in RC Elements
by Marco Domaneschi, Gianni Niccolini, Giuseppe Lacidogna and Gian Paolo Cimellaro
Appl. Sci. 2020, 10(9), 3248; https://doi.org/10.3390/app10093248 - 07 May 2020
Cited by 22 | Viewed by 2983
Abstract
This paper presents the structural and damage assessment of a reinforced concrete (RC) beam subjected to a four-point bending test until yielding of reinforcing steel. The deterioration progress was monitored using different nondestructive testing (NDT) techniques. The strain was measured by distributed fiber [...] Read more.
This paper presents the structural and damage assessment of a reinforced concrete (RC) beam subjected to a four-point bending test until yielding of reinforcing steel. The deterioration progress was monitored using different nondestructive testing (NDT) techniques. The strain was measured by distributed fiber optic sensors (FOSs), embedded prior to concrete pouring. The initiation and propagation of cracks were monitored by acoustic emission (AE) sensors attached to the surface of the material. The recorded AE activity results in good agreement with FOS strain measurements. The results of the integrated monitoring system are confirmed by visual observation of the actual crack pattern. At different loading steps, digital image correlation (DIC) analysis was also conducted. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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16 pages, 8894 KiB  
Article
Application of Impact-Echo Method to 3D SIBIE Procedure for Damage Detection in Concrete
by Katsufumi Hashimoto, Tomoki Shiotani and Masayasu Ohtsu
Appl. Sci. 2020, 10(8), 2729; https://doi.org/10.3390/app10082729 - 15 Apr 2020
Cited by 7 | Viewed by 2862
Abstract
In this study, to visualize damage and defects, such as cracks and voids in concrete, the SIBIE (stack imaging of spectral amplitudes based on impact echo) procedure is applied and numerically improved to construct a three-dimensional (3D) model of elastic wave propagation behavior. [...] Read more.
In this study, to visualize damage and defects, such as cracks and voids in concrete, the SIBIE (stack imaging of spectral amplitudes based on impact echo) procedure is applied and numerically improved to construct a three-dimensional (3D) model of elastic wave propagation behavior. A unit of arrayed accelerometers is installed to detect multi-channel signal waveforms in the frequency domain. The resonant frequencies due to reflections at each node in 3D lattice nodes are computed by using the distances from elastic wave input to multiple output locations. The amplitudes corresponding to the resonant frequencies in the spectrum are summed up as the reflection intensity of elastic wave at each node. The reflection intensity distribution is visualized finally in the targeted area three-dimensionally. Case studies are carried out on the proposal of the improved 3D-SIBIE procedure, applied to a concrete specimen with simulated-damage as well as in-situ highway RC (Reinforced Concrete) slabs in service. As for the signal detection, a non-contact elastic wave detecting system using a laser doppler vibrometer is also introduced to consider and validate the promising remote sensing and inspection technique for damage evaluation in concrete with the 3D SIBIE procedure. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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15 pages, 5962 KiB  
Article
Non-Destructive Tests for Damage Evaluation of Stone Columns: The Case Study of Sacro Monte in Ghiffa (Italy)
by Alessandro Grazzini, Sara Fasana, Marco Zerbinatti and Giuseppe Lacidogna
Appl. Sci. 2020, 10(8), 2673; https://doi.org/10.3390/app10082673 - 13 Apr 2020
Cited by 6 | Viewed by 2304
Abstract
The Italian Sacri Monti are heritage sites with some unique characteristics; they are a successful symbiosis between nature and art and are unconfined structures, therefore always being accessible but exposed to atmospheric agents, with many relevant consequences with regard to conservation problems. The [...] Read more.
The Italian Sacri Monti are heritage sites with some unique characteristics; they are a successful symbiosis between nature and art and are unconfined structures, therefore always being accessible but exposed to atmospheric agents, with many relevant consequences with regard to conservation problems. The paper discusses some aspects related to the application of non-destructive techniques (NDT) for the interpretation of degradation phenomena occurring in stone structural elements. Ultrasonic and impact tests were used to evaluate the structural properties of the stone columns in the Via Crucis portico, within the monumental complex of the Sacro Monte in Ghiffa (Piedmont, Italy), in order to determine their conditions of maintenance and to evaluate the portico static stability. Ultrasonic tests made it possible to obtain the value of the dynamic elastic modulus, which was variable at different points of the columns due to the diversified level of material damage. The impact test, performed with an instrumented hammer in the same points of the ultrasonic test, enables, by comparison, a deeper knowledge of the surface resistance of damaged columns. These results are the first step in a research path that will require further laboratory tests to better calibrate the diagnostic techniques applied to different levels of damage to surface materials. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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24 pages, 10685 KiB  
Article
Non-Invasive Identification of Vulnerability Elements in Existing Buildings and Their Visualization in the BIM Model for Better Project Management: The Case Study of Cuccagna Farmhouse
by Elsa Garavaglia, Anna Anzani, Fabio Maroldi and Fabio Vanerio
Appl. Sci. 2020, 10(6), 2119; https://doi.org/10.3390/app10062119 - 20 Mar 2020
Cited by 10 | Viewed by 2495
Abstract
Due to the conjunction between the European and African plates, complex tectonic phenomena take place in the Mediterranean basin. These phenomena cause more or less violent seismic resentments in the countries facing the basin itself. The diffused built historical heritage, characteristic of villages [...] Read more.
Due to the conjunction between the European and African plates, complex tectonic phenomena take place in the Mediterranean basin. These phenomena cause more or less violent seismic resentments in the countries facing the basin itself. The diffused built historical heritage, characteristic of villages in the Mediterranean countries, is the most vulnerable toward seismic action, and in case of a catastrophic event can cause the loss of human lives. In Italy, the protection of historic buildings is a significant issue, and many regions promoted policies to ensure the safety of the diffused built heritage. Research groups work in synergy to develop procedures for the vulnerability assessment of existing buildings and to define appropriate action plans. This research presents a little or not at all invasive procedure for investigating vulnerability. This procedure is easily replicable and able to support techniques already in use with innovative aspects such as laser scanning of the entire complex and visual identification of vulnerable elements through the BIM (building information modeling) methodology. The procedure applicability is shown in the study of a Milanese farmhouse that has been financed by Fondazione CARIPLO, Bandi 2017 Arte e Cultura-Beni culturali a rischio, Project PRE.CU.R.S.OR. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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17 pages, 3374 KiB  
Article
Simulation of Three Constitutive Behaviors Based on Nonlinear Ultrasound
by Zaifu Zhan, Shen Wang, Fuping Wang, Songling Huang, Wei Zhao and Zhe Wang
Appl. Sci. 2020, 10(6), 1982; https://doi.org/10.3390/app10061982 - 13 Mar 2020
Cited by 4 | Viewed by 1753
Abstract
Nonlinear ultrasound has attracted more and more attention. In classical acoustic nonlinear theory, the source of nonlinearity is the change of constitutive relation of materials. Structure response that distorts after a single tone ultrasound wave is important to detect imperfection. This is rarely [...] Read more.
Nonlinear ultrasound has attracted more and more attention. In classical acoustic nonlinear theory, the source of nonlinearity is the change of constitutive relation of materials. Structure response that distorts after a single tone ultrasound wave is important to detect imperfection. This is rarely found in current simulations. The current simulation always introduces defects which do not match to the classical acoustic nonlinear theory. In this manuscript, the recurrence expressions of three kinds of imperfect materials for subroutine are given. The verifying simulation model that is used for verifying recurrence equations and wave propagation model that are used for analysing the process of ultrasonic propagation are established. The results show that the two constitutive models are effective in the verifying simulation and the hysteresis material has some special characteristics. Finally, ultrasonic propagation in two types of materials produce the expected harmonics, which build foundations for simulations of nonlinear ultrasound. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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14 pages, 2913 KiB  
Article
Bonding Characteristics of Single- and Joggled-Lap CFRP Specimens: Mechanical and Acoustic Investigations
by Claudia Barile, Caterina Casavola, Vincenzo Moramarco, Carmine Pappalettere and Paramsamy Kannan Vimalathithan
Appl. Sci. 2020, 10(5), 1782; https://doi.org/10.3390/app10051782 - 05 Mar 2020
Cited by 11 | Viewed by 3338
Abstract
Two different configurations of adhesive-bonded carbon fiber-reinforced plastic (CFRP) specimens, joggled lap-joint specimens and single lap-joint specimens, are mechanically tested. The mechanical tests show that the joggled lap specimens have lower strength than the single lap specimens. The damage modes in both the [...] Read more.
Two different configurations of adhesive-bonded carbon fiber-reinforced plastic (CFRP) specimens, joggled lap-joint specimens and single lap-joint specimens, are mechanically tested. The mechanical tests show that the joggled lap specimens have lower strength than the single lap specimens. The damage modes in both the specimens are analysed by the Acoustic Emission descriptors recorded during the mechanical tests. The acoustic data as cumulative counts and cumulative energy show the critical points of failure in both the specimen groups under loading. Moreover, they also show that the damage modes in both the specimens are dissimilar. Finally, the data provided by acoustic emission descriptors are verified by fractographic analysis on the failed surface. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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16 pages, 3642 KiB  
Article
Inducing Damage Diagnosis Capabilities in Carbon Fiber Reinforced Polymer Composites by Magnetoelastic Sensor Integration via 3D Printing
by Dimitrios G. Dimogianopoulos, Panagiotis J. Charitidis and Dionysios E. Mouzakis
Appl. Sci. 2020, 10(3), 1029; https://doi.org/10.3390/app10031029 - 04 Feb 2020
Cited by 7 | Viewed by 2918
Abstract
This study investigates the possibility of inducing damage diagnosis capabilities in carbon fiber reinforced polymer composite slabs using custom-built integrated sensors and conventional, affordable equipment. The concept utilizes magnetoelastic strips integrated via 3D printing procedures in composite slabs. Under external mechanical loading, the [...] Read more.
This study investigates the possibility of inducing damage diagnosis capabilities in carbon fiber reinforced polymer composite slabs using custom-built integrated sensors and conventional, affordable equipment. The concept utilizes magnetoelastic strips integrated via 3D printing procedures in composite slabs. Under external mechanical loading, the strip magnetization changes due to the magnetoelastic phenomenon. Accordingly, electrical signals may be passively induced in conventional reception coil circuits placed at a distance from the slab. Since these signals quantify the vibrating slab’s response, which is affected by the slab’s structural integrity, damage may be detected when specific signal characteristics change. Two main issues are examined, namely the ability of receiving meaningful (with respect to noise) electrical signals from the built-in strips despite their contact-less passive reception, and the potential of diagnosing damage using such signals. Hence, slabs of various sizes and levels of structural damage (notches) have been vibrated at different frequencies and amplitudes. Treating the experimental data from integrated strips by applying the proposed processing framework allows for calculating eigenfrequencies sensitive to occurring damage (and its severity), as verified by finite element models of the vibrating slabs. Accordingly, damage may be detected and evaluated via the currently proposed experimental testing and analysis framework. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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15 pages, 6385 KiB  
Article
Stress Estimation Using the Acoustoelastic Effect of Surface Waves in Weak Anisotropic Materials
by Jihyun Jun, Young-Dae Shim and Kyung-Young Jhang
Appl. Sci. 2020, 10(1), 169; https://doi.org/10.3390/app10010169 - 24 Dec 2019
Cited by 3 | Viewed by 2710
Abstract
This paper proposes a novel stress measurement method using the acoustoelastic effect of surface wave to estimate the stress of a homogeneous material plate with orthogonal anisotropy, in which the surface wave velocities are measured in three different directions before and after loading [...] Read more.
This paper proposes a novel stress measurement method using the acoustoelastic effect of surface wave to estimate the stress of a homogeneous material plate with orthogonal anisotropy, in which the surface wave velocities are measured in three different directions before and after loading stress. The effectiveness of the proposed method was verified by numerical simulations and experiments. For the simulations, the surface wave velocities in three directions were obtained from a conventional perturbation model for weak anisotropic materials. The simulation results showed that the stress estimation error was less than 3% for an anisotropic rate up to 2% under stress conditions up to 90 MPa. Two specimens were prepared for the experiments, one was almost isotropic and another that had a relatively larger anisotropy rate of 2.6%. Then, the stresses loaded by a tensile test machine were estimated. The results showed good agreement with the given stresses for both specimens. These results confirm that the proposed method can be applied to estimate the surface stress state in anisotropic material plates. The proposed method is simple, practical, and is expected to be useful for monitoring changes of surface stress before and after machining such as the punching or bending of plate. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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11 pages, 1308 KiB  
Article
Using Acoustic Emission Measurements for Ice-Melting Detection
by Michael Stamm, Helge Pfeiffer, Johan Reynaert and Martine Wevers
Appl. Sci. 2019, 9(24), 5387; https://doi.org/10.3390/app9245387 - 09 Dec 2019
Cited by 7 | Viewed by 2889
Abstract
Aircraft operators being faced with water accumulation in fuel tanks on a daily basis and are looking for reliable detection systems to determine the remaining amount of accumulated ice during maintenance after flight. Using such a technology, an increase in the safety and [...] Read more.
Aircraft operators being faced with water accumulation in fuel tanks on a daily basis and are looking for reliable detection systems to determine the remaining amount of accumulated ice during maintenance after flight. Using such a technology, an increase in the safety and efficiency of the aircraft operation would be possible in this highly competitive market. This article presents the use of the Acoustic Emission Technique (AE) for the reliable and non-invasive monitoring of the melting of ice in fuel tanks. This technology is in principle based on the fact that a phase transition comes frequently along with stress relaxation that can be used for monitoring the process. Therefore, the melting of water can, in essence, be monitored with AE without accessing the ice directly. The analysis of the AE signals has been carried out in the time domain since it was the melting of ice needed to be monitored as a function of temperature rise time. The insights presented in this paper can possibly lead to new technologies for ice detection, especially in remote areas that are not easily accessible with other techniques. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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28 pages, 4846 KiB  
Article
The Teager-Kaiser Energy Cepstral Coefficients as an Effective Structural Health Monitoring Tool
by Marco Civera, Matteo Ferraris, Rosario Ceravolo, Cecilia Surace and Raimondo Betti
Appl. Sci. 2019, 9(23), 5064; https://doi.org/10.3390/app9235064 - 23 Nov 2019
Cited by 30 | Viewed by 2955
Abstract
Recently, features and techniques from speech processing have started to gain increasing attention in the Structural Health Monitoring (SHM) community, in the context of vibration analysis. In particular, the Cepstral Coefficients (CCs) proved to be apt in discerning the response of a damaged [...] Read more.
Recently, features and techniques from speech processing have started to gain increasing attention in the Structural Health Monitoring (SHM) community, in the context of vibration analysis. In particular, the Cepstral Coefficients (CCs) proved to be apt in discerning the response of a damaged structure with respect to a given undamaged baseline. Previous works relied on the Mel-Frequency Cepstral Coefficients (MFCCs). This approach, while efficient and still very common in applications, such as speech and speaker recognition, has been followed by other more advanced and competitive techniques for the same aims. The Teager-Kaiser Energy Cepstral Coefficients (TECCs) is one of these alternatives. These features are very closely related to MFCCs, but provide interesting and useful additional values, such as e.g., improved robustness with respect to noise. The goal of this paper is to introduce the use of TECCs for damage detection purposes, by highlighting their competitiveness with closely related features. Promising results from both numerical and experimental data were obtained. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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15 pages, 2233 KiB  
Article
The Rapid Detection Technology of Lamb Wave for Microcracks in Thin-Walled Tubes
by Shunmin Yang, Mingquan Wang and Lu Yang
Appl. Sci. 2019, 9(17), 3576; https://doi.org/10.3390/app9173576 - 01 Sep 2019
Cited by 3 | Viewed by 2363
Abstract
Thin-walled tubes are a kind of pressure vessel formed by a stamping and drawing process, which must withstand a great deal of sudden pressure during use. When microcrack defects of a certain depth are present on its inner and outer surfaces, severe safety [...] Read more.
Thin-walled tubes are a kind of pressure vessel formed by a stamping and drawing process, which must withstand a great deal of sudden pressure during use. When microcrack defects of a certain depth are present on its inner and outer surfaces, severe safety accidents may occur, such as cracking and crushing. Therefore, it is necessary to carry out nondestructive testing of thin-walled tubes in the production process to eliminate the potential safety hazards. To realize the rapid detection of microcracks in thin-walled tubes, this study could be summarized as follows: (i) Because the diameters of the thin-walled tubes were much larger than their thicknesses, Lamb wave characteristics of plates with equal thicknesses were used to approximate the dispersion characteristics of thin-walled tubes. (ii) To study the dispersion characteristics of Lamb waves in thin plates, the detection method of the A 0 mode was determined using the particle displacement–amplitude curve. (iii) Using a multi-channel parallel detection method, rapid detection equipment for Lamb wave microcracks in thin-walled tubes was developed. (iv) The filtering peak values for defect signal detection with different depths showed that the defect detection peak values could reflect the defect depth information. (v) According to the minimum defect standard of a 0.045-mm depth, 100,000 thin-walled tubes were tested. The results showed that the missed detection rate was 0%, the reject rate was 0.3%, and the detection speed was 5.8 s/piece, which fully meets the actual detection requirements of production lines. Therefore, this study not only solved the practical issues for the rapid detection of microcracks in thin-walled tubes but also provided a reference for the application of ultrasonic technology for the detection of other components. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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14 pages, 5678 KiB  
Article
A Deep Learning Based Method for the Non-Destructive Measuring of Rock Strength through Hammering Sound
by Shuai Han, Heng Li, Mingchao Li and Timothy Rose
Appl. Sci. 2019, 9(17), 3484; https://doi.org/10.3390/app9173484 - 23 Aug 2019
Cited by 10 | Viewed by 2726
Abstract
Hammering rocks of different strengths can make different sounds. Geological engineers often use this method to approximate the strengths of rocks in geology surveys. This method is quick and convenient but subjective. Inspired by this problem, we present a new, non-destructive method for [...] Read more.
Hammering rocks of different strengths can make different sounds. Geological engineers often use this method to approximate the strengths of rocks in geology surveys. This method is quick and convenient but subjective. Inspired by this problem, we present a new, non-destructive method for measuring the surface strengths of rocks based on deep neural network (DNN) and spectrogram analysis. All the hammering sounds are transformed into spectrograms firstly, and a clustering algorithm is presented to filter out the outliers of the spectrograms automatically. One of the most advanced image classification DNN, the Inception-ResNet-v2, is then re-trained with the spectrograms. The results show that the training accurate is up to 94.5%. Following this, three regression algorithms, including Support Vector Machine (SVM), K-Nearest Neighbor (KNN), and Random Forest (RF) are adopted to fit the relationship between the outputs of the DNN and the strength values. The tests show that KNN has the highest fitting accuracy, and SVM has the strongest generalization ability. The strengths (represented by rebound values) of almost all the samples can be predicted within an error of [−5, 5]. Overall, the proposed method has great potential in supporting the implementation of efficient rock strength measurement methods in the field. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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18 pages, 8508 KiB  
Article
Detecting the Void behind the Tunnel Lining by Impact-Echo Methods with Different Signal Analysis Approaches
by Rongning Cao, Meng Ma, Ruihua Liang and Chao Niu
Appl. Sci. 2019, 9(16), 3280; https://doi.org/10.3390/app9163280 - 10 Aug 2019
Cited by 15 | Viewed by 3650
Abstract
A void behind the lining in a tunnel is considered to be a critical condition as it can significantly impair the tunnel service life. In this study, we adopted the impact-echo (IE) method to detect the voids. We designed two test conditions (tunnel [...] Read more.
A void behind the lining in a tunnel is considered to be a critical condition as it can significantly impair the tunnel service life. In this study, we adopted the impact-echo (IE) method to detect the voids. We designed two test conditions (tunnel lining with and without a void) for our experiments performed in a laboratory environment. The influences of void size and impact-void position were analysed using numerical simulations. The vibration response signals were analysed in the time, frequency, and time–frequency domains using various signal analysis approaches. The results were comparatively analysed to determine the best approach for void detection. The study helped establish that a tunnel void can be evaluated through the vibration energy (amplitude and duration) in the time domain, the resonance frequency and dynamic stiffness in the frequency domain, and the energy distribution in time–frequency domain. The wavelet transform analysis is the most appropriate method to observe the energy flow during the state changing and the dynamic stiffness method can determine the void position precisely. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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14 pages, 5195 KiB  
Article
A PEC Thrice Subtraction Method for Obtaining Permeability Invariance Feature in Conductivity Measurement of Ferromagnetic Samples
by Dongdong Wen, Mengbao Fan, Binghua Cao, Zhian Xue and Ping Wang
Appl. Sci. 2019, 9(13), 2745; https://doi.org/10.3390/app9132745 - 07 Jul 2019
Cited by 8 | Viewed by 3001
Abstract
Conductivity, as an important index of structural health monitoring, can be used to evaluate heat treatment condition, and sort different materials or measure the stress of mechanical parts. However, the permeability of a measured sample has significant impact on the detected signal in [...] Read more.
Conductivity, as an important index of structural health monitoring, can be used to evaluate heat treatment condition, and sort different materials or measure the stress of mechanical parts. However, the permeability of a measured sample has significant impact on the detected signal in pulsed eddy current (PEC) testing, which is prone to measurement errors due to the effect of permeability change. In this paper, a thrice subtraction method is investigated and utilized to obtain a permeability invariance (PI) feature for reducing permeability effect in conductivity measurement of ferromagnetic samples. The thrice subtraction method is based on the PEC signals of sample and air, the difference signal between the difference PEC signal and its normalization signal, and the difference signal between the difference normalization signal and its standard deviation. In the thrice subtraction signals, the behavior of the obtained PI feature is analyzed by experiments and simulations. The results demonstrate that the thrice subtraction method is a practicable program and the PI feature is potential to measure the conductivity of ferromagnetic samples. The work reported in this paper provides an effective approach to obtain a PI feature for estimating the conductivity of ferromagnetic samples without a permeability effect. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT))
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16 pages, 2894 KiB  
Review
Mechanical Strength Evaluation of Elastic Materials by Multiphysical Nondestructive Methods: A Review
by Huiting Huan, Lixian Liu, Andreas Mandelis, Cuiling Peng, Xiaolong Chen and Jinsong Zhan
Appl. Sci. 2020, 10(5), 1588; https://doi.org/10.3390/app10051588 - 27 Feb 2020
Cited by 9 | Viewed by 3337
Abstract
The main purpose of industrial nondestructive testing (NDT) is to diagnose the stability, reliability and failure probability of materials, components and structures. Industrial component mechanical strength is one of the most important properties NDT is used to characterize. Subtle but perceptible changes in [...] Read more.
The main purpose of industrial nondestructive testing (NDT) is to diagnose the stability, reliability and failure probability of materials, components and structures. Industrial component mechanical strength is one of the most important properties NDT is used to characterize. Subtle but perceptible changes in stress-strain behavior can be reliable indicators of defect formation. A detailed review on the state-of-the-art NDT methods using optical-radiation, photoacoustic, and photothermal techniques for mechanical strength evaluation and defect pre-diagnosis is presented in this article. Mechanical strength is analyzed in terms of the deformation/strain field, the stress-strain relation, and the residual stress in an elastic material subjected to tensile or compressive loading, or impact. By introducing typical NDT experiments, the history and features of each methodology are revisited and typical applications are discussed. This review also aims to be used as a reference toward further research and development of NDT technologies characterizing mechanical strength of materials and components. Full article
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