Nondestructive Testing Applications Research Articles

Ultrahigh Frequency Ultrasonic Transducers (150MHz) Based on Silicon Lenses.

Acoustic microscopes and acoustic tweezers have great value in the application of microparticle manipulation, biomedical research and non-destructive testing. Ultrahigh frequency (UHF) ultrasonic transducers act as the key component in acoustic microscopes, and acoustic tweezers and acoustic lenses are essential parts of UHF ultrasonic transducers. Therefore, the preparation of acoustic lenses is crucial. Silicon is a suitable material for preparing acoustic lenses because of its high acoustic velocity, low acoustic attenuation and excellent machinability. In previous research, silicon lenses were mainly prepared by etching. However, etching has some drawbacks. The etching of large sizes is complex, time-consuming and expensive. Furthermore, vertical etching is preferred to spherical etching. Thus, a new method of ultra-precision machining was introduced to prepare silicon lenses. In this paper, silicon lenses with an aperture of 892 μm and a depth of 252 μm were prepared. Then, UHF ultrasonic transducers with a center frequency of 157 MHz and a -6-dB bandwidth of 52% were successfully prepared based on silicon lenses. The focal distance of the transducers was 736 μm and the F-number was about 0.82. The transducers had a lateral resolution of 11 μm and could distinguish the 13 μm slots on silicon wafers clearly.

An acoustic emission approach to the structural health monitoring of historical metallic tie-rods

The application of Non-Destructive testing and Structural Health Monitoring systems in historical buildings is of great interest and actuality due to the need to guarantee safety and conservation. The present memory focuses on the case study of the historical wrought iron tie-rods of Duomo di Milano, Italy. In recent years, two of these elements presented critical failures, making necessary the replacement. Consequently, a monitoring methodology, based on acoustic emission, was defined. First, the fracture toughness of historical wrought iron was experimentally characterized by employing standard small scale specimens taken from one of the failed tie-rods. At the same time, acoustic emission was acquired to define a methodology for detecting and localizing the events due to damage in the material, separating those due to background noise by applying suitable pattern recognition algorithms. Subsequently, a tensile test was performed on a full scale section of the same tie-rod. Before and after the test, phased-array ultrasonic testing and magnetic particles inspections were carried out to identify and map defects and their possible development due to load application. From the analysis, it was possible to conclude that magnetic inspections allow identifying the presence of surface defects effectively, phased-array ultrasonic testing allows to estimate the geometry of the defect accurately and acoustic emission has proved to be a promising technique for monitoring the structural integrity of in-service historical metallic tie-rods. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

Spectrally tunable near-infrared photoluminescence in MP3O9:Cr3+ (M = Al, Ga, In) phosphate phosphors.

Modulation of the octahedral crystal field environment of Cr3+ is an effective approach to achieve tunable emission. Here, we prepared a series of broadband MP3O9:Cr3+ (M = Al, Ga, In) near-infrared (NIR) phosphors, and cubic AlP3O9:Cr3+ (APO-c:Cr3+) and monoclinic AlP3O9:Cr3+ (APO-m:Cr3+) phosphors were prepared by controlling the synthesis temperature. The emission wavelength was tuned from 787 nm for APO-c:Cr3+ to 894 nm for monoclinic InP3O9:Cr3+ (IPO:Cr3+) by regulating the M ion and reducing the crystal field intensity. Excitingly, the MP3O9:Cr3+ (M = Al, Ga, In) family shows excellent thermal stability; the emission intensity of APO-c:Cr3+, APO-m:Cr3+ and monoclinic GaP3O9:Cr3+ (GPO:Cr3+) can still maintain 95.6%, 86% and 86% of that at room temperature when heating to 423 K, respectively. An NIR LED device was prepared by incorporating GPO:Cr3+ and a blue light LED, demonstrating the potential application in night vision and non-destructive testing.

Discussion on Non-destructive Testing Technology and Application of Material Surface

Discussion on Non-destructive Testing Technology and Application of Material Surface

Terahertz 2-D Imaging Framework for Detection Based on Dual Clustering Methods

The widespread use of high-performance materials in various fields poses a challenge for detection methods of internal structures and defects. Terahertz (THz) imaging is a highly promising method for nondestructive testing (NDT) of specific materials. However, conventional THz 2-D imaging methods usually lose a large amount of information and make the detecting results less reliable. Thousands of THz waveform data also make the accurate manual analysis very inefficient. Based on the clustering analysis methods, in this article, a THz 2-D imaging framework is proposed, in which the pulses and scanning points are clustered successively to obtain 2-D images with good quality. Pulses are extracted from the scanning data. The features of pulses are represented by two feature parameters, which will be used as the data set in the first clustering steps. The coding step makes the vectors of scanning points represent the pulses they contain. By the proposed framework, the pixel value can be well representative of the entire waveform features instead of a single parameter of the waveform. The proposed framework was tested with the actual samples. Experimental results verified that it can clearly image various physical structures of samples and make accurate distinctions of different areas. The impact of the parameters was also discussed. As an unsupervised learning-based framework, the proposed framework is fast, generalized, and does not require any prior data with labels, which can make industrial applications of NDT more automatic.

Sensing and Nondestructive Testing Applications of Terahertz Spectroscopy and Imaging Systems: State-of-the-Art and State-of-the-Practice

Sensing and Nondestructive Testing Applications of Terahertz Spectroscopy and Imaging Systems: State-of-the-Art and State-of-the-Practice

Inverse identification of pipeline steel mechanical state by means of coupled magnetic measurements and artificial neural networks

Artificial neural networks are widely used to develop models able to predict properties of interest by learning and establishing relationships between inputs and outputs of a system. It is particularly relevant for the inversion process in the framework of Non-Destructive Testing (NDT) involving strongly non-linear and non-monotonic behavior and/or saturations. The case-study considered in this work is a magnetic material subjected to uniaxial mechanical stress, plastic strain and magnetic field. An Artificial Neural Networks (ANN) model is proposed to predict the corresponding remanent magnetization, coercive field and the maximum magnetization as target properties. A series of experimental data made of various magneto-mechanical measurements are used to train, evaluate and validate the ANN model. The proposed model suitably predicts the magnetic properties of a second specimen of the material in the same magnetic field, plastic strain and stress ranges as the first specimen. An inverse ANN is then proposed to evaluate the mechanical loading and the plastic strain from the magnetic signature. Unique and accurate solutions are found that proves the relevance of machine learning approach in such NDT application.

Approach to nonlinearity parameter in liquids calculation based on the scaling theory of thermodynamic fluctuations

The nonlinearity parameter B/A is a characteristic of liquids and soft matter, which gains growing attention due to its sensibility to the composition of materials. This makes it a prospective indicator for nondestructive testing applications based on the ultrasound sounding suitable for a variety of applications from physic chemistry to biomedical studies. At the same time, the thermodynamic definition of the nonlinearity parameter requires extensive measurements at elevated pressures that are not always available; in addition, there are known certain contradiction of such data with the data obtained by methods of nonlinear acoustics. Objective. In this work, we consider a recently proposed approach to the prediction of the speed of sound at high pressures, which uses the property of invariance of the reduced pressure fluctuations and the data obtained at normal ambient pressure only. The method generalises the classic Nomoto model, which however gives only a qualitative picture, and results in the quantitative correspondence to the experimental values within their range of uncertainty. Methods. Analytical methods of the theory of thermodynamic fluctuations applied to the parameters of equations of nonlinear acoustics as well as numerical simulation in the COMSOL Multiphysics® environment. Results. Expressions for calculating the nonlinearity parameter with acceptable accuracy were obtained using thermodynamic data obtained only at atmospheric pressure. Numerical calculations were performed for toluene. In addition, the discrepancy between values of the nonlinear parameter obtained via the thermodynamic and nonlinear acoustic routes is analysed based on the numerical solution of the Westervelt equation; it is revealed that this deviation emerges when the effects of absorption of finite-amplitude waves were not properly taken into account.

Broadband ultrasonic focusing based on circular Airy-like beam

Convergence of ultrasonic energy is of great importance in the medical and engineering fields. In this work, ultrasonic focusing based on circular Airy-like beam (CALB) is numerically and experimentally demonstrated. The CALB focusing can be achieved simply using a planar resin ring lens immersed in water. At 2 MHz, the acoustic intensity at the focus can reach 257 times that for the incident wave. Arising from the self-healing feature of Airy beams, the CALB focusing can be well maintained even if there exists an obstacle in the acoustic path. Meanwhile, the focusing behaviour is well performed in a broad frequency range of 1.5 MHz to 3.1 MHz due to the simple and non-resonant design. By adjusting the frequency of the incident waves, the focal length can be modified without changing the lens structure. The CALB focusing and the corresponding planar lens may promote wide applications in ultrasound imaging, non-destructive testing, acoustic tweezing and medical diagnostic techniques.

Developing Novel Gas Discharge Emitters of Acoustic Waves in Air for Nondestructive Testing of Materials.

This study was devoted to the development of novel devices and a methodology intended for generating ultrasonic waves in an air medium by using atmospheric pressure gas discharge. In the proposed electrode system, the discharge process was accompanied by the generation of acoustic waves on the emitter surface and, consequently, in the ambient air. The gas discharge emitter vibrations were analyzed by applying the technique of Scanning Laser Doppler Vibrometry (SLDV). It was shown that the magnitude of displacements matched the corresponding characteristics of classical piezoelectric and magnetostrictive transducers. The use of the Fast Fourier transform procedure supplied amplitude-frequency spectra of vibrations generated by the gas discharge emitter. The amplitude-frequency spectrum analysis showed that the proposed emitter was able to generate acoustic waves in the air with frequencies from 50 Hz to 100 kHz, and such a device can be used for the nondestructive testing (NDT) of materials. The results of the statistical analysis of vibration displacements in the repetitive pulsed mode were discussed. A non-stable characteristic of the vibration displacement of the emitter membrane was demonstrated. The parameters of such instability were associated with the features of gas discharge processes. In the experiments, the proposed gas discharge emitter was used in combination with SLDV for inspecting carbon-fiber-reinforced polymer composites. The experiments demonstrated the possibility of using an air-coupled gas discharge transmitter to generate acoustic waves in NDT applications.

A Study on the Effectiveness of Spatial Filters on Thermal Image Pre-Processing and Correlation Technique for Quantifying Defect Size.

Thermal imaging plays a vital role in structural health monitoring of various materials and provides insight into the defect present due to aging, deterioration, and fault during construction. This study investigated the effectiveness of spatial filters during pre-processing of thermal images and a correlation technique in post-processing, as well as exploited its application in non-destructive testing and evaluation of defects in steel structures. Two linear filters (i.e., Gaussian and Window Averaging) and a non-linear filter (i.e., Median) were implemented during pre-processing of a pulsed thermography image sequence. The effectiveness of implemented filters was then assessed using signal to noise ratio as a quality metric. The result of pre-processing revealed that each implemented filter is capable of reducing impulse noise and producing high-quality images; additionally, when comparing the signal to noise ratio, the Gaussian filter dominated both Window Averaging and Median filters. Defect size was determined using a correlation technique on a sequence of pulsed thermography images that had been pre-processed with a Gaussian filter. Finally, it is concluded that the correlation technique could be applied to the fast measurement of defect size, even though the accuracy may depend on the detection limit of thermography and defect size to depth ratio.

ИДЕНТИФИКАЦИЯ СЛУЧАЕВ МОШЕННИЧЕСТВА ПО ОСАГО ПРИ РАССЛЕДОВАНИИ ДТП

Modern methods of restoring body parts of a car include many interrelated operations performed in accordance with certain requirements. Carried out repairs are usually con-trolled both by the organization that carried out the repairs and by the car owner. Often after the repair, there is disagreement in the assessment of quality.
 The article describes the methodology for de-termining the location of damage hidden from observation without using the destructive meth-od. Based on the application of non-destructive testing and analysis of chronology, conclusions are drawn about the cause of the formation of convex deformities of the sweat.
 Practical value. The article may be useful to specialists working in the field of body repair, as well as experts evaluating the quality of body repair.

Developing a face-shear lead-free piezoelectric transducer through anti-parallel co-poling and its application to an omnidirectional piezoelectric transducer

Face-shear deformation was observed in various square piezoelectric transducers prepared using the anti-parallel co-poling method, which led to uniform polarization and the generation and receipt of pure fundamental shear horizontal (SH0) waves without any Lamb wave. The amplitude of the SH0 wave was found to be proportional to the piezoelectric charge constant (d33) of the piezoceramic, suggesting that the d33 value can be used as a figure of merit for piezoelectric transducers with strong SH0 waves. The amplitude of the SH0 wave associated with the square piezoelectric transducer is large at 0° and 90° but almost zero at 45°; therefore, a piezoelectric transducer with good omnidirectional properties needs to be developed. A ring-type omnidirectional piezoelectric transducer was produced using eight trapezoidal piezoceramics. The minimum amplitude of the SH0 wave generated and received by the ring type-transducer exceeded 70% of the maximum amplitude. Hence, this ring-type transducer is highly omnidirectional and can be used for nondestructive testing and structural health-monitoring applications.

Correlation-based ultrasound imaging: A diagnostic enabler

Correlation-Based (CB) ultrasound imaging relies on the correlation of measured signals with signals from a simulated or measured database. The CB imaging algorithm Excitelet has demonstrated better ultrasound image quality in Non-Destructive Testing (NDT) applications. In medical applications, ultrasound imaging is characterized by weak image dynamics when compared with Magnetic Resonance Imaging (MRI) or Computed Tomography (CT). However, portable, low-cost, and reliable diagnostic tools based on ultrasound imaging could help reducing the delays between patient assessment and treatment. In order to see more ultrasound-based diagnostics, collective research efforts are still required.Recent work on the use of the CB framework in medical imaging has enabled new diagnostic modalities. Indeed, CB imaging extends the field of view due to the near perfect compensation of the intrinsic properties of the transducers (directivity, dynamics, imperfections, lenses). New automated tools allow using a measured signal database, as opposed to simulated database previously required in CB imaging. Due to its frequency formulation, a realistic signal database enables local acoustical impedance estimation through the reconstruction of the reflectors/diffusers local phase. It is herein proposed to overlay this color-coded phase information, as typically done in Doppler imaging, to enrich the ultrasound image, and facilitate image interpretation.

Application of Non-Destructive Testing in Reservoir Dam Safety Monitoring

Most reservoirs built in earlier years in China generally have major safety issues and leakage is a common problem with them. Nowadays as the technology of Non-Destructive Testing (NDT) has developed and matured greatly, it has been widely used in detecting internal seepage channels, voids, cracks of the dam body and is showing obvious advantages in these aspects. This paper employed a method integrating geological radar (geo-radar) with ultrasonic detection to conduct safety test on the dam body of the Xidachuan Reservoir located in the Linjiang City of Jilin Province of China. The NDT discovered main leakage risk positions of the dam, gave a safety evaluation of the dam body, and proposed targeted treatment measures. NDT can quickly and accurately inspect the quality problems with the dam without causing damages to the structure and it can provide reliable guarantees for the quality of dam projects.

Introduction to DIN 4871: Qualification of NDT Personnel in Civil Engineering (NDT-CE)

Recently, non-destructive testing in civil engineering (NDT-CE), in particular of concrete components, has successfully mastered the leap from research to practice. Several methods have been established for field inspections to determine the concrete cover of reinforcement or to estimate the compressive strength as well as other parameters related to the concrete material. In addition, the application of nondestructive testing is indispensable, if information about the inner structure - such as the location of rebars and tendon ducts or the damage-related condition assessment to detect grouting defects, honeycombs, delamination, or corrosion - is required. Besides the selection of a suitable NDT method and an appropriate inspection system, the reliability of the results depends largely on the person who applies the non-destructive inspection technique and evaluates the inspection results. To ensure a high quality of non-destructive concrete evaluation as well as to keep the uncertainty caused by the inspection personnel to a minimum, structured, consistent and regulated theoretical as well as practical training of inspection personnel is essential. To close this gap, the subcommittee of education (UA-A) within the committee for NDT-CE of the German Society for Nondestructive Testing (DGZfP) has been reactivated in 2018 to establish uniform training standards for nondestructive concrete inspections in the long term. The subcommittee consists of scientists, practitioners, authorities, and clients. So far, the national standard DIN 4871 “Non-destructive testing - Qualification and Certification of NDT personnel in Civil Engineering (NDT-CE)” was developed and is currently under review. This standard considers the civil-industry-specifics, for example, that standards for NDT of concrete, as well as related product standards with a few exceptions, still do not exist at the moment. Within this presentation, the concept, the connection to ISO 9712 and other standards as well as an overview of the developed German standard DIN 4871 will be presented.

Two-stage ultra-broadband luminescence of Cr3+-doped multisite layered phosphor Sr3Ga2Ge4O14 and its application in pc-LEDs

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have enormous potential for all kinds of applications, both non-destructive testing and biological applications. The development of broadband NIR phosphors with good thermal stability for a wide range of applications remains a challenge. This work successfully synthesized a layered structure ultra-broadband NIR phosphor Sr3Ga2Ge4O14:Cr3+ (SGGO:Cr3+) under 431 nm excitation and achieved a spectrum adjusted from 750 nm to 900 nm in a two-stage ultra-broadband emission with a full width at half maximum (FWHM) varying between 257 and 336 nm by controlling the Cr3+ concentration. In particular, SGGO:0.15Cr3+ has a FWHM of 257 nm and the internal quantum efficiency (IQE) of 36.67%, while the emission intensity at 423 K remained at 76% of room temperature. Finally, SGGO:0.03Cr3+ and SGGO:0.15Cr3+ phosphors were used with 430 nm blue light chips to produce NIR pc-LEDs devices and applied to night vision and human palm penetration, as well as plant illumination, revealing the potential of SGGO:Cr3+ for multiple applications. The potential of SGGO:Cr3+ for a variety of applications was demonstrated.

High range resolution wideband terahertz FMCW radar with a large depth of field.

Terahertz frequency modulation continuous wave (THz FMCW) imaging technology has been widely used in non-destructive testing (NDT) applications of non-metallic materials. However, THz FMCW real-aperture radar usually has a narrow bandwidth and small depth of field, thus restricting the application of THz FMCW NDT. In this paper, a wideband THz signal (220-500 GHz) generation method is proposed by time-division multiplexing. Moreover, a dual-band quasi-optical design with a large depth of field is proposed based on the THz Bessel beam, and a high-quality range profile is obtained. Especially, a signal fusion extended Fourier analysis algorithm without prior knowledge is proposed to further enhance the range profile accuracy, which improves the range resolution to 0.28 mm (λ/3, center frequency 360 GHz). The effectiveness and advantages of the proposed system are verified by artificially constructing composite materials.

Multiresolution spectrally-encoded terahertz reflection imaging through a highly diffusive cloak.

Turbid media, made of wavelength-scale inhomogeneous particles, can give rise to many significant imaging and spectroscopy challenges. The random variation of the refractive index within such media distorts the spherical wavefronts, resulting in smeared and speckly images. The scattering-induced artifacts can obscure the characteristic spectral fingerprints of the chemicals in a sample. This in turn prevents accurate chemical imaging and characterization of the materials cloaked with a diffusive medium. In this work, we present a novel computational technique for creating spatially- and spectrally-resolved chemical maps through a diffusive cloak using terahertz time-domain spectroscopy. We use the maximal overlap discrete wavelet transform to obtain a multiresolution spectral decomposition of THz extinction coefficients. We define a new spectroscopic concept dubbed the "bimodality coefficient spectrum" using the skewness and kurtosis of the spectral images. We demonstrate that broadband wavelet-based reconstruction of the bimodality coefficient spectrum can resolve the signature resonant frequencies through the scattering layers. Additionally, we show that our approach can achieve spectral images with diffraction-limited resolution. This technique can be used for stand-off characterization of materials and spectral imaging in nondestructive testing and biological applications.

Distribution of Magnetic Flux Density under Stress and Its Application in Nondestructive Testing

Carbon steels are commonly used in railroad, shipment, building, and bridge construction. They provide excellent ductility and toughness when exposed to external stresses. They are able to resist stresses and strains effectively, and guarantee safe operation of the devices through nondestructive testing (NDT). The magnetic metal memory (MMM) can be used as an NDT method to measure the residual stress. The ability of carbon steel to produce a magnetic memory effect under stress is explored here, and enables the magnetic flux density to be analyzed. The relationship between stress and magnetic flux density has not been fully presented until now. The purpose of this paper is to assess the relationship between stress distribution and the magnetic flux density measured by the experiment. For this, an experimental method for examining a carbon steel plate (SA 106), based on the four-point loading test, was used. The effect of stresses resulting from the applied loads on the response of the experimented SA 106 specimen was examined. A three directional tunnel magnetoresistance (TMR) measurement system was used to collect the triaxial magnetic flux density distribution in the SA 106 specimen. In addition, finite element method (FEM) analyses were performed, and provided information on the direction and distribution of the stress over the studied SA 106 specimen. Indeed, a correlation was derived by comparing the stress analysis by FEM and the measured triaxial magnetic flux density.