Nondestructive Evaluation Applications Research Articles

Elastic wave near-cloaking

Cloaking elastic waves has, in contrast to the cloaking of electromagnetic waves, remained a fundamental challenge: the latter successfully uses the invariance of Maxwell’s equations, from which the field of transformational optics has emerged, whereas the elastic Navier equations are not invariant under coordinate transformations. Our aim is to overcome this challenge, at least in practical terms, and thereby unlock applications in mechanics, ultrasound, vibration mitigation, non-destructive evaluation and elastic wave control. We achieve near-cloaking by recognizing that, despite the lack of invariance, a decoupling into a system of form invariant potential equations together with a quantifiable approximation, can be used effectively in many cases to control the flow of elastodynamic waves. Here, in particular we focus on the efficiency and practicability of the proposed near-cloaking which is illustrated using carpet cloaks to hide surface defects from incoming compressional and shear in-plane waves and from surface elastic Rayleigh waves.

Microwave-assisted infrared thermography: A tool for quality assessment of blast furnace feeds

Infrared thermography is a ubiquitous technique for surface non-contact temperature profile analysis and monitoring. The generated thermograms offer a plethora of applications in non-destructive evaluation (NDE) for detecting inhomogeneities in engineering structures. However, the potential of this technique is still in its infancy for quality assessment of minerals and ores. In steel plants, iron ore and coke are the most important raw materials fed into the blast furnace. The alumina content in iron ore and moisture percentage in coke play a significant role in determining ultimate product quality and blast furnace efficiency. Till date, plant operators have relied on time-consuming and cumbersome chemical analysis methods for quality analysis of ores. The present investigation reveals a microwave-assisted infrared thermography based non-invasive technique for fast and accurate quality evaluation of blast furnace feed material, in terms of alumina content in iron ores and moisture content in coke. The estimation of alumina content is based on the difference in dielectric constants of various iron ore constituents. Moisture analysis in coke involves the utilization of well-known black body radiation. The co-relation factor for the alumina content in iron ore is slightly lower than the moisture content in coke. The basic difference occurs owing to inherent limitation of the technique for two different substances. Such type of novel approach is scanty in open domain literature. This non-invasive, real time, precise and fast technique proved its enormous potential during validation for random plant samples and thus promising to improve feed quality and blast furnace efficiency.

Adaptive Synthetic Aperture Radar (SAR) Imaging for Optimal Cross-Range Resolution and Image Quality in NDE Applications

An adaptive scanning algorithm is proposed for reducing scanning time associated with generating synthetic aperture radar (SAR) images, for nondestructive evaluation (NDE) applications, while preserving optimal cross-range resolution and image quality. The proposed method is based on the fact that optimum SAR cross-range resolution is target depth, synthetic aperture dimension, and scanning step size dependent. Hence, in the proposed method, the target properties, such as position and depth, are first estimated using an initial coarse scan of the scene of interest. Then, a localized dense scan is performed for obtaining optimal spatial resolution and image quality. During this procedure, the synthetic aperture dimension of the localized dense scan is adaptively increased (optimized) by reducing pixel-by-pixel image root-mean-square (rms) intensity difference between the images produced before and after each increment increase in the synthetic aperture dimension of the localized dense scan. At the same time, scanning step size is determined in a manner, which is related to the target depth in order to reduce scanning time and to insure obtaining (close to) optimal spatial sampling. Results of several illustrative measurements are provided by which the efficacy of the proposed method is demonstrated. The proposed algorithm, which mainly applies for imaging a localized flaw or a strong-scattering target in a relatively homogenous environment, is common in NDE applications and can be implemented using an automated and adaptive process.

Simulation of 28 Element Ultrasound Transducer for Non-Destructive Evaluation (NDE) Applications

Quantitative ultrasound based Non-Destructive Evaluation (NDE) is one of the leading test procedures used in testing of finished products in manufacturing industry. It can detect surface as well as subsurface flaws accurately. It is also employed in medical diagnostic for various purposes. The main objective of this paper is to simulate 28 element ultrasound transducer pair for through transmission testing procedure. The simulation is done using k-Wave toolbox (open source toolbox) and MATLAB. The simulation results show that the received signal strength and resolution is far more improved over single and dual element transducer probes available in the market. The simulation of wave propagation through three layered aluminum material is also shown in the results. Based on results, it can be concluded that 28 element transducer pair are the optimum solution for NDE evaluation challenges with reference to cost, size, and design complexity.

Two-way collinear mixing of a longitudinal and a transverse plane wave in materials with cubic nonlinearity

ABSTRACT The resonance conditions of two-way collinear mixing are derived when a longitudinal wave and a transverse wave are propagating in the opposite directions based on cubic nonlinearity. The analytical solutions for mixing waves are obtained. An interesting result is that the resonant longitudinal wave and the resonant transverse wave can be generated, respectively, when considering different resonance conditions. This is different from the case with quadratic nonlinearity that only resonant transverse wave can be generated. For the convenience of applications, the wave mixing of a time-harmonic longitudinal pulse and a time-harmonic transverse pulse is also investigated. A clear mixing process is presented by discussing the parameters introduced in the derivation. Numerical calculation is conducted on material Al, the hexagonal waveforms of the resonant transverse waves are depicted when considering different cases. The results could provide new opportunities for mixing wave applications in nondestructive evaluation.

Guided waves propagation in sandwich cylindrical structures with functionally graded graphene-epoxy core and piezoelectric surface layers

As an ideal reinforcing nanofiller, graphene platelets (GPLs) can significantly improve physical properties of nanocomposites, which have attracted considerable attention for design and development of advanced lightweight nanocomposite structures in engineering. In this paper, a sandwich cylindrical structure is considered for dispersion properties of wave propagation by axisymmetric isogeometric analysis (IGA). The sandwich structure is composed of a functionally graded (FG) nanocomposite core and piezoelectric surface layers. Graphene platelets are dispersed in the interlayer by three typical distribution patterns through the thickness. In virtue of the symmetry and the advantages of isogeometric analysis, the sandwich cylindrical structure can be described by one-dimensional representation along the radial direction. Based on Hamilton’s principle, parameterized governing equation for wave propagation is obtained with the non-uniform rational B-splines (NURBS), which leads to an second-order eigenvalue problem. The modified wave finite element (WFE) method and the Chebyshev spectral element (SE) method are utilized to verify the reliability and accuracy of this approach. Then, the effects of several significant parameters of GPLs and geometric sizes of the sandwich structure on wave propagation characteristics are discussed in details. The results of this study are beneficial to deeply understanding and control of wave propagation in advanced piezoelectric composites for the applications in structural health monitoring and nondestructive evaluation.

Elastic metamaterial rod for mode filtering in ultrasonic applications

The proposed 1D elastic metamaterial rod finds application in non-destructive evaluation, as a filter in the transduction side, where only the torsional and flexural modes need to be generated by isolating longitudinal modes. In this Letter, this is achieved by obtaining a wide bandgap in low-frequency ultrasound regime. The novelty of the proposed design arises from the use of a high impedance mismatch between the materials selected for the rod. The proposed concept is demonstrated and verified with numerical simulations. The effectiveness of the proposed technique is confirmed by comparing the results obtained from the rod made of a single material.

Ultrasonic sharp autofocusing with acoustic metasurface

Ultrasound focusing manifests itself as the accumulation of ultrasound energy on the target. It attracts extensive interest owing to its substantial advantage in engineering detection and biomedical science. However, the conventional focusing technique leads to the undesirable off-target influence in the nonfocusing region, hindering its application such as ultrasound surgery. Here we propose an ultrasound beam with idiosyncratic sharp autofocusing properties and implement it with the binary metasurface. The beam shows a sharp accumulation at the focus with an abrupt increase of intensity by three orders of magnitude while keeping the unintended region intact. The sharp autofocusing is realized by the controlled transverse self-acceleration and collapse of caustic at the focus in a nonlinear fashion. The intensity contrast, width, and position of the beam are highly tunable to realize the freewheeling focusing with high efficiency. Remarkably, the possibility to synthesize the abrupt autofocusing by the phase-only modulation is revealed. As an implementation, we demonstrate that the precise control of the sharp converging beam can be realized by an extremely simple metasurface with binary elements. The sharp autofocusing beams would open an avenue to realize the diverse ultrasound focusing with promising applications in medical ultrasound imaging, therapy, and nondestructive evaluation.

Depth resolved pulse compression favourable frequency modulated thermal wave imaging for quantitative characterization of glass fibre reinforced polymer

InfraRed Thermography is an expeditiously growing non-destructive testing and evaluation technique widely used to estimate the subsurface defect details in fibre reinforced polymer materials due to its remote, fast, easy, safe and wide area monitoring abilities. In order to explore the details of subsurface anomalies in active infrared thermography, a modulated heat flux with a predefined intensity and bandwidth is employed to excite the test sample. Among various widely used active infrared thermographic techniques for non-destructive testing and evaluation applications, pulse based and modulated lock-in thermography are predominantly in use. However, these conventional techniques limits their applicability due to high peak power heat source requirements (pulse based techniques) and poor resolution (modulated lock-in thermography) for detecting the defects located at various depths of different lateral dimensions. The present paper highlights a pulse compression favourable frequency modulated thermal wave imaging which can be carried out with moderate peak power heat sources in a limited span of time with improved test resolution and sensitivity. Further the proposed experimentation is validated with the analytical as well as numerical simulations on glass fibre reinforced polymer samples having flat bottom hole defects.

Application of compact laser-driven accelerator X-ray sources for industrial imaging

X-rays generated by betatron oscillations of electrons in a laser-driven plasma accelerator were characterised and applied to imaging industrial samples. With a 125TW laser, a low divergence beam with 5.2±1.7 × 107photonsmrad−2 per pulse was produced with a synchrotron spectrum with a critical energy of 14.6±1.3keV. Radiographs were obtained of a metrology test sample, battery electrodes, and a damage site in a composite material. These results demonstrate the suitability of the source for non-destructive evaluation applications. The potential for industrial implementation of plasma accelerators is discussed.

Characterization of water-participant hydrogen bonds in oil-paper insulation investigated with terahertz dielectric spectroscopy

In this study, aiming to characterize the dynamic polarization behavior of water molecules affected by hydrogen bonding with oil-paper insulation, we performed dielectric spectroscopy on oil-paper insulation with moisture contents of 0.4–4.7% in the terahertz band (0.3–3.3 THz). A relaxation-resonance integrated polarization model considering water-participant hydrogen bond (WHB) effects is established to describe the complex dielectric constant of oil-paper insulation with moisture. The theoretical model is in good agreement with the experimental results. By analyzing the relationship between the polarization parameters and moisture content, three states of WHBs are found. The WHB type, strength and disorder show different characteristics with increased moisture. Furthermore, molecular simulation studies are carried out, and the calculation results provided a persuasive argument for the analysis of terahertz dielectric spectroscopy. This research reveals an important new strategy for studying the polarization behavior of water molecules affected by oil-paper insulation as an experimental supplement to molecular simulation. The proposed test and analysis method render effective and sustainable progress in practical applications of rapid nondestructive evaluation and 2D imaging of moisture content distributed in oil-paper insulation.

Crack localization by laser-induced narrowband ultrasound and nonlinear ultrasonic modulation

The laser ultrasonic technique is gaining popularity for nondestructive evaluation (NDE) applications because it is a noncontact and couplant-free method and can inspect a target from a remote distance. For the conventional laser ultrasonic techniques, a pulsed laser is often used to generate broadband ultrasonic waves in a target structure. However, for crack detection using nonlinear ultrasonic modulation, it is necessary to generate narrowband ultrasonic waves. In this study, a pulsed laser is shaped into dual-line arrays using a spatial mask and used to simultaneously excite narrowband ultrasonic waves in the target structure at two distinct frequencies. Nonlinear ultrasonic modulation will occur between the two input frequencies when they encounter a fatigue crack existing in the target structure. Then, a nonlinear damage index (DI) is defined as a function of the magnitude of the modulation components and computed over the target structure by taking advantage of laser scanning. Finally, the fatigue crack is detected and localized by visualizing the nonlinear DI over the target structure. Numerical simulations and experimental tests are performed to examine the possibility of generating narrowband ultrasonic waves using the spatial mask. The performance of the proposed fatigue crack localization technique is validated by conducting an experiment with aluminum plates containing real fatigue cracks.

A far-field scattering model in textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry

Modeling the scattering-induced attenuation of elastic waves in heterogeneous polycrystals has practical applications in seismology and non-destructive evaluation. However, attenuation modeling for polycrystals with preferred crystallographic orientation (statistically anisotropic or textured polycrystals) has not been well studied. The far-field approximation (FFA) model, which is applicable for arbitrary crystal (triclinic) symmetry and valid for the whole frequency range (Rayleigh region, stochastic regime, and geometric region), has been reported for texture-free polycrystalline materials. This paper extends the FFA model to textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry. This FFA model for textured polycrystals encompasses two advantages: a simple form of dispersion equation and high computational efficiency. Furthermore, this FFA model can predict both the attenuation and phase velocity of elastic waves in textured polycrystals. The FFA model in this study has also been validated by comparison with the full-wave second-order attenuation model on textured polycrystals of triclinic grains. This work provides a simple and efficient tool to predict the elastic wave behavior in heterogeneous polycrystalline materials.

Effects of and Compensation for Translational Position Error in Microwave Synthetic Aperture Radar Imaging Systems

Translational position error in microwave and millimeter-wave synthetic aperture radar (SAR) imaging systems can cause significant image quality degradation, particularly in nondestructive testing and evaluation (NDT&E) applications where the distance to the imaging object is relatively short. In this paper, this translational position error problem is fully studied through electromagnetic simulation. The results show that among possible geometrical causes of error, a translational position error, in the height direction, is the dominant factor in image quality degradation. Subsequently, a corresponding height position error compensation method is proposed and analyzed. The extensive simulations and measurement are performed in the X-band (8.2–12.4 GHz) frequency range. Then, by defining several evaluation metrics, the relationship between image quality and height position error is discussed quantitatively. The measured results show good agreement with the simulated results, which validates the effectiveness of the proposed analysis approach and the compensation method. The methodology proposed in this paper can be used to evaluate the feasibility or help define the required specifications of a microwave SAR imaging system for a specific application.

A capacitive-inductive dual modality imaging system for non-destructive evaluation applications

Abstract For many non-destructive evaluation (NDE) applications, more information can be obtained by using different techniques, especially when the techniques are sensitive to different types of defects. However separate inspections are not always practical due to time and cost constraints. Therefore, an inspection system combing more than one modalities would have many advantages. A dual modality imaging system is thus proposed which can automatically switch between capacitive imaging and inductive imaging modes. Instead of using a physical combination of two sensors, the proposed system employs a coplanar coil pair as a sensor, and the modality switching is done by changing the wiring schemes through program-controlled switch box. After a single scan over the specimen under test, two types of images, namely capacitive and inductive, can be obtained by the proposed system. For an insulated metallic structure, the capacitive image contains the defect information in the insulation layer and on the top surface of the conducting layer, while the inductive image contains the defect information within the conducting region. The proposed integration of the two imaging modalities in a single system does not introduce any interference between the modes and provides more information on the defects with a reduced testing time and production cost on hardware and software compared to using two NDE techniques separately. A theoretical explanation of the imaging mechanisms for the capacitive and inductive modes are provided. The results of finite element modelling show perturbation of the probing fields due to defects in the two imaging modes. Experimental results from a dual modality imaging system are also presented, demonstrating detection of defects in insulator-metal hybrid structures to verify the effectiveness of this approach.

Experimental analysis of the size and shape of time reversal chaotic cavities for nondestructive evaluation

Time reversal may be used as an energy-focusing technique. It is applied in many different ways including, for example, nondestructively evaluating cracks in structures, reconstructing a source event, and providing an optimal carrier signal for communication. In nondestructive evaluation applications, it is often of interest to study small samples or samples that do not lend themselves to the bonding of transducers to their surfaces. A chaotic cavity provides space for the attachment of transducers as well as a more reverberant environment, which is critical to the quality of time reversal focusing. Transducers are attached to the chaotic cavity which is attached to the sample under test. The goal of this research is to explore the dependence of the quality of the time reversal focusing on the size and shape of the chaotic cavity used. An optimal chaotic cavity will produce the largest focusing amplitude, best spatial resolution, and most linear focusing of the time reversed signal. The presentation will provide experimental results for time reversal focusing experiments conducted on various sized and shaped aluminum blocks.

Performance improvement of non-destructive evaluation by steering vector correlation using finite element method

In this research, in order to improve the performance of the beamforming algorithm for a nondestructive evaluation, two kinds of steering vector correlation method using the finite element analysis are proposed. First, for non-destructive evaluation applications of reinforced concrete structures, each steering vector is obtained by calculating the responses at the measurement positions for an arbitrary position of a debonded area instead of for an arbitrary position of a source. Then, the reflection effect from the boundaries of concrete samples can be minimized. Second, for the non-destructive evaluations of plates, the finite element analysis is used to investigate the geometric-induced decay model as a function of the distance from a source by applying a curve-fitting method and the obtained steering vector is applied to the MUSIC (MUltiple SIgnal Classification) algorithm to validate its performance.In this research, in order to improve the performance of the beamforming algorithm for a nondestructive evaluation, two kinds of steering vector correlation method using the finite element analysis are proposed. First, for non-destructive evaluation applications of reinforced concrete structures, each steering vector is obtained by calculating the responses at the measurement positions for an arbitrary position of a debonded area instead of for an arbitrary position of a source. Then, the reflection effect from the boundaries of concrete samples can be minimized. Second, for the non-destructive evaluations of plates, the finite element analysis is used to investigate the geometric-induced decay model as a function of the distance from a source by applying a curve-fitting method and the obtained steering vector is applied to the MUSIC (MUltiple SIgnal Classification) algorithm to validate its performance.

Calculations of neutron reflectivity in the eV energy range from mirrors made of heavy nuclei with neutron-nucleus resonances

We evaluate the reflectivity of neutron mirrors composed of certain heavy nuclei which possess strong neutron-nucleus resonances in the eV energy range. We show that the reflectivity of such a mirror for some nuclei can in principle be high enough near energies corresponding to compound neutron-nucleus resonances to be of interest for certain scientific applications in non-destructive evaluation of subsurface material composition and in the theory of neutron optics beyond the kinematic limit.

Metamaterial improved nonlinear ultrasonics for fatigue damage detection

This article presents an improved nonlinear ultrasonic technique for fatigue damage detection utilizing a kind of carefully designed aluminum-lead composite metamaterial. It focuses on developing a bandgap metamaterial to improve the accuracy and identifiability of the superharmonic features from fatigue cracks by eliminating the inherent nonlinear components in the nonlinear ultrasonic technique. The study starts with the unit cell design through modal analysis by applying the Bloch–Floquet boundary condition to obtain the band structure. Based on the local resonance mechanism, by adjusting the height ratio between the aluminum and lead cylinders, the bandgaps covering the required frequency ranges can be opened up. Then, a chain of regularly arranged unit cells is modeled to analyze the spectral response and verify the bandgap effect through harmonic analysis. The targeted ultrasonic frequency component of guided waves within the bandgap can be mechanically filtered out. Subsequently, a finite element model of the pitch-catch active sensing procedure for fatigue crack detection is constructed via the coupled-field transient dynamic analysis. Nonlinear ultrasonic experiments with the designed metamaterial are carried out to verify the theoretical and numerical investigations. This paper demonstrates that the metamaterial, with its outstanding wave manipulation capability, shows great potential on structural health monitoring and nondestructive evaluation applications. The paper finishes with summary, concluding remarks, and suggestions for future work.

Time-Reversal SAR Imaging for Nondestructive Testing of Circular and Cylindrical Multilayered Dielectric Structures

In this paper, a synthetic aperture radar (SAR) approach, for imaging internal structures of generally lossy layered dielectric cylindrical objects, is presented. This method which properly accounts for different transmission and refraction paths at each boundary between different layers produces a properly focused image of embedded targets. This approach is also capable of addressing imaging needs for asymmetrical multilayered cylindrical bodies. Consequently, this approach overcomes the limitation associated with the conventional methodology, in which free-space propagation is assumed. The calculation method of angular sampling criterion for circular and cylindrical SARs (i.e., circumferential and in height) is also presented. Electromagnetic simulations are performed on a three-layer cylindrical object, symmetrical and asymmetrical, with embedded targets to validate the approach. In addition, representative measurements are conducted at X-band (8.2-12.4 GHz), demonstrating the effectiveness of the approach for practical nondestructive evaluation applications.