Nondestructive Defect Detection Research Articles

Tuneable gradient Helmholtz-resonator-based acoustic metasurface for acoustic focusing

Conventional acoustic focusing requires an array of actuators or waveguides to form a complex wavefront, resulting in a high cost or bulky size. In this paper, an original gradient Helmholtz-resonator (HR)-based acoustic metasurface (AMS) is presented. The phase shift of AMS units can be precisely controlled over the full phase range and continuously tuned by varying the slit width. The transmission efficiency of the AMSs is relatively high, benefitting from the impedance matching. Several typical situations in acoustic focusing with different focusing parameters are realized by the designed AMSs. The results of the finite element method demonstrate that moving the position of the focal point or changing the incident angle can be realized by tuning the slit width distribution. A further analysis indicates that the discrete resolution is considerably fine, as a result of the suitable deep-subwavelength parameters of the AMS and the high accuracy of the phase shift of each unit. The acoustic intensities at the focal point reach 12.3 to 17.6 times that of the incident plane wave, owing to the high transmission efficiency. Due to these significant advantages, the designed gradient HR-based AMS is able to offer a tuneable acoustic lens in medical sonography, localized heating, nondestructive flaw detection and particle trapping.

Detection and Cause Analysis of Structural Defects in Lead Clamp Weld of Transformer

In this paper, the causes analysis of the cracking accident at the lead clamp weld-fusion line of transformer in the extra-high voltage substation was conducted.On-site non-destructive detection of weld defects was carried out to determine the size and location of the defects. An anatomical analysis of the clamp sample revealed that there was serious incomplete penetration and incomplete fusion in the internal structure of the weld, which seriously affected the structural strength of the weld. The causes of welding defects were further analyzed, and suggestions for improving product quality and strengthening inspection supervision were put forward.

Microstructure-based model of nonlinear ultrasonic response in materials with distributed defects

Nonlinear ultrasonic technique is one of several promising nondestructive evaluation methods for monitoring the evolution of nanosized defects such as radiation-induced defects in nuclear materials. In this work, a microstructure-based phase-field model of dynamic deformation in elastically nonlinear materials has been developed for investigating the dynamic interaction between distributed defects and a propagating longitudinal sound wave. With the model, the effect of second phase precipitates’ size and properties on the nonlinearity parameter β that describes the magnitude of the 2nd harmonic wave was simulated. The results showed that (1) the nonlinearity parameter β increases as the elastic inhomogeneity increases regardless of whether the precipitates are softer or harder than the matrix; (2) β linearly increases with the increase of lattice mismatch strain; and (3) for a given volume fraction of second phase precipitates, β strongly depends on the precipitate size. The predicted precipitate size dependence of β agrees with the experimental data. These results demonstrate that the developed model enables one to predict the contributions of different nonlinear sources to β, to explain the signal physics behind the measured nonlinear ultrasonic response, and to guide the development of nonlinear ultrasound nondestructive detection of material defects in nuclear reactor materials.

A feasibility analysis on the application of eddy current testing to the detection of the most detrimental defects in historical metallic tie-rods

Historical metallic tie-rods have a very important structural role in buildings characterized by arches and vaults because they balance the horizontal thrusts, avoiding the overturning of vertical supports. Nowadays, no information can be found in the literature about the non-destructive detection of possible defects in historical tie-rods and their effects on the in-service structural integrity. On the other hand, many Non-Destructive Techniques are commonly used to inspect modern metallic components and structures, but their viability for cultural heritage is still to be assessed.In this paper, the application of eddy current testing to the historical metallic tie-rods of the Milan cathedral (Italy) is evaluated, discussed and adapted. The considered historical structures are characterized by a very heterogeneous material, irregular surface geometry and high inherent defectiveness. Recently, in-service failures showed the most detrimental flaws in tie-rods consist of handmade straight scarf forged welds. A first experimental eddy current testing approach, based on off-the-shelf high and low frequency probes, was performed. Results were partially unsatisfactory and showed the challenge is not the maximization of sensitivity and spatial resolution, as in typical modern applications, but their suitable minimization. Consequently, a customized eddy current testing technique, based on a novel low frequency probe, was designed and optimized. Its performance was evaluated by numerical simulations as well as by experimental testing. Based on the satisfactory achievements, the customized eddy current testing technique was applied on site on seven tie-rods. The most significant discontinuities could be effectively detected.

Integrated Magnetic Sensor Probe and Excitation Wire for Nondestructive Detection of Submillimeter Defects

Eddy current testing with excitation and pickup coils is widely used to detect defects in metals. The detection of submillimeter defects is difficult because of limitations on pickup coil size. We have developed an integrated magnetic probe for detecting submillimeter defects in both nonmagnetic and ferromagnetic materials. The sensor probe consists of a tunneling magnetoresistance (TMR) device and an excitation wire. This probe can apply small, localized magnetic fields to a sample that is near the TMR sensor. The direction of the field excitation is perpendicular to the sensing direction of the TMR sensor to minimize magnetic coupling between the excitation wire and the sensor. A change in the line-scanned signal was detected when measuring pits from 0.5 mm to 1.0 mm in diameter at depths of more than 0.1 mm in both steel and aluminum plates. Signal changes depended on defect size. As the frequency was increased from 1 kHz to 50 kHz, the defect signal change for the aluminum plate increased due to an increase in eddy currents. A clear defect signal for the steel plate was obtained even at a low frequency of 1 kHz because the detected signal for steel consists of a frequency-dependent eddy-current component and a magnetization component even at low frequencies.

Frequency Response of a Moving Two-Dimensional Defect in Magnetic Flux Leakage Inspection

The detection of magnetic flux leakage (MFL) enables nondestructive detection and characterization of defects in magnetic structures. In this letter, Fourier transforms of the leakage fields from a two-dimensional surface defect are evaluated to produce analytical expressions for the frequency response of MFL signals detected by a flux-sensitive sensor. The expressions show the correlation between the spectral response of the leakage fields, defect dimensions, and sensing element lift-off spacing as a product of frequency-dependent defect-width loss function, spacing loss function, and thickness enhancement function. The lower and upper band edges of the band-limited leakage magnetic fields are theoretically identified. A spectral method for sizing of defects is proposed based on the frequency response.

Nondestructive detection of defects in friction stir welded lap joints using computed tomography

Based on computed tomography (CT), a method is developed for nondestructive detection of defects in friction stir welded (FSW) joints. Plates of AA6061-T6 and AA1050 are welded to produce short lap welds. Utilized is spindle speed of 1600 RPM and fifteen different tool feeds ranging from 25 to 1000 mm/min (dubbed welded cases #1 to #15). These joints are CT-scanned and DICOM images are produced for digitally sectioned zones within the welded joints. To demarcate metallic zones from defects, a threshold cutoff value for Hounsfield Unit (HU) is needed to create 2D segmented masks determining the periphery between metal pixels from air pixels. Otsu's thresholding selection method from grey-level histograms is utilized for this purpose. These cutoff values are found to vary slightly from one welded joint to another. From the 2D masks, 3D representations of the welded joints revealed the shapes, locations, and volumes of the detected defects. Cross-sectioning of welds is employed as a destructive test to corroborate the locations and areas of CT-detected defects. The results of the defect area analysis from the CT-scans are compared to the results from optical images obtained by computer vision (CV) in a pixel-based analysis.

A Solution to the Kinematics Problem for a Nondestructive Testing System

Over the past 20 years, polymer composite materials have become widespread in the aviation industry. The use of these materials can significantly reduce weight and improve the environmental parameters and efficiency of the aircraft. This, in turn, requires a high level of automation and robotization of the main technological processes in production; moreover, the nondestructive testing and flaw detection of the component parts and assemblies occupy about 30% of the labor intensity of the technological production process. The article presents a brief description of a nondestructive testing system developed to solve this problem consisting of the five-link manipulator with the X-ray emitter and portal with a radiation receiver. The kinematic diagrams of the system components are described, and a mathematical model of the solution of the problem of direct and inverse kinematics using the geometric method is presented for the manipulator and receiver. The testing of the constructed model is made, which shows its adequacy.

Temperature fringe method with phase-shift for the 3D shape measurement

Linear laser fast scanning thermography technology has a good application prospect in the nondestructive detection of defects. Meanwhile, due to the modulation of the surface topography, the thermal response fringes excited by the line laser are distorted in the scanning process, whereby the three-dimensional topography of the specimen can be reconstructed. However, the accuracy of this method is currently limited by unfavorable factors, such as background noise of the specimen surface and the extraction error of the deformed temperature fringes. In this paper, by optimizing the initial position difference during line laser scanning and converting the laser fringes with specific position difference into temperature fringes with specific phase difference, the phase shift technique is combined with the temperature fringe method. What's more, some post-processing algorithms were developed to further develop the temperature fringe method and greatly improve the accuracy of the method. By measuring some specimens with different shapes and different colors, the results show that the technology and algorithms developed here can obtain the three-dimensional shape of the measured specimen with high accuracy while having a non-destructive testing function, without interference from the surface color of the specimen.

Depth determination of defects in CFRP-structures using lock-in thermography

Abstract Due to the increasing application of CFRP in mass application, an economic repair process gains importance. As the typical repair process starts with the defect detection, the accuracy of the measurement system is a limiting factor of the repair process. Lock-in thermography is a promising approach for non-destructive defect detection. Since the phase images contain a superposition of depth information, the determination of the defects' depth is a challenge. Based on the complex wave field, this paper introduces a method to determine the thermal properties and the defects' depth in CFRP structures using lock-in thermography.

In situ high temperature microwave microscope for nondestructive detection of surface and sub-surface defects.

An in situ high temperature microwave microscope was built for detecting surface and sub-subsurface structures and defects. This system was heated with a self-designed quartz lamp radiation module, which is capable of heating to 800°C. A line scanning of a metal grating showed a super resolution of 0.5 mm (λ/600) at 1 GHz. In situ scanning detections of surface hole defects on an aluminium plate and a glass fiber reinforced plastic (GFRP) plate were conducted at different high temperatures. A post processing algorithm was proposed to remove the background noises induced by high temperatures and the 3.0 mm-spaced hole defects were clearly resolved. Besides, hexagonal honeycomb lattices were in situ detected and clearly resolved under a 1.0 mm-thick face panel at 20°C and 50°C, respectively. The core wall positions and bonding width were accurately detected and evaluated. In summary, this in situ microwave microscope is feasible and effective in sub-surface detection and super resolution imaging at different high temperatures.

Machine-Learning Approach in Detection and Classification for Defects in TSV-Based 3-D IC

A through-silicon via (TSV) is a conducting copper nail, which provides an electrical connection through a substrate, and is expected to be used extensively to provide high-speed interconnects between the top and bottom of an active die. However, some TSV structural defects such as pinholes and voids are difficult to capture as they commonly affect TSV performance parameters rather than TSV logical function. In order to electrically detect failures, it is necessary to study and analyze electrical characteristics of defects in advance. Testing TSV interconnects for manufacturing defects poses major challenges, and new design-for-test techniques are needed. Here, a novel nondestructive defect detection method using machine learning (ML) is proposed in order to detect void, short, and open defects in TSV-based 3-D ICs. A supervised ML approach is used to build a classification model from training S-parameter data sets containing the defected TSV and the normal TSV. The performance of the random forest classifier is tested for various amounts of void, short, and open defects in TSV-based 3-D-stacked ICs with satisfactory results.

Design and Testing of a Micro-thermal Sensor Probe for Nondestructive Detection of Defects on a Flat Surface

This paper presents a design and testing of a micro-thermal sensor probe for realizing the proposed concept of non-contact surface defect detection, in which a change in heat flow across the gap between the tip of the micro-thermal sensor probe and a target surface is utilized to recognize the existences of surface defects. In the proposed concept of surface defect detection, the probe tip, where the micro-thermal sensor is embedded, is required to be placed as close as possible to the target surface for highly sensitive surface defect detection. For the purpose, an optical tilt detection assembly based on the laser autocollimation is designed to detect relative tilt of the micro-thermal sensor with respect to a target surface. A sensor probe assembly, in which the fabricated micro-thermal sensor is embedded to the tip of a hollow-shaped piezoelectric actuator by using a homemade sensor mount, is also designed in such a way that the sensor element will face to a target surface. A prototype micro-thermal sensor probe is constructed by integrating the optical tilt detection assembly and the sensor probe assembly, and some experiments have been carried out to verify the basic performances of the prototype micro-thermal sensor probe.

Nondestructive Evaluation and Detection of Defects in 3D Printed Materials Using the Optical Properties of Gold Nanoparticles

Three-dimensional (3D) printing techniques are being rapidly adopted for prototyping and product development across fields as scientifically diverse as wind energy and regenerative medicine. Through materials processing advancements, the incorporation of nanomaterials within 3D printed parts and structures has begun to enable enhanced material functionalities. In this work, the optical properties of gold nanoparticles are harnessed via the development of functionalized printer filament to detect defects and missing print layers in 3D printed parts. Gold nanoparticles are incorporated within a poly(lactic acid) polymer host matrix, and filament compatible with stock 3D printers is fabricated. Consistent with Beer–Lambert’s Law for nanoparticles in solution, a linear relationship between absorbance intensity and the total number of print layers is observed. By analyzing changes in absorbance intensity, the presence, location, and extent of material defects as small as 0.2 mm are identified through a nondest...

Nondestructive Detection of Simulated Defects with Complicated shape under Painted Surface by Photoacoustic Method

Nondestructive Detection of Simulated Defects with Complicated shape under Painted Surface by Photoacoustic Method

Non-Destructive Defect Detection of Apples by Spectroscopic and Imaging Technologies: A Review

Abstract. Apples are susceptible to a wide range of defects that can occur in the orchard and during the post-harvest period. Detection of these defects by non-destructive sensing techniques is of great importance for the apple industry and has been an intensive research topic over the past two decades. This review presents an overview of common defects in apples, encompassing physiological disorders, mechanical damage, pathological disorders, and contamination. Presented and discussed in this review is research progress on the detection of defects in apples using various non-destructive spectroscopic and imaging techniques, including visible/near-infrared spectroscopy, fluorescence spectroscopy and imaging, monochromatic and color imaging, hyperspectral and multispectral imaging, x-ray imaging, magnetic resonance imaging, thermal imaging, time-resolved and spatially resolved spectroscopy, Raman spectroscopy, biospeckle imaging, and structured-illumination reflectance imaging. This review concludes with remarks on the prospects of these techniques and research needs in the future. Keywords: Apples, Defects, Imaging, Non-destructive detection, Quality, Safety, Spectroscopy.

Magnetite Core–Shell Nanoparticles in Nondestructive Flaw Detection of Polymeric Materials

Nondestructive flaw detection in polymeric materials is important but difficult to achieve. In this research, the application of magnetite nanoparticles (MNPs) in nondestructive flaw detection is studied and realized, to the best of our knowledge, for the first time. Superparamagnetic and highly magnetic (up to 63 emu/g) magnetite core-shell nanoparticles are prepared by grafting bromo-end-group-functionalized poly(glycidyl methacrylate) (Br-PGMA) onto surface-modified Fe3O4 NPs. These Fe3O4-PGMA NPs are blended into bisphenol A diglycidylether (BADGE)-based epoxy to form homogeneously distributed magnetic epoxy nanocomposites (MENCs) after curing. The core Fe3O4 of the Fe3O4-PGMA NPs endows the MENCs with magnetic property, which is crucial for nondestructive flaw detection of the materials, while the shell PGMA promotes colloidal stability and prevents NP aggregation during curing. The eddy current testing (ET) technique is first applied to detect flaws in the MENCs. Through the brightness contrast of the ET image, surficial and subsurficial flaws in MENCs can be detected, even for MENCs with low content of Fe3O4-PGMA NPs (1 wt %). The incorporation of Fe3O4-PGMA NPs can be easily extended to other polymer and polymer-based composite systems and opens a new and very promising pathway toward MNP-based nondestructive flaw detection in polymeric materials.

Fluorescence confocal microscopy as effective testing method of polypropylene fibers and single polymer composites

Single polymer composites are special type of composite made solely of one polymer. They are characterized by promising mechanical properties but the manufacturing process is very difficult to scale to mass production. In this paper a method of testing polymer fibers and single polymer composites was developed. The method provides fast and nondestructive detection of structural defects in fibers and delamination in single polymer composites, therefore it can be applied to quality control of the fibers as well as composites. The method based on the laser scanning confocal microscopy, that uses laser to scan the surface of the specimen and detect light of wavelength longer than laser beam. The results show that the luminescence occur only in the defected or delaminated spots of the sample. Raman and IR spectroscopies were used to analyze the source of the luminescence. The study indicates that the influence of impurities, additives and effects of chemical degradation of polymer doesn’t lead to luminescence of the specimen. As the explanation of the effect mechanical stress assisted photoluminescence was proposed.

Identifying Lamé parameters from time-dependent elastic wave measurements

In many sectors of today’s industry it is of utmost importance to detect defects in elastic structures contained in technical devices to guarantee their failure-free operation. As currently used signal processing techniques have natural limits with respect to accuracy and significance, modern mathematical methods are crucial to improve current algorithms. We consider in this paper a parameter identification approach for isotropic and linear elastic structures described by their Lamé parameters and a material density. This approach can be employed for non-destructive defect detection, location and characterization from time-dependent measurements of one elastic wave. To this end, we show that the operator linking the static parameters with the wave measurements is Fréchet differentiable, which allows to set up Newton-like methods for the non-linear parameter identification problem. We indicate the performance of a specific inexact Newton-like regularization method by numerical examples for a testing problem of a thin plate from measurements of the normal component of the displacement field on the boundary. As an extension, we further augment this method with a total variation regularization and thereby improve reconstructed parameters that feature edges.

Online defect detection of Al alloy in arc welding based on feature extraction of arc spectroscopy signal

In this paper, a novel methodology for real-time nondestructive defect detection, particularly hydrogen- assisted porosity of an aluminum alloy welded using pulsed gas tungsten arc welding is presented based on the plasma spectroscopy signal of the welding arc. The emission lines of the hydrogen atom at 656.3 nm and argon atom at 641.63 nm were analyzed to extract multiple feature parame- ters, fromwhich more sensitivefeatureswerethenselectedfor monitoringbymeans of Fisher distancecriteria. The threshold detectionmethodbasedonthe featuresselectedfromthespec- trum was found to be feasible in detecting the welding defect, i.e., porosity in real-time. Furthermore, the established predicting model based on SVM-CValso successfully identi- fied defect of porosity from normal welding with high accuracy.