•Hybrid structures based on combining metals and composites are introduced.•There are challenges in applying ultrasonic testing on metal to composite joints.•Signal from the joint is reflected even ...without defects in it.•Novel processing algorithm enables to detect the interface between material layers.•The proposed solution enables to detect the defects in the complex joints.
Ultrasonic inspection is widely used for non-destructive evaluation of composite adhesive joints. However, there are serious challenges in applying ultrasonic testing on metal to composite hybrid joints, because they are multi-layered, made out of dissimilar materials and relatively thin. The ultrasonic signals reflected by different layers are overlapped, scattered and attenuated. The aim of this research was to develop an ultrasonic inspection technique suitable for defect detection in hybrid metal to composite joints where the metal part has pin arrays, which entangle with the composite part. The immersion pulse echo technique was used to collect data. In order to overcome the problems related to the rough surface and non-parallel layers a novel signal post-processing algorithm for reconstruction of the joint area was developed and validated experimentally. It is shown that using the proposed technique the positions of different defects can be determined.
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•The IQY and EQY Gd3Zn0.8Ga3.4Ge0.8O12:5%Cr3+ reaches 79.6% and 31.2%, respectively.•The FWHM can reach 211 nm due to the change of local symmetry.•The obtained phosphors were made ...into pc-LEDs with blue light chips.
The rapid development of portable spectroscopic detectors has given rise to a great demand for small light sources, and near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are preferred for their compactness and low cost, while phosphors used in NIR spectroscopy require broadband emission, high quantum yield and good absorption efficiency as well as the spectral range required to achieve detection. Inspired by the tunable structure of Gd3Ga5O12 (GGG), a series of broadband phosphors Gd3ZnxGa5-2xGexO12:1.5%Cr3+ (x = 0–2.0) with continuously tunable emission in the long-wave direction were designed using Zn2+-Ge4+ instead of Ga3+-Ga3+ in GGG to modulate the crystal field environment of Cr3+. The crystal field intensity of the octahedra occupied by Cr3+ decreases with increasing co-substitution, and its full-width at half maximum (FWHM) from 105 nm to a maximum of 211 nm due to the change of local symmetry. In Gd3Zn0.8Ga3.4Ge0.8O12 (GZGG):5%Cr3+, the internal quantum yield (IQY) and external quantum yield (EQY) reaches 79.6% and 31.2% with impressive absorption efficiency (41.1%). The obtained phosphors were made into pc-LED with blue light chips, which was applied to glucose solution degree detection. The results show that the GZGG:Cr3+ will hopefully provide a new strategy for non-destructive testing.
Liquid moulded polymer matrix composites (LM-PMCs) are increasingly used in aerospace, automotive and other industrial applications. Liquid moulding processes featuring dry fibre preforms provide ...flexibility and enable cost reductions for secondary load-bearing structures. However, preform variability and manufacturing reproducibility remain major obstacles to wider use in primary structures. The open literature records only marginal use of non-destructive inspection (NDI) methods for dry multilayer preforms due to technological limitations and cost of NDI methods. In this work, terahertz time-domain spectroscopy (THz-TDS) is used for inspecting three dry multilayer glass fibre preforms featuring different defects, for the first time. A novel time-domain enhancement method is compared with classical image processing methods, aiming at improving image contrast and detecting potential defects. Furthermore, THz B-Scan is used for verifying the accuracy of interply defect detection. Finite difference time domain is simulated for analyzing THz magnitude variation in time-domain. Finally, quantitative evaluation is applied to further illustrate the significant potential of THz-TDS for the inspection of dry fibre preforms. The results show that the errors on defects lengths, widths, angles, and diameters for THz-TDS are in the ranges 8.2 %–34.3 %, 18.67 %–75 %, 0.29 %–6.67 %, and 1.33 %–10 % respectively.
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•Terahertz technology is used for multilayer dry glass fibre preforms inspection for the first time.•A novel time-domain image enhancement method is proposed.•A new method based on disturbances is used to verify the interply detection accuracy.•Quantitative evaluation is performed and the potential of industrial use is discussed.
In recent years, the frequent economically motivated adulteration (EMA) caused by component displacement, illegal addition, and other problems makes the food authenticity become a global issue, which ...requires appropriate identification methods. Raman spectroscopy combination with chemometrics becomes a rapid, non-destructive method to verify the nature or origin of food. This review assembles and comprehensively summarizes the principle, workflow, advantages, challenges and applications of Raman spectroscopy in food authenticity. Besides, existing problems and outlooking on Raman spectroscopy are also discussed.
•This work emphasized the Raman spectrum information processing in food authentication.•Various chemometrics methods to enhance the accuracy of Raman spectral modeling were systematically discussed.•Plenty of strategies for Raman spectroscopy application to specific food authenticity were comrehensively reviewed.•This work will be valuable to the deep research about food authentication.
This paper proposes a Convolutional Neural Network (CNN) based approach for the classification and prediction of various types of in-plane and through-the-thickness delamination in smart composite ...laminates using low-frequency structural vibration outputs. An electromechanically coupled mathematical model is developed for the healthy and delaminated smart composite laminates, and their structural vibration responses are obtained in the time domain. Short Time Fourier Transform (STFT) is employed to transform the transient responses into two-dimensional spectral frame representation. A convolutional neural network is incorporated to distinguish between the damaged and undamaged states, as well as various types of damage of the laminated composites, by automatically extracting discriminative features from the vibration-based spectrograms. The CNN showed a classification accuracy of 90.1% on one healthy and 12 delaminated cases. The study of the confusion matrix of CNN provided further insights into the physics of the problem. The predictive performance of a pre-trained CNN classifier was also evaluated on unseen cases of delamination, and physically consistent results were obtained.
In this paper, the impact of the magnetostriction mechanism is considered as the focus. An axisymmetric FEM model of the spiral‐coil electromagnetic acoustic transducers (EMAT) is established to ...conduct the simulation. The simulation results demonstrate that the directivity of ultrasonic wave can be controlled by manipulating the frequency. Furthermore, it is found that the direction of the dominant Lorentz force in the rail varies with time, while the magnetostrictive force compels the ultrasonic wave generated by the Lorentz force towards the axis. It effectively illustrates that the combined power of two mechanisms surpasses that of the Lorentz‐force mechanism alone, particularly at low frequencies.
The leakage of the reflected energy of the ultrasonic wave generated by electromagnetic acoustic transducers (EMAT) is outside the receiving range and then weakens the amplitude of ultrasonic echo. To reduce the leakage of the reflected energy, this paper takes the impact of magnetostriction mechanism on frequency manipulation ultrasonic steering in EMAT, especially at low frequency.
•A comprehensive system comprising several novel techniques is proposed for quality inspection and counterfeit detection of packaged integrated circuits (IC) using terahertz time-domain ...spectroscopy.•Counterfeit ICs are classified into three major types: Recycled, Blacktopped, and Reverse Engineered. All types of counterfeit ICs are detected using the proposed system.•Noninvasive 3-dimensional (3D) measurements of the size of the features inside the packaged ICs are realized using terahertz time-domain spectroscopy. In this regards, the size of the dies and bond wires and their lateral positions in the packaging is determined.•An innovative resolution enhancement (RET) technique is proposed for enhancing the resolution of the terahertz images, and as a result, accurate measurement of the size of the dies and bond-wires is achieved.
In this paper, a comprehensive set of techniques for quality control and authentication of packaged integrated circuits (IC) using terahertz (THz) time-domain spectroscopy (TDS) is developed. By material characterization, the presence of unexpected materials in counterfeit components is revealed. Blacktopping layers are detected using THz time-of-flight tomography, and thickness of hidden layers is measured. Sanded and contaminated components are detected by THz reflection-mode imaging. Differences between inside structures of counterfeit and authentic components are revealed through developing THz transmission imaging. For enabling accurate measurement of features by THz transmission imaging, a novel resolution enhancement technique (RET) has been developed. This RET is based on deconvolution of the THz image and the THz point spread function (PSF). The THz PSF is mathematically modeled through incorporating the spectrum of the THz imaging system, the axis of propagation of the beam, and the intensity extinction coefficient of the object into a Gaussian beam distribution. As a result of implementing this RET, the accuracy of the measurements on THz images has been improved from 2.4 mm to 0.1 mm and bond wires as small as 550 µm inside the packaging of the ICs are imaged.
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This paper presents the first successful application of ground penetrating radar (GPR) to the inspection of thick (≥100 mm) fiber-reinforced composites. These thick composites are found in wind/tidal ...turbine blades and composite-hulled ships, where sufficient non-destructive testing (NDT) remains challenging. Polyester-glass specimens, ranging in thickness from 100 to 120 mm, were created with delamination-mimicking damage. Specimen thickness, damage depth location, antenna orientation and damage dryness were the test variables. Finite-difference time-domain simulations indicated the method’s feasibility, and experimental results confirmed these findings. GPR effectively detected and precisely located dry, in-plane damage, with increased detectability for water-filled damage due to the enhanced contrast of electrical properties that creates the damage response in the signal. This capability is particularly advantageous for marine composites, where extensive damage may lead to water ingress. In a comparison with an ultrasonic inspection, GPR proved superior for the thicker composites (≥100 mm). As the first successful application of GPR to composite structures, these findings significantly advance the field of NDT of these materials.
Voids, the most studied type of manufacturing defects, form very often in processing of fiber-reinforced composites. Due to their considerable influence on physical and thermomechanical properties of ...composites, they have been extensively studied, with the focus on three research tracks: void formation, characteristics, and mechanical effects. Investigation of voids in composites started around half a century ago and is still an active research field in composites community. This is because of remaining unknowns and uncertainties about voids as well as difficulties in their suppression in modern manufacturing techniques like out-of-autoclave curing and parts with high complexity, further complicated by increased viscosity of modified resins. Finally, this is because of the increasing interest in realization of more accurate void rejection limits that would tolerate some voidage. The current study reviews the research on formation, characterization, and mechanical effects of voids, which has been conducted over the past five decades. Investigation and control of void formation, using experimental and modeling approaches, in liquid composite molding as well as in prepreg composite processing are surveyed. Techniques for void characterization with their advantages and disadvantages are described. Finally, the effect of voids on a broad range of mechanical properties, including inter-laminar shear, tensile, compressive, and flexural strength as well as fracture toughness and fatigue life, is appraised. Both experimental and simulation approaches and results, concerning voids' effects, are reviewed.
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