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• A multi-feature ultrasonic (MFU) method was proposed to evaluate the bonding condition of dual-layer coatings. • Parametric numerical studies were carried out to study the influence of stiffness at two interfaces on different ultrasonic features. • Stacked sparse autoencoder (SSAE) was applied to automatically extract multiple features from ultrasonic waveforms and spectra sensitive to the bonding quality of coating. • The correlation between feature sets extracted by SSAE and those traditional selected features was explored. • The proposed method is effective to detect both the topcoat debonding and primer debonding in the industrial coatings. Ultrasound has been extensively utilized to evaluate the bonding quality of coatings. However, current ultrasonic methods based on single temporal or spectral feature cannot accurately characterize the bonding quality within industrial coatings, especially for potential debonding at different layers. This paper proposed an ultrasonic method with multiple temporal and spectral features to evaluate the bonding condition of dual-layer coatings. Ultrasonic features were automatically extracted based on stacked sparse autoencoder (SSAE) to compare with the conventional selected features. Firstly, numerical simulations were carried out to analyze the variation of ultrasonic signals with different stiffnesses at topcoat and primer interfaces. Two temporal and three spectral features were manually extracted and show high sensitivity to different bonding conditions of the two interfaces. Meanwhile, a SSAE network was designed to automatically extract ultrasonic features. The high correlation between the manually and automatically extracted features demonstrates its effectiveness of automatic feature extraction via SSAE. Then, a 50 MHz ultrasonic pulse-echo system was applied to collect signals from 115 coating samples of laptop shell. Four sets of ultrasonic features were extracted via manual method and SSAE networks. Principal components analysis was then employed to reduce the feature space and support vector machine was applied to distinguish topcoat debonding and primer debonding from the intact coatings. The results show that the feature set including 64 temporal and spectral features extracted by SSAE exhibit the best classification with an accuracy of 95.652 %. This proposed multi-feature ultrasonic method can accurately assess the bonding quality of different interfaces in the multi-layer coatings. [ABSTRACT FROM AUTHOR]

Residual stress and its distribution are the key indicators to ensure structural integrity. However, current ultrasonic methods are not appropriate for complex stress measurement. Considering the proximity of zero-group-velocity (ZGV) mode with the cut-off frequency and its sensitivity to local material property, this paper proposed a local stress measurement method based on S1-ZGV mode. The stress field reconstruction was demonstrated numerically with a nonuniform plate. Then, a FE model was built to investigate the excitation of S1-ZGV mode by oblique incidence approach, proving that S1-ZGV mode can be effectively excited and received with a small distance. Thus, a contact ultrasonic system along with a tailor-made compact wedged transducer was built for experimental validation. Parametric studies were performed to obtain the optimal excitation conditions for S1-ZGV mode. At last, experimental validation was carried out by standard tensile testing. The stress coefficient between the frequency shift and the applied stress was obtained with a uniform plate. The stresses of the nonuniform plate at three different positions were measured, proving that S1-ZGV method is effective for local stress measurement in thin plates. [ABSTRACT FROM AUTHOR]

3D printing technique can be used to fabricating complex-structure ceramics, but the internal microstructure and properties along vertical and horizontal directions may show certain anisotropy due to the layer-by-layer process. This work aims to evaluate 3D printing anisotropy quantitatively for performance optimization via the stereolithography method. The square-shaped barium titanate (BTO) ceramics with three different solid contents (75 %, 80 % and 85 %) were prepared to characterize the differences between the vertical and horizontal directions of the ceramics, including microstructure, phase structure, electrical properties and mechanical properties. The electrical and mechanical performances of the printed BTO ceramics in vertical direction are superior to that of horizontal direction, and the differences firstly decrease with the solid contents increasing to 80 % and then increase slightly with further solid content increasing. Besides, the printed BTO ceramic with 80 wt% solid content has excellent electrical performance. This study may provide a potential way for achieving high performance and low anisotropy in the vertical and horizontal of printed ceramics. [ABSTRACT FROM AUTHOR]

The transparent [Li 0.04 (K 0.5 Na 0.5) 0.96 ]NbO 3 +0.5mol% Er 2 O 3 (KNNLN-Er) lead-free piezoelectric ceramics were prepared by stereolithography technique. The influence of different sintering holding time (4h∼8h) on the micromorphology, relative density, shrinkage, electric properties, and photoluminescence properties were systematically investigated. The KNNLN-Er ceramics show the coexistence of orthorhombic and tetragonal structures. The grain size increases obviously and then decreases slightly with the holding time increasing. The KNNLN-Er ceramics exhibit good piezoelectric performance (piezoelectric constant d 33 ∼97 pC/N, electromechanical couple coefficient k t ∼0.36) and the moderate transparency of 34% when the holding time is 6h during sintering at 1120°C. Besides, the intensity of the photoluminescence emission spectra increases with the holding time increasing. Furthermore, in order to estimate the properties of the KNNLN-Er transparent ceramics, an ultrasonic transducer with a center frequency of 10.5 MHz was fabricated, which can be used for photoacoustic and fluorescence imaging. The results indicate that the KNNLN-Er ceramics have potential for multimode imaging applications. [ABSTRACT FROM AUTHOR]

• Boundary-driven acoustic streaming (AS) induced by both flat and curved walls is studied experimentally and numerically. • The Chladni figures formed in a semi-circular channel are similar to those observed in a circular channel. • PIV accurately measures the AS fields generated by the motion of 1 µm particles, which aligns with simulations. • The ratio of AS velocity generated by the curved wall and that by the flat wall depends on the acoustic modes. While boundary-driven acoustic streaming in fluids surrounded by flat walls has been extensively studied in the literature, theoretical studies on boundary-driven acoustic streaming generated by curved walls have recently emerged. This paper aims to present a quantitative analysis of acoustic streaming fields driven by forces induced by both flat and curved walls. A semi-circular channel made of stainless steel was designed to serve as a model channel with both flat and curved boundaries. A multi-layered glass-steel-glass device, actuated by a piezoelectric transducer, was assembled for experimental characterization of boundary-driven acoustic streaming in such scenarios. First, the various standing acoustic modes in the semi-circular channel were measured through the acoustophoretic patterning of 20 µm polystyrene particles. Next, the acoustic radiation force fields and boundary-driven acoustic streaming patterns under various resonant acoustic modes were characterized through micro-particle-image-velocimetry measurements of the motion of 20 µm and 1 µm polystyrene particles, respectively. Finally, the experimental results were explained using efficient finite element simulations of acoustofluidics and acoustophoresis in a semi-circular reduced-fluid model, with a focus on analyzing the streaming velocities driven by the flat and curved walls. Both experimental and numerical results demonstrated that the ratio of streaming velocities induced by the flat wall and the curved wall in this semi-circular channel depends on the resonant acoustic modes. This research highlights the diverse boundary-driven acoustic streaming patterns that arise in irregular channels and provides a theoretical foundation for choosing strategies for shape optimization to suppress acoustic streaming in acoustofluidic devices. [ABSTRACT FROM AUTHOR]

Abstract: Computed laminography (CL) is different from conventional computed tomography(CT) for its specialization in testing plate-type structures, such as integrated circuit boards (ICB), multilayer printing circuit boards (MPCB), and ball grid arrays (BGA). It adopts a different scanning way to successfully produce cross-sectional images of the plate-type objects, while the conventional CT cannot be used. According to the CL reconstruction algorithm, precise determination of the origin of the projection coordinate system is the first step during cone-beam CL scanning system calibration. But unfortunately, for the practical CL scanning system, it is impossible to measure the position of the X-ray focus projection by direct means. A new method to determine the X-ray focus projection coordinates with high accuracy is proposed. Firstly the angle between the central X-ray and the axis of rotation is set to zero by rotating the X-ray source and detector synchronously. Acquiring digital radiography (DR) images of several spherical objects at two geometrical magnification ratio positions in the cone X-ray beam, the two DR images are combined to one image, on the base of which image processing methods are employed to get the center points of each projection of the spherical object. And every two-positioned center points of the same spherical object determine a line, so all couples of projection centers of all the spherical objects construct a group of lines, mathematically an over-determined equation set. After solving the over-determined equation, the X-ray focus projection coordinates are finally obtained. The experimental results prove that the accuracy of this method can satisfy the requirements of the practical scanning system, meanwhile it is feasible to realize. [Copyright &y& Elsevier]