Plate-like Structures Research Articles

Superabsorbent polyacrylamide nanocomposite hydrogels with cashew tree gum: Investigation of the effect of laponite on swelling capacity and rheological properties.

Superabsorbent nanocomposite hydrogels based on polyacrylamide (PAAm), cashew tree gum (CG), and laponite (LAP) were synthesized in different concentrations to investigate swelling, thermal, morphological and rheological properties. Vibrational modes confirmed the formation of hydrogels, while X-ray diffraction patterns reveal the semi-crystalline structure of the hydrogels. Thermal analysis showed that higher LAP content and CG-LAP interactions improved the thermal stability of the hydrogels. Morphology analysis presented porous structures in CG-based hydrogels, contrasting with irregular plate-like structures in those without CG. The swelling capacity had better results in hydrogels with CG that were subjected to alkaline hydrolysis, mainly in a buffer solution with a pH > 4, due to the ionization of the hydrophilic groups. Hydrogels containing LAP maintained swelling degree stability at pH 10 and 12. In rheological tests, the addition of LAP increased the viscosity of the hydrogels, significantly improving the mechanical resistance of the hydrogels. Rheological parameters, such as the storage modulus (G') and loss modulus (G″), indicated that the materials exhibited predominantly solid behavior, particularly in CG-LAP-rich hydrogels. Low mortality of Artemia salina nauplii in toxicity tests confirmed material safety. The results indicate that CG-LAP hydrogels are promising for agricultural applications, offering optimized swelling properties, thermal stability, and mechanical strength.

Impact Damage Localization in Composite Structures Using Data-Driven Machine Learning Methods.

Due to the uncertainty of material properties of plate-like structures, many traditional methods are unable to locate the impact source on their surface in real time. It is important to study the impact source-localization problem for plate structures. In this paper, a data-driven machine learning method is proposed to detect impact sources in plate-like structures and its effectiveness is tested on three plate-like structures with different material properties. In order to collect data on the localization of the impact source, four piezoelectric transducers and an oscilloscope were utilized to construct an experimental platform for impulse response testing. Meanwhile, the position of the impact source on the surface of the test plate is generated by manually releasing the steel ball. The eigenvalue of arrival time in the time domain signal is extracted to build data sets for machine learning. This paper uses the Back Propagation (BP) neural network to learn the difference in the arrival time of each sensor and predict the location of the impact source. The results demonstrate that the machine learning method proposed in this paper can predict the location of the impact source in the plate-like structure without relying on the material properties, with high test accuracy and robustness. The research work in this paper can provide experimental methods and testing techniques for locating impact damage in composite material structures.

Reversible phase transition and tunable band gap in zinc telluride induced by acoustic shock exposure.

In this study, Zinc Telluride (ZnTe) was subjected to acoustic shock waves with a Mach number of 1.5, transient pressure of 0.59 MPa, and a temperature of 520 K to analyze its stability against shock wave impact. ZnTe was exposed to different shock pulses, such as 100, 200, 300, and 400. The stability was assessed through multiple characterization techniques such as Powder X-ray diffraction (PXRD), Raman spectroscopy, Ultraviolet diffuse reflectance spectroscopy (UV-DRS) analysis, Photoluminescence (PL) spectroscopy, and Scanning Electron Microscopy (SEM). The X-ray diffraction pattern revealed a phase transition at 300 shock pulses from cubic (F4̄3m) to cubic (Fm3̄m). Interestingly, at 400 shock pulses, the original cubic (F4̄3m) phase was restored. The Raman spectrum showed the disappearance, intensity variation, and shift of Raman peaks, particularly at 300 shock pulses, which reverted to the original state at 400 pulses, indicating a reversible phase transition. The absorption spectrum exhibited a lower angle shift and a change in band gap from 2.85 eV to 2.63 eV at 300 shock pulses. However, the band gap was reduced to 2.8 eV at 400 shock pulses. The photoluminescence spectrum showed high intensity specifically at 300 shock-loaded conditions. Morphological analysis revealed a change from irregular shapes to plate-like structures at 300 shock pulses. The results confirm that shock waves significantly impact ZnTe, inducing a reversible phase transition.

Investigation of networked SSHI configurations for plate-based piezoelectric energy harvesters

Piezo-patch energy harvesters attached to plate-like structures can be used to extract multimodal vibrational energy. For each piezo-patch, SSHI circuits can boost the harvested power compared to standard rectifier circuits. However, the effect of using different configurations of the SSHI network for multiple piezo-patches on plate structures has not yet been understood. This study aims to assess the performance of the networked SSHI configurations compared to networked rectifier configurations and investigate the optimum configurations for energy harvesting purposes. For this, three piezo-patches are bonded to an aluminum plate and connected to single and/or multiple circuits. The equivalent circuit model (ECM) of the electromechanical system is developed from the experimentally validated analytical model and utilized in simulation software LTspice. The performances of considered configurations are evaluated regarding peak power outputs, and the optimal load resistances are obtained. Based on the experimental findings, the best configuration is determined and verified by simulations. The results show that by using respective SSHIs, the power output can be improved by preventing charge cancellation despite the cost of increased diode loss. This study contributes to our understanding of optimal energy harvesting techniques by investigating the effectiveness of networked SSHI configurations for multiple piezo-patches on plate structures.

Filter feeding in devil rays is highly sensitive to morphology.

Mobulid rays (manta and devil rays) use a highly specialized filtering apparatus to separate plankton food particles from seawater. Recent studies have indicated that captive vortices form within the microscale pores of the filter, which enhance filtration efficiency through a novel mechanism referred to as ricochet separation. The high throughput and clog resistance of this filtration process have led to the development of several bioinspired engineered filtration systems. However, it is still unclear how changes to the filter morphology influence the surrounding flow patterns and filtration efficiency. We address this question by examining the flow fields around and filtering properties of mobulid filters with systematically varied morphologies, using a combination of computational fluid dynamics and experiments on physical models. While the pore size is the principal determinant of filtration efficiency in a sieve filter, we found that the captive vortices in a mobulid filter grow or shrink to fill the pore, and changes in the pore size have modest effects. By contrast, the filtration efficiency appears to be highly sensitive to the orientation of the filter lobes (microscale plate-like structures). These results provide a foundation for interpreting the morphological differences between species and also for generating optimized bioinspired designs.

Physics-guided neural network for structural health monitoring with lamb waves through boundary reflection elimination

Lamb-wave-based structural health monitoring (SHM) technology for damage location in plate-like structures relies on the postprocessing of captured signals after interacting with damage. Traditional methods typically leverage the time of flight (ToF) of scattered waves from damage. However, these methods are prone to reflected waves from structural boundaries which mix with scattered waves from damage. This is a vital problem faced by most ToF-based detection methods, which seriously narrows the inspection area. To tackle this problem, a machine learning framework, consisting of a multiscale spatiotemporal (MSST) fusion network, is proposed to facilitate the accurate extraction of the ToF of scattered waves through eliminating the influence of boundary reflections. Experiments are conducted with the time-domain Lamb wave signals recorded by a tactically designed piezoelectric sensor array on a 2-mm-thick Al-6061 plate. A pair of circle magnets is attached onto the plate as the wave reflectors. Through step-by-step moving of the magnets in the predefined grids, the corresponding Lamb wave signals are measured to construct a database. An MSST is subsequently designed to minimize the error between estimated and theoretical ToFs, with wavelet coefficients of the signals and transducer position as inputs. The model is trained with the Adam algorithm where 80% of samples in the database are used for training and the rest for evaluation. The final validations are conducted with the scatters off the predefined grids. Results demonstrate that the designed neural network architecture can effectively eliminate boundary reflections and enable precise ToF extraction of the scattered waves from damage. This allows the enlargement of the detection area and presents a promising and useful tool for enhancing the detection performance of existing SHM methods in complex structures.

Superconductivity and surface structures in iron-doped bulk compound Bi2Sr2Ca2(Cu0.99Fe0.01)3O10+δ

Nowadays, researchers are extremely fascinated with the study of the doping effects of nanostructures of different materials, sizes and concentrations in high [Formula: see text] superconductors. This paper presents the presence of nanorods (N) structures, which have not previously been observed in the bulk HTSCs materials, and the influence of Iron doping in Bi-2223 superconductor using composition Bi2Sr2Ca[Formula: see text](Cu[Formula: see text]Fex)nO[Formula: see text], ([Formula: see text]) for ([Formula: see text] and 0.01). The composition is prepared through a solid state route (SSR). The obtained samples are characterized with XRD, FESEM with EDX, HR-TEM and FTIR, and categorized into two samples ([Formula: see text]) and ([Formula: see text]) Bi2Sr2Ca2Cu3O[Formula: see text], and Bi2Sr2Ca2(Cu[Formula: see text]Fe[Formula: see text])3O[Formula: see text], respectively, which show Lattice dimensions [Formula: see text][Formula: see text]Å, [Formula: see text][Formula: see text]Å, [Formula: see text][Formula: see text]Å and [Formula: see text][Formula: see text]Å, [Formula: see text][Formula: see text]Å, [Formula: see text][Formula: see text]Å with Orthorhombic crystal structure, respectively. The FE-SEM micrographs show plate-like layered structures and (N) in the samples, which are uniformly distributed. The obtained size of crystallite nanoparticles is 2[Formula: see text]nm–100[Formula: see text]nm, calculated by the Scherrer method, and verified with HR-TEM data. The HR-TEM study also confirmed the layered form in the orthorhombic phase. The FESEM-EDX energy peaks in the spectrum confirm the presence of the elements in both samples ([Formula: see text]) and ([Formula: see text]). The HRTEM-EDX confirms the extant iron in the sample in the form of (N). The FTIR bond stretching 1630.89[Formula: see text]cm[Formula: see text] and 1629.657[Formula: see text]cm[Formula: see text] of the samples ([Formula: see text]) and ([Formula: see text]), respectively, confirms the superconductor bismuth-based 2223 phase, respectively. The electrical resistivity study of ([Formula: see text]) and ([Formula: see text]) samples shows the critical temperature ([Formula: see text]) of 63.083[Formula: see text]K and 22.8195[Formula: see text]K, respectively. The onset temperature for both samples is measured at 115.1785[Formula: see text]K and 68.314[Formula: see text]K, which represent the Bi-2223 phase. The magnetoresistance is obtained at low temperatures by a physical properties measurement system (PPMS) and with the increasing order of applied magnetic field from 0 to 12 Tesla, an increase in the resistivity in the pure sample ([Formula: see text]) and also a decrease in transition temperature are observed. These results are as similar to those obtained in the Bi-2223 Superconductor. The results show the growth of nanoparticles in the iron-doped Bisco superconductors.

On a fully three-dimensional bending analysis of very thick smart composite cube-like bulk structures

Here we discuss the behaviour of very thick composite plates considering electro-magneto-elastic coupling of various types using fully three-dimensional (3D) kinematics. Published research highlights a lack of studies on the 3D mechanics of smart composite plates that integrate both higher-order (flexoelectric/flexomagnetic) and lower-order (piezoelectric/piezomagnetic) multiple physical fields (electro-magneto-elastic). The common approach to achieving the targeted and desired mechanical behavior within such composites could involve using structural elements. This gap can potentially be addressed by amalgamating the term ∂/∂z with the 2D governing equations of plates. This expression indicates alterations in thickness, in which z is the coordinate dedicated to the thickness. The governing equations can be created by operating on the variational method which enables us to establish and settle the 3D bending equations of the bulk structure. The pointed-out equations have been influenced by the implementation of additional hypotheses, such as von Kármán’s strain and complicated 3D tensor relations. Inserting the term ∂/∂z into the mathematical model renders that the analytical solution techniques are unable to assist us in obtaining numerical results. Consequently, a semi-analytical solving method grounded on the polynomial phrases facilitates the acquisition of the required solution. This fully 3D bending study of very thick piezocomposite cube-like bulk structures (CBS) can be an original reference in the field of mechanics of intelligent plate-like structures.

Guided wave tomography for quantitative thickness mapping using non-dispersive SH0 mode through geometrical full waveform inversion (GFWI)

Guided wave tomography plays a significantly important role in quantitatively mapping thickness variations in plate-like structures and pipelines in the petrochemical industry for accurate measurement of corrosion, as guided waves enable rapid screening of large areas without needing direct access. Several inverse algorithms have been implemented in guided wave tomography; however, almost all of them use a primary assumption: the three-dimensional (3D) guided wave thickness reconstruction is simplified as a two-dimensional (2D) acoustic wave velocity inversion, which is then mapped to thickness variation using the dispersive nature of guided waves. Although this assumption simplifies the inverse procedure, it makes it impossible to use non-dispersive modes in reconstructions. Geometrical full waveform inversion (GFWI) is promising to overcome this limitation since it can reconstruct corrosion profiles through geometry optimization using a data-fitting procedure, where velocity-to-thickness mapping is not needed. In this work, GFWI-based guided wave tomography is developed in plate-like structures, and is applied to reconstruct thickness maps in a series of corrosion defects using the non-dispersive SH0 mode, demonstrating high performance and achieving an improved reconstruction resolution.

Research on the fusion imaging method of sign coherence and time reversal for Lamb wave sparse array

Time-reversal imaging struggles to detect plate-like structures due to interference from Lamb wave mode conversion and the processing demands, leading to less effective outcomes. This paper proposes a sign coherence factor and time reversal fusion (SCF-TR) imaging method based on amplitude and phase estimation. This method removes the coherence of array signals during signal reversal and refocusing. It reintroduces the sign coherence component to reduce interference from non-target scattered waves and partially overcome the constraints imposed by the Rayleigh criterion. The method allows imaging at a resolution smaller than the wavelength of Lamb and enhances the quality of the resulting images. In addition, a sparse array design utilizing the White Shark Optimisation Algorithm (WSO) is proposed to streamline the SCF-TR calculation process. This design utilizes sparse full matrix data to improve imaging efficiency. The experimental results show that for single blind hole defects, the SCF-TR method improves the array performance metrics and signal-to-noise ratio by 22.46% and 42.50%, respectively, compared to the TR method. For multiple asymmetric blind hole defects, when the defect size exceeds the resolution threshold, SCF-TR accurately reflects the position and morphology of defects smaller than the wavelength. When the defect size is below the resolution threshold, SCF-TR achieves super-resolution imaging. The sparse array designed using the White Shark Optimization algorithm demonstrates good sidelobe characteristics, effectively reducing sidelobe noise without reducing the array aperture. Moreover, the SCF-TR imaging time is reduced by approximately half while maintaining imaging accuracy.

Physical Sensors Based on Lamb Wave Resonators

A Lamb wave is a guided wave that propagates within plate-like structures, with its vibration mode resulting from the coupling of a longitudinal wave and a shear vertical wave, which can be applied in sensors, filters, and frequency control devices. The working principle of Lamb wave sensors relies on the excitation and propagation of this guided wave within piezoelectric material. Lamb wave sensors exhibit significant advantages in various sensing applications due to their unique wave characteristics and design flexibility. Compared to traditional surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors, Lamb wave sensors can not only achieve higher frequencies and quality factors in smaller dimensions but also exhibit superior integration and multifunctionality. In this paper, we briefly introduce Lamb wave sensors, summarizing methods for enhancing their sensitivity through optimizing electrode configurations and adjusting piezoelectric thin plate structures. Furthermore, this paper systematically explores the development of Lamb wave sensors in various sensing applications and provides new insights into their future development.

Damage detection and localization in plate-like structures using sideband peak count (SPC) technique

This paper addresses the critical issue of detecting and localizing damage in plate-like structures, which are commonly encountered in aerospace, marine and other engineering applications. To address this challenge, the current study introduces the sideband peak count (SPC) technique as the foundation for diagnostic imaging for damage detection in plate structures. The proposed damage detection algorithm requires only a limited number of sensor responses, streamlining the detection process. It does not rely on a reference baseline, thereby enhancing its efficiency and accuracy. This approach enables rapid and precise identification of damage and its location within the plate structure. To validate the effectiveness and applicability of the proposed method, finite element simulation results are utilized. These results demonstrate the capability of the proposed technique to accurately detect and localize damage, providing a promising solution for enhancing the structural health monitoring of plate-like structures in various engineering domains.

Sound transmission loss of constrained layer damping composites featuring elastic plates embedded with acoustic black hole

This paper preliminarily investigates the influence of an elastic layer with an acoustic black hole (ABH) on the airborne sound insulation of a constrained layer damping (CLD) composite plate. ABHs represent a continuous impedance reduction in a local area of the structure, achieved by reducing material thickness. They efficiently dampen structure-borne sound in plate-like structures, resulting in excellent airborne sound attenuation performance. In the CLD composite structure, a damping layer is inserted between the elastic layers. This configuration achieves noise reduction and provides excellent airborne sound attenuation performance. By incorporating an ABH on one side of the elastic layer within the constrained damping composite structure and utilizing the damping layer as the terminal damping material for ABH, we achieve a lightweight structure with outstanding airborne sound insulation performance. Using finite element numerical calculations, we assess the airborne sound transmission loss of ABHs embedded within the CLD plate. Our analysis compares their transmission losses within the frequency range of 10 to 4000 Hz under normal-incidence and random incidence acoustic field excitations. While the ABH does not enhance the overall sound isolation performance of the CLD plate, it significantly improves the sound isolation dip at the resonance frequency.

Damage detection by means of broadband local wavenumber estimation in plate-like structures

This short communication evinces the ability of the CFAT methodology [Q. Leclère, JSV, 2015] to detect and characterize thickness-loss defects on homogeneous flat panels. A contactless measurement of the velocity field of an aluminium plate is performed by scanning laser vibrometry, from which the equivalent rigidity (apparent bending stiffness) is locally estimated within a wide frequency band in the ultrasonic domain. The method allows imaging thickness-reduction defects on the hidden face of an aluminium plate up to several hundreds of kilohertz. The first part details the experimental protocol, followed by a second enhancing the identification of the wavenumbers of symmetric S_0 and antisymmetric A_0 modes. The comparison with theoretical Lamb waves dispersion curves reveals the precision of the method. Finally, the methodology validates the possibility to precisely estimate the local material thickness and as a consequence the location, size and depth of a reference defect in the shape of a flat bottom hole (assuming homogeneous material properties of the plate).

A Hybrid GAN-Inception Deep Learning Approach for Enhanced Coordinate-Based Acoustic Emission Source Localization

In this paper, we propose a novel approach to coordinate-based acoustic emission (AE) source localization to address the challenges of limited and imbalanced datasets from fiber-optic AE sensors used for structural health monitoring (SHM). We have developed a hybrid deep learning model combining four generative adversarial network (GAN) variants for data augmentation with an adapted inception neural network for regression-based prediction. The experimental setup features a single fiber-optic AE sensor based on a tightly coiled fiber-optic Fabry-Perot interferometer formed by two identical fiber Bragg gratings. AE signals were generated using the Hsu-Nielsen pencil lead break test on a grid-marked thin aluminum plate with 35 distinct locations, simulating real-world structural monitoring conditions in bounded isotropic plate-like structures. It is demonstrated that the single-sensor configuration can achieve precise localization, avoiding the need for a multiple sensor array. The GAN-based signal augmentation expanded the dataset from 900 to 4500 samples, with the Wasserstein distance between the original and synthetic datasets decreasing by 83% after 2000 training epochs, demonstrating the high fidelity of the synthetic data. Among the GAN variants, the standard GAN architecture proved the most effective, outperforming other variants in this specific application. The hybrid model exhibits superior performance compared to non-augmented deep learning approaches, with the median error distribution comparisons revealing a significant 50% reduction in prediction errors, accompanied by substantially improved consistency across various AE source locations. Overall, this developed hybrid approach offers a promising solution for enhancing AE-based SHM in complex infrastructures, improving damage detection accuracy and reliability for more efficient predictive maintenance strategies.

Ultrasonic imaging of concrete-embedded corroded steel liners using linear and nonlinear evaluation

ABSTRACT This study explores the efficacy of horizontally polarised shear (SH) waves in ultrasonic inspection of concrete-embedded steel liner plates, focusing on corrosion detection. SH-waves are found to significantly improve the localisation and potential dimensional assessment of embedded plate-like structures compared to compressional (P) waves, as evidenced by SH C-scans. Anomalies corresponding to severe corrosion are discernible in SH C-scans, whereas they are minimally visible in P-wave scans. Nonlinear evaluation explores harmonic-based imaging, including second harmonic generation (SHG) and third harmonic generation. Nonlinear SH-wave evaluation accurately locates the most severely corroded embedded plate, whereas comparative P-wave evaluations fail. However, potential FFT sidelobe contamination in the results warrants consideration. These results suggest a promising use for nonlinear waveform distortion in SH-wave-based corrosion detection though conclusive evidence of the source of SHG is uncertain. Experiments utilised an automatic scanner system for consistent control. The concrete specimen investigated herein contained pre-corroded plates which hint at heightened nonlinear effects when corrosion occurs post-embedment due to corrosion-induced cracking. These findings encourage further investigation into SH-waves for nonlinear ultrasonic detection of concrete-embedded steel liner plates and the development of instrumentation tailored to such methods.

A frequency steerable electromagnetic acoustic transducer

Abstract Electromagnetic acoustic transducers (EMATs) are convenient for non-destructive evaluation of plate-like structures since they can generate, without the need for contact with the medium under test, different types of ultrasonic guided waves. Guided-wave EMATs usually generate waves omnidirectionally or in a principal propagation direction. Beam steering is desirable in several applications, such as in inspections of large-area structures. This is usually achieved with several independently controlled elements forming a phased array. Alternatively, mono-element transducers with directional-dependent spectral content can steer the generated wave beam by altering the frequency of the excitation signal. A piezoelectric transducer with this characteristic, namely a frequency steerable acoustic transducer, was previously proposed. Its design was addressed in the wavenumber domain, leading to unconventional transducer shapes, but still reproducible with a piezoelectric patch, albeit unfeasible to implement as an EMAT. Here, we propose a new kind of EMAT, namely, frequency steerable EMAT (FSEMAT), whose design is addressed in the spatial domain in order to ensure its physical realization with a coil-magnet arrangement whilst still effectively presenting steering capability. The novel EMAT was designed to generate the A 0 Lamb wave mode in a frequency range from approximately 100 to 600 kHz. The FSEMAT was fabricated and experimentally evaluated in an aluminium plate at different frequencies within the designed frequency range, where each frequency corresponded to a specific propagating direction with high directivity, assessed by half-power beam widths of approximately 10 degrees. Furthermore, its theoretical directivity was computed by means of a wavenumber spectrum-based model, and showed good agreement with experimental results. The new transducer allows great flexibility effectively providing beam steering with a single EMAT.

Coarse-grained WC–6Co hardmetals with dual-scale and plate-like WC structures fabricated by convention powder metallurgy process

In this work, coarse-grained WC–6Co hardmetals featuring dual-scale and plate-like structures were successfully fabricated via conventional powder metallurgy process using W, ultrafine WC, Co and carbon black as raw materials. The investigation focuses on the effects of two critical factors, sintering temperature and ultrafine WC powder content, on the microstructures, densities, and mechanical properties. The results demonstrate that increasing the sintering temperature accelerates the growth of WC grains via 2D nucleation growth mechanism, thus enhancing the plate-like structure of WC grains. The addition of ultrafine WC powder reduces the mean WC grain size and eliminates the preferential orientation of WC grains because of its separating effect on coarse WC grains. Moreover, the dual-scale and plate-like structures can be achieved with sufficient ultrafine WC content (≥ 20 wt%) and adequate sintering temperature (≥ 1500 °C). Notably, the coarse-grained WC–6Co alloy sintered at 1550 °C with the addition of 20 wt% ultrafine WC powder exhibits good comprehensive mechanical properties: hardness of 1493 ± 7 HV30, transverse rupture strength of 2698 ± 58 MPa and fracture toughness of 16.93 ± 0.65 MPa·m1/2.

Thickness-extensible higher order plate theory with enforced C1 continuity for the analysis of PEEK medical implants

Plate-like structures had been thoroughly studied in literature over years to reduce the computational space from 3D to 2D. Many of these theories suffer either from satisfying the free traction condition or thickness extensibility in addition to the consistency of transverse shear strain energy. This work presents a higher order shear deformation thickness-extensible plate theory (eHSDT) for the analysis of plates. The proposed eHSDT satisfies the condition of free traction as other theories do but it also satisfies the condition of consistency of transverse shear strain energy which is neglected by many theories in the area of plates and shells. The implementation of the proposed theory in displacement-based finite element procedure requires continuity of derivatives across elements. This necessary condition was achieved using the penalty enforcement method for derivative-based nodal degrees of freedom across the standard 9-nodes Lagrange element. The theory was tested for elastic bending deformation of Polyether-ether-ketone (PEEK) which is one of the basic materials for medical implants. The theory showed good accuracy compared to experimental data of the three-points bending test. The present eHSDT was also tested for different conditions with a wide range of aspects ratios (thin to thick plates) and different boundary conditions. The accuracy of the proposed eHSDT was verified against exact solutions for these conditions which showed the advantage over other approaches and commercial finite element packages.

Nonlinear ultrasonic Lamb wave phased array imaging based on hybrid array and time-reversal of harmonic

Fatigue cracks, as one of the early performance deteriorations of plate-like structures, are critical to be detected in a timely manner to prevent further failures and disastrous accidents. But the intimate contact of crack interfaces is difficult to form a significant scattering field of traditional ultrasonic Lamb waves, resulting in the insensitivity of Lamb wave phased array-based imaging methods to crack imaging. To break through the detecting limitations of conventional Lamb wave phased array, the nonlinear Lamb wave-based phased array method is first proposed to realize fatigue crack imaging, which is achieved by a new form of phased array with hybrid elements, signal processing for harmonic enhancement and time-reversal based harmonic field focusing. The hybrid array is designed for efficient transmission and capture of fundamental wave and harmonics, and Pulse-inversion technology and continuous wavelet transform filter are used to extract and enhance second harmonic response, and the images are obtained by the time domain topological energy imaging algorithm. Finally, the imaging results of barely visible fatigue cracks and through-holes in metallic plate structures using linear and nonlinear Lamb wave-phased array are compared. The nonlinear ultrasonic Lamb wave-phased array demonstrates excellent capability of fatigue crack imaging.