Search

Mechanical frequency up-conversion is a technique whereby a high-frequency oscillation is induced from a low-frequency source and aims to address inherent problems in low frequency vibration energy harvesting. This work presents a novel 1:2:6 internal resonances based frequency up-converting harvester in which the operation frequency is 6 times up-converted. Compared to traditional conceptual mechanisms (e.g. mechanical impact, mechanical plucking, impulsive acceleration), the proposed harvester can operate at much lower acceleration level, the missing of sound during the frequency conversion also reduces the energy consumption. Experimental measurements and theoretical simulations demonstrate that the proposed design can collect energy from ultra-low frequency (< 5 Hz) vibration sources. In addition, the harvester shows very high performance compared to the current state-of-the-art devices, a maximum 2.07 mW of average power is obtained from the fabricated prototype at the excitation frequency and level of 1.71 Hz & 0.19 g, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The harvester can scavenge energy from ultra-low frequency vibrations. • The harvester can capture vibration energy from any direction. • The harvester can up-convert the excitation frequency through internal resonance. • The harvester is designed with a novel piezoelectric spring based on binder clips. • A significant generated power of 13.29 mW (at 0.26 g, 2.03 Hz) is obtained. Abstract Low frequency vibration is a ubiquitous energy existing in our environment, but a large efficient harvesting of which remains challenging. This paper presents a simple piezoelectric spring architecture based on a common binder clip structure. The harvester with pendulum spring allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric transducer. Due to the basic characteristics of spring pendulums, the proposed harvester can efficiently scavenge not only ultra-low frequency but also multi-directional vibrational energies. Modeling and design are conducted and a normalized expression of the harvester behavior is given. Chirp and human motion excitations are used to evaluate the proposed harvester's performances. Simulation and experimental results are in good agreement. The proposed device could generate a high output power (13.29 mW) at a low operating frequency (2.03 Hz), which shows great application prospects in the power supply of wearable products, ocean buoys, etc. [ABSTRACT FROM AUTHOR]

In view of low conductivity and thin layer structure of carbon fiber reinforced polymer (CFRP), the high frequency eddy current testing (HF-ECT) technique operating in the frequency range up to 100 MHz is considered to be better suited for this less conductive material. However, high frequency ECT method is more susceptible to various interference factors, causing many difficulties in the system construction and implementation. Concerning this issue, the feasibility of using low frequency ECT method for CFRP inspection was fully explored in this paper, and on this basis a high precision low frequency ECT system with the working frequency up to 250 kHz was developed. The system is mainly involving the small-size transmitter-receiver (T-R) type of probe, weak-signal extraction method using the lock-in amplifier and the C-scan imaging technique. The true skin depths of eddy current generated in unidirectional and orthogonal CFRP plates by small air-cored coil were calculated with 3D finite element simulation, thereby determining the high sensitivity of low frequency ECT for surface and near surface defects in CFRP. With the developed system, the direction of different fiber plies was successfully detected, and the location and size of different damages were also clearly visualized in the scan image. The proposed research can play a role of guiding the development of highly effective low frequency ECT method and detecting system for CFRP material. [ABSTRACT FROM AUTHOR]

This paper presents a FEM model for the simulation of delamination in composite materials under fatigue loads using extended cohesive interface elements. A virtual fatigue damage variable is proposed to continually locate the crack tip elements with local element information only. The proposed method allows for a fully automatic identification of crack tip elements without any global information. Once crack tip elements are identified, the fatigue damage accumulation is determined by a modified Paris-law with a strain energy release rate correction method to reduce mesh sensitivity. The predicted delamination growth rates of different mesh sizes were compared with experimental results from open literature using a mode-I Double Cantilever Beam specimen and a mode-II 4-point End Notch Flexure specimen respectively. In all cases good agreement was obtained with weak mesh dependency. [ABSTRACT FROM AUTHOR]

Reconstruction of the nine stiffness coefficients of two different composites was implemented by inverting the measured Lamb waves phase velocities. The inversion was carried out through genetic algorithms (GAs) by minimizing the error between the calculated and the measured velocities. Forward problem of calculating phase velocities for a material properties individual in GAs was solved using a third-order shear deformation theory (ToSDT). Lamb wave propagation was visualized with a laser generation based imaging (LGBI) system which uses a laser source to generate ultrasonic waves. The experimental phase velocities were evaluated directly based on the position-time diagrams of Lamb waves. The nine stiffness coefficients were reconstructed using phase velocities of S 0 mode and A 0 mode measured along only three propagation directions. The reconstructed material properties were verified by comparing their corresponding theoretical velocities with the experimentally measured velocities. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical and experimental analysis of broadband sound transmission control of an aluminum panel in the frequency range between 30 Hz and 1 kHz. Based on the analysis of characteristics of sensor-actuator pairs, piezoelectric patches bonded on the structure are used as actuators, and collocated accelerometers are used as sensors. Then a hybrid decentralized control law is derived, which has a broad control band and puts more control authority on the most sound radiation effective mode. This control law comprises two parts: one is the direct velocity feedback controller, and the other one, relatively new, is called the negative acceleration feedback (NAF) controller. The control architecture is decentralized, which means each controller works independently. Due to the second-order dynamic property of the NAF controller and the fact that the structure’s frequencies may shift, the Hilbert-Huang method is used for quick and automatic identification of the natural frequency. Finally, open loop and closed loop experiments are presented to support the theoretical analysis. The active control results demonstrate that the panel’s vibration level can be suppressed by 16.7 dB and the broadband sound pressure level could be lowered by more than 7 dB. [ABSTRACT FROM AUTHOR]

Highlights: [•] The MPFs’ piezoelectric properties are lower than those of bulk ceramic counterpart. [•] The effect of geometrical shape is a main cause of the low-properties. [•] The effect of polarization also is the cause of the low-properties of the MPFs. [•] There is excellent agreement between the expected and experimental measurements. [ABSTRACT FROM AUTHOR]

Quaternary piezoelectric ceramics Pb(Ni1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–Pb(Zr0.3Ti0.7)O3–xZnO (PNN–PFN–PZT–xZ, x=0.0–0.08 in molar ratio) were prepared by the conventional mixed-oxide method. The effects of ZnO content on the microstructure and piezoelectric properties were systematically investigated. Increasing ZnO additive promotes the phase structure transformation from rhombohedral to tetragonal, indicating the presence of the morphotropic phase boundary in the ZnO-modified PNN–PFN–PZT system. The results show that ZnO doping significantly improves the coercive field (E c ), Curie temperature (T c ), and temperature stability (Δf r /f r 30°C, Δd 31/d 31 30 °C) of the PNN–PFN–PZT–xZ ceramics, although the piezoelectric constant (d 33, d 31) decreases slightly with increasing ZnO content. Taking into consideration the piezoelectric property and temperature stability, the obtained ceramic sample with x=0.04 exhibited favorable properties, which are listed as follows: d 33=810pC/N, k p =0.647, ε r =6243, tan δ=2.74%, E c =4.7kV/cm, and T c =136°C. [ABSTRACT FROM AUTHOR]

Abstract: (K, Na)NbO3-based lead free materials have been found to exhibit good piezoelectric properties due to the orthorhombic–tetragonal polymorphic phase transition (PPT) temperature compositionally shifted downward to near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties. In this work, new quaternary (1−x) (K0.4425Na0.52Li0.0375)(Nb0.8925Sb0.07Ta0.0375)O3 (KNLNST)–xSrTiO3 (ST) lead-free piezoelectric ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were also studied. The results of X-ray diffraction reveal that SrTiO3 diffuses into the KNLNST lattices to form a new solid solution with a perovskite structure. After the addition of SrTiO3, tetragonal–orthorhombic phase transition shifts to lower temperatures. The good piezoelectric properties of 0.995 KNLNST–0.005 ST material were found to be d 33∼295pC/N, k p∼42%, and ε r∼1902, with greatly improved temperature stability over the temperature range of 0–100°C, demonstrating practical potential for actuator and ultrasonic transducer applications. [Copyright &y& Elsevier]

Abstract: Two-step sintering was applied to manufacture a typical Li- and Ta/Sb-modified alkaline niobate-based lead-free piezoelectric ceramics. The sintering condition dependences of dielectric constants and piezoelectric properties were investigated. Under the optimal condition, dense specimens have an average grain size of approximately 5μm, and show good dielectric and piezoelectric properties. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics sintered under the condition “1130/10/1020/15” show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), and dielectric constant (ɛ), which are 281pC/N, 50% and 1500, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Furthermore, the KNLNST ceramics maintain relatively low dielectric loss over wide temperature ranges. The result indicates that the KNLNST ceramics sintered by two-step sintering exhibit good temperature stability. [Copyright &y& Elsevier]

Abstract: Lead-free (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 piezoelectric ceramics were prepared by the conventional sintering method. The effects of the Sb content on the phase structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the (K0.4425Na0.52Li0.0375) (Nb0.9625−x Sb x Ta0.0375)O3 ceramics were investigated. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.05 to 0.09, all samples exhibit a single perovskite structure with an orthorhombic phase over the whole compositional range, and the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb5+ for Nb5+. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics show the peak values of the piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p ), and dielectric constant (ɛ), which are 304pC/N, 48% and 1909, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Besides, the underlying mechanism for variations of the electrical properties due to Sb5+ substitution was explained in this work. [Copyright &y& Elsevier]

Abstract: BaTiO3 (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d 33 value is over 190 pC/N) was obtained from the BT powder synthesized at 250°C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature. [Copyright &y& Elsevier]

Abstract: Terfenol-D composites attract much attention recently due to their large magnetostriction, small eddy energy loss and large operation frequency bandwidth. Binder layer in the composite usually mechanically weakens the composite and reduces the effective properties. A typical kind of magnetostictive composite is composed of Rare Earth metallic compound powder, matrix material and resin binder. The binder, which is usually flexible and forms mechanically weak interface in the composite, inevitably influences the overall magnetostriction of composites. In this paper, a theoretical model was developed to treat a simple deformation case of this kind of mechanically weak interface, in which the flexible layer has low stiffness to withstand deformation but no de-bonding or cracking. An infinite magnetostrictive plane with a circular inclusion was considered, where the matrix and inclusion are all general magnetostrictive materials which can be modeled by the standard square constitutive relation of magnetostriction. The binder layer of a certain thickness was modeled as a set of springs with no thickness but with an equivalent stiffness. The mathematical formulation was brought into the complex variable framework. The magnetoelastic field was solved and the effective magnetostriction was explicitly obtained. Comparisons with experimental results were also presented. In terms of this analysis, the interfacial stiffness has significant influences on the overall magnetostriction of composite. Increasing the interfacial stiffness can lead to large magnetostriction of composites. The measure for improving the interfacial stiffness includes increasing the binder modulus and reducing its thickness. [Copyright &y& Elsevier]

We describe a novel magnetic force control method. The method employs a mechanical stress applied to a magnetostrictive material to control the attractive force between fixed and movable members of a magnetic circuit that includes a permanent magnet. The method has the advantage over electromagnet control that a constant force can be maintained without energy consumption. We discuss the variation of the magnetic force with compression of several magnetostrictive materials. The experimental results agree with theoretical predictions of magnetic force based on analysis of an equivalent magnetic circuit and the piezomagnetic properties of the magnetostrictive materials. [ABSTRACT FROM AUTHOR]

Employing the laser ultrasonic system, information on fatigue evolution can be captured and explicitly stored in the frequency‐wavenumber wavefield of the guided wave. This paper presents a deep‐learning architecture for processing the frequency‐wavenumber wavefield, which comprises two distinct steps: fatigue characterization and evolution prediction. Firstly, the fatigue characterization step employs a convolutional autoencoder (CAE) for compressing the frequency‐wavenumber wavefield and a fully connected network (FCN) for obtaining the fusion fatigue characteristic. Due to the high cost of experimental samples, extensive simulation‐generated wavefields are used to pre‐train the network. Subsequently, the fatigue evolution prediction model based on the latent ordinary differential equation (Latent‐ODE) is trained for the step‐by‐step prediction of fatigue evolution with a small amount of composite fatigue test data. The results validate the effectiveness of the deep‐learning architecture in characterizing fatigue and predicting its evolution, as well as the feasibility of the frequency‐wavenumber wavefield compression of guided wave. Highlights: The deep‐learning architecture for fatigue evaluation and prediction is proposed.The frequency‐wavenumber wavefield of guided wave is fused for fatigue evaluation.The fatigue evolution prediction is achieved using the Latent‐ODE model.The fatigue life of the composite specimen is predicted. [ABSTRACT FROM AUTHOR]

The macro fiber composites (MFCs) with uniform and repeatable electromechanical performance have been a popular choice in various applications like structural actuation, vibration control, structural health monitoring, and energy harvesting. Herein, the strains of lead zirconate titanate based MFCs subjected to various driving signals were conducted via the strain-electrometry method. The formation mechanism of the strains was profoundly expounded, and the variation of the strains as a function of peak to peak value, frequency and superimposed DC bias voltage was further explored. The results demonstrate that both longitudinal and transverse strain-voltage curves with the voltage cyclic loading are closed "ellipse-like" hysteresis loops, in which the strain of ascending branch is smaller than that of the descending branch. Both strains increase with increasing the peak to peak value of driving signal and the increase is more remarkable at smaller bias voltage and lower frequency, while decrease with increasing the positive DC bias voltage and the decrease is specially obvious at larger peak to peak value and lower frequency. Besides, the dispersive effect of the strains induced by larger peak to peak value, particularly with smaller superimposed bias voltage, is more apparent than that induced by smaller peak to peak value. The longitudinal and transverse strains of MFCs with an active area of 40 mm × 30 mm range from 74.8 με to 1688.3 με, and 20.3 με to 488 με, respectively. This research indicates that through properly and carefully synthetical modulation of electrical parameters of driving signal, a notably enhanced strain can be achieved in MFCs for the specific applications such as actuation and high frequency structural control. [ABSTRACT FROM AUTHOR]

The acoustic black hole (ABH) effect is realized in thin plate structures with a decreasing thickness according to a power-law function, and offers potential applications for structure vibration damping enhancement and free-field noise radiation suppression. In this paper, a wavenumber domain method (WNDM) is proposed for the analysis of vibro-acoustic coupling and internal noise reduction mechanism of a pentahedral cavity enclosed by a flexible plate with a two-dimensional ABH indentation, subject to a point force excitation. The system response of the ABH plate-cavity is computed by a validated finite element model. The relationship between the space-averaged sound energy inside the cavity and the spectra of the structural displacement and the acoustic mode of the cavity is established. This allows revealing a dual physical mechanism behind the observed noise reduction: amplitude reduction and mismatching between the wavenumber spectra of the plate displacement and the acoustic field, which results in a weakened vibro-acoustic coupling. An additional configuration with an ABH embedded in an irregular pentagonal wall of the cavity is examined. Despite the increasing complexity in the geometry of the coupling interface and its coupling with the cavity, numerical analyses confirm the generality of the observed physical phenomena and the applicability of the proposed WNDM to more complex system configurations. [ABSTRACT FROM AUTHOR]

The acoustic black hole (ABH) is a feature commonly found in thin-walled structures that is characterized by a diminishing thickness and damping layer with an efficient wave energy dissipation effect, which has been extensively studied. The additive manufacture of polymer ABH structures has shown promise as a low-cost method to manufacture ABHs with complex geometries, exhibiting even more effective dissipation. However, the commonly used elastic model with viscous damping for both the damping layer and polymer ignores the viscoelastic changes that occur due to variations in frequency. To address this, we used Prony exponential series expansion to describe the viscoelastic behavior of the material, where the modulus is represented by a summation of decaying exponential functions. The parameters of the Prony model were obtained through experimental dynamic mechanical analysis and applied to finite element models to simulate wave attenuation characteristics in polymer ABH structures. The numerical results were validated by experiments, where the out-of-plane displacement response under a tone burst excitation was measured by a scanning laser doppler vibrometer system. The experimental results illustrated good consistency with the simulations, demonstrating the effectiveness of the Prony series model in predicting wave attenuation in polymer ABH structures. Finally, the effect of loading frequency on wave attenuation was studied. The findings of this study have implications for the design of ABH structures with improved wave attenuation characteristics. [ABSTRACT FROM AUTHOR]

Ultrasonic guided wave methods are widely used to determine the stiffness coefficients of anisotropic composites. When faced with the challenge of multiple stiffness coefficients, the sensitivity of ultrasonic waves to each stiffness coefficient should be analyzed to ensure the reliability of the identified results. In this paper, a novel method is developed to directly relate the wave velocities to the decoupled stiffness coefficients, allowing for efficient sensitivity analysis and providing good explanations for the sensitivity behaviors using the wave structure properties. Numerical sensitivity analysis is performed for various propagation directions, mode types and frequencies. Experiments are carried out based on the sensitivity results to reconstruct the material properties by inversion of suitable wave velocities measured using a non-contact laser ultrasonic system. [ABSTRACT FROM AUTHOR]

Lamb wave-based damage detection technology shows great potential for structural integrity assessment. However, conventional damage features based damage detection methods and data-driven intelligent damage detection methods highly rely on expert knowledge and sufficient labeled data for training, for which collecting is usually expensive and time-consuming. Therefore, this paper proposes an automated fatigue crack detection method using Lamb wave based on finite element method (FEM) and adversarial domain adaptation. FEM-simulation was used to obtain simulated response signals under various conditions to solve the problem of the insufficient labeled data in practice. Due to the distribution discrepancy between simulated signals and experimental signals, the detection performance of classifier just trained with simulated signals will drop sharply on the experimental signals. Then, Domain-adversarial neural network (DANN) with maximum mean discrepancy (MMD) was used to achieve discriminative and domain-invariant feature extraction between simulation source domain and experiment target domain, and the unlabeled experimental signals samples will be accurately classified. The proposed method is validated by fatigue tests on center-hole metal specimens. The results show that the proposed method presents superior detection ability compared to other methods and can be used as an effective tool for cross-domain damage detection. [ABSTRACT FROM AUTHOR]

In this paper, the S 0 -mode Lamb wave phase velocity at low frequency range is chosen to characterize fatigue damages accumulated in composite laminates under cyclic loadings. A stiffness/velocity degradation model is proposed based on three distinctive damage mechanisms: fiber breaks, matrix cracks and delamination, all of which are always involved in fatigue damage process. In order to reduce the complexity of the damage model, fiber damage is treated as an independent damage and delamination is coupled with matrix cracks. An approximation of shear-lag model is then proposed to avoid any direct measurements of crack density for it is highly impractical in real applications. Following this, energy release rate for formation of matrix cracks is extracted based on measured phase velocity and damage evolution is realized by incorporating a modified Paris law. Controlled fatigue experiments were conducted where in-situ phase velocity was measured by a laser ultrasonic system. The fatigue damages were then characterized using the proposed damage model with the measured velocity. Finally, the ability of proposed model to predict residual lives was also validated and good accuracy has been obtained. [ABSTRACT FROM AUTHOR]

Noise and vibration induced by turbulent boundary layer (TBL) wall pressure is a widespread issue for aircrafts and vehicles. One way to alleviate this problem is to enhance the structure’s sound isolation performance using active structural acoustic control. It is often difficult and costly to generate TBL excitation in laboratories for academic research, especially when the convection velocity is high. Thus, a numerical investigation in the early stages of research is appropriate. This paper proposes a prototyping method. The updated TBL semi-empirical model is chosen through a detailed survey of relevant literature. A tensioned panel used as a control target is intended to simulate realistic aircraft flight conditions. Decentralized control law is considered for active control. A finite element model is built which takes into account the property of TBL excitation. A model reduction technique is also adopted to decrease the order of the analysis model. Numerical simulation results show that the pre-stress effect and the hydrodynamic coincidence have a significant influence on plate vibro-acoustic performance and control channel number selection. Decentralized control of the tensioned plate structure under the pressure of TBL excitation is revealed in this work. A virtual prototyping loop justifies the control law’s effectiveness for analyzing TBL excitation. Finally, the procedure proposed may be extended to use in other models or real-life applications. [ABSTRACT FROM AUTHOR]

This paper characterizes laser-generated guided waves in a metal-lined composite-overwrapped pressure vessel (COPV) to assess typical damage, including interfacial debonding and low-velocity impact damage. First, an eigenfrequency approach that avoids additional coding is utilized to theoretically analyze the dispersion characteristics of a COPV. The theoretical results show that interfacial debonding significantly alters dispersion curves, and the wavenumber of the L(0, 1) mode is sensitive to impact damage. Experimental verifications were conducted based on the full wavefield acquired using a scanning laser-ultrasonic system with a repetition rate of 1 kHz. By comparing the experimental dispersion curves with the theoretical ones, it was found that the metal-composite interface was not bonded. In addition, a local wavenumber estimation method was established to detect the impact damage by obtaining the spatial distribution of the wavenumber of the L(0, 1) mode. [ABSTRACT FROM AUTHOR]

In this work, a novel aircraft door sealing structure driven by shape memory alloys (SMAs) is proposed that offers much improved sealing capability than traditional sealing plates. The two-way shape memory effect (TWSME) of SMAs is utilized so that the proposed sealing plate can change its shape through heating and cooling of the driving SMA unit. Considering the inhomogeneous temperature and recovery strain field the SMA exhibits while being trained, a modified finite element (FE) model of the sealing structure is established to predict the deflection of the SMA-based sealing plate. Finally, verification experiments are carried out. The experimental results show good agreement with the FE predictions, indicating good accuracy of the modified FE model as well as the effectiveness of the proposed sealing structure. [ABSTRACT FROM AUTHOR]

Macro fiber composites (MFCs) are widely used in various fields due to their excellent piezoelectric performance. This paper presents a novel method that combines analytical and finite element analysis to accurately model MFCs. The method iteratively calculates the nonlinear poling field generated by interdigital electrodes (IDEs), leading to reliable estimates of the local orientation and properties of the piezoceramic. The local poling state is then incorporated into a 3D representative volume element (RVE) model to determine the strain response of the device under realistic loading conditions. The influence of the poling voltages, piezoceramic fiber thickness, and IDE geometries on the poling and actuating performance of the device is studied. Furthermore, considering the complexity of the modeling the entire MFC device, a simplified method is further presented that is much more efficient and maintains the same level of accuracy. [ABSTRACT FROM AUTHOR]

• A defect model modification method with surface heat flux identification is proposed for thermal protection system. • Levenberg–Marquardt method is adopted to identify surface heat flux, and whether the defect has occurred is determined. • A defect model modification method is proposed from the knowledge of the identified heat flux. • An experiment is designed to prove good accuracy of the proposed method. Thermal protection systems (TPS) have become a key issue in ensuring the reliability of hypersonic flights. Aimed at monitoring the thermal loads and possible defects for TPS, a defect model modification method with surface heat flux identification is proposed in this paper. Firstly, by the measured temperature from a distributed sensor network and the initial TPS model, the surface heat flux was identified with the Levenberg–Marquardt Method (LMM). If there existed outliers in the identified heat flux distribution, it can be visually indicated that the defect occurred. Then, defects were represented by shape parameters and can be determined by the model modification from the knowledge of the identified heat flux and the measured temperature. The effectiveness of the proposed method was verified numerically using TPS containing a surface defect. Meanwhile, the effects of various factors on the identified results were investigated in detail, such as defect sizes, defect shapes, sensor locations, and real aerodynamic heating. Finally, the proposed method was successfully applied to an experiment, and results demonstrated that the proposed method can achieve good identification results by experimentally measured temperature. [ABSTRACT FROM AUTHOR]

The poling of macro fiber composites (MFCs) as a vital part for manufacturing usable samples, is related with but different from that of their piezoelectric phase owing to the existence of interdigitated electrodes. Herein, beginning with the quantitative relationship between effective electric field and external electric field obtained by finite element analysis, the prediction and optimization of poling condition for lead zirconate titanate (PZT) based-MFCs was presented. The results demonstrate that the predicted values agree with the experimental results, specifically, the poling field range of the investigated MFCs is from 16.7 kV/cm to 33.3 kV/cm. The piezoelectric and dielectric properties of MFCs are improved by adjusting the poling condition up to a suitable value, whereas are degraded due to the interaction of domain alignment and electric field concentration. The optimal poling condition of the MFCs is 26.7 kV/cm for 10 min at room temperature. This research contributes to realizing the personalized-customization of MFCs. • A prediction for the poling field range of macro fiber composites (MFCs) is presented. • The prediction is based on the quantitative relationship between effective and externally applied electric field. • The predicted values agree with the experimental results, specifically, ranging from 16.7 kV/cm to 33.3 kV/cm. • The change in properties with poling condition are due to the interaction of domain alignment and electric field concentration. • The optimal poling condition of the MFCs is 26.7 kV/cm for 10 min at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: A novel scheme of neural network model reference adaptive control is proposed for arbitrary complex nonlinear discrete-time systems, i.e., non-minimum phase system, time-delay system and minimum phase system. An improved nearest neighbor clustering algorithm using an optimization strategy is introduced as the on-line learning algorithm to regulate the parameters of the RBFNN, which can simplify the neural network structure and accelerate the convergence speed. The clustering radius can be regulated automatically to guarantee the rationality of radius. Through constructing the pseudo-plant, the direct NNMRAC is also effective to the nonlinear non-minimum phase system. With the help of simulations, the control strategy based on direct RBFNN model reference adaptive control can not only make the multi-dimension nonlinear plants track multi-dimension reference signals quickly, but also endow the control systems with satisfying robustness. [ABSTRACT FROM AUTHOR]

Because of the good piezoelectric properties among polymers, poly(vinylidene fluoride) (PVDF) has been extensively applied in constructing flexible sensors and energy harvesters. Recent progress towards high performance sensors and energy harvesters has trigged significant interest in the fabrication of PVDF materials with superior piezoelectricity and good thermal piezoelectric stablility. Herein, we reported a flexible PVDF based nanocomposite that maintained high and stable piezoelectricity over a wide temperature range from 10 to 100 °C through the strong multi-interface effect. In this work, PVDF was firstly blended with poly(vinylidene fluoride- co -hexafluropropylene) (PVDF-HFP), and then dopamine modified BaTiO 3 hollow nanoparticles were introduced into the blend polymer matrix. Through optimizing the fabrication process and modulating the mass ratio of PVDF-HFP and BaTiO 3 , notably strenghthened ferroelectricity and piezoelectricity was achieved in the final composites, wherein the piezoelectric coefficient d 33 reached a peak of 40 pC/N and showed good retention with increasing temperatures up to 100 °C. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate Pb(Zr x Ti 1- x )O 3 (PZT) films with a composition x  = 0.52 near the morphotropic phase boundary were deposited on dense CoFe 2 O 4 (CFO) ceramic substrates using a chemical solution deposition. The PbO seeding layer was introduced to induce the (100) texture of PZT films. PZT film-on-CFO ceramic (PZT-CFO) composites with 2-layered PbO exhibits a (100) orientation degree of 0.62, while that for PZT-CFO composites without the PbO is only about 0.37. Accordingly, the ferroelectricity, dielectricity and magnetoelectric coupling in the PZT-CFO composites dramatically changes and the maximum ME coefficient exhibits great enhancement from 21.4 to 50.8 mV/cm · Oe. [ABSTRACT FROM AUTHOR]

Defects and/or damage of the bonding surfaces of scarf-repaired CFRP laminates can be detected with nondestructive testing technologies. However, it is difficult to judge whether the defect and/or damage is severe enough to affect the normal use of the repaired structure. Destructive testing is usually required to access the residual strength, which is not ideal for real world applications. In this paper, a nondestructive strength prediction approach is proposed that comprises of a high-fidelity finite element model, an efficient convolutional neural network model and visualized damage-strength heat map model to form a hierarchical surrogate model. The tensile strength of the structures can be rapidly obtained with an average error of 1.4% by comprehensively considering the angle of the scarf joints, the interfacial strength of the adhesive film, the stacking sequence of laminas, together with the size and location of the damage which are visualized by nondestructive testing. In addition, the residual tensile strength of repaired structures containing damage can be calculated more conveniently and intuitively with simple multiplication operation by the proposed heat map model without scarifies in accuracy. [ABSTRACT FROM AUTHOR]

Sodium niobate nanopowders (N-NaNbO 3 ) and submicron powders (M-NaNbO 3 ) were synthesized by the solvothermal and hydrothermal route, respectively. Subsequently, their sintering activities were comparably investigated through a modified solid-state sintering process. It's found that N-NaNbO 3 green bodies presented an apparent shrinkage after the calcination at 650 °C, and dense N-NaNbO 3 ceramics can be obtained at 950 °C. Besides, the optimized sintering temperature of N-NaNbO 3 ceramics was 100 °C lower, yet the shrinkage was four times larger when compared with M-NaNbO 3 samples. Importantly, N-NaNbO 3 samples showed improved dielectric properties in the whole frequency range, and the room temperature relative dielectric constant (ε r ) of N-NaNbO 3 samples sintered at 950 °C was as high as ~8000. The improved permittivity of N-NaNbO 3 samples was attributed to the compact microstructure, unique crystalline structure and less oxygen vacancies. At the same time, the effect of abnormal phase transition behavior originated from the metastable structure was considered to explain the enhanced room temperature permittivity. It's believed that the solvothermal route has great potentials in the synthesis of alkali niobate ceramics powders with high activity for low-temperature sintering. [ABSTRACT FROM AUTHOR]

A magnetoelectric composite of Pb(ZrTi)O film-on-CoFeO ceramic was prepared by spin-coating Pb(ZrTi)O films of 300 nm in thickness on the LaNiO-buffered highly dense CoFeO ceramics. The X-ray diffraction, ferroelectric loops, piezoelectric curves, and magnetoelectric coupling effects were all measured at room temperature to investigate the effect of LaNiO thickness on the magnetoelectric response of the composites. The introduction of the metallic oxide LaNiO efficiently enhanced the magnetoelectric coefficient α by improving the electric-related outputs. However, too thick LaNiO layer would also hinder the strain (stress) transferring across the interface between the Pb(ZrTi)O and CoFeO phases. A peak α value was obtained in the sample with a LaNiO thickness of about 60 nm, which was 2.5 times larger than that in the composite of Pb(ZrTi)O film on the CoFeO ceramic without the LaNiO layer. Further enhancement could be anticipated by optimizing the LaNiO layer and/or Pb(ZrTi)O films. [ABSTRACT FROM AUTHOR]

Propagation characteristics of electromagnetic field (EMF) is crucial to identify and position the potential defects when using eddy current testing (ECT) method for conductive medium. Therefore, in this work, the EMF propagation characteristics in carbon fiber reinforced polymer (CFRP) composites are thoroughly investigated by using finite element (FE) method. Considering the layered structure, stacking sequence, and interlaminar interface, we utilize a contact impedance interior boundary condition to model CFRP laminates, and then discuss the calculation accuracy and mesh refinement. The numerically solved results are compared to the theoretically calculated ones, and clearly point out the significant discrepancy between the true skin depth and the standard one. The findings reveal that the electrical anisotropy is one of the important factors in affecting the EMF propagation. The strong anisotropy results in more power loss and a frequency-independent decay rate than the ones in the weak and isotropic cases, which is proved by introducing Poynting theorem. Additionally, the other critical factor affecting the EMF attenuation is the lay-up stacking sequence of CFRPs, which is quite different from that of the isotropic mterials. Besides, the driving coil geomerty is another factor in affecting the EMF propagation characteristics from the point of the incident field. [ABSTRACT FROM AUTHOR]

• Tikhonov regularization is suitable for reconstruction of smooth profile forces and sparse regularizations are suitable for impact identification. • A large number of calibration points are time-consuming, even though the more calibration points on plate, the better the results. • The method performs well on identifying both sparse and smooth forces without prior information on the force nature, and also locating the unknown loads acting on plate structures. • The method performs well on sparse calibration grids which reduce the number of calibrations to model the whole plate. An adaptive parameter optimization algorithm (APOA) is proposed for simultaneous force history and location identification in this work. Because extensive calibrations are time consuming and not suitable for real structures, the APOA is designed to work with sparse calibration array, improving the efficiency in modeling the whole plate structures. In order to verify the effectiveness of the proposed method, numerical simulations and experimental impact tests are carried out. Various force profiles and locations are considered in numerical simulations, with an 80 mm × 100 mm rectangle calibration area. Furthermore, multiple impacts and calibration areas are discussed in experimental tests, with an aluminum plate as the specimen and an impulse hammer as the impactor. An 80 mm × 80 mm area is calibrated by a 9 × 9 array. Force identification results show good performance in using the AOPA, including the stability of force locating, the accuracy of time history estimation and the adaptability under sparse calibration. [ABSTRACT FROM AUTHOR]

Cu 2 S thin films were successfully grown in situ on Cu foil by an easy hydrothermal method. The effects of surfactant and reaction time on the formation of the Cu 2 S films were studied by X-ray diffraction, field-emission scanning electron microscopy and ABIOS profilometry. Results showed that the thin films consisted of nanoparticles, and their crystallization and surface roughness depended on the structures of surfactants and reaction time. Photocatalytic studies indicated that the film obtained at 1 h by the EDTA-2Na surfactant exhibited a good methylene blue degradation rate of 83.7%, and higher values of 89.2% and 90% were obtained with increased reaction time to 3 and 4 h. Even the decomposition rate remained at high (82%) after reuse. This good catalytic performance can be attributed to the heterojunction formed between Cu and Cu 2 S, the special surface from the reaction between [Cu-EDTA] - ion and S 2− , and the further crystal orientation with prolonged reaction time. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate Pb(Zr x Ti 1− x )O 3 films with various Zr/Ti ratios of 20/80, 40/60, 52/48, 60/40 and 80/20 are deposited on highly dense CoFe 2 O 4 ceramics using a simple chemical solution deposition. All Pb(Zr x Ti 1− x )O 3 films are polycrystalline and have no preferential orientations. The dielectric, ferroelectric, piezoelectric and magnetoelectric properties strongly depend on the Zr/Ti ratio. And the Pb(Zr x Ti 1− x )O 3 films with a Zr/Ti ratio close to morphotropic phase boundary exhibit best properties, whose magnetoelectric coefficient is over 1.5 times larger than those of other Zr/Ti ratios. The introduction of a PbO seeding layer between the Pb(Zr 0.52 Ti 0.48 )O 3 films and CoFe 2 O 4 substrates facilitates the (100)-texture. Therefore, the magnetoelectric coefficient was enhanced by 1.5 times. The further improvement of the magnetoelectric coupling could be anticipated by fabricating Pb(Zr 0.52 Ti 0.48 )O 3 films with more or absolute (100)-texture and using conductive interfacial layer between two phases. [ABSTRACT FROM AUTHOR]

Composites comprising TiO 2 @MWCNTs (shell@core) nanoparticles and poly(vinylidene fluoride) (PVDF) were prepared through a two-step method, including solution cast and mechanical rolling, inducing a highly oriented structure with both PVDF lamellar and TiO 2 @MWCNTs. A systematic study was performed to investigate the crystalline structure and piezoelectric properties of composites. The obtained results reveal that greatly enhanced breakdown strength and piezoelectric properties can be achieved in composites by the incorporation of highly aligned TiO 2 @MWCNTs. A maximum piezoelectric coefficient d 33 of ∼41 pC/N can be achieved in composites at a loading level of 0.3wt.%, which is nearly double that of the pure PVDF. [ABSTRACT FROM AUTHOR]

Monodisperse Dy-doped BaTiO 3 nanopowders ( x DBT) with x =0, 1, 2, 3, 4, 5 mol% has been synthesized via a modified sol-hydrothermal method. And the influence of Dy 3+ on the crystal structure, micromorphology and dielectric properties of x DBT ceramics has been investigated. It’s found that Dy 3+ slightly affects the shape of the x DBT nanopowders, whereas excess Dy 3+ would cause the formation of the Dy(OH) 3 impurity. In addition, the grain growth during a sintering process is suppressed with the Dy 3+ incorporation. Further, the possible occupation of the Dy 3+ has been extrapolated based on the variation of lattice volume and phase composition. A self-compensation mode involving the simultaneously occupation at Ba-site and Ti-site is observed in the samples with 4 mol% Dy. Importantly, stabilized temperature-dependent dielectric properties has been achieved at x =4 mol%, resulting from the diffuse phase transition behaviors (the calculated diffuse factor γ =1.952) induced by chemical inhomogeneity. [ABSTRACT FROM AUTHOR]

The typical nano-carbon materials, 1D fiber-like carbon nanotubes (CNTs) and 2D platelet-like graphene nanosheets (GRNs), that have attracted tremendous attention in the field of polymer nanocomposites due to their unprecedented properties, are used as conducting filler to induce a considerable improvement in the mechanical, thermal and electrical properties of the resulting graphene/polymer nanocomposites at very low loading contents. This study deals with the preparation and electro-stimulus response properties of polyurethane (PU) dielectric elastomer films with such 1D and 2D nanocarbon fillers embedded in the polymer matrix. The various forms of carbon used in composite preparation include CNT, GRN and CNT-GRN hybrid fillers. Results indicate that the dielectric, mechanical and electromechanical properties depend on the carbon filler type and the carbon filler weight fraction. Here, it has been also established that embedding CNT-GRN hybrid fillers into pristine polyurethane endows somewhat better dispersion of CNTs and GRNs as well as better interfacial adhesion between the carbon fillers and matrix, which results in an improvement in electric-induced strain. Therefore, the nanocomposites seem to be very attractive for microelectromechanical systems applications. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic criterion for improving the performance on fatigue life and failure probability prediction of GFRP laminates using Lamb wave velocity. A statistic damage model is built upon a Lamb wave velocity degradation model by introducing a normal distributed random variable to represent the uncertainties. The posterior distributions of the model parameters are obtained by Bayesian inference and Metropolis-Hastings algorithm with noninformative and informative prior distributions. Most importantly, a dynamic criterion is proposed to obtain a specimen-specific failure threshold value based on an assumption that the critical damage stage (CDS) of each specimen differs due to the randomicity of initial flaws. Experimental validation is conducted to compare the predicted fatigue life with both the dynamic criterion and traditional static criterion. The results show that applications of the dynamic criterion can improve the predicting accuracy and consistency, especially during early stages when available data is limited. [ABSTRACT FROM AUTHOR]

Fiber reinforced plastics (FRPs) are widely used in aerospace engineering industry. When the composite structure is subjected to the cyclic load, the initiation, propagation and accumulation of the fatigue damage in FRPs lead to structural failure. This paper presents a guided wave based fatigue property evaluation method to characterize matrix crack accumulation in FRPs, which provides a potential way to predict the remaining useful life of the structures. In this paper, a finite element model for FRPs is firstly developed to simulate the fatigue induced matrix cracks, which are randomly distributed in the structures. Both the initiation and propagation behaviors of the matrix cracks are modeled by the regulation of the random parameters, such as the number of fatigue elements and the degree of the stiffness reduction. Based on a series of models representing the fatigue evolution process of FRPs, the mode conversion effect of the guided wave is then investigated. A guided wave characteristic MCI (Mode Conversion Index) quantifying the mode conversion effect is used to evaluate the fatigue property of FRPs. Compared with the macroscopic stiffness, MCI shows higher sensitivity to the degree of matrix crack accumulation. Finally, controlled fatigue tests under different stress levels are carried out by using a fatigue testing machine, in which a laser ultrasonic system is employed to obtain the guided wave propagation in FRPs with different numbers of load cycles. The relationship between MCI and macroscopic stiffness is also obtained, providing a basis for using mode conversion feature to predict fatigue life. [Display omitted] [ABSTRACT FROM AUTHOR]

A simple low-temperature solid-state reaction in the presence of the surfactant PEG400 was developed to obtain ZnO/CdS nanocomposites. The effects of synthesis temperature and reaction time on crystal structure and optical properties of the nanocomposites were investigated by several technologies. X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) characterizations showed that the products consisted of the nanoparticles, and the grain growth kinetics of the cubic CdS and the hexagonal ZnO phase in the nanocomposites was described. The mechanism analysis suggested that sufficient grinding and heating treatment was a key to form the ZnO/CdS nanocomposites, and the surfactant PEG400 was proved not to involve the reaction and prevent the nanoparticles from aggregating to larger in whole grinding and heat-treatment process. Ultraviolet–visible (UV–vis) spectra revealed that the band gaps of the nanocomposites could be tuned by the reaction temperature and reaction time. Photoluminescence (PL) spectra showed that the changing position and the intensity of the emission peaks resulted from the rate of electron transfer and recombination probability under the different conditions. [ABSTRACT FROM AUTHOR]

Abstract: Li/Ta/Sb co-doped lead-free (K0.4425Na0.52Li0.0375)(Nb0.93−x Ta x Sb0.07)O3 (abbreviated KNLNST x ) piezoelectric ceramics, with Ta-doping ratio of x ranging from 0.0275 to 0.0675, were synthesized using the conventional solid-state reaction method at the sintering temperature of 1130°C. The effects of Ta content on the microstructure, dielectric properties, and phase transition behavior of the prepared ceramics were systematically investigated. The X-ray diffraction results show that all KNLNST x ceramics formed a secondary phase, which is assigned to the tetragonal tungsten-bronze type (TTB) structure phase, and showed a phase transition from an orthorhombic symmetry to a tetragonal symmetry across a composition region of 0.0375

• The two-dimensional MXene nanosheet demonstrates to be novel effective reinforcement for piezoelectric PVDF polymer. • Upon a small loading of 0.4 wt.%, the piezoelectric coefficient d 33 of MXene/ PVDF hybrid film reach the peak of 43 pC/N. • The sensor based on MXene/ PVDF hybrid film perform superior voltage sensitivity up to 0.0480 V/N. The rapid advances in intelligence terminal devices have raised expectations for highly sensitive, reliable and flexible pressure sensor. Herein, we present a highly sensitive flexible pressure sensor based on piezoelectric MXene/poly(vinylidene fluoride) (PVDF) hybrid film. Making use of MXene nanosheet reinforcement, one can efficiently promote the piezoelectric output and consequently sensitivity of PVDF. For instance, upon a small loading of 0.4 wt%, the piezoelectric coefficient d 33 of MXene/PVDF hybrid film reaches the peak of 43 pC/N. Meanwhile, the incorporation of MXene nanosheet is advantageous to strengthen the mechanical performance of PVDF. With the excellent piezoelectric response and mechanical property, the MXene/PVDF hybrid film sensor demonstrates to perform superior voltage sensitivity up to 0.0480 V/N, which is double that of PVDF based sensor. Meanwhile, the novel hybrid film sensor also exhibits fast recovery time of 3.1 ms and stable operation capability under cyclic force, confirming their applicability as reliable pressure sensor. [ABSTRACT FROM AUTHOR]

• A statistical cohesive element model is proposed for predicting the failure probability of delamination in composite laminates. • The local mean and standard deviation of cohesive elements are corrected to ensure the accuracy and eliminate mesh sensitivity. • Benchmark models under both pure-mode and mixed-mode loadings are given with good correlations between theory and FE simulations. • A parametric study is given to demonstrate the effect of the model parameters on the predicted results. One major characteristic associated with fatigue behavior in fiber reinforced composites is the large quantity of uncertainty, which needs to be considered for more reliable evaluation of composite structures. In this work, a novel method for predicting the probability of delamination is proposed. Fatigue cohesive elements are utilized to model the propagation of delamination under cyclic loadings, where delamination path tracing is realized by a non-local algorithm, which also enables the propagation of uncertainty information between adjacent elements. A local mean and standard deviation (std) correction scheme is proposed that compensates for the mismatch of uncertainty information caused by the discretization of the delamination area as well as eliminates mesh size sensitivity. Numerical verifications are conducted under both pure-mode and mixed-mode loadings. Kullback–Leibler (KL) divergence is used as a metric to evaluate the performance of the proposed method, where good correlations between the numerical and analytical results are obtained. [ABSTRACT FROM AUTHOR]

Abstract: A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders. The influence of Ta doping and K+/(K+ +Na+) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O3 ceramics from the obtained powders were investigated. The piezoelectric coefficient (d 33), electromechanical coupling coefficient (k p), dielectric constant (ɛ r), and remnant polarization (P r) of the sample sintered at 1180°C show optimal values of 210pC/N, 34.0%, 2302, and 19.01μC/cm2, respectively. [Copyright &y& Elsevier]

Abstract: (K, Na)(Nb, Sb)O3 (KNNS) lead-free peizoceramic powders were successfully synthesized by hydrothermal treatment at 240°C for 8h using the KOH, NaOH, Nb2O5 and Sb2O3 as raw materials. Effects of Sb-doping on the crystal structure and morphology of the as-prepared powders were investigated by powder X-ray diffraction (XRD), Raman spectra (Raman), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The Sb element was successfully doped into the alkaline niobate perovskite structure to form crystalline (K0.7Na0.3)(Nb0.95Sb0.05)O3 lead-free piezoelectric ceramic powder, which has a hexagonal morphology due to the aggregation growth of small grains. Phase and morphology evolutions with the reaction time were also studied, and a possible formation mechanism was proposed. [Copyright &y& Elsevier]

In this work, we propose a novel deep learning (DL) approach to directly process and characterize the guided wave information measured from an interrupted tensile-tensile fatigue test on fiber-reinforced polymer (FRP) laminates using laser ultrasonic technique. The DL model is constructed with artificial neural networks that consists of a convolutional autoencoder (CAE) for wave feature extraction, a recurrent neural network (RNN) for fatigue loading condition recognition and a neural ordinary differential equation (Neural ODE) to model the evolutional behavior of the extracted wave feature. The training of the neural network utilizes an unsupervised strategy in order for the DL model to learn the underlying dynamics of the wave feature for fatigue damage characterization. Meanwhile, in order to improve the interpretability of the learned DL model, domain knowledge is infused into the training process as physics-informed constraints. The model is trained with laser-excited ultrasonic guided wave signals obtained from acoustic emission (AE) sensors installed on the surface of fatigue specimens, where the raw signal is minimally processed to avoid human intervention as much as possible. A high-fidelity finite element (FE) model is also built to generate virtual samples to be used in a transfer learning strategy. The results show that the DL model has learned to characterize fatigue damage through latent wave features, which can be further interpreted as a meaningful physical quantity with physics-informed constraints applied. Finally, a parametric study is given to demonstrate the capacity of the learned characterization model by the DL approach. [Display omitted] • A DL model is proposed to characterize fatigue damage through UGW signals. • UGW signals are measured with a laser ultrasonic system and AE sensor. • FE model is utilized to generate virtual samples to enrich the training data set. • A physical constraint is applied to infuse domain knowledge into the DL model. • The DL model outputs an ODE that describes the evolutional behavior of UGW signals. [ABSTRACT FROM AUTHOR]

A one-step surfactant-free hydrothermal route is developed to prepare platelike NaNbO3 template powders. At optimal KOH concentration, pure platelike NaNbO3 with rhombohedral structure (width and thickness of 20 and 2 μm, respectively) is obtained at 200°C for 16 h. After calcination at 600°C for 4 h, the structure of the hydrothermally synthesized NaNbO3 changes from rhombohedral to orthorhombic, whereas the initial platelike morphology is maintained. Such characteristics in terms of phase structure, elemental composition, and morphology render our hydrothermally synthesized NaNbO3 suitable for textured ceramic fabrications. [ABSTRACT FROM AUTHOR]