Characteristics of piezoceramic and 3–3 piezocomposite hydrophones evaluated by finite element modelling

The transducer characteristics of hydrophones manufactured from porous 3–3 piezocomposites are compared with dense piezoceramic disc hydrophones using finite element modelling. Due to the complex porous structure of the 3–3 piezocomposites, a real-size 3-dimensional model was developed while a 2-dimensional axisymmetric model was constructed for the simple dense disc hydrophone. The electrical impedance and receiving sensitivity of the hydrophones in water were evaluated in the frequency range 10–100 kHz. The model results were compared with the experimental results. The sharp resonance peaks observed for the dense piezoceramic hydrophone were broadened to a large extent for porous piezocomposite hydrophones due to weaker coupling of the structure. The receiving sensitivity of piezocomposite hydrophones is found to be constant over the frequency range studied. The flat frequency response suggests that the 3–3 piezocomposites are useful for wide-band hydrophone applications.     

Electro-mechanical load transfer from a fiber in a 1–3 piezocomposite with an imperfect interface

This paper considers the electro-mechanical interaction between a fiber and a matrix material in a 1–3 piezocomposite due to an axial load and electric charge applied to the fiber. The fiber–matrix interface is assumed to be mechanically imperfect and is represented by a spring-factor model. The interface is either electrically open- or short-circuited. The analytical general solutions corresponding to an infinite piezoelectric fiber with a vertical body force and an electric body charge are derived by using Fourier integral transforms. These solutions together with the analytical general solutions for a transversely isotropic elastic medium are used to formulate the fiber–matrix interaction problem. Selected numerical results for the fiber axial force and vertical electric field, and interfacial stresses are presented for representative 1–3 piezocomposites. The influence of the interface stiffness on the electro-mechanical load diffusion is also examined.     

Anisotropy of Young's modulus and tensile properties in cold rolled α′ martensite Ti–V–Sn alloys

Young's modulus and tensile properties of cold rolled Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloy plates consisting of α′ martensite were investigated as a function of tensile axis orientation in this work. A single phase of α′ (hcp) martensite is obtained in Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloys by quenching after solution treatment. By 86% cold rolling, acicular α′ martensite microstructures change into extremely refined dislocation cell-like structure with an average size of 60 nm, accompanied with the development of cold rolling texture in which the basal plane normal is tilted from the plate normal direction (ND) toward transverse direction (TD) at angles of ±49° for Ti–8% V alloy and ±46° for (Ti–8 mass% V)–4 mass% Sn alloy. No apparent anisotropy of Young's modulus (E) is observed for as-quenched Ti–8% V (E = 76–83 GPa) and (Ti–8% V)-4%Sn (E = 69–79 GPa). In contrast, Young's modulus increases with increasing angle from the rolling direction (RD) to TD for cold rolled Ti–8% V (E = 72–94 GPa) and (Ti–8% V)–4%Sn (E = 63–85 GPa). The observed anisotropy of Young's modulus can be reasonably explained in terms of the cold rolling α′ texture.0.2% proof stress and tensile strength are independent of tensile orientation for cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys. In contrast, larger elongation to fracture is obtained in specimens deviated by 30°, 45° and 60° from RD than by 0°, 75° and 90°. Scanning electron microscopy (SEM) fractographs reveal that quasi-cleavage-like fracture plane appears in 0° specimen of cold rolled Ti–8% V which shows brittle fracture and other specimens of cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys are fractured accompanied with necking and dimple formation. It is suggested from these results that brittle fracture is related to the activation of limited number of slip system and Sn addition leads to the activation of multiple slip systems.     

Design of 1-3 piezocomposite hydrophones using finite elementanalysis

The 1-3 piezocomposite material was originally developed because of its perceived good performance under hydrostatic operating conditions. Several constrained-dimensional models for piezocomposite hydrophones have been proposed but were found to lack accuracy when compared with experimental data. In addition, they could not be easily extended to include the effect of ancillary components such as cover plates, on the transducer behavior. In this work a finite element model is used for modelling of 1-3 piezocomposite hydrophones to help overcome these two shortfalls. A finite element model initially developed for modelling of thickness mode operation has been extended to include lateral pressures typical of the hydrostatic environment. The response of the new model has been compared with experiment with satisfactory results, allowing an extensive set of simulations to be presented for comprehensive evaluation of 1-3 piezocomposite design as an actuator or a hydrophone. The best hydrostatic performance was obtained by using a low volume fraction composite of PZT-5H and a soft, compressible polymer, with potential enhancements by the incorporation of stiff cover plates covering the ceramic pillars. It is shown that the aspect ratio of the ceramic pillars should be minimized to maximize stress transfer. Additionally, ceramic pillar shape and distribution do not exert a major influence on the hydrostatic behavior     

Effects of anisotropy and annealing on microhardness of In x Bi2−x Te3 (x=0·1 to 0·5) single crystals

The crystals of In _x Bi_2−x Te₃ (x=0·1 to 0·5) have been grown by zone-melting method. In order to study anisotropy exhibited by the (0001) plane of the crystals, the directional hardness was determined by producing indentations at various azimuthal orientations of the indentor with respect to the surface over a range 0–180°. The crystal was rotated about the indentor axis in steps of 15° while keeping applied load and loading time constant at 50 g and 20 sec, respectively. For annealing study, the sample was kept at a temperature of 375°C. It was observed that softening of crystal takes place and the hardness decreases to a considerable extent.     

Change in anisotropy of mechanical properties with β-phase stability in high Zr-containing Ti-based alloys

High Zr-containing β-type Ti-based alloys were designed using electronic parameters to investigate experimentally the effect of β-phase stability on their elastic and plastic properties. Texture structures formed by cold rolling or recrystallization were related closely to the β-phase stability and hence affected the mechanical properties. In tensile tests, as the β-phase stability decreased, non-linearity in the elastic zone was enhanced and the work hardening tended to be diminished. Also, it was found that the lower β-phase stability led to the weaker anisotropy of plastic properties, but to the stronger anisotropy of elastic properties.     

ZnO Nanorods on a LaAlO3–SrTiO3 Interface: Hybrid 1D–2D Diodes with Engineered Electronic Properties

Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode‐type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO₃–SrTiO₃ interface. Tunable insulator‐to‐metal transitions, absent in the individual components, are observed as a result of the competing temperature‐dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler–Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials.     

Mechanical and anisotropic behaviors of Mg–Li–Zn alloy thin sheets

This study examined the mechanical property and formability of the cold-rolled Mg–Li–Zn alloy sheets with two different Li contents. Uniaxial tension and press-forming tests were carried out at room temperature. The tensile properties and formability parameters were correlated with the forming limit diagrams. The test results indicated that the Mg–Li–Zn alloy with a Li content of 6 wt% exhibited reasonable strength levels with moderate fracture elongation and that it did not show good stretchability and drawability at room temperature. The alloy with a Li content of 9 wt% presented excellent ductility even at room temperature and the strength levels were somewhat inferior. From the analysis, it was found that formability of the alloy with a higher Li content of 9 wt% was superior compared to that of the alloy with a Li content of 6wt%. Moreover, the fracture surfaces of the press-formed samples were considered and studied under a scanning electron microscope (SEM). The results showed that the partly ductile and partly brittle fracture pattern was observed in the tension–tension strain condition for both the alloys.     

The effects of heterogeneity and anisotropy on the size effect in cracked polycrystalline films

A model is developed for quantifying the size effect due to heterogeneity and anisotropy in polycrystalline films. The Monte Carlo finite element calculations predict the average and standard deviation of the microscopic (local) stress intensity factors and energy release rate of a crack in a columnar aggregate of randomly orientated, perfectly bonded, orthotropic crystals (grains) under plane deformation. The boundary of the near-tip region is subjected to displacement boundary conditions associated with a macroscopic (far field or nominal) Mode-I stress intensity factor and average elastic constants calculated for the uncracked film with a large number of grains. The average and standard deviation of the microscopic stress intensity factors and energy release rate, normalized with respect to the macroscopic parameters, are presented as functions of the number of grains within the near-tip region, and the parameters that quantify the level of crystalline anisotropy. It is shown that for a given level of anisotropy, as long as the crack tip is surrounded by at least ten grains, then the expected value and standard deviation of the crack tip parameters are insensitive to the number of crystals. For selected values of crystalline anisotropy, the probability distributions of Mode-I stress intensity factor and stress ahead of the crack are also presented. The results suggest that the size effect due to heterogeneity and anisotropy is weak; crack initiation load and direction are governed only by the details of the grains in the immediate vicinity of the crack tip. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two-dimensional electroacoustic model of transducer array based on 1-3 piezocomposite materials

An analytical model is presented to achieve simultaneous prediction of the elementary electroacoustic response and directivity pattern of a one-dimensional (1-D) piezocomposite array. The theoretical approach was based on guided wave theory in a multilayered structure in which the 1-3 piezocomposite material is considered as a homogeneous piezoelectric plate. A matrix method was applied to simulate the displacement fields generated at the surface of the array when one element was excited with an electrical pulse. A test device was manufactured, then characterized through measurements of displacement performed with an interferometric laser probe when the array vibrated in air and in water. The experimental results are presented and compared with theory.     

Hierarchical α‐MnO2 Nanowires@Ni1‐xMnxOy Nanoflakes Core–Shell Nanostructures for Supercapacitors

A facile two‐step solution‐phase method has been developed for the preparation of hierarchical α‐MnO₂ nanowires@Ni_1‐xMn_xO_y nanoflakes core–shell nanostructures. Ultralong α‐MnO₂ nanowires were synthesized by a hydrothermal method in the first step. Subsequently, Ni_1‐xMn_xO_y nanoflakes were grown on α‐MnO₂ nanowires to form core–shell nanostructures using chemical bath deposition followed by thermal annealing. Both solution‐phase methods can be easily scaled up for mass production. We have evaluated their application in supercapacitors. The ultralong one‐dimensional (1D) α‐MnO₂ nanowires in hierarchical core–shell nanostructures offer a stable and efficient backbone for charge transport; while the two‐dimensional (2D) Ni_1‐xMn_xO_y nanoflakes on α‐MnO₂ nanowires provide high accessible surface to ions in the electrolyte. These beneficial features enable the electrode with high capacitance and reliable stability. The capacitance of the core–shell α‐MnO₂@Ni_1‐xMn_xO_y nanostructures (x = 0.75) is as high as 657 F g^?1 at a current density of 250 mA g^?1, and stable charging‐discharging cycling over 1000 times at a current density of 2000 mA g^?1 has been realized.     

A 3D fourth order fabric tensor approach of anisotropy in granular media

We propose a micromechanical approach for granular media, with a particular account of the texture-induced anisotropy and of the strain localization rule. The approach is mainly based on the consideration of a fourth order fabric tensor able to capture general anisotropy which can be induced by complex distribution of contacts. Incorporation of this fourth order fabric tensor in a suitable homogenization scheme allows to determine the corresponding macroscopic elastic properties of the granular material. For this purpose, in addition to the classical Voigt upper bound, a new kinematics-based localization rule is proposed. It generalizes the one formulated by Cambou et al. [B. Cambou, Ph. Dubujet, F. Emeriault, F. Sidoroff, Eur. J. Mech. A/Solids 14 (1995) 225–276] in the case of an isotropic contact distribution. The results of the complete model compare well to numerical simulations results when available [C.S. Chang, C.L. Liao, Appl. Mech. Rev. 47 (1 Part 2) (1994) 197–207] (case of isotropic distribution of contacts). Finally, the interest of the fourth order fabric tensor based approach combined with the proposed localization rule is shown for different distributions of contacts by comparing its predictions to those given by a second order fabric tensor approach.     

Distorted yield surfaces – modelling by higher order anisotropic hardening tensors

Most of the constitutive models for metallic materials assume yield functions of von Mises or generalized Tsai–Wu type. Isotropic and/or kinematic evolutions are developed for hardening, which correspond to affin expansions or simple shifting of original yield surfaces, whereas experimental results show a distinctive change of the shape of yield surfaces (rotated or dented) depending on loading conditions and load paths. To cover the material behaviour with distorted yield surfaces a hierarchical expansion of yield functions to hardening tensors of the fourth and the sixth order is proposed. Parameters of corresponding evolutionary equations are determined by model parameter optimization. The extended model is investigated comparing numerical results to cyclic experimental data in biaxial σ–τ space.     

Thermisch gespritzte Schichten im System Al2O3–Cr2O3–TiO2 – ein Update

With exception of ZrO₂, the individual oxides and binary compositions in the system Al₂O₃–Cr₂O₃–TiO₂ are the most important oxide materials for the preparation of thermally sprayed coatings. In this contribution selected results of recent own research activities are summarized. This includes the comparison of microstructures, phase compositions, and properties of coatings, deposited by atmospheric plasma spraying (APS) and high velocity oxy‐fuel (HVOF) spraying. The possibilities arriving from the use of suspensions as feedstock are reviewed. Special attention is paid to the advantage of use of binary compositions in this system. Tribological, electrical and corrosion properties of the coatings are discussed.