Saturated domain orientation textures of three types of pseudocubic (tetragonal, rhombohedral, and orthorhombic) ferroelectric ceramics after complete electric and uniaxial tension (compression) poling is studied analytically in this paper. A one-dimensional orientation distribution function (ODF) of the domain polar vectors is explicitly derived from the uniform inverse pole figures of the poling field axes on a stereographic projection with respect to the fixed crystallite coordinates. The analytical ODF is used to obtain the analytical solutions of saturated polarization and strain after electric/mechanical poling. Based on the closed form solution of the saturated domain orientation textures, the resultant intrinsic electromechanical properties of ferroelectric ceramics, which depend only on the ODF and properties of the corresponding single crystals, are obtained. The results show how the macroscopic symmetries of ferroelectric crystals change from 4mm (tetragonal), 3m (rhombohedral), and mm2 (orthorhombic) single crystals to a ∞mm (transversely isotropic) completely poled ceramic.

We report the comparative in situ fracture toughness testing on single-edge V/U-notched multilayer graphenes and boronitrenes in a high-resolution transmission electron microscope (HRTEM). The nanostructures of notch tips and fracture edges of the tested specimens are unambiguously resolved using HRTEM. By analyzing the notch tip stresses using finite element method, the fracture toughness of multilayer graphenes and boronitrenes is determined to be 12.0 ± 3.9 and 5.5 ± 0.7 MPa√m, respectively, taking into account the notch tip blunting effects.

Piezoelectric actuators are increasingly used in fuel injectors due to their quick response, high efficiency, accuracy, and excellent repeatability. Current understanding of their thermo-electro-mechanical performance under dynamic driving conditions appropriate for fuel injection is, however, limited. In this paper, the thermo-electro-mechanical performance of soft Lead Zirconate Titanate (PZT) stack actuators is experimentally investigated over a temperature range of -30°C to 80°C, under driving electric fields of up to 2.0 kV/mm (using an AC drive method and a biased DC offset), different frequencies, and a constant preload of about 5 MPa. Experimental results show that the dynamic stroke of the actuators increases with the magnitude and frequency of the applied electric field, as well as ambient temperature. The dynamic stroke was also found to increase with decreased driving field rise time, which is equivalent to increasing the driving field frequency. At driving frequencies lower than the resonance frequency of the test apparatus (~500 Hz), the strain-electric field behavior under different temperatures agreed well with previously obtained quasi-static results. The duty cycle was found to have a minimal effect on dynamic stroke but significantly affected the amount of heat generated under high electric field magnitudes and/or frequencies. The temperature increase due to self-heat generation under a continuous AC driving field (100% duty cycle) was very high, and limited the maximum driving field magnitude and/or frequency. Reducing the duty cycle significantly decreased the amount of heat generation.

Quasi-static thermo-electro-mechanical performance of annular and solid cylindrical piezoelectric actuators was studied by experimental means under electric fields varying from 0.3 to 1.8 kV mm −1 with a preload of 4.6 MPa over the temperature range of −30 to 125 • C. It was found that, for both annular and solid actuators, the electrically induced stroke increases steadily with temperature. Under electric fields larger than 1.0 kV mm −1 , a nonlinear transition zone exists in the stroke-temperature plot over the temperature range 25-50 • C. The dielectric constant was also found to increase with temperature. Preload dependence of displacement was measured up to 42 MPa at room temperature and found to be negligible below 30 MPa. A mathematical model that includes the linear piezoelectric effect and 90 • domain switching effect was used to model the experimental results. The model shows reasonable agreement with experimental results at low and high driving fields.

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The fundamental shear horizontal (SH0) wave in plate-like structures is extremely useful for non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive.However, currently the SH0 wave is usually excited by electromagnetic acoustic transducers and PZT-5H ceramics via lateral compression under elevated temperature. It was found that when bonded on a 1 mm-thick aluminum plate, the 36 d type PZT-4 exhibited better face-shear performance than PZT-5H. We then successfully excite SH0 wave in the aluminum plate using a face-shear PZT-4 square patch and receive the wave using a face-shear PMN-PT patch. The frequency response and directionality of the excited SH0 wave were also investigated. The SH0 wave can be dominate over the Lamb waves (S0 and A0 waves) from 160 kHz to 280 kHz. The wave amplitude reaches its maxima along the two main directions (0° and 90°). The amplitude can keep over 80% of the maxima when the deviate angle is less than 30°, while it vanishes a) Author to whom all correspondence should be addressed, Email: lifaxin@pku.edu.cn 2 quickly at the 45° direction. The excited SH0 wave using piezoelectric ceramics could be very promising in the fields of NDT and SHM.

The non-dispersive fundamental shear horizontal (SH) wave in plate-like structures is of practical importance in non-destructive testing (NDT) and structural health monitoring (SHM). Theoretically, an omnidirectional SH transducer phased array system can be used to inspect defects in a large plate in the similar manner to the phased array transducers used in medical B-scan ultrasonics. However, very few omnidirectional SH transducers have been proposed so far. In this work, an omnidirectional SH wave piezoelectric transducer (OSH-PT) was proposed, which consists of a ring array of twelve face-shear (d) trapezoidal PZT elements. Each PZT element can produce face-shear deformation under applied voltage, resulting in circumferential shear deformation in the OSH-PT and omnidirectional SH waves in the hosting plate. Both finite element simulations and experiments were conducted to examine the performance of the proposed OSH-PT. Experimental testing shows that the OSH-PT exhibits good omnidirectional properties, no matter it is used as a SH wave transmitter or a SH wave receiver. This work may greatly promote the applications of SH waves in NDT and SHM.

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