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The microstructure, strain behavior, and piezoelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT-Sn) piezoelectric ceramics modified with Sn4+ ions were systematically studied. The experimental results indicated that the Sn4+ ion doping was a viable and effective method to promote the electromechanical properties and the strain behavior of the BNKT ceramics. When the Sn content was 0.02 mol, the resultant BNKT ceramics exhibited excellent electrical properties with a density of 5.92 g.cm–3, a dielectric constant (er) of 1235, a dielectric loss (tanδ) of 0.048, the electromechanical coupling factors of 0.36 (kp) and 0.39 (kt), a piezoelectric coefficient (d33) of 171 pC/N, and a mechanical quality factor (Qm) of 125. Moreover, a large unipolar strain of 0.45% and a high normalized strain of 865 pm/V were achieved at 50 °C. The main achievement of this study was the large normalized strain (d33*) of 876 pm/V at the SnO2 content of 0.04 mol.

The paper aims at introducing an analysis of thin-walled functionally graded sandwich beams for general non-uniform quadrilateral cross-sections. Generally, the materials are assumed to be graded through the thickness following a predefined shape while Poisson's ratio kept as a constant due to its less domination. The cross-section linearly varies from one end to another end of the beam. In order to relax the difficulties in modeling as well as capturing the behaviors of thin-walled functionally graded beams, a higher-order approach has been applied including warping, coupling distortions as well as Poisson's distortion. A multi-separated beam on each edge of the cross-section which is an application of the so-called beam-frame-modal method is adopted. Subsequently, the effects of these major importance along with anisotropy of materials are then fully considered. As a consequence, the analysis is able to extensively applied to closed-section beam-shells with different curvatures. In order to illustrate the accuracy and computational efficiency of the method, various examples have been conducted in which the results obtained from finite element package as ABAQUS are employed. Keywords: quadrilateral cross-section; thin-walled FG beam; higher-order coupling; beam frame modal.

In this study, a novel magnetorheological brake (MRB) with tooth-shape rotor is developed. In this new MRB, traditional cylindrical rotor is replaced by a new one with tooth-shaped rotor. The teeth on the rotor act as multiple magnetic poles of the brake. Two magnetic coils are placed on side-housings of the brake to generate a mutual magnetic field of the MRB. The inner face of each side-housing has tooth shaped features as well. These tooth shaped features interact with the rotor teeth via magnetorheological fluid (MRF) medium. By using the tooth shaped rotor, more interface area between the rotor and the working MRF can be archived, which can improve performance characteristics of the proposed MRB such as compact size, low power consumption and high braking torque. After an introduction of state of the art of MRB development, the schematics and working principle of the MRB with tooth-shaped rotor is proposed. The modeling of the MRB is then derived based on magnetic finite element analysis and Bingham rheological model of MRF. Optimal design of the MRB considering mass and braking torque of the MRB is then conducted. From the optimal design result, it is shown that the mass and power consumption of the proposed MRB are significantly smaller than those of previously developed ones. In details, at high value of the maximum braking torque (100 Nm), the proposed MRB mass is only around 31.3% of the mass of the thin-wall single-coil and 42.6% of the mass of the thin-wall double coil MRB. In addition, at small values of the maximum braking torque (5 Nm), power consumption of the proposed MRB is only around 33% of that of the thin-wall single-coil and 45.5% of that of the thin-wall double coil MRB. Experimental works on prototypes of the proposed MRB are then performed for validation.

This research focuses on development of a new bidirectional magneto-rheological actuator (BMRA), especially for force feedback system. The BMRA composed of two input shafts rotating in opposite directions at the same speed, on which the two magnetic discs are assembled. The two discs are placed inside a housing which is connected to the output shaft. On each side of the housing, magnetic coils are integrated to create corresponding magnetic field on required. The gap between the discs and the housing is filled magnetorheological fluid (MRF). A thin wall is employed to separate the coils with the MRF. This allows the MRF duct being manufactured more easily and accurately. After a review of state of the art of MR actuators, the new configuration and working principle of the proposed BMRA is presented. After that, equation for calculation of the output torque of the proposed BMRA is derived and optimal design of the BMRA is conducted considering its maximum output torque and mass. Based on the optimal results, a prototype of the BMRA is manufactured and performance characteristics of the proposed BMRA are then investigated with both experimental and simulated results.