Applied Mechanics and Materials Vols. 303-306

Abstract: In this study, structural vibration control using semi-active shunt piezoelectric damping circuits is presented. A piezoelectric patch with an electrical shunt circuit is bonded to a base structure. When the structure vibrates, the piezoelectric patch strains and transforms the mechanical energy of the structure into electrical energy, which can be effectively dissipated by the shunt circuit. Hence, the shunt circuit acts as a means of extracting mechanical energy from the base structure. In this study, a pulse-switching circuit is imposed as the semi-active shunt piezoelectric damping to reduce the structural vibration. The switch-law for the pulse-switching circuit is discussed in detail, and the detailed numerical calculations are given and discussed. It is found that the pulse-switching circuit is more stable than passive piezoelectric circuit (such as RL series circuit) with regard to structural stiffness variations.

Abstract: La1-xSrxMnO3 thin films with x=0.2 and 0.33 were prepared by magnetron sputtering method for its potential application on thermal control of spacecraft. The materials show a phase transition from ferromagnetic metal phase with a low infrared emittance to paramagnetic insulator phase with a high emittance. Because of the thermochromic property, they can automatically change their infrared emittance greatly in response to environment temperature and thermal load and keep the spacecraft electronic components working normally. A superconduction quantum interference device magnetometer was used to study magnetization over the temperature range 100–315 K. Temperature dependence of total hemispherical emittance was carried out in a liquid nitrogen cooled vacuum chamber by a steady state calorimetric method. Thermal emittance results indicate an obvious tuneability of both La0.8Sr0.2MnO3 and La0.67Sr0.33MnO3 thin films. Compared to La0.8Sr0.2MnO3 thin film, La0.67Sr0.33MnO3 thin film has a higher transition temperature and bigger emittance tuneability. Based on phase separation concept, the thermal emittance was fitted by two-energy-level Boltzmann distribution of metal phase volume fraction fH. The measured magnetization curves were fitted in terms of mean-field approximation theory. The volume fraction of ferromagnetic phase fM was not coinciding with the fH very well. This result showed the fH and the fM plays a different role on thermal emittance property.

Abstract: In order to improve damping properties of polyurethane/vinyl ester resin interpenetrating polymer network (PU/VER IPN), a series of Lead Zirconate-Titanate/IPN (PZT/IPN) composites were prepared by adding PZT into PU/VER IPN by in-situ polymerization process and were polarized. The optimal polarization process is obtained. The influence of PZT contents on microstructure, damping performances, mechanical performances, relative dielectric constant and piezoelectric constant (d¬33) was studied. The results show that PZT particles disperse in composites uniformly. The optimal polarization parameters of PZT/IPN composites are as follows: polarization temperature 100°C, polarization field strength 6kV/mm and polarization time 40min. Mechanical loss tangent (tanδ) values of the optimal PZT/IPN composites with 75 wt.% PZT are higher than 0.3 from –31°C to higher than 120°C, which meets the requirement of damping materials with excellent performances.

Abstract: To study the magnetic-electrical-mechanical coupling mechanism of microwave ME (magnetoelectric) tri-layered structures, we proposed a theoretical model of electric tunable FMR (Ferromagnetic Resonance) frequency shift for bias magnetic field in different directions through the theory of Smith-Beljers and free energy density of ferrite. A deformation produced by the applied electric field called strain could be obtained through the theory of classical laminated plate. This model effectively predicts the stress of laminated structure increases when the piezoelectric coefficient increases, the shift of electric field tunable FMR frequency is more obvious when saturation magnetization and magnetostriction coefficient of ferrite increase. Moreover, it qualitatively explains the experimental phenomena that the directions of FMR frequency shift are opposite when apply the in-plane and out-of-plane magnetic field respectively, and provides a theoretical basis for electric field and magnetic field dual tunable microwave devices.

Abstract: In this paper, the first order buoyancy force of ferrofluid is simulated calculation under external magnetic field in ferrofluid devices. The relationship between first order buoyancy force and displacement of nonmagnetic body under different relative permeability of ferrofluid，and the relationship between first order buoyancy force and relative permeability of ferrofluid are obtained.

Abstract: There is an important effect on road safety with no lighting facilities near the wild road. With the piezoelectric materials embedded in the asphalt concrete as the smart aggregates, the piezoelectric asphalt concrete transforms the vibrational energy of road surface into electrical energy, to supply the road lighting facilities or be stored up. In this study, the electrical energy of piezoelectric-embedded asphalt mixture by using UTM and wheel tester. The results show that PMnS-PZN-PZT ceramic doped with 0.45wt% Fe2O3 (4mm×8pieces) be embedded in the AC-10 asphalt concrete which can obtain well road performance and micropower electrical energy.

Abstract: As a newly emerging frontier interdiscipline, smart materials and structures possesses the great development potential and wide application prospect, and has become one of the research focuses at home and abroad.The research status of smart materials and structures is summarized, and its key technologies are analyzed. the future development of smart materials and structures is presented.

Abstract: This paper presents a new method for sensing the radiation mode amplitudes by using piezoelectric fibers for vibrating beams with different boundary conditions. Two straight and one curved fibers bonded on the surface of the beam are taken as a sensor. The sensor output is defined as the output current of the curved fiber subtracting the output currents of the other two straight fibers. By means of designing the appropriate shape of the curved piezoelectric fiber, the sensor output can directly lead to the corresponding radiation mode amplitude of the beam. The equations which define the curved sensor shapes are independent of the type and position of the external excitation. Finally, a numerical example is given and the effects of shape error and location error of such type sensor are discussed.

Abstract: Coal Face Gas Concentration Overrun Is the Leading Cause of China Coal Mine Fatal Gas Explosion Accidents Reasons. Therefore, Research and Development of Rapid Detection of Gas Sensor Can Avoid Gas Explosion Accident Key. this Paper Studies the Al2o3 Nanometer Powder Preparation Technology, by Doping Rare Earth Material so that the Gas Sensor Detection Element Surface Area Was Greatly Improved; its Sensitivity and Stability Are Greatly Improved. According to the Test Results Show that, the Rapid Gas Sensor for Methane Reaction Time Is 6 Seconds, Recovery Time of 8 Seconds.