Fabrication and experimental characterization of d31 telescopic piezoelectric actuators

A popular and useful piezoelectric actuator is the stack. Unfortunately with this type of actuation architecture the long lengths normally required to obtain necessary displacements can pose packaging and buckling problems. To overcome these limitations, a new architecture for piezoelectric actuators has been developed called telescopic. The basic design consists of concentric shells interconnected by end-caps which alternate in placement between the two axial ends of the shells. This leads to a linear displacement amplification at the cost of force; yet the force remains at the same magnitude as a stack and significantly higher than bender type architectures. This paper describes the fabrication and experimental characterization of three different telescopic prototypes. The actuator prototypes discussed in this paper mark a definitive step forward in fabrication techniques for complex piezoceramic structures. Materials Systems, Inc. has adapted injection molding for the fabrication of net shape piezoceramic actuators. Injection molding provides several advantages over conventional fabrication techniques, including: high production rate, uniform part dimensions, uniform piezoelectric properties, and reduced fabrication and assembly costs. Acrylate polymerization, developed at the University of Michigan, is similar to gelcasting, but uses a nonaqueous slurry which facilitates the production of large, tall, complex components such as the telescopic actuator, and is ideal for the rapid manufacture of unique or small batch structures. To demonstrate these fabrication processes a five tube telescopic actuator was injection molded along with a very tall three tube actuator that was cast using the acrylate polymerization method. As a benchmark, a third actuator was built from off-the-shelf tubes that were joined with aluminum end-caps. Each prototype's free deflection behavior was experimentally characterized and the results of the testing are presented within this paper.     

Water consumption of the early-age paste and the determination of “time-zero” of self-desiccation shrinkage

Self-desiccation shrinkage (SDS) is closely related to the interior water consumption and the relative humidity (IRH) drop in the cement paste. Substantial self-desiccation shrinkage has been observed at very early-age for high performance concrete. However, it is difficult to investigate the IRH by conventional method of hygrometer at this time because the materials are still in the superhygroscopic range. In this paper, an automatically measuring system of meniscus depression is developed on the base of the mechanism of tensiometer and Laplace formula. The interior water consumption and the IRH changing within the paste could be automatically monitored at the very early-age (here specially refers to the stage from the beginning of casting till several hours after final setting). By using this system, the effects of water to binder ratio and replacement of cement by fly ash and ground granulated blast furnace slag on the self-desiccation were investigated for the very early-age cement paste. Experimental results could potentially explain the mechanism of the SDS at very early-age as well as determine the “time-zero” of SDS corresponding to its definition.     

糯扎渡水电站地下引水发电系统的施工方法

糯扎渡水电站地下引水发电系统不仅施工难度大，而且施工工期长、干扰多。对其施工通道布置、主要洞室施工方法及施工期通风等施工关键技术进行了分析研究，进而探讨了大型地下洞室群施工的施工方法。     

Preparation and properties of polymer/LDH nanocomposite used for UV curing coatings

The thermal and mechanical properties of UV curing coatings consisted of urethane acrylates as an oligomer and a diacrylate monomer were reinforced by using layered double hydroxide (LDH). The LDH was organically modified by an ion-exchange process, in which the nitrate anions were replaced by long alkyl sulfate anions. With organic modification, the d-spacing of inorganic LDH layers was greatly enlarged to 2.75 from 0.78 nm, leading the LDH to be organophilic. During in situ photopolymerization process, the d-spacing of LDH layers was further enlarged to 4.29 nm, indicating the intercalation of polymer chains. For comparison, polymer/LDH nanocomposite filled with un-modified LDH was also prepared, and showed less enhancement in thermal and mechanical properties.     

瓷石尾砂玻璃马赛克的研制

根据瓷石尾砂的矿物工艺特性，采用合理科学的配方和相应的熔融法生产工艺技术，以瓷石尾砂为主要原料，取代石英砂和部分熔剂原料，成功地研制出尾砂玻璃马赛克，产品性能按国标ＧＢ７６９７－８７检测，各项指标完全达到要求。研究成果为瓷石尾砂的综合利用开辟了新领域。     

Direct and transfer hydrogenation of furfural over MOF-derived Pd-Cu@C catalysts

Owing to the self-reducing ability of palladium acetate in solutions, an ethanol solution containing Pd⁰ particles was prepared and coated in-situ into copper metal–organic framework (Cu-MOF), forming Pd@Cu-MOF in a coated structure. The Pd@Cu-MOF was reduced under N₂ or H₂ to form carbon-coated Pd-Cu@C. The pyrolysis and carbonization of Cu-MOF and the reduction of Cu²⁺ were studied. The Cu-MOF under either N₂ or H₂ was pyrolyzed and carbonized, but the Cu²⁺ reduction mechanisms were different. The high-temperature carbothermic reduction of Cu²⁺ under N₂ produced Cu⁰, but during low-temperature reduction under H₂, the reducing H₂ reduced Cu²⁺ to Cu⁰. Furfural hydrogenation experiments showed that compared with H₂, the Pd-Cu@C prepared under N₂ reduction displayed higher furfural hydrogenation activity. The catalytic activity of Pd-Cu@C prepared from in-situ Pd⁰ coating was higher than the Pd/Cu@C prepared from the impregnation method. With i-propanol as the solvent, the catalytic hydrogenation of furfural under H₂ consisted of direct catalytic hydrogenation with molecular hydrogen as the hydrogen source and catalytic transfer hydrogenation with i-propanol as the hydrogen donor. The catalytic activity of direct catalytic hydrogenation is higher than the catalytic transfer hydrogenation.     

Compound-element modeling accounting for semi-rigid connections and member plasticity

A general model of a compound element is proposed in this article to consider the combined influence of semi-rigid connections and plasticity on the non-linear responses of steel frameworks. The stiffness degradation of semi-rigid connections is modeled by a moment–rotation relationship with four parameters, while the plasticity formation of a member end from initial yield to full yield is modeled by an elliptic moment–rotation relationship. The compound element resulting from the combined influence of member plasticity and semi-rigid connection behaviour is used to facilitate the derivation of member stiffness coefficients where the effects of geometrical non-linearity and member shear deformation are also included for the progressive-failure analysis. On the basis of member plasticity behaviour, the categories of semi-rigid connections are investigated. Three semi-rigid steel frameworks are analysed to illustrate the proposed analysis method, and the results are compared with those obtained from experiments and the application of other methods.