Silicone–Poly(hexylthiophene) Blends as Elastomers with Enhanced Electromechanical Transduction Properties

Dielectric elastomers are progressively emerging as one of the best‐performing classes of electroactive polymers for electromechanical transduction. They are used for actuation devices driven by the so‐called Maxwell stress effect. At present, the need for high‐driving electric fields limits the use of these transduction materials in some areas of potential application, especially in the case of biomedical disciplines. A reduction of the driving fields may be achieved with new elastomers offering intrinsically superior electromechanical properties. So far, most attempts in this direction have been focused on the development of composites between elastomer matrixes and high‐permittivity ceramic fillers, yielding limited results. In this work, a different approach was adopted for increasing the electromechanical response of a common type of dielectric elastomer. The technique consisted in blending, rather than loading, the elastomer (poly(dimethylsiloxane)) with a highly polarizable conjugated polymer (undoped poly(3‐hexylthiophene)). The resulting material was characterised by dielectric spectroscopy, scanning electron microscopy, tensile mechanical analysis, and electromechanical transduction tests. Very low percentages (1–6 wt %) of poly(3‐hexylthiophene) yielded both an increase of the relative dielectric permittivity and an unexpected reduction of the tensile elastic modulus. Both these factors synergetically contributed to a remarkable increase of the electromechanical response, which reached a maximum at 1 wt % content of conjugated polymer. Estimations based on a simple linear model were compared with the experimental electromechanical data and a good agreement was found up to 1 wt %. This approach may lead to the development of new types of materials suitable for several types of applications requiring elastomers with improved electromechanical properties.     

Temperature dependence of electrical and electromechanical properties of Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thin films

The electrical and electromechanical properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (PMN–PNN–PZT, PMN/PNN/PZT = 20/10/70) on Pt/Ti/SiO₂/Si substrates by chemical solution deposition was investigated. The PMN–PNN–PZT films annealed at 650 °C exhibited slim polarization hysteresis curves and a high dielectric constant of 2100 at room temperature. A broad dielectric maximum at approximately 140–170 °C was observed. The field-induced displacement was measured by scanning probe microscopy, the bipolar displacement was not hysteretic, and the effective piezoelectric coefficient (d₃₃) was 66 × 10⁻¹² m/V. The effective d₃₃ decreased with temperature, but the value at 100 °C remained 45 × 10⁻¹² m/V.     

磁控形状记忆合金主动控制系统及试验研究

对磁控形状记忆合金材料进行了磁力学性能试验研究,建立了预加压力-磁场-应变等磁力学本构模型;系统地分析了磁控形状记忆合金作动器的工作原理和构造方法,并进行了相应的磁场-作动性能试验研究,得出了磁控形状记忆合金作动器的本构模型,集成和开发了主动控制系统,并对一凯威特型模型结构进行了相应的控制性能试验。结果表明,研发的磁控形状记忆合金主动控制系统可有效控制网壳结构的地震响应。     

The Vitality of Matter and the Instrumentalisation of Life

Artists and researchers Oron Catts and Ionat Zurr of SymbioticA, based at the School of Anatomy, Physiology and Human Biology at the University of Western Australia, are internationally renowned as pioneers in the field of biological arts, challenging audiences with their tissue engineering projects. Catts and Zurr discuss how synthetic biology has increasingly become ‘the new frontier for exploitation’ and why there is currently ‘a resurgence of the application of engineering logic in the fields of the life sciences’ in which life itself becomes a raw material.     

Misalignment effects on the load capacity of a hydraulic cylinder

Analytical and experimental investigations of typical hydraulic cylinders have indicated that their load capacities are significantly different from those obtained from simple buckling analysis of idealized systems. In any case, an increase in the friction coefficient at the restrained ends changes the actuator's limit load, while an increase in the initial maximum deflection (initial misalignment) decreases the limit load. A common practice of most cylinder manufacturers is to use a safety factor (between 2.5 and 4) to determine the service load after the critical load (buckling) is obtained by simple analytical procedures treating the cylinder as a perfect stepped column. The intricate aspects of friction effects have been deliberately left aside in this present work. Nevertheless, friction and interaction between mechanism and actuator in the buckling characteristics will be presented in the ongoing paper, which will follow this work. Authors know that, in a real system, the cylinder tube-rod interface is not rigid. Due to the flexibility of guide rings and clearances between components, misalignment (an angular deflection which increases with increasing axial load) exits at the interface. When initial imperfection angle exists, there is no sudden buckling. Then, stresses and deflections increase with increasing load. After repetitive use, the tolerance between the parts will become larger, consequently increasing the initial deflection, which has been proved to considerably decrease the load capacities of the power cylinders. From this analysis, a theoretical and experimental work has been carried out in order to show the advantages and disadvantages of the current design methods, characterizing the critical factors that cause the collapse and proposing useful design criterions. The present work aims to describe the behaviour of actuators under load capacity with experimental validation.     

Active Control of a Piezoelectric Actuated Four-Bar Mechanism Deployed in Robotics Applications

This work presents a new micro-positioning system that is implemented in an inchworm robot to move into desired locations. The system consists of four-bar mechanism; one link is fixed, and each one of the remaining links carries a piezoelectric actuator (PZT). PZTs are specifically chosen since they provide fast response and small displacements; up to ±30 µm for ±100 Volts. The system’s mathematical model is derived and is numerically simulated by MATLAB. Three fuzzy PI controllers, which are tuned automatically by genetic algorithm, are designed to control the system. Results indicate an error of less than 1% although disturbances present.     

Novel piezoelectric ceramics and composites for sensor and actuator applications

 Novel piezoelectric ceramic, and ceramic /polymer composite structures were fabricated by solid freeform fabrication (SFF) for sensor and actuator applications. SFF techniques including: Fused Deposition of Ceramics (FDC), and Sanders Prototyping (SP) were utilized to fabricate a variety of complex structures directly from a computer aided design (CAD) file. Many novel and complex composite structures including volume fraction gradients (VFG), staggered rods, radial and curved composites, and actuator designs such as tubes, spirals and telescoping were made using the flexibility provided by the above processes. Radial composites with various connectivities in the radial direction were made for towed array applications. VFG’s were incorporated into some of these designs, with the ceramic content decreasing from the center towards the edges. Many new designs are also being used to manufacture high authority actuators utilizing the FDC technique. The telescoping actuation of the device is the summation of actuation of all individual tubes making of the actuator, therefore, increasing the number of the tubes which are the driving component of the actuator will further enhance the displacement. The design, fabrication and electromechanical properties of these sensor and actuator structures are discussed in this paper. Received: 2 November 1998 / Reviewed and accepted: 2 November 1998     

Buckling optimization of composite laminated adaptive structures

This paper deals with the optimal design of laminated composite plates with integrated piezoelectric actuators. Refined finite element models based on equivalent single layer high-order shear deformation theories are used. These models are combined with simulated annealing, a stochastic global optimization technique, in order to find the optimal location of piezoelectric actuators and also to find the optimal fiber reinforcement angles in both cases having the objective of maximizing the buckling load of the composite adaptive plate structure. To show the performance of the proposed optimization models, two illustrative and simple examples are presented and discussed. In one of these examples a comparison between the simulated annealing technique and a gradient based optimization scheme, is carried out.     

Geometrically non-linear analysis of composite structures with integrated piezoelectric sensors and actuators

This paper deals with the geometrically non-linear analysis of thin plate/shell laminated structures with embedded integrated piezoelectric actuators or sensors layers and/or patches. The motivation for the present developments is the lack of studies in the behavior of adaptive structures using geometrically non-linear models, where only very few published works were found in the open literature.

The model is based on the Kirchhoff classical laminated theory and can be applied to plate and shell adaptive structures with arbitrary shape, general mechanical and electrical loadings.

The finite element model is a non-conforming single layer triangular plate/shell element with 18 degrees of freedom for the generalized displacements and one electrical potential degree of freedom for each piezoelectric layer or patch.

An updated Lagrangian formulation associated to Newton–Raphson technique is used to solve incrementally and iteratively the equilibrium equations.

The model is applied in the solution of four illustrative cases, and the results are compared and discussed with alternative solutions when available.