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Particle-stabilized liquid foams provide a general route for producing low-density macroporous materials from melt-processable and intractable thermoplastic polymers. In this paper, we demonstrate how these liquid foams can be used to design macroporous polymers with tailored microstructures and properties by adjusting the various processing parameters. By varying the size, concentration, and wettability of the particles in the colloidal suspensions and controlling the frothing, drying, and sintering conditions, macroporous materials with porosities between 33 and 95% and median pore sizes (D50) between 13 and 634 μm were obtained. This foaming process is applicable to a wide range of hydrophobic materials and is demonstrated here on commercially available polymeric powders of poly(tetrafluoroethylene) (PTFE), poly(vinylidene fluoride) (PVDF), poly(ether imide) (PEI), and poly(ether ether ketone) (PEEK). [ABSTRACT FROM AUTHOR]

In this communication, we describe a general, straightforward route to produce highly porous bulk materials from melt-processable and intractable polymers using particle-stabilized liquid foams. [ABSTRACT FROM AUTHOR]

The characterization of the ferroelectric properties of piezoelectric ceramic fibers is paramount for optimizing their manufacturing processes, for quality control purposes, and for modeling the response of components and structures. Until now, fibers were generally characterized by measuring the so-called 1-3 composites, fiber arrays embedded in a polymer matrix. The fiber properties can then be extracted, provided the volume fraction and stiffness of each phase, the fiber piezoelectric charge constant as a function of the electrical field strength, and the matrix permittivity are known. This implies a large amount of time and experimental effort. This article presents a comprehensive procedure for the direct characterization of single piezoelectric ceramic fibers in terms of butterfly and polarization loops, as well as their blocking force. The experimental setup is composed of a waveform generator, a high-voltage amplifier, a dynamic mechanical analyzer, a current/charge measuring circuit, and an oscilloscope. The active circuitry used for reliably collecting the charge generated by a single fiber is presented in full detail. The very good repeatability of the measurements showed the proposed procedure to be robust. The comparison between single fiber measurements and the investigation of 1-3 composites revealed both procedures to be equal, at 99.9%, in determining the average strain and polarization properties. In addition, the single fiber measurement provides an estimation of the variation in fiber properties within a single production batch. This information is essential to understand how to optimize processing routes and build robust devices. [ABSTRACT FROM AUTHOR]

Active fiber composites are electromechanical actuators based on piezo‐ceramic fibers, which are embedded in a polymer matrix. The fibers are electrically contacted through so‐called interdigitated electrodes (IDEs). State‐of‐the‐art metallic IDEs only contact the fibers at two small sections of their circumference at the top and bottom of the composite ply, respectively. This paper presents an original technique to manufacture IDEs made of a conducting polymer (polypyrrole/p‐toluene sulfonic acid), where the polymer electrodes contact the fibers around their whole circumference. The necessary process steps are discussed, namely design of the master electrodes and electrochemical polymer growth with and without fibers. Processing issues are discussed and solutions are suggested. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Smart material based variable internal connectivity has the potential to overcome the inherent conflicting requirements of lightweight shape adaptable structures by reducing the actuation force required for shape adaptation, and, consequently, volume and mass of the actuation system, by increasing the compliance of the structure temporarily. In this paper, we consider shape adaptable sandwich panels with a truss core and implement smart material based variable connections, called mechanical switches, in the trusses of the core. We present three concepts of mechanical switches based on electro-bonded laminates, dielectric elastomer actuators and shape memory alloys, and evaluate their performance in terms of variation in stiffness and in maximum transferable force. Based on these results, we show how the implementation of variable connections in the core trusses can be used to reduce the actuation force by different orders of magnitude for three simple types of deformation of the panel: change in thickness, in transverse shear angle and bending. Further, considering the influence of the mechanical switches on the out-of-plane stiffness of the core, we demonstrate that this approach can be used to obtain changes in thickness of the panel, a kind of deformation that is not possible to obtain with other approaches found in literature. Moreover, we show that mechanical switches can be used to selectively vary the shear stiffness of the panel in the desired direction. Finally, we analyze the limitations of this technology in terms of mechanical properties in order to identify possible applications. [ABSTRACT FROM AUTHOR]

This paper reports on the first implementation of an integrated programmable hybrid phononic crystal (hPC) for wave propagation control. At the core of the novel hPC is a newly developed and tested miniaturized array of virtual floating inductances with programmable properties. The inductance is the building block for a discrete programmable electrical transmission line aimed at wave propagation control in a 1D hPC. The hybrid characteristic is the result of the coupling between a mechanical waveguide in the form of an elastic beam, and an electrical transmission line. The medium features attenuation of mechanical wave motion due to an energy transfer to the electrical domain. Over the frequency range of wave attenuation the dispersion curves of the hPC are characterized by eigenvalue mode veering. An analytical model, based on the transfer matrix method is presented, to expeditiously calculate the dispersion curves of the hPC. Furthermore, this paper provides numerical and experimental transmittance results which validate the efficiency and tunability of the programmable electrical transmission line. The novelty of this contribution is an analytical model for calculating the dispersion curves of the 1D hPC, and a miniaturized programmable virtual inductance which gives way to a ‘smart’ material. [ABSTRACT FROM AUTHOR]

The aerodynamic performance of wing structures is directly related to their external geometry. The idea of seamless shape adaptation of the wing geometry (or morphing) has emerged to provide the capability of operating optimally in a wide range of conditions. Of particular importance to realize the potential of morphing is the ability of the wing skin to conform to the different geometrical contours. Several concepts for morphing skins have been presented to address this design challenge, each presenting peculiar strengths and weaknesses depending on the chosen combination of material and structural arrangement. This paper investigates the generic structural properties of a passive morphing skin design to allow for optimal shape adaptation through cambering. The properties of the morphing skin are included among the design variables to identify their optimal value; multi-objective optimizations are used to obtain parametric results. The results indicate the need for a high anisotropy, both between membrane and bending properties and between the skin’s principal directions. The impact of the skin weight on the wing design is also shown. [ABSTRACT FROM AUTHOR]