Prediction of Effective Permittivity of Foam-Polymer Materials

Porous plastics are used in various fields of industry, including radio- and electrotechnical fields. They are characterized by good heat- and sound isolating, dielectric and mechanical properties as well as by resistance to effect of various external factors during operation. The problem of estimation of effective permittivity of foam-polymer materials with a large volume fraction of pores, in particular, polyepoxide foam materials, has been considered. Two methods for solving it, both based on the matrix have been proposed. In the first method the matrix is considered as a polyepoxide binder, and the cavities filled with gas are taken as inclusions. In the second method the polyepoxide walls, separating cavities, are taken as inclusions, and gas filling cavities is considered as a matrix. To obtain the formulas for calculation, both methods use a generalized singular approximation of the theory of random fields. Based on the obtained expressions, the model calculations of the effective permittivity of a macroscopically isotropic foam material with a polymer binder based on E-20 and the cavities filled with freon, depending on the apparent density of the material, have been made. The calculations in the generalized singular approximations have been carried out for two of its variants: when the matrix was considered as a comparison medium; and, also by the self-consistent method. In the calculations using the second method two variants of the shape of the cells of the material have been considered: a weakly leaked or heavily leaked polyhedron. The calculated dependences obtained by all me-thods have shown the qualitative compliance with the experimental data.

Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn

The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork's bill ( Erodium ) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells.

Integrating Advanced Composite Materials Into the Chassis of a Sports Car

This work evaluated the feasibility of replacing the current stamped-steel floor-pan bulkhead assembly (FBA) of a popular street car with one made of fiber reinforced polymer matrix composite material. To evaluate the feasibility, a finite element model was constructed which incorporated much of the midsection of the vehicle’s chassis. Each part of the chassis section assembly was modeled, meshed, and constrained such that the actual physical assembly relations were upheld. Shell elements were used to model the FBA, and brick and tetrahedron elements modeled the surrounding chassis. Six loading cases were considered: a torsion case, a bending case, and four seat load cases. The chosen composite consisted of an intermediate modulus fiber (AS4) and a typical thermal-set epoxy (3501-6). Four laminate stacking sequences were studied: two quasi-isotropic laminates, a zero-dominated laminate, and a symmetric laminate. A sandwich laminate case was also studied, which utilized quasi-isotropic face-sheets and an isotropic foam core. For comparison a steel case was also simulated. The overall result of the model showed that the sandwich case proved to be superior with the smallest displacements and stresses while reducing weight. The overall weight saving was an astonishing 3% of total vehicle weight which represents a significant savings for an automobile. Based on the results it was determined that the replacement of the steel FBA with a composite FBA is feasible.