Functionally graded viscoelastic core characteristics on vibroacoustic behavior of double-walled cylindrical shells in a subsonic external flow

The present study is concerned with an analytical solution for calculating sound transmission loss through an infinite double-walled circular cylindrical shell with two isotropic skins and a polymeric foam core. Accordingly, the two-walled cylindrical shell is stimulated applying an acoustic oblique plane wave. The equations of motion are derived according to Hamilton’s principle using the first-order shear deformation theory for every three layers of the construction. Additionally, by the aid of employing the Zener mathematical model for the core of polymeric foam, mechanical properties are determined. To authenticate the results of this study, the damping of the core layer goes to zero. Therefore, the numerical results in this special case are compared with those of isotropic shells. The results prove that the presented model has high accuracy. It is also designated that decreasing the power-law exponent of the core leads to improving the sound transmission loss through the thickness of the construction. Besides, in addition to probe some configurations versus alterations of frequencies and dimensions, the convergence algorithm is provided. Consequently, it is realized that by increasing the excitation frequency, the minimum number of modes to find the convergence conditions is enhanced. The results also contain a comparison between the sound transmission loss coefficient for four different models of a core of a sandwiched cylindrical shell. It is comprehended that the presented model has a transmission loss coefficient more than the other types of the core at high frequencies.

A review on manufacture of polymeric foam cores for sandwich structures of complex shape in automotive applications

In this work, polymeric foam thermoforming, foam injection moulding, bead foaming and film foaming were reviewed in an effort to explore feasible processes to manufacture sandwich structures of complex geometry for automotive applications. Injection moulded foams generally suffer from high density, poor cell morphologies and unnecessary skin layers. Foamable films currently available are pressure-induced. In order for foamable films to produce foam, high uniformly-distributed pressure needs to be applied, which makes it difficult to manufacture foam parts of three-dimensional complex geometry with foamable films. The majority of commercial high-performance foam cores can be thermoformed. Ideally, thermoformed foam cores would have good mechanical properties if high-performance foam sheets are used. However, the mechanical properties of foams might be reduced during the process of thermoforming, especially around corners. Bead foaming offers a high level of freedom in foam geometry to be moulded, and inserts can be integrated into foam cores during the process of moulding. Moreover, foam cores with high density in high stressed areas and low density in low stressed areas can be manufactured with foam beads of different densities. However, due to nonhomogeneous degree of fusion and weak bonds and voids between beads, bead foams generally show mechanical properties lower than their block counterpart. Relatively speaking, thermoforming with high-performance foam sheets and moulding with high-performance foam beads hold great potentials for mass production of sandwich cores of complex geometry for automotive applications. However, further investigation on the mechanical properties of thermoformed foams and high-performance bead foams is still in need to confirm their suitability.

Characteristics of pre-strained polyisocyanurate foam: Deformation recovery and compressive mechanical behavior at cryogenic temperature

In this study, mechanical characteristics of pre-strained polyisocyanurate foam were investigated based on the uniaxial compression test. The compression test procedure was divided into two steps: pre-straining and the typical compression test for the recovered specimen. To evaluate the effect of pre-straining, four different compressive strains were considered, and the temperature and the strain rate dependencies on its mechanical characteristics were analyzed. Test results showed that the recovery ratio decreased substantially for 0.85 (ambient temperature) and 0.25 (cryogenic temperature), and polyisocyanurate foam pre-strained at cryogenic temperature revealed an earlier start of densification. Based on the deformation mechanism of the polymeric foam, the collapse of cells in the pre-strained polyisocyanurate foam was addressed to explain the distinguished features in compressive mechanical characteristics regarding test conditions.

Fabrication of Silica (SiO2) Foam from Rice Husk Ash (RHA): Effects of Solid Loadings

Silica (SiO2) foams have been widely applied in numerous fields, mainly filters and catalysts supports, due to their characteristics of high permeability, high porosity and specific surface area. In this study, foams of SiO2 from rice husk ash (RHA) was fabricated via polymeric sponge replication method. Polymeric foam initially was used as template and dipped into SiO2 slurry followed by drying and sintering to yield the replica of the original polymeric foam. Different solid loadings of SiO2 as-derived from RHA (20 to 35 wt. %) slurry and sintering temperature of 1150 °C were applied. Phase identification and chemical composition of the green and sintered foams were conducted using X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF). Morphological observations were performed using Scanning Electron Microscopy (SEM). Density and porosity of the SiO2 foams were characterized using Archimedes method. Compressive strengths of the foams were determined as per ASTM C773-88 (1999). XRD analyses confirmed that the SiO2 as derived from the RHA were of tridymite and cristobalite phases with as high as 93% purity, as confirmed by XRF analyses. The density of SiO2 foams fabricated was in the range of 0.614 to 0.989 g/cm3, whereas the porosity values was in the range of 70% to 82%%. Compressive strengths were found to increase from 0.05 to 0.30 MPa respectively, proportionate with the increased SiO2 solid loading. Excellent properties of the SiO2 foams definitely signifies that the polymeric replication method is indeed a promising technique for SiO2 as derived from RHA foam fabrication.

Effect of multi-layer prosthetic foam liner on the stresses at the stump–prosthetic interface

The prosthetic liner plays a significant role in the redistribution of the pressure between the stump and the socket, as it adding a cushioning layer between the stump and the socket which relieves pain and makes the prosthesis more comfortable. This study employed nonlinear finite element analyses to investigate the peak pressure and shear stress at stump–prosthetic interface in the case of multi-layer prosthetic foam liner, this liner having an inner polymeric foam layer Surrounded by another type of polymeric foam layer, we used three different types of foams in different order to define this liner (flexible polyurethane foam, polyurethane-shape memory polymer foam, and natural rubber latex foam). That’s allows comparing 6 deferent configuration of multi-layer prosthetic foam liner.