Papers by Keyword: Sandwich

Abstract: In this investigation, the mechanical behavior of sandwich hollow cylinders under internal pressure is carried out numerically. Functionally Graded (FG) foam core sandwich hollow cylinders are fabricated by employing filament winding technique with [±55] carbon fiber/epoxy as skins with the FG foam core made using centrifugal casting technique of polyurethane foam with epoxy resin. A finite element (FE) model is developed employing a FE commercial code to determine the stresses and deformations. Numerical analysis is performed to find the effect of one particular functional grading on the deformation and stresses. The results are compared with similar tubes using uniform PU foam core. The results show that grading the foam core affects the displacements and stresses in a significant way. The FG foam sandwich core tube possesses a lower displacement magnitude and higher maximum stresses taking into account the mass of the two types of pipes and rigidity compared to uniform PU foam core under internal pressure of 10 MPa.

Abstract: This report reviews biomimetic studies performed in China on the beetle forewing, noting that Chinese scholars studying bionics have substantially advanced various branches of biomimetic research in beetles. The report also proposes the development of branches of bionic research and establishes the foundation for corresponding experiments and theories. Then, using the A. dichotoma forewing as a an example, the cross-sectional shape, orientation of the laminated fiber layers, structure of the trabeculae, and respective mechanical properties of the forewing, as well as their biological significance, are reviewed. 1) The forewing has a lightweight border frame structure and an optimal design of variable cross-sections suitable for different positions, which achieves the specific second moment of inertia required for flight. 2) Due to the non-equiangular, laminated structure of the forewing, there are two types of tensile fracture morphologies: fiber breakage and residual bridging. This study demonstrates the anisotropy and the effectiveness of the forewings tensile strength by analyzing the orientation direction of the fibers. 3) The trabecular structure can be used to efficiently improve the peel resistance of the laminated composites. Based on the above points, possible directions for future work are also indicated in this paper.

Abstract: This paper describes the result of an experimental investigation on the impact damage on woven natural silk/epoxy composite face-sheet and PVC foam core sandwich panel. The test panels were prepared by hand-lay-up method. The low-velocity impact response of the composites sandwich panels is studied at three energy levels of 32, 48, and 64 joule respectively. The focus is to investigate damage initiation, damage propagation, and mechanisms of failure. It was observed that absorption energy capability decreased as impact energy increased. There was deflection on each impact load configuration at some point but their margin was insignificant. Physical examination of the specimen show that damage areas increased with increase in impact load. The novelty of this research is the use of woven natural silk fabric as a reinforcement fibre.

Abstract: The structures, stabilities, and bonding features of neutral M(η⁵-P₅)₂ (M = Fe, Ru, and Os) and cationic M(η⁵-P₅)+ have been investigated using density functional theory (DFT) (hybrid B3LYP and pure BP86 methods). The eclipsed (D5h) structure has been predicted to be the global minimum for this triad bis(pentaphospholyl) metallocenes, and the staggered (D5d) structure to be the rotational transition state. The distances between the metal and cyclo-P5 center in bis(pentaphospholyl) metallocenes are longer than in the corresponding M(η⁵-P₅)+ by 0.28-0.38 Å. The M(η⁵-P₅)+ complexes may be tighter binding with the shorter metal-ring distances, the possible reason is that there being stronger metal-ring π interactions in M(η⁵-P₅)+ than in M(η⁵-P₅)₂, even though latter satisfies the 18-electron rule. The electron densities are found to accumulate at the metal centers, this novel situation may have an impact on the mechanism of some potential catalysis reactions.

Abstract: In recent decades, a new magnetic sensor based on magnetoresistance effect is highly researched and developed intensively. GMR material has great potential as next generation magnetic field sensing devices. It has also good magnetic and electric properties, and high potential to be developed into various applications of electronic devices such as: magnetic field sensor, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory. GMR material can be developed to be solid state magnetic sensors that are widely used in low field magnetic sensing applications. A solid state magnetic sensor can directly convert magnetic field into resistance, which can be easily detected by applying a sense current or voltage. Generally, there are many sensors for measuring the low magnetic field, such as: fluxgate sensor, Hall sensor, induction coil, GMR sensor, and SQUID sensor. Compared to other low magnetic field sensing techniques, solid state sensors have demonstrated many advantages, such as: small size (<0.1mm²), low power, high sensitivity (~0.1Oe) and good compatibility with CMOS technology. The thin film of GMR is usually prepared using: sputtering, electro deposition or molecular beam epitaxy (MBE) techniques. But so far, not many researchers reported the manufacture of thin film of GMR by dc-Opposed Target Magnetron Sputtering (dc-OTMS). In this paper, we inform the development of GMR thin film with sandwich and spin valve structures using dc-OTMS method. We have also developed organic GMR with Alq3 as a spacer layer.

Abstract: Dynamic response and damage mechanism of two-core sandwich panels with foam and honeycomb cores and glass fiber/epoxy composite sheets under low-velocity transverse impact are investigated. The emphasis is focused on the contact force response and crash mechanism of the two-core sandwich panels. Effects of configurations, impact energy levels and types of the cores on the dynamic response are investigated. A modified drop-test experiment is carried out to obtain contact force history of the two-core sandwich structures under different impact energies. The experimental results show that the 10:10 configurations for both honeycomb and foam core sandwich structures under lower impact energy absorb more impact energy than the other two structures. However, under higher impact energy, the honeycomb core sandwich structures of 15:5 configuration absorbs a little more impact energy than the other two, while for the foam core sandwich structures the 5:15 configuration shows a little better impact resistance. Results also show that when impact energy is low foam core sandwich structures do better in absorbing impact energy than the honeycomb ones.

Abstract: A sandwich structure is obtained from two skins or soles, with good mechanical characteristics, bonded to a core made of a lightweight material of low resistance. Glued to a core made of a lightweight material of low resistance. The strength and modulus of elasticity of the skin condition the bending behavior of a sandwich. Bending, the skins of the sandwich are solicited in traction and in compression, while the core is subjected to shear. Our study focuses on the experimental characterization under flexural load of new composite sandwich combined. The sandwich proposed constituted of two skins armed by metal grids impregnated with epoxy matrix type STR and souls composed of hybrid corrugated cardboard reinforced by fabric. Several configurations of souls made from cardboard cellulosic and fabrics were taken into account. An experimental and numerical investigation is conducted to analyze the behavior of these structures. The results show that the failure mode is strongly influenced by the stacking sequence considered.

Abstract: Heat conductive materials, which are widely used in the fields like electronic information, electrical engineering and aerospace, are required high thermal conductivity, excellent electrical insulation, corrosive resistance, chemical stability and so on. In this paper, steel/unsaturated polyester (UP) sandwich composite is designed to use as heat conductive material. The capacity of composite thermal transmission with steel wire arrangements in longitudinal and transverse directions are analyzed by software ANSYS. Finally, equivalent thermal conductivity of composite is calculated. The results show that capacity of composite’s thermal transmission increases quickly with increasing number of steel wire in the longitudinal direction，but it increases slowly with the increasing number of steel wire in the transverse direction.

Abstract: In this work, the hybrid fabrics of carbon and quartz fibers as filters were adopted in PMI core sandwich structures for low-observable radomes. The advantages of fabric composite frequency selective surfaces (FCFSSs) are easily fabricated by braiding and shaped into curved surfaces. This paper mainly studied the electromagnetic (EM) transmission characteristics of the low-observable radome wall with composite FSS by 3-dimensional electromagnetic analysis software. First of all, the accuracy of the simulation model composed of up and down composite face sheets, a layer of composite FSS and PMI core was validated by comparing with experimental results. Then, the studies on electromagnetic transmission characteristics of the sandwich structure with composite FSS and the sensitivity analysis about the thickness and permittivity of face sheets and PMI core were carried out. The results show that the sandwich structure with single layer composite FSS can realize the function of frequency selection, limit the reflection at the resonance frequency and decrease the sensitivity of EM transmission loss about the thickness of sandwich structures.

Abstract: FMR and SWR spectra of exchange-coupled structures NiFe/Cu/NiFe, NiFe/Ag/NiFe and NiFe/DyCo/NiFe have been investigated. We revealed that the optical satellites of the exchange spin-wave modes are characterized not by the standard Kittle-dependence but by their own resonance field dependence on the mode number: H_r^opt(n) ~ n^5/2.