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Feng L.,Huaihai Institute of Technology | Feng L.,Harbin Institute of Technology | Feng L.,Jiangsu Marine Resources Development Research Institute | Feng L.,The Composites Group | And 2 more authors.
Materials | Year: 2014

Carbon nanofiber (CNF), as one of the most important members of carbon fibers, has been investigated in both fundamental scientific research and practical applications. CNF composites are able to be applied as promising materials in many fields, such as electrical devices, electrode materials for batteries and supercapacitors and as sensors. In these applications, the electrical conductivity is always the first priority need to be considered. In fact, the electrical property of CNF composites largely counts on the dispersion and percolation status of CNFs in matrix materials. In this review, the electrical transport phenomenon of CNF composites is systematically summarized based on percolation theory. The effects of the aspect ratio, percolation backbone structure and fractal characteristics of CNFs and the non-universality of the percolation critical exponents on the electrical properties are systematically reviewed. Apart from the electrical property, the thermal conductivity and mechanical properties of CNF composites are briefly reviewed, as well. In addition, the preparation methods of CNFs, including catalytic chemical vapor deposition growth and electrospinning, and the preparation methods of CNF composites, including the melt mixing and solution process, are briefly introduced. Finally, their applications as sensors and electrode materials are described in this review article. © 2014 by the authors.

Erber A.,The Composites Group
JEC Composites Magazine | Year: 2016

In the future, lightweight design will become more important for ecological and sustainable mobility due to the shortage of resources, especially fossil fuels. Therefore, new design concepts and high-performance materials like carbon fibre-reinforced polymers [CFRP] are required. In addition to these ecological challenges, the economic constraints of global markets have to be taken into account as well. There is still a high demand on cost-efficient materials, especially when it comes to high-volume production, to enable profitable processes.

Polycrystalline layered structure SrBi4Ti4O15 (SBT) ferroelectric ceramics were synthesized via the solid-state reaction method. The high energy mechanochemical processing resulted in nanometer sized particles of SBT phase. The complete phase formation of layered structure SBT was observed after calcination at 800 °C. Highly dense SBT ceramics were obtained after sintering at 1200 °C in an oxygen atmosphere. The presence of oxygen during sintering reduced the porosity and dense microstructures were obtained. The density was found to be >96% of theoretical density. The phase formations in steps from milled to sintered were observed from XRD pattern and the SEM micrograph exhibited platelet-like morphology of SBT. TEM was done to estimate the particle size of the powders. Electrical properties of SBT ceramics viz. dielectric, piezoelectric charge coefficient and ferroelectric hysteresis measurements were made. Resonance measurements were made in order to determine the electromechanical coefficient and elastic compliances. The results of all of the aforementioned are presented in this paper. © 2014 Elsevier Ltd and Techna Group S.r.l.

Monsalve-Cano J.F.,The Composites Group | Aristizabal-Ochoa J.D.,National University of Colombia
Engineering Structures | Year: 2016

A complete beam-column classification and the corresponding characteristic equations for the stability and undamped natural frequencies of 3D orthotropic Timoshenko beam-columns with singly symmetric closed section and with elastic end connections subjected to an eccentric end axial load are presented and derived using three different approaches. The first two approaches are those by Engesser and Haringx that include the shear component of the applied axial force proportional to the slope (du/dx and dv/dx in planes xz and yz, respectively) and to the angle of rotation of the cross-section (θx and θy in planes yz and xz, respectively) along the span of the member, respectively. The third approach is a simplified formulation based on the classical Euler theory that includes the effects of shear deformations but neglects the induced shear component of the applied axial force along the member. The proposed methods and characteristic equations are capable of determining the critical axial loads and undamped natural frequencies of beam-columns with elastic end connections. Four comprehensive examples are included that show the effectiveness and simplicity of the proposed method and the results obtained are compared with experimental results available in the technical literature. It is shown that: (1) the natural frequencies and critical axial loads of beam-columns increase as the shear stiffness GAs, the degrees of fixity and lateral bracings at the ends of the member increase; (2) the natural frequencies calculated using the three approaches are identical to each other when the applied axial load is zero; (3) the critical axial load in compression using the Engesser approach is lower than the one obtained using the Haringx approach; (4) the critical axial loads in compression are highly affected by the degree of flexural fixity at the supports, but those in tension are not affected much; and (5) the Haringx approach is the only one among the three approaches capable of capturing the phenomena of tension buckling observed in seismic isolators. © 2016 Elsevier Ltd.

Wang B.J.,The Composites Group | Chui Y.H.,University of New Brunswick
Wood Science and Technology | Year: 2012

The purpose of this study was to develop a cost-effective method to manufacture high-performance laminated veneer lumber (LVL) from mountain pine beetle (MPB)-affected veneers through partial resin impregnation and optimum board layup. Dry MPB-affected veneer sheets were segregated into two stress grades based on dynamic modulus of elasticity (MOE). A new phenol formaldehyde resin with a 30% solids content was formulated for resin impregnation. To reduce resin consumption, only veneer sheets used as outer layers were dipped in the resin for 5 min and then dried to manufacture 13-ply LVL. The bending properties, shear strength and dimensional stability of these LVL billets were examined and compared to those from the controls made from entirely untreated veneers. The results demonstrated that high-grade (E1) MPB-affected veneers had lower resin solids uptake than low-grade (E2) counterparts based on a 5 min dipping. Compared with the controls, the LVL billets made from resin-impregnated veneers for outer layers yielded increased surface hardness, significantly improved dimensional stability, shear strength and modulus of rupture on both edgewise and flatwise as well as better appearance with no cosmetic concerns. However, the improvement in LVL bending MOE was dependent on initial veneer stress grade. For high-grade (or density) E1 veneers, the use of impregnated veneers resulted in insignificant improvement in bending MOE. The optimum product layup was to place one ply of impregnated E1 grade veneer each for product face and back. By contrast, for lowgrade (or density) E2 veneers, the use of impregnated veneers yielded a significantly higher flatwise bending MOE compared to the controls. The recommended product layup was the placement of two plies of impregnated E2 grade veneer sheets each for product face and back. © Springer-Verlag 2012.

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