High performance fibre-reinforced cementitious composite (CARDIFRC) - Performance and application to retrofitting

This paper describes first some of the recent performance checks on the high performance fibre-reinforced cementitious composite CARDIFRC and then its application to the retrofitting of damaged concrete beams. It is shown that an even distribution of fibres throughout the bulk of the material is crucial to its excellent fatigue performance and to the reduction in the autogenous shrinkage strains. The distribution of fibres in beams, cylinders and strips is examined using computerised tomography imaging and traditional image analysis. Thin strips of CARDIFRC are used to retrofit damaged concrete beams which are subjected to thermal cycling. It is shown that neither the load carrying capacity of the retrofitted beams nor the bond between retrofit strips and concrete deteriorates with thermal cycling. The load carrying capacity of retrofitted beams is predicted with a model based on fracture mechanics, and the predictions are shown to be in good agreement with test data. © 2006 Elsevier Ltd. All rights reserved.

Corrugated all-composite sandwich structures. Part 2: Failure mechanisms and experimental programme

A novel corrugated composite core, referred to as a hierarchical corrugation, has been developed and tested experimentally. Hierarchical corrugations exhibit a range of different failure modes depending on the geometrical properties and the material properties of the structures. In order to understand the different failure modes the analytical strength model, developed in part 1 of this paper, was used to make collapse mechanism maps for the different corrugation configurations. If designed correctly, the hierarchical structures can have more than 7 times higher weight specific strength compared to its monolithic counter part. The difference in strength arises mainly from the increase in buckling resistance of the sandwich core members compared to the monolithic version. The highest difference in strength is seen for core configurations with low overall density. As the density of the core increases, the monolithic core members get stockier and more resistant to buckling and thus the benefits of the hierarchical structure reduces. © 2008 Elsevier Ltd. All rights reserved.

Collapse of a composite beam made from ultra high molecular-weight polyethylene fibres

Hot-pressed laminates with a [0/90]48 lay-up, consisting of 83% by volume of ultra high molecular-weight polyethylene (UHMWPE) fibres, and 17% by volume of polyurethane (PU) matrix, were cut into cantilever beams and subjected to transverse end-loading. The collapse mechanisms were observed both visually and by X-ray scans. Short beams deform elastically and collapse plastically in longitudinal shear, with a shear strength comparable to that observed in double notch, interlaminar shear tests. In contrast, long cantilever beams deform in bending and collapse via a plastic hinge at the built-in end of the beam. The plastic hinge is formed by two wedge-shaped microbuckle zones that grow in size and in intensity with increasing hinge rotation. This new mode of microbuckling under macroscopic bending involves both elastic bending and shearing of the plies, and plastic shear of the interface between each ply. The double-wedge pattern contrasts with the more usual parallel-sided plastic microbuckle that occurs in uniaxial compression. Finite element simulations and analytical models give additional insight into the dominant material and geometric parameters that dictate the collapse response of the UHMWPE composite beam in bending. Detailed comparisons between the observed and predicted collapse responses are used in order to construct a constitutive model for laminated UHMWPE composites. © 2013 Elsevier Ltd.

Viability and performance of demountable composite connectors

Material production, and associated carbon emissions, could be reduced by reusing products instead of landfilling or recycling them. Steel beams are well suited to reuse, but are difficult to reuse when connected compositely to concrete slabs using welded studs. A demountable connection would allow composite performance but also permit reuse of both components at end-of-life. Three composite beams, of 2 m, 10 m and 5 m length, are constructed using M20 bolts as demountable shear connectors. The beams are tested in three-, six- and four-point bending, respectively. The former two are loaded to service, unloaded, demounted and reassembled; all three are tested to failure. The results show that all three have higher strengths than predicted using Eurocode 4. The longer specimens have performance similar to previously published comparable welded-connector composite beam results. This suggests that demountable composite beams can be safely used and practically reused, thus reducing carbon emissions. © 2013 Elsevier B.V. All rights reserved.

Photoelectrochemical behavior of a novel composite In0.15Ga0.85As/GaAs vertical bar GaAs/Al0.3Ga0.7As multiple quantum well electrode

A novel composite InxGa1-xAs/GaAs/GaAs/AlxGa1-xAs multiple quantum well material with different well widths was studied as a new kind of photoelectrode in a photoelectrochemical cell. The photocurrent spectrum and photocurrent-electrode potential curve were measured in ferrocene nonaqueous solution. Pronounced quantization effects and strong exciton absorption were observed in the photocurrent spectrum. The effects of surface states and interfacial states on the photocurrent-electrode potential curve are discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

Nafion/PTFE composite membranes for fuel cell applications

Porous polytetrafluoroethylene (PTFE) membranes were used as support material for Nafion((R))/PTFE composite membranes. The composite membranes were synthesized by impregnating porous PTFE membranes with a self-made Nafion solution. The resulting composite membranes were mechanically durable and quite thin relative to traditional perfluorosulfonated ionomer membranes (PFSI); we expect the composite membranes to be of low resistance and cost. In this study, we used three kinds of porous PTFE films to prepare Nafion/PTFE composite membranes of different thickness. Scanning electron micrographs and oxygen permeabilities showed that Nafion resin is distributed uniformly in the composite membrane and completely plug the micropores, there is a continuous thin Nation film present on the PTFE surface. The variation in water content of the composite and Nafion 115 membranes with temperature was determined. At the same temperature, water content of the composite membranes was smaller than that of the Nafion 115. In both dry and wet conditions, maximum strength and break strength of C-325(#) and C-345(#) were larger than those of Nafion 112 due to the reinforcing effect of the porous PTFE films. And the PEMFC performances and the lifetime of the composite membranes were also tested on the self-made apparatus. Results showed that the bigger the porosity of the substrate PTFE films, the better the fuel cell performance; the fuel cell performances of the thin composite membranes were superior to that of Nation 115 membrane; and after 180 h stability test at 500 mA/cm(2), the cell voltage showed no obvious drop. (C) 2002 Published by Elsevier Science B.V.

The research of rheology and thermodynamics of organic-inorganic hybrid membrane during the membrane formation

To clarify the mechanism of organic-inorganic hybrid membrane formation by phase-inversion method, the thermodynamical and theological properties of PSF/TiO2 casting solution were investigated by the viscosity measurement and the triangle phase diagram, respectively. TiO2 introduction decreased the non-solvent tolerance of casting solution with non-solvent 20% ethanol aqueous solution, which caused thermodynamic enhancement of phase separation, and also resulted in the change of theological properties from Newtonian fluid to non-Newtonian fluid and the viscosity increase of casting solution, which induced rheological hindrance in demixing process

Sulfonated poly(ether ether ketone)/clay-SO3H hybrid proton exchange membranes for direct methanol fuel cells Journal of Power Sources

A new type of sulfonated clay (clay-SO3H) was prepared by the ion exchange method with the sulfanilic acid as the surfactant agent. The grafted amount of sulfanilic acid in clay-SO3H was 51.8 mequiv. (100 g)(-1), which was measured by thermogravimetric analysis (TGA). Sulfonated poly(ether ether ketone) (SPEEK)/clay-SO3H hybrid membranes which composed of SPEEK and different weight contents of clay-SO3H, were prepared by a solution casting and evaporation method. For comparison, the SPEEK/clay hybrid membranes were produced with the same method.

Sulfonated poly(ether ether ketone)/aminopropyltriethoxysilane/phosphotungstic acid hybrid membranes with non-covalent bond: Characterization, thermal stability, and proton conductivity

Sulfonated poly(ether ether ketone) (SPEEK) and aminopropyltriethoxysilane (KH550) hybrid membranes doped with different weight ratio of phosphotungstic acid (PWA) were prepared by the casting procedure, as well as PWA as a catalyst for sol-gel process of KH550. The chemical structures of hybrid membranes were characterized by energy dispersive X-ray spectrometry (EDX) and Fourier transform infrared spectroscopy (FTIR). The morphology of hybrid membranes was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results had proved the uniform and homogeneous distribution of KH550 and PWA in these hybrid membranes.

Highly ordered mesoporous carbons as electrode material for the construction of electrochemical dehydrogenase- and oxidase-based biosensors

In this work, the excel lent catalytic activity of highly ordered mesoporous carbons (OMCs) to the electrooxidation of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H2O2) was described for the construction of electrochemical alcohol dehydrogenase (ADH) and glucose oxidase (GOD)-based biosensors.

Fabrication, thermal stability and mechanical properties of novel composite hardmetals obtained by solid-state reaction and hot-pressing sintering

A novel cemented carbides (W0.7Al0.3)C-0.65-Co with different cobalt contents were prepared by solid-state reaction and hot-pressing technique. Hot-pressing technique as a novel technique was performed to fabricate the bulk bodies of the hard alloys. The novel cemented carbides have superior mechanical properties compared with WC-Co. The density, operate cost of the novel material were lower than WC-Co system. The novel materials were easy to process nanoscale sintering and get the rounded particles in the bulk materials. There is almost no eta-phase in the (W0.7Al0.3)C-0.65-Co cemented carbides system although the carbon deficient get the astonished 35% value.

Nanostructured bulk novel hard material with "rounded" grains obtained by nanocrystalline "rounded" (W0.5Al0.5)C powders

A novel nano-scaled bulk hard material (W0.5Al0.5)C-Co with "rounded" grains was prepared by nanocrystalline "rounded" (W0.5Al0.5)C powders with "rounded" particle shape in this study. The nano-scaled "rounded" particles do not contain sharp edges, which form local tensile stress concentrations on loading of the composite, thus leading to improved toughness and reduced sensitivity to crack. Nanocrystalline (W0.5Al0.5)C powders with "rounded" particle shape were used as starting materials. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to characterize the samples.

Fabrication, thermal stability and mechanical properties of novel (W0.5Al0.5)C-0.8-Co composite prepared by mechanical alloying and hot-pressing sintering

A novel cemented carbides (W0.5Al0.5)C-0.8-Co with different cobalt contents were prepared by mechanical alloying and hot-pressing technique. Hot-pressing technique as a common technique was performed to fabricate the bulk bodies of the hard alloys. The novel cemented carbides have superior mechanical properties compared to WC-Co. The density, operating cost of the novel material were much lower than WC-Co. There is almost no eta-phase in the (W0.5Al0.5)C-0.8-Co cemented carbides system although the carbon deficient get the value of 20%, and successfully got the nanostructured rounded (W0.5Al0.5)C-0.8 particles.

A novel (W-Al)-C-Co composite cemented carbide prepared by mechanical alloying and hot-pressing sintering

Novel cemented carbides (W0.4Al0.6)C-0.5-Co With different cobalt contents were prepared by mechanical alloying and hot-pressing technique. Hot-pressing technique as a common technique was performed to fabricate the bulk bodies of the hard alloys. The novel cemented carbides have good mechanical properties compared with WC-Co. The density and operation cost of the novel material were much lower than the WC-Co system. It was easy to process submicroscale sintering with the novel materials and obtain the rounded particles in the bulk materials. There is almost no eta-phase in the (W0.4Al0.6)C-0.5-CO cemented carbides system although the carbon deficient obtains the astonishing value of 50%.