Bounding the size of square-free subgraphs of the hypercube

AbstractWe investigate the maximum size of a subset of the edges of the n-cube that does not contain a square, or 4-cycle. The size of such a subset is trivially at most 3/4 of the total number of edges, but the proportion was conjectured by Erdős to be asymptotically 1/2. Following a computer investigation of the 4-cube and the 5-cube, we improve the known upper bound from 0.62284… to 0.62256… in the limit

Glass fibre strength : a review with relation to composite recycling

The recovery and reuse of glass fibres from manufacturing waste and end-of-life composites in an environmentally-friendly, cost-effective manner is one of the most important challenges facing the thermosetting polymer composites industry. A number of processes for recycling fibres from such materials are available or under development. However, nearly all options deliver recycled glass fibres that are not cost-performance competitive due to the huge drop in strength of recycled glass fibre compared to its original state. A breakthrough in the regeneration of recycled glass fibre performance has the potential to totally transform the economics of recycling such composites. This paper reviews the available knowledge of the thermally-induced strength loss in glass fibres, discusses some of the phenomena that are potentially related and presents the status of research into processes to regenerate the strength and value of such weak recycled glass fibres

Categorical models for equivariant classifying spaces

Starting categorically, we give simple and precise models of equivariant classifying spaces. We need these models for work in progress in equivariant infinite loop space theory and equivariant algebraic K-theory, but the models are of independent interest in equivariant bundle theory and especially equivariant covering space theory.Comment: 29 pages. Revised version, to appear in AGT. Considerable changes of notation and organization and other changes aimed at making the paper more user friendl

Strength of thermally conditioned glass fibre degradation, retention and regeneration

Commercially manufactured E-glass fibres were heat-conditioned to mimic the effects of thermal recycling of glass fibre thermosetting composites. Degradation in the strength and surface functionality of heat-treated fibres was identified as a key barrier to reusing the fibres as valuable reinforcement in composite applications. A chemical approach has been developed to address these issues and this included two individual chemical treatments, namely chemical etching and post-silanisation. The effectiveness of the treatments was evaluated for both thermal degraded fibres and corresponding composites. Drastic reduction was observed in the properties of the composites with the heat-conditioned preforms indicating thermally degraded glass fibres have no value for second-life reinforcement without further fibre regeneration. However, significant regeneration to the above properties was successfully obtained through the approach developed in this work and the results strongly demonstrated the feasibility of regeneration of thermally degraded glass fibres for potential closed-loop recycling of thermosetting composites

Investigation of the effect of hot water and water vapour treatments on the strength of thermally conditioned E-glass fibres

The processing and reuse of end-of-life composite products in an environmentally friendly manner is an important challenge facing the industry. The development of an economically viable process for regenerating the properties of thermally recycled glass fibres would have significant technological, economic and environmental impacts. Thermal recycling processes for composites are relatively technologically advanced; however, they present a substantial challenge when considering their use for recycling of glass fibre reinforced materials. A combination of exposure to elevated temperatures in the region 450 – 600 °C and to mechanical damage has been shown to cause significant strength loss in glass fibres of up to 90 % of their original value. The recovered fibres are thus unsuitable for use as reinforcement in a second generation composite. Methods of strength recovery that may be applied to such recycled fibres are therefore of interest, particularly if these methods are relatively technologically straightforward. An investigation of possible strength recovery methods using hot water or water vapour was carried out on E-glass fibres. The methods were derived from similar studies on silica in which significant strengthening effects were presented alongside theoretical frameworks to explain the phenomenon [1–3]; a maximum threefold increase in strength following water vapour treatment at 250 °C was demonstrated on silica artificially weakened by abrasion

SAGE II Measurements of Stratospheric Aerosol Properties at Non-Volcanic Levels

Since 2000, stratospheric aerosol levels have been relatively stable and at the lowest levels observed in the historical record. Given the challenges of making satellite measurements of aerosol properties at these levels, we have performed a study of the sensitivity of the product to the major components of the processing algorithm used in the production of SAGE II aerosol extinction measurements and the retrieval process that produces the operational surface area density (SAD) product. We find that the aerosol extinction measurements, particularly at 1020 nm, remain robust and reliable at the observed aerosol levels. On the other hand, during background periods, the SAD operational product has an uncertainty of at least a factor of 2 during due to the lack of sensitivity to particles with radii less than 100 nm

Analysis of the microbond test using nonlinear fracture mechanics

Microbond tests composed of single fibre and matrix droplet are often used to determine the properties of fibre reinforced composites. Interfacial shear strength is quantified by the maximum pull-out force assuming a uniform stress distribution along the fibre. Here, nonlinear finite element analyses are performed to investigate the validity of this assumption.Comment: Submitted to 17th international conference on composite materials (ICCM-17

Investigation of the strength of thermally conditioned basalt and e-glass fibres

It is projected that the total global production of composite materials will significantly exceed 10 million tons by 2015 of which over 90% will contain glass fibre reinforcement. Traditionally most of this composite material would be directed to landfill at end of life. Thus, recycling composites has started to gain great importance due to environmental and commercial aspects. The development of an efficient process to enable cost-effective regeneration of the mechanical properties of fibre for recycling, could result in a huge decrease of landfill disposal as well as the attenuation in CO2 emissions. There are several processes available for recycling composites but the most technologically advanced is thermal recycling. However, during the recycling process glass fibres that are treated at temperatures in a range between 300 up to 600 °C exhibit a huge drop in strength and as a result sometimes are considered as not reusable or unsuitable for reprocessing [1]. Although basalt fibre has been available for some time, recent development in the processing and production of basalt has resulted in the availability of continuous basalt fibre in similar form to traditional glass fibre. It is often stated that basalt has better high temperature resistance compared to E-glass fibre [2,3]. If this were true then basalt fibre may show better prospects to survive an end-of-life composite thermal recycling process as a useful reinforcement. The present work investigates and compares the changes in the mechanical properties of basalt fibres and E-Glass fibres when heat-treated to between 300 – 600 °C. Since the fibre surface plays an important role in the retained strength of brittle fibres, the investigation used fibre with similar epoxy compatible sizings in order to maximise the quality of the comparison. Results of single fibre testing of tensile strength and modulus are presented and discussed

The ReCoVer Project : regeneration of thermally recycled glass fibre for cost-effective composite recycling

Global production of composite materials in 2015 will significantly exceed 10 million tons. Glass fibre reinforced composites account for more than 90 % of all the fibre-reinforced composites currently produced. Development of economically viable processes for recycling end-of-life glass fibre composites would have major economic and environmental impacts. This paper introduces and reviews the initial results of the ReCoVeR projects on enabling cost-effective performance regeneration of glass-fibres from thermal recycling of end-of-life automotive and wind energy composites. ReCoVeR technology targets treating glass fibre thermally reclaimed from GRP waste in order to regenerate a performance level which is equivalent to new fibres. Composite materials reinforced with ReCoVeR glass fibres can currently attain over 80 % of the reinforcement performance of composites produced with pristine glass fibres