Showing papers by "Peter Davies published in 2008"

Effect of recycling on mechanical behaviour of biocompostable flax/poly(L-lactide) composites

Abstract: The biocompostability of natural fibre-reinforced biopolymers, also known as biocomposites, makes them attractive alternative to glass fibre-reinforced petrochemical polymers. The aim of this work is to study the capacity of flax/PLLA (poly(l-lactide)) biocomposite (20% and 30% fibres by weight) to be recycled. Mechanical properties were evaluated initially, and shown to be similar to those of glass/PP and superior to hemp/PP and sisal/PP composites. Then after repeated injection cycles tensile properties were shown to be conserved until the third cycle. Matrix degradation and fibre aspect ratio were followed using molecular weight measurements, thermal and rheological analyses, image analysis of sections and SEM fractography. These techniques revealed a lower molecular weight, lowering of glass transition temperature, reduction of fibre length, and separation of fibre bundles with injection cycles. Nevertheless, the property retention after three cycles under extreme recycling conditions (100% recycling with no added virgin polymer) indicate the promising recyclability of these materials.

Primary Production in Tropical Streams and Rivers

Abstract: Net primary production is a fundamental ecological process that reflects the amount of carbon synthesized within an ecosystem, which is ultimately available to consumers. Although current ecosystem models of streams and rivers have placed variable emphasis on the importance of instream primary production to aquatic food webs, recent research indicates that aquatic algae are a significant contributor to food webs in tropical rivers and streams. This is in contrast to many well-studied north temperate latitude streams in deciduous forest ecosystems, which are thought to depend mainly upon terrestrial leaf litter and detritus-based food webs. A review of available literature suggests that rates of in-stream primary production in tropical regions are typically at least an order of magnitude greater than comparable temperate systems. Although nutrient status can significantly modify rates, the ultimate driver of aquatic primary production is light availability. Rates of benthic gross primary productivity in tropical streams range from 100 to 200mgCm-2 d-1 under shaded conditions to much higher values associated with open canopies. Light inputs to the channel can be controlled by stream orientation, with east-west channels receiving much more light compared to those orientated north-south. Rates of production for large tropical rivers are similar to those for streams, although factors that regulate production are different and hence they respond differently to human impact. Values for rivers range from 10 to 200mgCm-2 d-1 to more than 1000mgCm-2 d-1. Production is often limited by turbidity, which tends to be at a maximum after high flow events. In polluted tropical rivers, productivity responds to nutrient enrichment and can attain rates of 6000mgCm-2 d-1. The highest rates of production in tropical river systems typically occur in floodplains subject to seasonal inundation, where aquatic vascular plants dominate total productivity. These macrophytes (herbaceous vascular plants that can be primarily terrestrial or aquatic) can proliferate in situ or be transported from upstream. Rooted aquatic plants with emergent or floating leaves respond to the rising water level, sometimes elongating their stems at a rate of 20cmd-1, and many terrestrial plants tolerate prolonged submergence. These ecosystems can attain very high rates of primary production that rival those of intensively managed agro-ecosystems. Floodplain forest can also be a productive component of these ecosystems. Both attached algae (periphyton) and phytoplankton contribute substantially to algal production in floodplain waters. Floodplains are important for fodder and for nursery habitat for fish, which re-invade main channels when floods recede. Tropical rivers may flow into coastal mangrove ecosystems, where rates of productivity are variable and often dependent of methodologies of measurement. Rates of mangrove production range from 1300mgCm-2 d-1 in the T鲭inos Lagoon, Mexico to 1900-2700mgCm-2 d-1 in the Fly River estuary (Papua New Guinea). However, rates of phytoplankton growth within mangrove forests are low, probably controlled by shading and turbidity, and are comparable to those of tropical streams. As pressures for water resource development intensify, tropical fluvial ecosystems are coming under increasing pressure. It is important to understand how these ecosystems function and to ensure problems of developing water resources in temperate regions are not repeated in the tropics.

Transverse properties of carbon fibres by nano-indentation and micro-mechanics

Abstract: In this study the transverse modulus of three high modulus (M40, M46 and K63712) carbon fibres has first been measured directly by nano-indentation measurements. Transverse tensile tests on unidirectional epoxy composites were then performed, and the comparison was made between transverse fibre properties from indentation and those needed to obtain the measured transverse composite modulus using micromechanics expressions. The latter tended to underestimate values from indentation, by up to 36%, and reasons for this are discussed. Values of transverse fibre modulus determined by both methods decrease as longitudinal fibre modulus increases.

‘Learning Study’ as a model of collaborative practice in initial teacher education

Abstract: Learning Study provides a distinctive model for collaborative practice in teacher development. It combines the intensive ‘plan–teach–review’ model developed by the Japanese ‘Lesson Study’ model with a focus on the outcomes of learning using variation theory. We present an argument for expecting this approach to help trainees in initial teacher education to progress to more sophisticated conceptions of teaching. We also present findings from the implementation of Learning Study in the initial teacher education programme at one UK university over a period of two years. We conclude that it is practicable and beneficial to use Learning Study in this context and that the representational device of a ‘Learning Outcome Circle’ helps trainees to understand the implications of variation theory and opens up their vision of teaching.

Hydrological change escalates risk of ecosystem stress in Australia's threatened biodiversity hotspot

Abstract: The southwestern corner of the Australian continent has been identified as a global “biodiversity hotspot”, defined as an area where “exceptional concentrations of endemic species are undergoing exceptional loss of habitat”. In this paper we reconsider the reasons for this conservation priority. We briefly review significant characteristics of the flora and fauna, and the way threatening processes are escalating ecosystem stress to these conservation values. Our specific aim is to examine the ecological consequences of hydrological change, including emergent issues such as climate change, and focus on the coastal plains in higher rainfall zones where the majority of the Western Australian population resides. Here we argue that human-driven and/or climaticallydriven hydrological change deserve greater attention, since they: i) directly escalate the risk of extinction for some components of the biota, or ii) are underlying and/or contributing factors in the manifestation of other threats to the biota, and may complicate or exacerbate some of those threats (such as fire, Phytophthora and the spread of weeds). This paper briefly outlines the challenges to the region’s biodiversity posed by hydrological change. We suggest a societal adoption of approaches based on water literacy will be necessary to avoid irreversible changes associated with a continued reliance on water resource developments and other energy/water intensive industrial activities.

Embedding threshold concepts: from theory to pedagogical principles to learning activities

Abstract: Book Description: Threshold Concepts within the Disciplines brings together leading writers from various disciplines and national contexts in an important and readable volume for all those concerned with teaching and learning in higher education. The foundational principle of threshold concepts is that there are, in each discipline, ‘conceptual gateways’ or ‘portals’ that must be negotiated to arrive at important new understandings. In crossing the portal, transformation occurs, both in knowledge and subjectivity. Such transformation involves troublesome knowledge, a key concern for contributors to this book, who identify threshold concepts in their own fields and suggest how to deal with them.Part One extends and enhances the threshold concept framework, containing chapters that articulate its qualities, its links to other social theories of learning and other traditions in educational research.Part Two encompasses the disciplinary heart of the book with contributions from a diversity of areas including computing, engineering, biology, design, modern languages, education and economics. In the many empirical case studies educators show how they have used the threshold concept framework to inform and evaluate their teaching contexts. Other chapters emphasise the equally important ‘being and becoming’ dimension of learning. Part Three suggests pedagogic directions for those at the centre of the education project with contributions focusing on the socialisation of academics and their continuing quest to be effective teachers.The book will be of interest to disciplinary teachers, educational researchers and educational developers. It also is of relevance to issues in quality assurance and professional accreditation.

Socioeconomic background, gender and subject choice in secondary schooling

Abstract: Background: The desirable extent of curriculum choice to be offered to students remains a central policy question in England. Previous studies of the impact of the introduction of a common curriculum for 14-16 year olds in 1988 have suggested that some gender differences were narrowed as a result. These studies examined subject choice either in terms of students' ex ante preferences in advance of enrolling for subjects or in terms of ex post aggregate data on examination entries. There is some conflict between the evidence provided by these two sources. One possible reason for this conflict could be that existing ex post evidence does not examine the interaction between student characteristics or the effect of school-level variables. Purpose: This study aims to identify effects of social class and gender on subject choice for 14-16 year olds in England over and above effects that are attributable to students' ability. Effects that operate at school level are separated from those that act at the level of the individual. Sample: The sample is drawn from the schools that participated in the Yellis system for providing analysis of the examination results achieved by 16-year-old students. The sample of 664 schools and 112,412 16-year-old students was selected by including all schools who had participated in the Yellis project for at least five years during the period 1994-2002. All of the sample schools were participating in the scheme in 1998, the year for which a cross-sectional analysis is presented in this paper. Design and methods: Statistical (probit) models are used to investigate effects of student and school characteristics on the probability of a student entering for examination in each of six option subjects: Business Studies, French, Geography, German, History and Home Economics. The models take account of levels in the data and identify interactions between the student characteristics. Results: After taking prior ability into account socioeconomic background effects, taken together, exert a stronger effect than gender on the likelihood of entering for examination in history. Socioeconomic background effects are also stronger in the case of business studies. The effect of socioeconomic background is stronger for females than for males. There are also strong social effects operating through the characteristics of the cohort of students at the school. The proportion of students eligible for free school meals has a significant effect on the probability of entering for examination in geography, German or History. Conclusions: In so far as the results from this study can be compared with previous research they support the conclusions of previous ex post studies rather than ex ante studies in terms of gender preferences in subject choice. This might suggest some difficulty in generalising from the kind of ex ante data gathered previously. The evidence of the effect of socioeconomic background at individual and school level suggests that current policy aiming to increase subject choice within and between schools will deepen differences between the subjects studied by students from different socioeconomic backgrounds.

Characterization of Polyester Mooring Lines

Abstract: Fibre ropes are extensively used in marine applications. One critical area of interest is their application as mooring lines for floating offshore platforms, for which primarily polyester is now employed in various regions (offshore Brazil - now for 10 years, West Africa, Gulf of Mexico). Evaluating the response of the system requires a description of the load-elongation properties of the rope. A practical model involving two sets of stiffness data is currently used, and procedures for their measurement are available. This paper presents an overview of this model, then focuses on recent work on the quasi-static stiffness of polyester ropes. This is addressing the variations of the mean tension in the lines, at a very slow rate, under changing weather conditions. Extensive tests were performed, principally on polyester sub-rope samples. Some tests were also performed on a full size 800-ton MBS rope. Besides standard tests, specific tests were performed over an extended range of loading, to cover the situations that may be found in a wide range of systems and design conditions. The factors (measurement accuracy, test conditions, etc...) affecting the values are discussed along with the presentation of tests and results. Results are interpreted to provide practical data for mooring analysis, in the form of a quasi-static load-elongation characteristic. These results also give a better insight into the visco-elasto-plastic response of polyester fibre ropes. For the dynamic stiffness of polyester ropes, an overview of recent and earlier test data is presented. The dependence of dynamic stiffness on testing parameters is discussed, highlighting mean load as the principal parameter under real stochastic loading, and confirming the current practice for modelling dynamic stiffness in design.Copyright © 2008 by ASME

Deepwater moorings with high stiffness polyester and PEN fiber ropes

Abstract: The benefits of synthetic fiber ropes for deepwater station keeping are now well established and their use is expanding. Nearly all current applications use a single grade of polyester fiber, but for different supports and environments this may not be the optimal choice. Properties of polyester fibers can be modified by adjusting processing parameters and there are other fibers available such as PEN, which offer higher stiffness. This study examines the benefits of intermediate stiffness fibres, stiffer than standard polyester but less stiff than the high performance fibers. The results indicate that there is scope for improving mooring line performance and reducing line weight by careful evaluation of material options. Introduction Polyester fiber ropes are finding increasing applications in offshore mooring systems as production moves to deeper water. Following successful installations offshore Brazil in the late 1990’s [Pellegrin 1999] the first Gulf of Mexico mooring was for the Mad Dog spar [Bugg 2004] in 2004, which employed 1200 tons of polyester down to 1670 meters water depth. The recently installed Independence Hub platform also used polyester moorings, in 2440 meters water depth [Paganie 2007]. Different rope constructions have been used but these mooring lines were all composed of similar high tenacity polyester fibers. The Red Hawk spar [Haslum 2005], also installed in 2004, used a modified polyester fiber with a higher initial stiffness to facilitate installation, and this raised the question of whether a higher fiber stiffness might be beneficial for other supports and allow rope diameter to be reduced. Previous work within the French Mooring line project [Davies et al 2002] studied high performance fibres such as aramids and HMPE and concluded that their very high stiffness, while allowing much smaller rope diameter and weight, did not improve durability as it would result in high fatigue loading of the metallic components of the mooring line. However, there is an intermediate stiffness region, shown in Figure 1, situated between the currently used fibres, with initial tensile modulus around 10-15 GPa, and the high performance fibers (> 60 GPa) which has not been explored previously for deepwater mooring applications.

Marine Composites Based on Low Styrene Content Resins. Influence of Lamination Procedure and Peel Plies on Interlaminar Resistance

Abstract: Delays between lamination of structures and secondary bonding are common in boatbuilding. This paper presents results from an experimental study of the influence of manufacturing procedure on the bond strength of unidirectional glass fibre reinforced polyester composites. Continuously laminated panels are taken as the reference and compared with panels overlaminated after delays of one week with and without peel ply protection. A standard polyester and low styrene DCPD formulation were tested. ILSS testing is shown not to be sensitive to the procedure but crack propagation tests show very large differences in mode I fracture energy. A small drop in fracture energy is measured for a delay of one week between lamination of the first and second halves of the specimen without peel ply. When a nylon peel ply is applied and removed just before overlamination of the second half very large drops in propagation energy, around 75%, are noted for both materials. Surface abrasion after peel ply removal enables fracture energy to be recovered for the standard polyester and to a lesser extent for the low styrene DCPD composite.

Characterisation of long term behaviour of polyester fibres and fibre assemblies for offshore mooring lines

Abstract: As the oil industry is looking into exploiting fields in deeper and deeper water, the conventional steel wire ropes used for platform moorings have to be replaced. Polyester lines are being progressively introduced as a lighter alternative anchoring system, but a lack of knowledge on the behaviour of such structures, especially long term, leads to the use of excessively high safety factors in the mooring design process. This paper focuses on three of the technical issues that have to be investigated for the optimisation of synthetic moorings: the choice of polymer, the determination of a relevant experimental scale for studying the behaviour of ropes, and the long term characterization. Mechanical characterisation is presented for two different materials: Polyethylene Terephthalate (PET), which is already used for offshore mooring, and Polyethylene Naphthalate (PEN), a recently developed polymer with rather few applications which is twice as stiff as PET. Results for both types of fibre show very similar behaviour, and suggest that PEN could be a possible competitor for offshore mooring application, its higher stiffness resulting in lower offset and smaller mooring lines. The characterisation was performed at different scales, from that of the approximately 20 micron-diameter fibres to an assembled rope of several hundred tons breaking load. Although some of the rope’s characteristics are related to its construction geometry, results show that its global behaviour is controlled by that of the fibre, which is the fundamental component. Finally, in order to obtain information on the long term behaviour of these structures, an accelerated creep test known as the Stepped Isothermal Method was used. The method enables creep data for simulated times of several hundred years to be obtained from 24 hour tests.

Influence of Fibre Stiffness on Deepwater Mooring Line Response

Abstract: Polyester fibre ropes are now an accepted solution for deepwater mooring of production platforms and a single high tenacity fibre grade is widely used. Few studies of other fibres have been reported but polyesters can be produced with a range of properties by varying drawing parameters, and other stiffer fibres are also available. This paper presents a study of these alternative fibre rope solutions, performed within the French Mooring Line project. First, in order to obtain the input data necessary for mooring line analyses an extensive test program was performed to characterize polyester, improved polyester, PEN, LCP, aramid and HMPE fibre ropes from yarns up to 800 ton break load ropes. Tests at different scales have allowed property transfer to be quantified. Rope modelling has been used in parallel to examine the influence of material and structural parameters. Then, using these data, a series of analyses was run by engineering contractors, which quantified the benefits of higher stiffness for different supports (semi-submersible, production platform and offloading buoy) down to 2500 meter depth. Under certain conditions the stiffer ropes can result in significantly reduced rope diameter and weight.Copyright © 2008 by ASME

Process-mechanical properties relationship for an aircraft wing spar: comparison of prepreg, lri and rfi techniques

Abstract: An aircraft wing spar made of carbon fibres and epoxy resin has been manufactured using different industrial techniques: Preg: considered as the reference, this process is also the most expensive, and this justifies the development of alternative low cost processes. LRI: Liquid Resin Infusion, this is a promising technique because it requires little equipment to obtain an acceptable quality, two different pressures were examined. RFI: Resin Film Infusion aims to combine both the advantages of using the same resin as the one used for prepreg and low cost manufacturing facilities. This study constitutes an important database for the evaluation of the mechanical properties obtained from different industrial processes. A set of tensile, bending, impact and damage tests has been conducted. Some particularities are highlighted, like the effect of the waviness defect of one side of the laminate which affects the bending strength, especially for processes from dry fabrics. Preg is a reference for all the mechanical properties but remains expensive; It justifies the emergence of alternative techniques which require lighter facilities and shorter lay-up durations like the LRI process. For the RFI process, it seems that the conditions for good manufacturing are not optimized.

Durability of Aramid Ropes in a Marine Environment

Abstract: This paper presents first results from a study of the long term marine durability of aramid fibers. The program was started based on the experience of IFREMER using aramid fiber ropes for instrumentation and deep sea handling lines, which is described here. Instrumentation lines showed no degradation after recovery, but results from testing of handling ropes after service indicated significant strength reduction. This led to the development of specific test facilities to study bend-over-sheave performance. The overall aim is to improve understanding of the roles of both the fiber and the rope construction in a marine environment, in order to improve long term strength retention of aramid marine ropes.Copyright © 2008 by ASME

Applications marines des matériaux composites - Cas des voiliers de compétition

Abstract: En raison de leur importante qualite, les materiaux composites sont tres largement utilises dans le domaine « marine ». Ils y ont supplante la construction classique en bois depuis nien des annees. L’objectif de cet article est de s’interesser aux applications marines des materiaux composites de facon generale, mais plus precisement au cas des voiliers de competition. En effet, le domaine de la voile de competition oblige de toujours progresser dans la conception, la mise en oeuvre ou encore l’utilisation des composites a hautes performances, tant il constitue un moteur de developpement important. Les structures, les materiaux utilises, la conception, le calcul des structures marines et la durabilite sont autant d’aspects etudies dans cet article.

Applications marines des matériaux composites - Cas des voiliers de compétition

Abstract: En raison de leur importante qualite, les materiaux composites sont tres largement utilises dans le domaine « marine ». Ils y ont supplante la construction classique en bois depuis nien des annees. L’objectif de cet article est de s’interesser aux applications marines des materiaux composites de facon generale, mais plus precisement au cas des voiliers de competition. En effet, le domaine de la voile de competition oblige de toujours progresser dans la conception, la mise en oeuvre ou encore l’utilisation des composites a hautes performances, tant il constitue un moteur de developpement important. Les structures, les materiaux utilises, la conception, le calcul des structures marines et la durabilite sont autant d’aspects etudies dans cet article.

How twist can affect braided marine ropes

Abstract: Traditionally synthetic fiber ropes based on nylon and polyester fibers have been widely used in the marine industry. In recent years, as the offshore petroleum industry has moved to depths beyond 1000 meters, these have attracted more attention for both mooring and deep sea handling, and high performance ropes (high modulus polyethylenes (HMPE), aramids) are also being studied. Ocean energy converters will also require mooring systems with long term reliability. Following pioneering work by Petrobras large polyester fiber ropes are now being used in station keeping of floating platforms off Brazil and in the Gulf of Mexico [1]. This application followed extensive development projects and sea trials, and has resulted in a large database of tensile properties. Tension is clearly the dominant loading in most marine applications but torsion and flexure may also be present. Torsion can be induced during tension loading, due to the unbalanced construction of some ropes (e.g. 6+1 wire ropes). However, even in a balanced construction, the movement of an adjacent unbalanced steel wire loaded in tension may introduce twist. Torsion may also arise during handling or installation operations. Bending occurs whenever ropes pass over pulleys, and can rapidly degrade high performance ropes. A thorough understanding of all these phenomena is therefore essential for safe design. Over the last ten years IFREMER has been involved in several projects concerned with both offshore and oceanographic applications of fiber ropes. The present paper will briefly describe tests developed specifically to address: Tension-torsion coupling in large steel and polyester ropes, Twist effects on braid strength of HMPE, and Bend over sheave performance of high performance ropes.