The compounding of short fibre reinforced thermoplastic composites

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique

Phyllonorycter messaniella (Zeller, 1846), new record for the Maltese Islands (Lepidoptera: Gracillariidae)

Phyllonorycter messaniella is recorded for the first time from the Maltese Islands. Data about life history, ecology and distribution is included.peer-reviewe

Spatial relations, histories from below and the makings of agency: Reflections on The Making of the English Working Class at 50

In this paper we propose a conversation between work in labour history and labour geography, in part centring on the formative contribution of E.P. Thompson. We contend that the commitment to multiple and political forms of agency and working-class experience and the positioning of class as process, which are lasting contributions of The Making of the English Working Class, offer resources for re-invigorating debates on agency within labour geography and beyond. The paper scrutinizes the spatial politics at work in Thompson’s account of agency and experience through drawing on critiques of Thompson by feminist and post-colonial scholars. The paper explores the significance of Thompson’s work for asserting a spatial politics of labour and argues for attention to the diverse agentic spatial practices shaped through labour organizing and struggles. The paper concludes by setting out some key aspects of the terms of a conversation between labour geographies and labour histories

Optimal bounds for the densities of solutions of SDEs with measurable and path dependent drift coefficients

We consider a process given as the solution of a stochastic differential equation with irregular, path dependent and time-inhomogeneous drift coefficient and additive noise. Explicit and optimal bounds for the Lebesgue density of that process at any given time are derived. The bounds and their optimality is shown by identifying the worst case stochastic differential equation. Then we generalise our findings to a larger class of diffusion coefficients.Comment: 24 pages and 1 figur

Understanding Digital Technology’s Evolution and the Path of Measured Productivity Growth: Present and Future in the Mirror of the Past

Three styles of explanation have been advanced by economists seeking to account for the so-called 'productivity paradox'. The coincidence of a persisting slowdown in the growth of measured total factor productivity (TFP) in the US, since the mid-1970's, with the wave of information technology (It) innovations, is said by some to be an illusion due to the mismeasurement of real output growth; by others to expose the mistaken expectations about the benefits of computerization; and by still others to reflect the amount of time, and the volume of intangible investments in 'learning', and the time required for ancillary innovations that allow the new digital technologies to be applied in ways that are reflected in measured productivity growth. This paper shows that rather than viewing these as competing hypotheses, the dynamics of the transition to a new technological and economic regime based upon a general purpose technology (GPT) should be understood to be likely to give rise to all three 'effects.' It more fully articulates and supports this thesis, which was first advanced in the 'computer and dynamo' papers by David (1990, 1991). The relevance of that historical experience is re-asserted and supported by further evidence rebutting skeptics who have argued that the diffusion of electrification and computerization have little in common. New evidence is produced about the links between IT use, mass customization, and the upward bias of output price deflators arising from the method used to 'chain in' new products prices. The measurement bias due to the exclusion of intangible investments from the scope of the official national product accounts also is examined. Further, it is argued that the development of the general-purpose PC delayed the re-organization of businesses along lines that would have more directly raised task productivity, even though the technologies yielded positive 'revenue productivity' gains for large companies. The paper concludes by indicating the emerging technical and organizational developments that are likely to deliver a sustained surge of measured TFP growth during the decades that lie immediately ahead.