5,731 research outputs found
Butt fusion welding of polyethylene pipes
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The butt fusion process is extensively used in the joining of polyethylene (PE) pipes by the water and gas industries. This welding process although deceptively simple, is rather poorly understood, with much of the initial developments being of a rather empirical nature. The Water Research centre (WRc) have funded the present research in an attempt to optimise the welding of high pressure pipeline (PE100) systems. The main aims of this research were to investigate the effect of different welding conditions on the physical and mechanical properties of the joints produced and to investigate these effects on the micro- and macro-structures
of the joints produced. A series of welds were made using Eltex Tub 124 and Rigidex
002-50 pipes of 180mm diameter. The fusion pressure and heatsoak times were varied. A milling machine witha twin cutter arrangement was used to obtain the test specimens from around the circumference of the pipes. Differential scanning calorimetry was used to study the effect of sample
preparation methodology on the thermo-oxidative stability. Polarised light microscopy and image analysis were used to
study the macro- and micro-structural developments in the weld joint. Joint strength was evaluated via standard and
non-standard tensile test methods. Milling the samples to produce the test specimens was found to decrease significantly the thermo-oxidative resistance of the polymer. Reasons for this behaviour have been proposed. In order to achieve high quality thin films from microtomy, custom-made blades were used. This programme also developed the optimum polishing method for the microtomed blades. The macro-structure of the bead: its shape and dimensions were
found to be a function of temperature and pressure. Correlation was found between the bead geometry and the position around the circumference of the pipe. The macrostructures within the weld zone also showed this dependence on the position along the circumference of the pipe. An examination of the microstructures of each weld had shown the presence of five different zones. The feasibility of using microtomed thin sections in a tensile test was demonstrated. The test method provides a
means to study failure initiation and propagation in the tensile test specimen. Initial deformation was found to occur
in the centre of the melt-affected zone (MAZ) and the final failure occurs at the junction of the weld bead and the bulk
polymer. Tests on films without the weld bead showed that maximum deformation occurred at the centre of the sample
within the MAZ. The presence of the bead and the asymmetry in the test specimens caused by the welding process were found to have a
significant influence on the failure mode and the failure strain. The strain rate was also found to play a significant role in both beaded and debeaded samples. The failure was initiated from the pseudo notches in the beaded samples. In the debeaded sample the failure was within the MAZ
The long-term behaviour of butt fusion welds in polyethylene pipeline systems
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The objective of the study was to examine factors that influence the strength of butt welds and gain an understanding of the
process of failure. The study was divided into several sectors. The first and primary part of the programme was to determine the
extent to which the pipe system's long-term strength under both internal fluctuating and constant pressure is reduced by the presence of axially misaligned butt welds. The second objective was to examine fracture initiation sites and crack propagation paths of the failed aligned and misaligned butt welded samples in relation to the melt flow zone and the weld bead in order to establish the cause of failure. Finally the project considered the influence of selected welding parameters on the fatigue performance of aligned butt fusion welds and an investigation into the influence of elevated temperature (79°C) testing technique on the basic material's properties. Fatigue and stress-rupture lifetimes were found to decrease significantly with increasing axial misalignment at the butt fusion weld in 63,90 and 125mm MDPE pipe systems at 79°C in a water environment. In the butt fusion weld having axial misalignment of 20 per cent of the wall thickness and above, the reduction in the fatigue and stress-rupture lifetime was greater than 50 per cent compared to the aligned weld. It was not clear whether there is a pipe size effect or not; there was no marked change in the fatigue performance of misaligned butt welds for the three pipe diameters examined. However, the fatigue
performance of the aligned butt welds in 90 and 125mm was noticeably better compared to 63mm pipe systems. The stress rupture performance of misaligned butt welds in 90 and 125mm MDPE pipes was more than halved compared to those in 63mm pipe systems. Both the fatigue and stress rupture performance of misaligned butt welds could be explained in terms of amplified axial stress and in general, the Ory expression for evaluating the increase in axial stress due to misalignment appears to be valid. The temperature dependence of the fatigue performance of aligned and misaligned butt fusion welds in 63 and 90mm MDPE pipe systems suggests that if continuous internal fluctuating pressure under the conditions examined is maintained, then the butt fusion welds with axial misalignment of below 10 per cent of the wall thickness may well meet the design lifetime of 50 years at the service termperature. Under stress-rupture
conditions, all the misaligned butt welds considered in the three pipe diameters surpassed the minimum specified requirement
of 170 hours at 79°C. The fatigue was the most aggresive condition of the two for minor misalignment. Examination of the circumferential butt weld failures revealed
that the crack invariably initiated from the notch located at the inner weld bead and no preferred crack propagation path was taken in relation to the melt flow zone. It was proved that the notch was responsible for the observed circumferential failure of aligned butt welds in 63mm MDPE pipes by testing these butt fusion welds where the internal weld bead was machined off. The
failure site for the internal weld bead machined off sample was in the pipe remote from the weld inferring that the material in
the melt flow zone does not constitute any weakness. The effect of elevated temperature (79°C) testing in 63mm HDPE pipe was found to increase the density (and crystallinity)
signifying a slow annealing process in the material. However, the changes in these parameters were not of sufficient scale to
strongly influence the performance. The main effect of elevated temperature testing in water environment appears to be the
extraction of stabiliser from the base polymer as was indicated by the rapid decrease in oxidation induction time with the
ageing times.This work is supported by the Engineering Directorate of the SERC, the Water Research Centre (Engineering) and the Associated Octel
Company Ltd
Morphological and physiological interactions of NG2-glia with astrocytes and neurons
No full textModels of central nervous system (CNS) function have historically been based on neurons and their synaptic contacts - the neuronal doctrine. This doctrine envisages glia as passive supportive cells. However, electrophysiological and imaging studies in brain slices show us that astrocytes, the most numerous cells in the brain, express a wide range of neurotransmitter receptors that are activated in response to synaptic activity. Furthermore, astrocytes communicate via calcium signals that are propagated over long distances by the release of 'gliotransmitters', the most abundant being adenosine triphosphate (ATP). This has led to the concept of the neuron-astroglial functional unit as the substrate of integration in the CNS. Recently, a novel glial cell type has been characterized by expression of the proteoglycan NG2. These NG2-glia receive presynaptic input from neurons and responds to neurotransmitters released at synapses. Now, studies on transgenic mice in which fluorescent proteins are specifically expressed by subclasses of glia are helping to address the question of where NG2-glia fit in the neuron-astroglial model of integrated brain function. NG2-glia, as well as astrocytes, have been shown to respond to neuronal and astroglial signals by raised intracellular calcium, which is a potential communications mechanism by which NG2-glia may be active partners in neuron-glial circuits. Moreover, a current concept of NG2-glia considers them to be 'neural stem cells' and an exciting prospect is that neuron-glial signalling may regulate the differentiation capacity of NG2-glia and their response to injury.</p
Isreal Shank and Len Butt
No full textPhotograph - Past president Isreal C. Shank congratulates newly-elected president Len Butt at the annual meeting of the Canadian Gladiolus society, on August 15, 1980, Bowmanville, Ontari
butt head ? butt heads ?
No full textbutt headAn' they went up to haul her in an' there's no way (to) tighten her 'cause the butt heads come out (of her). (At) last they had to build (a) slip an' haul her up an' make a slight repair on her. (part of ship which helps to keep her watertight?)J. D. A. WIDDOWSON JUL 1973Not usedNot usedWithdraw
Containment and reciprocity in biological systems : a putative psychophysical organising principle
No full textThe stuff of life, the living substance that is common to all biological organisms, is the aqueous society of biochemical activity ongoing in every cell in every living body. The basic biochemical ‘reactions’ of life are largely similar with variations of a theme played out in different cells living in different environment, e.g. the core biochemical metabolic processes of all life likely stem from an ancient, early-earth ancestor (Smith & Morowitz, 2004). However, even more common to life than shared biochemistry are the basic structural properties of all cells and all living organisms into complexes of compartmentalised units. In this paper, I will argue there are common feelings driving the generation of these ubiquitous structures in nature and that these feelings may constitute one of several primary forms of feeling in living systems
butt
No full textbuttCourse, the arms o' the seine would be very _ would be light,you know,maybe made out o' twelve feet o' twine,see. But the butt,you know,that's be heavy. You want _ you want two awful men,see,the strongest men that was about, to heave it out o' skiff. (main body (?) of cod seine ?)YesDNE-cit J. D. A. WIDDOWSON JUL 1973Not usedNot usedWithdrawn'butt' appears in DNE but not with this sense; stamped but not use
Experimental analysis of AA5083 butt joints welded by CO2 laser
No full textLaser butt-welding of AA5083 has been investigated using a high quality CO2 laser in continuous wave regime. The effect of laser power, welding speed and specimen thickness on mechanical properties of the welded joints were evaluated by employing a general full factorial experimental plan design. The experimental results indicate important suggestion to choose proper combinations of process parameters and achieve high strength butt welded joints
butt (n)
No full textbuttTake up your butt then an' haul it an' tuck un_(up_ - load your boat an' go on with (it). (part of cod seine)YesDNE-cit J. D. A. WIDDOWSON JUL 1973Not usedNot usedWithdrawn'butt' appears in DNE but not with this sense; stamped but not use
Near-capacity iterative decoding of binary self-concatenated codes using soft decision demapping and 3-D EXIT charts
No full textIn this paper 3-D Extrinsic Information Transfer (EXIT) charts are used to design binary Self-Concatenated Convolutional Codes employing Iterative Decoding (SECCC-ID), exchanging extrinsic information with the soft-decision demapper to approach the channel capacity. Recursive Systematic Convolutional (RSC) codes are selected as constituent codes, an interleaver is used for randomising the extrinsic information exchange of the constituent codes, while a puncturer helps to increase the achievable bandwidth efficiency. The convergence behaviour of the decoder is analysed with the aid of bit-based 3-D EXIT charts, for accurately calculating the operating EbN0 threshold, especially when SP based soft demapper is employed. Finally, we propose an attractive system configuration, which is capable of operating within about 1 dB from the channel capacity
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