Staff publications (SAS)

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Open Access
The influence of imposed strain rate on fracture of surface oxides.
(Elsevier Science B.V., Amsterdam., 1993-01-01T00:00:00Z) Hancock, P.; Nicholls, John R.; Mahmood, K.
The mechanical properties of chromium rich scales formed on 304 stainless steel have been investigated as a function of deformation rate and operating temperature. At 900C at slow strain rates < 10-6 per second no cracking was observed at strains up to 10%. At rapid strain rates in excess of 10-4 per second oxide cracking was found to be independent of strain rate and controlled by the fracture toughness of the oxide. In the intermediate region, with strain rates between 10-4 per second and 10-6 in the temperature range 700 to 950C, the behaviour is determined by the creep deformation and fracture mode of the oxide. The mechanism of surface oxide failure is examined and an equation to predict cracking density over the full range of both monotonic tensile and creep fracture modes is sugg
Open Access
Evapotranspiration Estimates for Water Balance Scheduling in the UK
(1996-01-01T00:00:00Z) Hess, Tim M.
This paper compares the use of different methods for estimating reference evapotranspiration (ETo) for irrigation scheduling in the UK. Methods include use of long-term averages, daily weather data and evaporimeters. The results from a single trial in Silsoe in 1996 suggest that, with careful maintenance and measurement, a modified atmometer such as the ETgage, can give estimates of ETo which are close to those obtained using the Penman-Monteith equation.
Open Access
Evaluation of the behaviour of particulate polymeric coatings in a corrosive environment. Influence of the concentration of metal particles
(Elsevier Science B.V., Amsterdam., 1996-06-01T00:00:00Z) Kouloumbi, N.; Tsangaris, G. M.; Skordos, Alexandros A.; Kyvelidis, S.
In this work pretreated steel specimens were coated by a spinning process with particulate polymeric composites consisting of an epoxy resin (DOW 331) and iron powder. Applied coatings were roughly 70 Î¼m thick and the contained quantity of iron particles was varied (7.5, 15, 30% wt./wt.). The effect of the presence of iron particles in the coatings as well as the influence of their concentration on the evaluation of the coatings' behaviour in a corrosive environment (3.5% NaCI) was studied. Electrochemical impedance spectroscopy, corrosion potential, corrosion current density (Tafel) and dielectric measurements were performed. Minor differences in the anticorrosive behaviour of the coatings were observed irrespective of the iron content in the coating. Effective resistance inhibition action of the composite coatings was diminished with the increase of exposure time to the corrosive environment being in all cases very close to that of the pure epoxy resin coating
Open Access
Irrigation Demand and On-Farm Water Conservation in England and Wales
(1997-01-01T00:00:00Z) Weatherhead, E. K.; Knox, Jerry W.; Morris, Joe; Hess, Tim M.; Bradley, R. Ian; Sanders, Catherine L.
The study confirmed that water use for agricultural irrigation is increasing, both in area irrigated and depths applied, and is increasingly concentrated on the more valuable crops. Underlying volumetric growth was 3% per annum from 1982 to 1995. On-farm reservoir capacity doubled from 1990 to 1995, but 90% of the water still came from summer abstraction in 1995, mostly from rivers and streams.
Open Access
Modelling heat generation and transfer during cure of thermoset composites processed by resin transfer moulding (RTM)
(1997-09-01T00:00:00Z) Skordos, Alexandros A.; Maistros, George M.; Turmel, Denis J-P; Partridge, Ivana K.
The development of a heat transfer model for the curing stage of the RTM process is presented. Despite the intense interest in the modelling and simulation of this process the relevant work is currently limited to development of flow models of the filling stage. The principles of heat transfer modelling of composites cure have already been reported and applied to the autoclave process by many investigators. In the present investigation, the same concept is used for the implementation of Galerkin finite element approach to RTM curing. The mathematical basis of the resulting semidiscrete model is presented here and the temporal algorithm is described. The experimental mould, which will be used to evaluate and validate the model is also described.
Open Access
Lag phases in the adsorption of lysozyme to Si(Ti)O2 surfaces in the presence of sodium thiocyanate. Part I. Phenomenology.
(Royal Society of Chemistry, 1999) Ball, Vincent; Lustig, Ariel; Ramsden, Jeremy J.
The adsorption kinetics of hen egg white lysozyme (HEWL) in the presence of NaSCN at pH 7.4 onto Si0.8Ti0.2O2 surfaces were measured by means of time-resolved optical waveguide lightmode spectroscopy (OWLS). The adsorption kinetics were characterized by the presence of a lag phase whose duration decreased with increasing lysozyme bulk concentration. This lag phase was followed by rapid growth of the interfacial protein film which ceased at a surface coverage close to that predicted for a monolayer. At bulk concentrations lower than about 50 µg cm-3, the maximum rate of adsorption was equal to the rate predicted for a transport-controlled process from the solution to the surface and at higher bulk concentrations such lag phases were no longer observed. Storage of lysozyme solution prior to adsorption reduced the duration of the lag phase, but analytical ultracentrifugation measurements showed the absence of significant aggregation even at bulk concentrations of 103 µg cm-3. These features are consistent with an adsorption process requiring the adsorption of a small critical nucleus preformed in solution followed by the completion of the adlayer by a mechanism akin to crystal growth. The size of this critical nucleus was estimated to be of the order of only a few lysozyme molecules.
Open Access
Minimising the environmental impacts of irrigation by good scheduling
(1999-01-01T00:00:00Z) Hess, Tim M.
Irrigation constitutes a major user of water resources at a time, and in places, where resources are at their lowest. Also, by maintaining the soil in a wetter state, it increases the annual drainage, which can affect the leaching of nitrates into the groundwater. Irrigation scheduling involves, firstly, deciding the most appropriate irrigation plan (i.e. what soil water deficit to allow and how much to apply at that deficit) and secondly, deciding what is the soil water deficit on any particular day. Good scheduling will aim to meet the goals of irrigation (optimise production / quality / aesthetics) whilst minimising the water used and other adverse environmental impacts. The main techniques for scheduling irrigation in the UK are direct measurement of soil water content and water balance modelling. ‘Bad’ irrigation scheduling can result from an inappropriate irrigation plan, inaccurate soil water measurement, errors in water balance modelling or uncertainty over the actual amount of water applied at each irrigation. Either will result in under- or over-watering. A case study for potatoes grown in a medium textured soil in Silsoe (Beds) examined the impact of poor scheduling on average annual irrigation water requirement and the risk of nitrate leaching. The water requirement is very sensitive to errors in estimating evapotranspiration or the field-capacity water content of the soil, but less so to errors in the amount of water applied. Increasing the trigger soil water deficit can also minimise the water requirement. Over-irrigation, due to a poor irrigation plan can increase the summer drainage and risk of nitrate leaching, however, over-watering due to inaccurate scheduling predominantly results in increased winter drainage which may have a positive impact on nitrate concentrations and winter recha
Open Access
Effects of agroforestry on farm biodiversity in the UK.
(The Royal Scottish Forestry Society, 1999-01-01T00:00:00Z) Burgess, Paul J.
One advantage claimed for agroforestry is that it can bring onto farmland some of the biodiversity benefits associated with woodlands. The aim of this paper is to review recent research in order to describe the potential impact of agroforestry systems on the diversity of plants and animals on British farms. The review suggests that the introduction of silvopastoral systems can lead to an increase in the diversity of invertebrates and perhaps birds on grassland farms. The introduction of silvoarable systems can also lead to an increase in the diversity of airborne arthropods, small mammals and possibly birds on arable farms; however the effects on arable pests are likely to be mixed.
Open Access
Monitoring and Heat Transfer Modelling of the Cure of Thermoset Composites Processed by Resin Transfer Moulding.
(1999-10-06T00:00:00Z) Skordos, Alexandros A.; Partridge, Ivana K.
Experimental studies have demonstrated the existence of significant thermal gradients during the cure stage of Resin Transfer Moulding (RTM). Presence of such thermal gradients can affect the final degree-of-cure distribution and cause the development of residual stresses, leading to a deterioration of the final composite component properties. Therefore the incorporation of heat transfer modelling in the general context of RTM modelling and monitoring of the process is necessary. The present work focuses on the application of combined monitoring and heat transfer modelling to the process. A finite element heat transfer model incorporating resin cure kinetics has been developed and tested. An inverse solution of the heat diffusion model has been implemented in order to extend the local measurements given by in-situ monitoring to global information about the temperature distribution and the degree-ofcure distribution during the cure.
Open Access
Human error in the engineering design process.
(Professional Engineering Publishing, 2000) Busby, Jeremy S.
A study was conducted of human error in the engineering process of 5 organisations that designed industrial equipment. Approximately 150 errors that had taken place were analysed individually and then coded according to the particular design activity that failed. Modes of error that were common to error in different activities were then identified. Among the primary modes of error were cases where designers failed to elicit the constraints and requirements presented by the outside world, but did so because they had fallacious beliefs that were nonetheless reasonable inferences from limited historical experience. Error was also associated 1) with the emergence of latent constraints when scaling up a design, 2) with refining designs that made them vulnerable to uncertainties in the external world, 3) with modifying existing designs whose rationale was obscure, and 4) with design tools which provided inadequate feedback for users learning by trial and error. The most promising way of reducing error may be to make designers more knowledgeable about the types of error accompanying different activities.
Open Access
A dielectric sensor for measuring flow in resin transfer moulding.
(Iop Publishing Ltd, 2000-01-01T00:00:00Z) Skordos, Alexandros A.; Karkanas, Panagiotis I.; Partridge, Ivana K.
The development, analysis and experimental validation of a novel flow and cure sensor for use in the resin transfer moulding of composites are presented. A linear relationship is established between the flow front position in the mould and electrical admittance measurements gathered using the sensor setup, allowing accurate flow front location. The sensor performance as an indicator of flow front position is evaluated using visual verification. Its efficiency for monitoring of the curing stage is assessed by comparison of the measurements with data obtained from more conventional microdielectrometry. Experimental results demonstrate that the sensor can locate the flow front accurately. The measurement output is in the form of a complex number; this suggests a potential qualitative self-assessment method. The monitoring of the cure process using the new sensor shows performance similar to that of the established microdielectrometric techniques.
Open Access
A Mechanism for the Erosion of EB PVD TBCS
(Trans Tech Publications, Switzerland., 2000-07-10) Wellman, R. G.; Nicholls, John R.
Since the introduction of electron beam (EB) physical vapour deposition (PVD) TBCs and their application to moving components in the hot gas stream, erosion has become a prime concern. This project has been involved in determining the erosion mechanism of EB PVD TBCs, in order to develop a computational erosion model. The unique columnar microstructure of the EB PVD TBCs precludes the use of the classical brittle erosion mechanisms. This meant that a thorough investigation into the erosion mechanism of the coatings was necessary before it would be possible to develop a model to predict material wastage.
Open Access
Some observations on erosion mechanisms of EB PVD TBCS
(Elsevier Science B.V., Amsterdam., 2000-07-10T00:00:00Z) Wellman, R. G.; Nicholls, John R.
Following the successful application of electron beam (EB) physical vapour deposition (PVD) thermal barrier coatings (TBCs) to moving parts of turbine engines, the erosion resistance of these coatings has been of interest among researchers. However, although there are a number of papers on the erosion rate of these coatings, little has been reported on their erosion mechanism. This paper provides observations on the erosion damage of EB PVD TBCs and discusses the type of damage caused by erosion, as well as proposing a possible mechanism of erosion. The aim of the project as a whole was to model the erosion of EB PVD TBCs, but before modelling could begin, it was necessary to determine the erosion mechanism of these coatings. It was found that in all cases examined, the erosion of the coatings proceeds through the accumulation of damage in the form of horizontal cracks in the columns of the coating and subsequent removal of the fractured sections. Since it appears as though the contact radius is important in the erosion process, the effect of varying the elastic properties of the erodent and the target on the contact radius was assessed.
Open Access
Dielectric flow sensing in resin transfer moulding of carbon fibre reinforced composites.
(Maney Publishing, 2000-08-01T00:00:00Z) Skordos, Alexandros A.; Partridge, Ivana K.
An in situ dielectric technique for sensing flow is outlined and shown to be suitable for use in moulding of composites from liquid resins containing continuous conducting fibres. This work builds upon the recent development of a sensor for monitoring flow and cure in thermosetting composites with (non- conductive) glass reinforcements. The linear relationship between the position of the flow front in the mould and the electrical admittance of the sensor system, which is observed in resins with non-conductive reinforcements, was found to extend to resins containing conducting fibres. The performance of the sensor in detecting the position of the flow front was evaluated by comparison with visual observations. The capability of the sensing system to monitor the cure of the resin after mould filling was also investigated. The results demonstrate that the sensor can both locate the flow front accurately and monitor the cure, identifying vitrification in a way that is similar to conventional microdielectrometry. Data from flow measurements are output in complex number format, which offers the potential to produce a method that can be used to evaluate the performance of the sensor system quantitatively.
Open Access
Evaluation of a manufacturing task support system using the Task Technology Fit Model
(Production and Operations Management Society, 2001) Tjahjono, Benny; Fakun, D.; Greenough, Richard M.; Kay, John M.
This paper presents an exploratory study of a Task Support System (TSS) supporting manufacturing task operations. The study investigated the degree to which a TSS, in use in a company, actually supports the task of the shop floor personnel. The approach has been to adopt the Task-Technology Fit (TTF) instrument to measure the degree of fitness between the TSS and the associated task. The analysis gives an indication of the state of the TSS and the potential improvements that can be made. The study also shows that the instrument can be used as a foundation for the development of a hypermedia TSS and a benchmarking tool for a TSS.
Open Access
e-Knowledge: an approach to fostering manufacturing know-how at the shop floor
(Production and Operations Management Society, 2001) Tjahjono, Benny; Bin, Wu
This paper presents an application of the web technology in promoting knowledge management at the shop floor, known as e-knowledge. The system is expected to promote sharing and reusing various levels of manufacturing information from assembly cell to testing area, and from documentation to training. The implementation of such a system has been made possible by utilising the web-programming environment. To investigate how the e-knowledge works, a case study involving a major cellular telecommunication industry is presented.
Open Access
Transformation dependence of lead zirconate titanate (PZT) as shown by PiezoAFM surface mapping of Sol-gel produced PZT on various substrates
(Taylor and Francis, 2001) Dunn, Steve; Whatmore, Roger W.
PZT was grown on STP (Si/SiO2/Ti/Pt (Ti 5nm, Pt 100nm)), SAP (Si/Si3N4/Al/Ti/Pt (Al 100nm, Ti 10nm, Pt 15nm)) and GI (Glass/ITO(Indium Tin Oxide)). In each case the PZT underwent the same heat treatment, 200ºC for 2 minutes and then 530ºC for 5 minutes. The extent of perovskite formation was evaluated using Piezoresponse force microscopy (PFM). This provided information about the domain orientation and spatial distribution of ferroelectric material in the PZT film. This showed that PZT/STP underwent complete transformation to the perovskite phase. However, for the PZT/SAP and GI incomplete transformation to the perovskite occurred. A system of rosettes surrounded by an amorphous matrix developed. The size and density of the PZT rosettes on the surface was found to be substrate dependent. For Gi/PZT the density of rosettes formation is ca. 1/μm2, compared to 4/μm2 for PZT/SAP. The rosettes for the PZT on GI grow a maximum size of 2μm, which compares to 1μm for PZT on SAP. Differences in the observed growth rate and nucleation density are associated with the back electrode stability and crystal structure, effects that will be discussed in this paper.
Open Access
Integrated models of livestock systems for climate change studies. 1. Grazing systems.
(Blackwell Publishing Ltd, 2001-01-01T00:00:00Z) Parsons, David J.; Armstrong, A. C.; Turnpenny, J. R.; Matthews, A. M.; Cooper, K. C.; Clark, J. A.
The potential impact of climate change by the year 2050 on British grazing livestock systems is assessed through the use of simulation models of farming systems. The submodels, consisting of grass production, livestock feeding, livestock thermal balance, the thermal balance of naturally ventilated buildings and a stochastic weather generator, are described. These are integrated to form system models for sheep, beef calves and dairy cows. They are applied to scenarios representing eastern (dry) lowlands, western (wet) lowlands and uplands. The results show that such systems should be able to adapt to the expected climatic changes. There is likely to be a small increase in grass production, possibly allowing an increase in total productivity in some cases.
Open Access
A comparison of the responses of mature and young clonal tea to drought.
(Cambridge University Press, 2001-01-01T00:00:00Z) Nixon, D. J.; Burgess, Paul J.; Sanga, B. N. K.; Carr, M. K. V.
To assist commercial producers with optimising the use of irrigation water, the responses to drought of mature and young tea crops (22 and 5 years after field planting respectively) were compared using data from two adjacent long-term irrigation experiments in Southern Tanzania. Providing the maximum potential soil water deficit was below about 400-500 mm for mature, and 200-250 mm for young plants (clone 6/8), annual yields of dry tea from rainfed or partially irrigated crops were similar to those from the corresponding well-watered crops. At deficits greater than this, annual yields declined rapidly in young tea (up to 22 kg (ha mm)-1) but relatively slowly in mature tea (up to 6.5 kg (ha mm)- 1). This apparent insensitivity of the mature crop to drought was due principally to compensation that occurred during the rains for yield lost in the dry season. Differences in dry matter distribution and shoot to root ratios contributed to these contrasting responses. Thus, the total above ground dry mass of well-irrigated, mature plants was about twice that for young plants. Similarly, the total mass of structural roots (>1 mm diameter), to 3 m depth, was four times greater in the mature crop than in the young crop and, for fine roots (<1 mm diameter), eight times greater. The corresponding shoot to root ratios (dry mass) were about 1:1 and 2:1 respectively. In addition, each unit area of leaf in the canopy of a mature plant had six times more fine roots (by weight) available to extract and supply water than did a young plant. Despite the logistical benefits resulting from more even crop distribution during the year when crops are fully irrigated, producers currently prefer to save water and energy costs by allowing a substantial soil water deficit to develop prior to the start of the rains, up to 250 mm in mature tea, knowing that yield compensation will occur later.
Open Access
Expert Judgement in Cost Estimating: Modelling the Reasoning Process.
(Sage Publications, 2001-01-01T00:00:00Z) Rush, Christopher; Rajkumar, Roy
Expert Judgement (EJ) is used extensively during the generation of cost estimates. Cost estimators have to make numerous assumptions and judgements about what they think a new product will cost. However, the use of EJ is often frowned upon, not well accepted or understood by non-cost estimators within a concurrent engineering environment. Computerised cost models, in many ways, have reduced the need for EJ but by no means have they, or can they, replace it. The cost estimates produced from both algorithmic and non-algorithmic cost models can be widely inaccurate; and, as the work of this paper highlights, require extensive use of judgement in order to produce a meaningful result. Very little research tackles the issues of capturing and integrating EJ and rationale into the cost estimating process. Therefore, this paper presents a case with respect to the wide use of EJ within cost estimating. EJ is examined in terms of what thought processes are used when a judgement is made. This paper highlights that most judgements are based on the results of referring to historical costs data, and then adjusting up or down accordingly in order to predict the cost of a new project. This is often referred to as analogy. The reasoning processes of EJ are identified and an inference structure has been developed, which represents an abstraction of the reasoning steps used by an expert as they generate an estimate. This model has been validated through both literature and interviews with cost estimating experts across various industry sectors. Furthermore, the key inferences of the experts are identified. These inferences are considered as those where many of the assumptions and expert judgements are made. The thesis of this paper is that through modelling the reasoning processes of EJ, it becomes possible to capture, structure, and integrate EJ and rationale into the cost estimating process as estimates are being generated. Consequently, the rationale capture will both improve the understanding of estimates throughout a product life cycle, and improve management decisions based upon these cost estimates.