Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT)
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Item Open Access Design Project 1974/75 A 74 Aircraft Elevator Design.(Cranfield University, 1975-05) Mani Abraham, P.; Howe, D.; Tetlow, R.; Ward, R. E.Part 1 of this thesis contains the symmetric loading calculations and evolution of the design of elevator for the A 74 Reduced Take off and landing aircraft. Part 2 contains the analysis of final design of elevators. The aircraft is designed to the specifications of DES 7400 and satisfies the British Civil Airworthiness Requirement. A 74 project aircraft has longitudinal control from the tail plane and elevator combination. Tail plane is used for trimming and elevators for pitch controls. All control surfaces are hydraulic power operated. The tailplane uses an inverted supercritical section. The elevator is a four piece arrangement with duplicated hydraulic actuator system. It is of round nose type and the elevator hinge line is at 0.6 C. perpendicular to the aircraft centre line. As elevators are fully power operated mass balancing is not provided. Section 5 in part 1 gives the schemes considered in the design of elevator leading to the final choice of each major part. Section 6 gives the description of final design. Elevator is made of conventional built up construction using Aluminium alloy L 72 sheets and L 65 forgings. Part 2 gives the detailed stress analysis of the final design in accordance with normal aircraft design practise.Item Open Access A zero-dimensional model of turbulent combustion in a homogeneous charge spark ignition engine.(1989-05) De Castro, F. L. J.; Moss, J. B.In the present work a zero-dimensional model of turbulent combustion has been developed for the spark ignition engine. In addition to the prediction of thermodynamic state properties, the model includes the following elements: heat transfer from the combustion chamber, a geometrical model of turbulent spherical flame propagation and detailed post flame chemical equilibria. The model is responsive to such engine operating parameters as spark timing, equivalence ratio, engine speed and also to such design parameters as compression ratio, spark plug position and combustion chamber geometry. Two different geometries were studied extensively with the program, namely the disc chamber and the bowl-in-piston chamber. Ethanol and isooctane were investigated as fuels during the numerical simulations at variable conditions of spark advance, equivalence ratio, engine speed and compression ratio The model was employed in a partly diagnostic role to predict the engine performance using different correlations for a critical model parameter, the flame speed ratio. These were taken from the work of different researchers and included both empirical correlations, derived from engine experiments, and correlations derived from more fundamentally-based turbulent combustion studies. Comparison between prediction and experiment was made possible by a diagnostic investigation of the expanding flame front into the combustion chamber of a homogeneous charge spark ignition engine, performed in a Ricardo E6 research engine. The turbulent flame speed was determined experimentally by a dual-beam laser deflection technique. The measurement of flame transit times was performed using a specially designed and built system incorporating equipment for data acquisition based on a microcomputer. The results obtained experimentally and those obtained by the numerical simulation in general show good agreement. In the absence of detailed in-cylinder turbulence information the more fundamentally-based turbulent flame propagation models often do not perform as satisfactorily as those developed specifically for zero-dimensional ( or thermodynamic ) engine simulation.Item Open Access Fracture of modified urethane - methacrylate resins(1993-03) Zhang, Xiangcheng; Bucknall, CliveFracture and toughening mechanisms in rubber modified and hybridized urethane-methacrylate resins have been investigated. Fracture mechanisms are defect-dominated in the unmodified resin. The relationships between defect size and fracture strength are characterized through the critical stress intensity factor KIC. Low fracture toughness and high crack sensitivity of the unmodified resin is due to lack of plastic deformation at the crack tip. A 10-fold increase in fracture resistance in the resin has been achieved through rubber modification. The main reason for the improvement is due to occurring of intensive plastic deformation in the presence of rubber, which effectively eases stress concentrations and spreads them away from the crack tip. Deformation mechanisms in rubber-modified resins are shear-dominated. Cavitation of rubber plays a key role in inducing shear deformation in the matrix. Fracture processes in rubber-modified resins start from coalescence and linkage of voids initiated inside rubber particles within rubber domains, which leads to final fracture in the resin matrix. Further increase in KIC was also obtained by incorporation of filler in a matrix toughened with rubber. This increase is not due to the effect of crack front pinning but due to increase in Young’s modulus in the presence of rigid filler. The same deformation and fracture mechanisms operate in the hybrid resins as in the rubber-modified ones.Item Open Access Combined gas/steam cycle power generation from a user’s viewpoint(1990-05) Wright, M. R.; Singh, R.Gas turbines have been used since the 1940's to provide electric power at times of peak demand, but this is due to low initial cost and short starting times. Historically low efficiency and a higher quality fuel requirement has kept the gas turbine on the high end of the load curve. The combined cycle uses a gas turbine as the prime engine, then uses an exhaust heat recovery boiler to raise steam for a steam turbine cycle. High efficiencies are achievable and the gas turbines can now b u m fuels from natural gas through to crude oil and coal via gasification. High efficiency, short construction time,, competitive installation costs and smaller plant power ratings, has led to increasing and extensive use of the combined cycle. During the next two decades large numbers of gas turbines will be purchased for all load curve requirements with combined cycles in the mid to base load range. Gas turbines and combined cycles are studied in a holistic way, from performance theory to issues of procurement and maintenance. Gas turbines are discussed more fully than steam turbines as they are a less mature technology and dictate the operation of the combined cycle. A mathematical, model of a hypothetical engine is used to find performance trends. This model includes the gas turbine, single pressure boiler and steam turbine. Off design of the gas turbine is studied using the Cranfield program Turbomatch. A mathematical model of the off design of the boiler is developed to give off design trends for the combined cycle. Other issues discussed are applications, fuels, rating, operation, maintenance and various configurations. Past development, current state-of-the-art and future prospects are also discussed.Item Open Access Establishing an effective economic regulatory policy for the European airline industry(1990-06) Williams, George; Hofton, A. N.Unfettered competition in the US and Canada has resulted in a much more efficient airline industry, but the considerable economies derived from the resulting structural change has lead to greater levels of concentration than previously existed. Arguments postulated in the early 1980!s concerning the contestability of airline markets have been clearly shown to be erroneous. Megacarriers now have substantial power which they use to organise and manipulate their markets in order to extract economic rent and restrain potential rivals. Wresting organisational control from an increasingly powerful group of carriers in order to obtain a more equitable distribution of the benefits that deregulation has brought will be both expensive and highly controversial. In Europe similar opportunities exist for efficiency gains, but here it should be possible to achieve these without having to hand over market control to powerful airlines. In order to do this however a considerable reorientation and modification of existing regulatory policy is required. The priority of protecting producers' interests by limiting the competitive pressures they face is no longer warranted. Sustaining competition should now form the primary concern of regulators. The adoption of a system of route franchising with carriers being forced periodically to compete for licences provides a means by which this could be achieved.Item Open Access Gas liquid mixing in tall vessels fitted with multiple impellers(1992-10) Whitton, M. J.; Sanderson, M. L.The dispersion of air into water was studied in a tall agitated vessel (ungassed liquid depth = 2.4 x vessel diameter) fitted with four different triple impeller combinations: 1. Three identical Rushton turbines 2. One Rushton turbine + 2 pitched blade turbines (both pumping down) 3. One Rushton turbine + 2 pitched blade turbines (both pumping up) 4. One Rushton turbine + 2 LE20 impellers (both pumping down) Two vessel scales, of identical geometry, were studied: 1. 0.61 m diameter, 0.420 m3 liquid volume 2. 0.95 m diameter, 1.570 m3 liquid volume. For a range of impeller speeds and gas flow rates, measurements were made of the power draw for each impeller, gas holdup, liquid mixing rates and mass transfer rates. The impeller combinations were compared on the basis of these parameters. The performance of the individual impellers in each combination were also compared with single impellers mounted in standard geometry vessels. ; In terms of power draw and gas holdup many of the trends observed in standard geometry vessels can be directly applied to tall vessel, multiple impeller geometries. A method of estimating the gassed power draw of multiple Rushton turbines is presented. All impeller combinations studied, produced compartmentalised flow patterns. Aeration was found to have a significant effect on liquid mixing rates, and the magnitude of this effect was a function of the impeller combination used. Liquid mixing with multiple impellers was found to be very complex and geometry specific. Simple staged models, used previously in the literature, were found not to apply to the impeller combinations tested in this thesis. An economic comparison is presented, of the options available for improving mass transfer rates in an existing reactor. For the range of conditions considered, increasing the back pressure in the vessel was generally found to be a cheaper option than increasing the power input from the impellers, increasing the gas flow rate, or enriching the inlet gas.Item Open Access Multilevel optimum design of large laminated composite structures(1986-08) Watkins, R. I.; Morris, Alan J.A general method for the optimal design of large laminated composite structures, that allows full design variable (ply thickness and orientation) freedom, has been developed .. The number of variables and constraints, and hence the problem size, being dealt with at any given moment in the optimization process is kept within reasonable bounds by using a multilevel optimization scheme. The optimization process is split into a system level and an element level. At the system level the entire structure is considered and the individual laminae thicknesses (not ply angles) are sized so as to minimize the total structural weight within the constraints placed on the system. These constraints can include strain, displacement, buckling and gauge limits. Once the design has converged at this level the optimization process then switches to the element level. The objective function at the element level combines a weight function and a strain energy change function into a utility function which is minimized and in which the relative importance of each part is reflected by weighting coefficients. Minimizing the change in strain energy ensures load path continuity when switching between the two levels of optimization, and so decouples the problems at the two levels. Continuous lamina thickness and ply-angle variation is used to minimize the element level objective function while satisfying strain, buckling and gauge constraints. In this way optimum use is made of the material in each element, without changing the the load paths in the overall structure and thereby ensuring that the constraints at the system level are still satisfied. The procedure switches between the two levels until overall convergence has been achieved. Structures representative of straight, forward swept and delta wings are used to illustrate the effectiveness of the system and to show that the optimal designs produced are feasible and realistic, and compare favourably with designs obtained by more conventional and intuitive methods.Item Open Access An alternative approach to inventory control and forecasting methods in the public and private sectors(1989-10) Southworth, M. S.; Saw, R.This research was spawned by the questions and answers from the 33rd report of the committee of Public Accounts session 1983-84. The Key to the ensuing arguments about the report hinged on 3 words "Best Commercial Practice". In order to deduce a baseline the present systems of public and private concerns were investigated to find out what is actually being done. The thesis research examined what is actually happening today and in certain instances where companies have been prepared to speculate (and be open) what they believe they will be doing in the future. A review of the American and Germany Army systems has been included to ensure that the question 'best practice' could be examined between other systems having identical constraints^ The research includes both new and old literature by both academics and practitioners of the science of inventory. The hypothesis is that inventory is regarded in the singular whereas for all large concerns it should be considered in the plural, how the plural should be defined, what and how these sub inventories are and how they should be identified. The hypothesis whilst proven has the caveat that it only relates to inventories which are subject to similar structures and constraints. The effect of implementing the hypothesis in a working environment, possible areas for future work and research, largely due to the embryonic technical breakthroughs in information technology are examined briefly. The recommendations and conclusions represent an alternative approach to inventory control and forecasting not previously covered by either theoretical or practical work.Item Open Access The prediction of transonic flows using a potential method(1986-09-26) Toolsie, K. O.; Goulas, A.; Elder, R. L.Transonic flows are simulated within convergent divergent nozzles and within turbomachinery blade rows. The flow is represented by the conservative full potential equation approximated by a nine-node central-difference scheme, which is third order accurate. Artificial viscosity is included into the central-difference approximation of the potential equation, in regions where the flow is locally supersonic. The approximation of the potential equation by central-differences, with an artificial viscosity term included, is equivalent to the approximation by upwind differences and ensures that the upwind nature of the domain of dependence of supersonic flows is correctly modelled. The exact form of this artificial viscosity term is derived and contains third order derivatives of velocity-potential. The inclusion of artificial-viscosity allows the potential equation to be approximated everywhere by central-differences and the flow equation is everywhere elliptic. The Neuman boundary-condition is applied, along solid surfaces, if an inviscid solution is desired. Viscous effects are incorporated by the modification of this condition so as to allow a transpiration flow through the solid surfaces. A standard Successive-Line-Over-Relaxation technique, developed for the solution of simultaneous elliptic equations, is used to solve the discretized potential flow equations. Predictions are presented for both the inviscid and the viscous-corrected potential codes applied to the simulation of transonic flow through nozzles and cascade blade-rows. Comparisons are made with other theoretical models and with experimental data. The problem of non-uniqueness is considered and an estimate of numerical error is made by the application of the inviscid code with two computational grids of different levels of refinement. The stability of this potential code is examined and is found to depend on the level of smearing of the shock discontinuity predicted by the theoretical model.Item Open Access A study of swirling flow in an orifice plate flowmeter(1988-10) Tello-Campos, A.; Hemp, J.This thesis presents a theoretical and experimental study of swirling flow in an orifice plate flowmeter. Firstly, a solid body rotation was considered as the inlet velocity profile of an orifice plate. The beta ratio considered was 0.4. The Reynolds number was 7.82xl04 . As a result, a theoretical value of the discharge coefficient was obtained. Secondly, Laser doppler anemometry was used to determine the axial and tangential velocity profiles at 3 upstream and 2 downstream cross-sections of an orifice plate with a beta ratio of 0.4. A double right angle bend in two perpendicular planes was placed 6.5 diameters upstream of the flowmeter. The axial velocity profile was found to be slightly asymmetrical. The corresponding tangential profile was found to have a form of a solid body rotation. A 20" mercury manometer was used to measure the pressure difference across the orifice. The results showed that the discharge coefficient decreased. Thirdly, a commercial computer program was used to calculate the swirling flow through an orifice plate. A solid body rotation was considered at the inlet of the orifice. With the pressure field calculated, the corresponding discharge coefficient was determined. An additional simulation was performed with a 1/7 power law inlet profile. The discharge coefficient under swirling flow conditions was smaller than the one under non swirling flow conditions. Based on the experimental and computational results, we can see that the swirling flow produced by a double bend greatly affects the performance of an orifice plate. It is recommended that the flowmeter must be located 70 diameters downstream of a double bend. The BS 1042 does not provide a reasonable straight length for this type of disturbance.Item Open Access The distribution of solids in a mechanically stirred liquid(2000-09) Taylor, David J.; Brown, D. E.The literature available on the effect of vessel geometry, particle properties and liquid properties on the distribution of solids in a mechanically stirred vessel has been examined. This has shown that there are wide discrepancies between different authors on each of these areas. Solids concentrations have been measured using an electrical conductivity probe at various positions in two stirred vessels 0.61m and 1.83m in diameter. Different impeller designs were examined using A 310s and Pitched Blade Turbines to distribute the solids in the vessel. Pitched Blade Turbines with different diameter ratios of D=T/3 and D=T/2 were used. The sand particles used-had diameters from 150 pm - 1050 pm. It has been shown that constant power per unit volume is a reliable design rule for: 1. The effect o f vessel scale 2. The effect o f impeller diameter 3. The effect o f impeller design on the distribution of solids in a mechanically agitated stirred standard vessel. It has also been shown that the solids concentration data presented here can be correlated on the basis of N mod = N (C )da{yPo~lD~5 J and the vessel operating conditions can be characterised by a design methodology based on its use. Two methods of modelling the data are presented which describe the system in terms of: 1. An array of oscillating spheres and 2. The 1-d sedimentation dispersion model. These methods were found to model the data with different degrees of success and were generally disappointing.Item Open Access Investigation of belt misalignment effects on metal pushing v-belt continuously variable transmission(1997-10) Tawi, K. B.; Robertson, A. J.The existence of belt misalignment in the Van Doorne metal pushing V-belt continuously variable transmission (CVT) has always been recognised by researchers and the manufacturers themselves. However, its effect has always been assumed to be negligible and search through the literature reveals no work published so far to verify this assumption. Misalignment of the belt may increase losses and the need to improve efficiency is now of paramount importance. This work is an initial effort by the author to address this area and study the geometrical behaviour of the belt misalignment theoretically. An equation to represent this geometrical behaviour has been developed and it is able to calculate the magnitude and position of the belt misalignment at different speed ratios and at different assembled zero belt misalignment speed ratios. The condition necessary to minimise the magnitude of the belt misalignment has been determined. Verification of the equation was obtained by using a solid modeller from Unigraphics Version 10.4.0 CAD package and by experimental results. Proceeding from the above, another model to predict the belt misalignment effect on the transmission efficiency has been developed based on Coulomb friction theory. The model is able to predict the transmission efficiency trends reasonably well but not its absolute values. The results from the experimental work seems to agree only partially with the developed model. The main suspect of this disagreement would probably due to the inevitable belt slip phenomena of the belt and secondly, could be due to the vibration of the transmission which needs to be addressed in future experimental work. Nevertheless, this investigation has succeeded in showing that increasing belt misalignment does have a small effect on the transmission performance which is sometimes favourable and sometimes not. The results of the experimental work on using optical instrumentation to measure belt misalignment, has illustrated the possibilities and potentials of the system to carry out the belt misalignment measurements to a reasonable accuracy.Item Open Access The application of electrolytic photoetching and photopolishing to AISI 304 stainless steel and the electrolytic photoetching of amorphous cobalt alloy(1986-01) Talib, Talib Naji; Allen, DavidThe results presented cover broad aspects of a quantitative investigation into the elecrolytic etching and polishing of metals and alloys through photographically produced dielectric stencils (Photoresists). A study of the potential field generated between a cathode and relatively smaller anode sites as those defined by a dielectric stencil was carried out. Numerical, analytical and graphical methods yielded answers to the factors determining lateral dissolution (undercut) at the anode/stencil interface. A quasi steady state numerical model simulating the transient behavior of the partially masked electrodes undergoing dissolution was obtained. AISI 304 stainless steel was electrolytically photoetched in 10% w/w HC1 electrolyte. The optimised process parameters were utilised for quantifying the effects of galvanostatic etching of the anode as that defined by a relatively narrow adherent resist stencil. Stainless steel was also utilised in investigating electrolytic photopolishing. A polishing electrolyte (orthophosphoric acid —glycerol) was modified by the addition of a surfactant which yielded surface texture values of 70nm (Ra) and high levels of specular reflectance. These results were used in the production of features upon the metal surface through photographically produced precision stencils. The process was applied to the production of edge filters requiring high quality surface textures in precision recesses. Some of the new amorphous material exhibited high resistance to dissolution in commercially used spray etching formulations. One of these materials is a cobalt based alloy produced by chill block spinning. This material was also investigated and electro etched in 10% w/w HC1 solution. Although passivity was not overcome, by selecting suitable operating parameters the successful electro photoetching of precision magnetic recording head laminations was achieved. Similarly, a polycrystalline nickel based alloy also exhibiting passivity in commercially used etchants was successfully etched in the above electrolyte.Item Open Access Vehicle active suspension system design using strategies based on state estimation by Kalman filters(1990-06) Shakir, A. A.; Borrie, J.The suspension system of a ground vehicle moving on or off road can be improved by so called "active control" using control strategies which require feedback of all or some of the system states. A stochastic state estimator, or "Kalman filter", can be used to estimate these states. Various Kalman filters suited to this problem are developed, and optimal control strategies suited to these Kalman filters are specified and assessed. It turns out that there are basic problems of unobservability and uncontrollability inherent in the behaviour of such suspension systems, and original solutions to these problems are suggested and explored. A laboratory equipment is designed and constructed to reveal the behaviour of hydraulic actuators in this context, and this is used to ensure that the strategies suggested are realistic. An Intel 8086 microprocessor based circuit in which a practical Kalman filter can be realized is designed. A considerable number of computer simulations are also used to test and assess the estimation and control strategies. All these represent original work by the author.Item Open Access Biosensor and bioelectrocatalysis studies of enzymes immobilized on graphite electrode materials(1987-05) Schneider, B. H.; Higgins, I. J.; Turner, Anthony P. F.The immobilization of glucose oxidase and lipoamide dehydrogenase on graphite electrodes was studied for their application in mediated bioelectrochemical systems. These are techniques where the electrons involved in an enzymatic redox reaction are either supplied by, or given to an electrode from the enzyme. In the biosensor mode, where a current is measured due to product oxidation, the immobilized enzyme may be used to monitor its substrate, for example a biosensor for glucose based on the enzyme glucose oxidase. In the bioelectrosynthesis mode, when a cathodic potential is applied to the electrode, electrons may be transferred to the enzyme via a mediator thereby driving a thermodynamically difficult reaction, such as the reduction of the coenzyme NAD+ . A glucose sensor based on glucose oxidase immobilized onto graphite foil electrodes which had been doped with the mediator dimethylferrocene was found to produce both a linear and rapid response to changes in glucose concentration in solution. The kinetics of this particular system were studied in depth in order to explain its behaviour. Results showed that the porous nature of the electrode material resulted in immobilization of the enzyme throughout a number of layers• Consequently, diffusion of glucose into the electrode became the rate limiting process at low glucose concentrations, which resulted in linear calibration curves. This was characterized by a substrate modulus, which was found to be sufficiently large to predict diffusional limitations. From this the effective rate of glucose diffusion within the electrode was estimated, and found to be up to 5 times smaller than that in free solution. The rapid response of the sensor, on the other hand, was due to the absence of any mass transfer limitations external to the electrode surface. When lipoamide dehydrogenase was employed in the same system it was found that complications arose due to coupling of NADH oxidation with the adsorbed mediator. By employing a less anodic potential of +150 mV vs. Ag/AgCl at NADH concentrations below 1 mM the detection of enzymatic oxidation of the coenzyme was achieved. Enzymatic reduction of NAD+ was achieved using lipoamide dehydrogenase immobilized onto graphite felt electrodes. This reaction was mediated by methyl viologen, with the enzyme-modified electrode used to reduce the mediator at a potential of -0.7 V ( vs. SCE ). In this fashion the reduced form of methyl viologen was recycled, thereby driving the reduction of NAD . By coupling this system to lactate dehydrogenase it was possible to effect the reduction of pyruvate.Item Open Access An experimental and theoretical study of flow in a vortex controlled diffuser(1980-09) Saad, E. A; Adkins, R.The flow inside a vortex controlled diffuser was studied experimentally and theoretically. The experimental side of the study included the following: (1) The selection of a suitable laser Doppler velocimeter for the measurement of the mean velocity and the Reynolds' stresses. (2) An experimental optimisation of the geometry of a diffuser model was conducted. The results were used in the design of the diffuser model which was later used for the measurement with the LDV. (3) The distribution of the statin pressures the components of the mean velocity and the Reynolds' stresses in the diffuser model were measured. The results wore presented and discussed. Tile analysis of the results established a comprehensive hypothesis about the flow mechanism. This enhanced the present knowledge about the flow behaviour inside this particular diffuser. (4) Suggestions for further development of the design of the diffuser were proposed.Item Open Access The relationship between the welding conditions, thermal cycles, microstructure and toughness of weld metal in C»~Mn steels(1978-02) Rodrigues, Pedro Eduardo Leal Barbosa; Rogerson, J. H.Submerged arc weld deposits were produced using a 40 mm thick low Sulphur, low Phosphorous, Carbon Manganese microalloyed steel to B»S. 45d0 : 50D. The welding consumables used were a 4 mm diameter C. 1'2/fc Mn Wire (SD5) in conjunction with the OP 41 TT ffully basicf flux. Two series of three welds were made at three different calculated heat inputs of 5.8 EJ/nnn, 3.9 KJ/mm- and 2.9 KJ/mm. For the first series . the welding current was kept constant at 650 amp and the welding speed was varied from 200 mn/min to 400 mm/min. For the second series the welding speed was kept constant at 300 mm/min, but the welding current varied from 850 amp to 480 amp. For both the sub-surface and root regions of each weld the relationship between weld metal post solidification cooling cycle, transformation temperature, weld metal microstructure and toughness was examined and it was shown primarily that there is not a simple relationship between heat input as conventionally measured and the weld metal cooling cycle. The weld metal cooling cycle was found to be dependent upon various factors such as : 1. The actual heat input, measured in terms of weld metal bead volume. 2. Weld bead shape measured in terms of width to depth ratio, 3. Flux consumption measured in weight of the slag removed per unit volume of weld bead. 4. The relationship between the size of the weld bead and the geometry of the immediately surrounding plate. 5. The post solidification thermal effects imposed by the subsequent weld runs. From the thermal analysis measurements made whilst welding was in progress, two transformation reactions were identified. À high temperature transformation occuring at approximately 85Q°C identified by subsequent metallographic examinations as the pro-eutectoid ferrite transformation, and a low temperature transformation occuring at approximately 650 C identified as the acicular ferrite phase trans-. formation. The thermal analysis results also showed that .the weld metal cooling rate had an effect on the weld metal transformation temperatures. For each transformation an increase in the weld cooling rate lead to a depression of the transformation Temperature. The present results indicate that the most desirable welding condition from a toughness point of view, should give a weld metal cooling cycle which was "slow" for the 1400°C - 900°C temperature range, but "fast" below the temperature of 900°C. This would lead to a microstructure formed of large columnar grains, but with a high acicular ferrite volume fraction. 1 All welds showed a through thickness toughness variation. These differences in the through thickness properties were mainly attributed to the large differences in the thermal history between the sub-surface and the root beads which in turn lead to different microstructures, the sub-surface beads were formed by a larger columnar grain and a higher volume fraction of acicular ferrite than the root beads. The root beads Charpy V specimens also contained some refined equiaxed ferrite grains while the sub-surface Charpy V specimens contained solely as deposited weld metal. These differences in the microstructure features between the sub-surface and the root beads in turn appear to be, for the present welds, the main cause for the differences in the through thickness properties. The overall conclusion from the present work is therefore that the weld metal deposits made at the same calculated heat input do not necessarily show the same toughness properties. This results from the fact that the cooling cycle, transformation temperature and amount of weld metal reheated by the subsequent runs are determined by the precise welding conditions.Item Open Access Integration of global positioning and inertial reference system data inside a flight management computer(1992-01) Richards, N. P.; Thomasson, P. G.A Kalman filter is used to integrate the outputs from a Global Positioning System and an Inertial Reference System inside a Flight Management Computer. To initialise the Kalman filter, account is taken of the 1RS errors that get set up during alignment. Algorithms are developed that allow the Kalman filter to be initialised to several 1RS specific alignment conditions.Item Open Access Prediction of the onset of detectable multiple site damage in a RAF VC10 circumferential butt joint using extended fatigue specimen testing of retired fuselage structure(2004) Ralph, Steven; Irving, Phil E.The in-flight pressure fuselage failure of an Aloha Airlines Boeing 737 near Maui, Hawaii on 28 April 1988 brought the issue of Ageing Aircraft and in particular the dramatic destructive potential of Widespread Fatigue Damage (WFD) and Multiple Site Damage (MSD) to the attention of the World. The accident led to a substantial amount of research and development work into the WFD phenomenon and civil regulators mandating WFD assessments of ageing aircraft. Although military aircraft are not regulated by civil requirements, military airworthiness requirements require the completion of Ageing Aircraft Audits (AAA), which do require an evaluation of the potential of WFD. This Thesis predicts the onset of detectable MSD in a, less researched and highly loaded, circumferential butt joint at the crown of a RAF VC10 aircraft fuselage. The onset of detectable cracking is determined using a theoretical Monte-Carlo probabilistic simulation, which incorporates the results of extended fatigue specimen testing, to failure, of retired RAF VC10 fuselage structure using stresses derived from an in-service stress spectrum of the Joint. A biaxial fatigue analysis of the longitudinal bending and circumferential hoop stresses at the Joint, identifies that the large longitudinal stress from this rear engine large T-tail aircraft are dominant in determining the fatigue endurance of the Joint. Fracture surface analysis, however, identifies that the applied test load is different to the stress state experienced in the fuselage. A possible cause for the discrepancy is identified as secondary bending due to the asymmetry of the butt joint and the unrestricted out-of-plane displacement of the specimens during testing. All the specimens exhibited small (50x1 O'6 m) pre-existing cracks and corrosion pits which, in comparison to ‘similar’ pristine specimens, suggests (not substantiated) that environmental and operational degradation contributes to reducing airframe joint rivet hole fatigue endurance and standard deviation.Item Open Access Fusion characteristics in P-GMAW of mild steel(1986-04) Quintino, Luisa; Apps, R. L.The influence of process parameters on deposition and fusion characteristics of mild steel with Pulsed Gas Metal Arc Welding has been investigated using a transistorized power supply. A simple model of melting behaviour has been developed which allows the prediction of dilution behaviour and explains the interplay between mass and heat in P-GMAW. In order to predict heat affected zone area, a model driven from the former one has also been developed. Deposition characteristics were studied taking the care of studying the influence of each welding parameter at each time, whenever it was possible. Emphasis was given to shielding gas mixture which was found to significantly influence metal transfer mode and arc stability. A systematic approach to choose process parameters in Pulsed Gas Metal Arc Welding with a constant current power supply is proposed. It was found that mean current and welding speed play the most important role in determining fusion characteristics, thus, based on a simple model, methods of controlling these aspects are suggested. Emphasis was placed on understanding dilution behaviour. It was found possibility to develop.procedures allowing the independent choice of deposition rate and dilution behaviour and to give an account of many observations with simple models of melting phenomena. The developed model is combined with calorimetric heat transfer measurements to investigate the result that only a small fraction of the total process power is required to melt the observed fusion areas. A "dual Heat" source fusion model is suggested where plate melting is largely in response to direct arc heating, providing means of optimising plate dilution and thereby reducing the risk of fusion defects. A generalized representation of fusion characteristics is given which allows independent selection of required fusion characteristics to be assessed.