Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT)

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Open Access
The time-dependent behaviour of anisotropic low density polyethylene
(1971-03) Clayton, David; Hall, M. M.
'Low density polyethylene has been oriented into a state of transverse isotropy by cold-drawing an originally isotropic blank in uniaxial tension, and the non-linear creep behaviour of the material has been completely characterised for the first time. The compliance matrix describing the deformation behaviour is characterised by five independent material parameters. Four of the parameters have been determined from uniaxial tensile creep experiments on specimens cut at 0° and 90° to the draw direction, and the fifth from torsional creep studies on a specimen cut parallel to the draw direction. The- development and proof of experimental techniques for use with the respective apparatii have formed an important and necessary part of the work, and the accuracy and internal consistency of the results have been found to be excellent. Measurements of the compliances have been made at ten different: degrees of anisotropy - measured by the draw ratio - over a range of strains from the pseudo-linear to the highly nonlinear region. The anisotropy of the deformation behaviour at a given draw ratio, and the trends of anisotropy with draw ratio, have been interpreted in terns of current structural knowledge. At low draw ratios the deformation is dominated by a c-axis shear mechanism and an inter-lanellar shear mechanism, and a relaxation mechanism has been discovered in specimens cut at 90 to the draw direction. At high draw ratios an inter-fibrillar shear mechanism is dominant in specimens cut: at angles away from the 0° and 90° direction. A simple engineering analysis of the results has examined the applicability- of the formalisms of linear elasticity and viscoelasticity theory to the non-linear, anisotropic visco-elastic state. Also, the assumption of a constant volume deformation, which is commonly used in polymer science for the determination of the Poisson’s ratio terms, has been investigated over the range of strains and compared with directly measured values. The measured values represent the first systematic study of Poisson1s ratio in anisotropic polymers. The constant volume assumption is shown to be in error at all draw ratios.
Open Access
Studies in hypersonic viscous interactions
(1972-12) Murthy, A. V.; Clarke, J. F.
The literature on the leading edge viscous interaction phenomena has "been reviewed. Theoretical studies of the leading edge bluntness and the boundary - layer displace¬ment effects have been made by using a combination of tangent wedge + centrifugal force pressure law relation and also using the 2nd order tangent wedge formula suggested by Lees . These analyses, when applied to concave surfaces show a mild oscillatory behaviour compared to the highly oscillatory results of Cheng's theory. Further, an integral approach due to Chernyi has been applied to concave surface flows and the damping of the oscillations present in Cheng’s theory is demonstrated. Experiments have been conducted at a Mach number Of 1 2 .2 in a gun tunnel, on flatplates and on a concave surface with a sharp leading edge. The results are compared with the predictions of various interaction theories.
Open Access
Ignition of a turbulent flowing gaseous mixture
(1973-01) Ballal, D. R.; Defebvre, A. H.
The basic properties of arcs in flowing ga-,es, minimum ignition energy and quenching distances are the\focal points of this research. The flow parameters turbulence, pressure, velocities, fuel-air ratio etc. are varied over a wide range to simulate high altitude relight conditions of a gas turbine combustion chamber. — It is found that a constant-power energy release in the spark gap, having an optimum duration of 60)/s, more than halved the minimum ignition energy requirements over most of the flammability range of propane-air mixtures. At large quenching distances, lengthening of discharge path by the flowing stream results in significant reduction in heat losses to the electrodes and improvements in minimum ignition energy. The large scale intensity of turbulence tends to increase the minimum ignition energy but the quenching distance is significantly affected only by intensity. In the light of the above experimental research some discussion is presented on the practical aspects of the aircraft relight problem. Finally the various theories on ignition in turbulent flowing gases have been studied and compared with the experimental results of the present work.
Open Access
The high temperature oxidation and - corrosion of irons and steels
(1973-09) Davies, M.; Hurst, R. C.
This research has been concerned with the oxidation and corrosion of iron and mild steels, with particular reference to the importance of the mechanical properties of the surface oxides formed. A vibration technique has been used as the basic means of investigation, complemented by hot stage microscopy, thermobalance, microscopy, etc., where applicable. It has been found that the oxides formed on iron and steel become partially detached at the scale/metal interface continually during growth. This form of damage has been ,· found to have a profound effect on the dynamic modulus of the oxides, and on its behaviour under thermal shock or corrosive conditions. A particular EN2 steel has been found to be largely resistant to sodium chloride and sodium sulphate corrosion when preoxidised. This enhanced corrosion resistance has been attributed to the presence of a thin adherent oxide layer on the metal surface, whose adherence is due to the concentration of nickel in that region during oxidation. The vibration apparatus and specimens have been modified to enable tensile loading during oxidation such that the strains that a surface oxide is able to withstand before cracking may be measured. It has been found that the strains to fracture increases with increasing temperature. The application of the vibration technique in this role as a crack detection system has been shown to be very satisfactory.
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.
Open Access
Influence of liquid properties on plain-jet airblast atomization
(1976-04) Lorenzetto, G. E.; Lefebvre, A. H.
This thesis reports the results of a detailed programme of research on airblast atomization carried out using a specially designed plain-jet atomizer in which the fuel is injected into a high velocity airstream in the form of a discrete jet. Because recent studies on airblast atomization have been mainly confined to sheet and then subjected on both sides to the atomizing action of high velocity air, information was needed to carry out a comparison between^the two mechanisms of atomization. It was in order to obtain such information that the present investigation was undertaken and the study essentially resolved into a detailed experimental exploration of the spray characteristics of 1plain-j et1 airblast atomizers. Specially prepared liquids were employed to distinguish between the separate effects on S.M.D. (Sauter Mean Diameter of spray) of viscosity, surface tension and density. The liquids employed represented a range of values of viscosity from 1 .0 to 76 x 10 Kg/ms,/while surface tension and density were varied -3 3 between 26 and 73 x 10 N/m and 794 and 218oKg/m respectively. Atomizing air velocities covered the range of practical interest to the designers of continuous combustion systems and varied between 70 and 180 m/s. The effect of scale on S.M.D. was studied using several different fuel injectors varying in orifice diameter between 0.39 and 1.58 mm. A detailed description of the light-scattering technique for drop size measurement is included...
Open Access
Static and dynamic characteristics of an hydrodynamic journal bearing
(1976-05) Parkins, D. W.
Hydrodynamic oil film bearings exhibit lateral flexibility which influences the dynamics of rotors they support. This lateral flexibility is specified by coefficients which relate forces generated by the oil film to the instantaneous journal centre velocity and its displacement from an equilibrium position. Previous investigators adopted a linear treatment by taking uniform viscosity with small displacement and velocity increments. Relatively large journal centre velocities are possible in rotating machinery. Therefore, this thesis investigates the non-linear behaviour of these oil film coefficients. Coefficient calculations allowed viscosity to vary with temperature and pressure rendering the governing Reynolds Equation non-linear. A range of positive and negative displacement and velocity increments were examined. Novel experimental techniques have been developed which allow determination of coefficient variation with respective displacement and velocity. Coefficients were deduced from specially chosen, imposed vibration orbits arising from two mutually perpendicular external oscillating forces of variable relative magnitude and phase. Journal centre displacement and velocity were measured using high speed data logging equipment. A unique feature was the ability to obtain, experimental displacement coefficients from the results of both dynamic and incremental loading. It was found necessary to establish the bearing centre separately for each warm-up/load combination. Journal clearance in the hot rotating condition could not be measured to the precision required by its sensitivity to calculated load. Clearance and cavitation zone pressures were deduced from simultaneous predictions of the measured vertical load and attitude angle. Theoretical oil film tensile forces were necessary, a proposition supported by recently published experimental findings. Theoretical results for an equivalent uniform viscosity combined with experimental data gave a simple static locus design procedure. A temperature profile was assumed for theoretical work but choice thereof was found to be not critical. Coefficients are defined in terms of a "zero" value and linear gradient. Using realistic criteria, measured coefficient variation was found to be significant at eccentricity ratios greater than 0.78. Theory adequately predicted most "zero" values but not gradients. It is concluded that improvement in the coefficient prediction will
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.
Open Access
Airblast atomization : the effect of linear scale on the mean drop size
(1978-12) El-Shanawany, M. S. M. R.; Lefebvre, A. H.
Stationary prefilming-cup airblast atomizers, in which the fuel is first spread into a thin cylindrical sheet and then exposed on both sides to high velocity air, have several important advantages over other common methods of fuel injection in their application to continuous combustion systems. This thesis reports the results of a detailed programme of research on airblast atomization directed primarily to the investigation of the effect of atomizer linear scale, or size, on the mean drop diameter of sprays and, to the provision of a comprehensive picture of the performance of thin-sheet airblast atomizers over a wide range of working conditions. Three geometrically similar atomizers giving cross-sectional areas in the ratio of 1 : 4 : 16 were used; covering the range of prefilming cup diameter, D, from 19.05mm. to 76.20 millimeters, and were capable of handling various liquids at flow rates from 0.003kg/s up to 0.225 kg/s, at fuel pressures below 33 x 10^ N/m^ (about 50 p.s.i.). . It was found that atomizer scale has an appreciable direct effect on atomization quality. The Sauter mean diameter of low liquid viscosity sprays increases with the 0.44 power of atomizer linear dimension (D), while for liquids of high viscosity this effect is slightly higher.
Open Access
The behaviour of polyurethane foam beams reinforced with thin walled steel sections for use in bus structures
(1980-08) Gaafar, Labib A.; Tidbury, G. H.
The thesis is directed to the theoretical determination of the behaviour of rigid skin polyurethane foam beams reinforced with thin walled steel sections. The aim is to enable the designer to predict the behaviour of bus body structure during accident situations in order to build safe buses. A literature search has revealed that very little work has been done in this particular field of research. Thus a preliminary test programme was made to investigate the beam behaviour in bending particularly at high deflection. The test results shown in Chapter 1 gave promising results for continuing the research. Chapter 2 is directed to elastic analysis of composite beams. One of the advanced methods to predict the elastic stiffness of sandwich beams is the interfacial shear method. This assumes an interfacial shear between the core and the faces of sandwich beams. So, by considering a similar assumption, i.e. an interfacial shear between the matrix and the reinforcement, an analysis was made to predict the stiffness of composite beams. Although this method highly overestimated the stiffness, it represents a good basis for the inelastic bending analysis which is more important for the present study. Chapter • 3 shows the inelastic bending analysis of composite beams. This analysis is based on TIMOSHENKO and JAMES curvature area method. The experimental verification of the theory is shown in Chapter 4. The theory shows good agreement with the experimental results. The shape of the reinforcement was optimised for uniaxial bending. This optimum composite section showed a weight saving when it was compared with equivalent energy absorbing rectangular steel tube. Impact tests were made using a pendulum designed specially to test cantilever beams at different speed and impact energies. The test results are presented in Chapter 5. These results showed that the composite beams behaviour is similar for both static and dynamic loading. To compare the composite beam with the constituent beams, the large deflection behaviour of thin walled channel section beams made of thin sheet steel has been investigated. The experiments consisted of cantilever bending tests with the beam loaded through the shear centre and through the centroid. When loaded through the shear centre the beam buckling took place in the compression flange at the root of the cantilever. When loaded through the centroid however, it was noted that the compression flange buckled at a fixed distance from the fixed end. The general theory of thin walled beams developed by Vlasov was applied to the problem and indicated that the maximum compression stress at the free edge of the flange would be a maximum at some distance from the fixed end. The value of the maximum compression stress obtained by the general linear theory was small and its position did not coincide with the experimental position. The Vlasov analysis has been modified to include the increase in the twisting moment due to the lateral deformation- of the beam along its length. Good agreement between the modified theory and experiment both for the position of the maximum compressive stress and for the twist of the cantilever at three points along its length. Because of the very low torsional stiffness of thin walled channel sections, the small deflection theory is only applicable for small bending loads applied through the centroid and the modified theory should be used for practical loading cases.
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.
Open Access
Metal transfer in MIG welding
(1982-10) Ma, Jilong; Apps, R. L.
The metal transfer process in MIG welding has been investigated. The heat balance of the melting process, forces acting on the wire tip and droplets, and droplet movement were examined quantitatively both under steady current and pulsed current conditions. A novel transistorised power source was employed for precision current adjustment which with the use of high speed cinephotography and careful metallographic techniques has allowed a re-assessment of current theories to be made. A new metal transfer mode designated as ’Drop Spray* has been discovered. This transfer mode is located between the well known globular and spray transfer modes and only occurs in a very narrow current range of 20A, but it has several important features. The relationship between metal transfer mode and the welding variables has been established quantitatively for the first time. It was found that the extension resistance and heat content of droplets are determined by current and hence metal transfer modes. The amount of spatter and fume was also found to be determined by transfer mode. Metal transfer under pulsed current was also investigated. It was found that the metal transfer modes under pulsed current are the same as that of steady current. It was also found that the first drop of every pulse is of drop spray mode and the subsequent droplets will be stream spray. Careful observations and measurements have been made at various stages of the current pulse to enable greater understanding of the influence of the pulse parameters. Based on the results mentioned above, a concept of controlled MIG welding was proposed, based on the control of metal transfer mode. By this concept any predetermined feature of conventional MIG welding can be achieved consistently and repeatedly. As an application of the proposed concept, drop spray transfer was reproduced over a wide current range by means of metal transfer control. A new controlled MIG process designated as ’controlled drop spray MIG' has been developed which features high efficiency, all positional ability, freedom from spatter, low fume generation and good bead appearance. The preliminary bead on plate trial shows that all the expected results have been achieved although many more trials are necessary to fully prove the process.
Open Access
Acoustic emission pulse analysis: an integrated system for transducer calibration and signal processing
(1982-10) Oliveras, Juan M.; Bannister, R. H.
The present thesis covers the pioneering effort of establishing an infrastructure for conducting research into the analysis of Acoustic Emission signatures, with emphasis being placed upon the recovery of the true surface waveform for a given transient input. The topics covered in this work are: The p·rovi s ion of the necessary computer software for the handling and processing of the data. Here, a method is included for the correction of phase errors introduced by the sampling/multiplexing of ·the signals, which provides the basis for the implementation of data convolution.techniques in the frequency domain. J°he development of an experimental rig and source of excitation, later applied to the design of transducers. The development of a new transducer configuration, capable of producing a relatively flat frequency response (±7dB) over the frequency range 300 KHz - 2 MHz. The development of a procedure for the calibration of transducers, based upon a modified reciprocity method. The technique produces the calibration of transducers in relative terms, requiring a comple- . . mentary method to provide the reference level for the calibration. As a means of assessing the proposed techniques, the transducer calibration was applied to the de-convolution of pulses generated with a step forcing function, and the results compared with an equivalent theoretical model previously published.
Open Access
A theoretical and experimental investigation of erosion prone areas on the blade surfaces of a centrifugal impeller handling granular solids.
(1982-11) Ahmad, Khaled; Goulas, A.
The erosion prone areas on the blade surfaces of a centrifugal impeller handling granular solids have been investigated both theoretically and eperimentally. The objective of the theoretical study is to develop software to predict the erosion prone areas on the blade surfaces of a slurry handling impeller. The basic concept in the theoretical study has been to find the particle trajectories inside the impeller. The governing equations of the motion of particles within the impeller are solved in a stepwise manner with time for a given flow field. The flow field is calculated by solving the conservation equations for the flow, using a finite difference method. The number density of the particles in the cross-section of the pipe through which the particles enter the impeller is calculated by applying a discretization procedure to the insitu concentration profile of the particles. The damage to the surface caused by impacting particles is estimated by calculating the velocity and the angle at which the particles impact on a surface. The material property of the particle or the surface does not explicitly enter into calculations. It is shown that for a given combination of particles and surface material, the material property of the particles and the surface can be isolated. In this way a relative measure of the depth of volume loss at different positions of the surface can be calculated. The surface can then be divided into a number of erosion prone areas. The model is tested by undertaking a number of experiments using a commercially available slurry pump which handled a mixture of fine pea gravels in water. The predicted erosion pattern suggested the area near the leading edge to be the most erosion prone zone. The agreement with the experimental results in this respect was satisfactory. The extent of the erosion zone on the blade surface as suggested by the analytical model was in close agreement with the experimental values. The analytical model also suggested that the major part of the erosion areas would lie near the back shroud of the impeller. This was in close agreement with the experimental results.
Open Access
Unsteady aerodynamic response of the rotor blades of an axial flow compressor operating under conditions of circumferential inlet distortions and rotating stall
(1983-08) Ozcanli, S. C.; Das, D. K.
The aim of this work is to study the unsteady response of rotor blades of a lightly loaded single stage axial flow compressor experiencing inlet flow distortions in forms of circumferential pressure distortions and rotating stall . Recent developments in pressure transducer and microprocessor technology have enabled the research scientist to study the aerodynamic behaviour of rotor blades . Two rotor blades of the axial flow compressor have been instrumented with sixteen miniature pressure transducers , eight of which are on the pressure surface of one of the blades , while the remaining eight are on the suction surface of the other blade . An on-line microprocessor based data acquisition system has been developed to record simultaneously , measurements from each blade . Four different circumferential wire mesh screens of different extents and densities were employed at a distance of one chord length upstream from the blade leading edge to generate circumferential square wave pressure distortions . Also the compressor was run under conditions in the rotating stall regime . Flow parameters ahead of the rotor have been measured by using high response 3-hole cylindrical probes and a conventional 3-hole wedge probe . The values of the dynamic normal force coefficient were derived from instantaneous wall static pressure measurements on the two blade surfaces . The results obtained from the experiments were compared with the theoretical predictions.
Open Access
Wind-turbine studies: the power augmentation of flexible sail systems
(1984-03) Fleming, P. D.; Probert, S. D.
The origin of the wind-turbine is discussed and its subsequent development reviewed. Various types of sail wind-turbine are described and their advantages and different types detailed. Their appropriateness for driving water pumps in developed, as well as in developing, countries is examined and their benefits for rural communities of less developed countries outlined. The theoretical analysis of the behaviours of both propeller-type wind-turbines and of two-dimensional yacht sails are reviewed and their possible notifications to describe the performances of flexible-sail wind-turbines discussed. A novel, wind-turbine recorded. variable sail profile, vertical-axis Savonius has been developed and its power characteristics Self-regulating peristaltic displacement pumps are proposed to be driven by the horizontal or vertical-axis wind-turbines and their operating characteristics are described. A theoretical analysis relating the torque characteristic of the wind-turbine to that of the pump is outlined. Data are presented for the power augmentation of a horizontal-axis, flexible-sail type wind-turbine, using a shroud, tip-fins and centre-bodies. Considerable power enhancements are achievable using the basic, cheap wind-turbine power augmentors tested in this investigation.
Open Access
Numerical techniques for predicting aerodynamic characteristics of bodies
(1986-01) Deo, H. S.; Christopher, P. A. T.
Two methods are presented characteristics of bodies SUMMARY for predicting the aerodynamic in inviscid and irrotational flow. The first method is limited to incompressible flow and makes use of panels of ring sources to approximate the body surface. The technique is dedicated to single, axisymmetric body configurations in either uniform longitudinal or rectilinear motion. The versatility of the method is due to the use of sources as singularities placed on the body surface, allowing discontinuous body profiles to be analysed. The method has been compared for accuracy and efficiency with experimental and theoretical results. Further investigation showed that at present there existed no numerical technique which could predict the aerodynamic behaviour of multiple bodies in compressible flow. Hence, a fully three-dimensional method was developed which made use of the Full Potential Equation (F.P.E.) in conservative form. A computational mesh is placed around the body configuration and at each mesh node the F.P.E. is satisfied ~n finite difference form. The method is able to give a complete description of the flow around the bodies at transonic mach numbers. Comparisons to test the accuracy and efficiency of the method are limited to either, purely subsonic flow for two body configurations or zero incidence for transonic flow around a single body.
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, David
The 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.
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.
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.