PhD, EngD, MPhil and MSc by research theses (SAS)

Permanent URI for this collection

https://dspace.lib.cranfield.ac.uk/handle/1826/23

Browse

Now showing 1 - 20 of 699

Open Access
Superplasticity in Zn-based alloys
(Cranfield University, 1972-02-17) Naziri, Hurmuze; Pearce, Roger
This thesis is concerned with two-basic zinc-based superplastic . alloys, the virtually. single-phase Zn --0.4 wt % Al alloy and the two-phase Zn - Al eutectoid alloy. -The first investigation is concerned with superplasticityin the Zn - 0.4 % wt Al alloy, while the second investigation is devoted to the effect-of copper additions on-the behaviour of the Zn. - Al eutectoid superplastic alloy and the possible mechanisms operating during deformation. A-zinc - 0.4 Al alloy was developed, which showed a. remarkable degree of superplasticity. at room. temperature, and. elongations of greater than 500% could be obtained at the relatively fast crosshead velocity of 0.1 inch/min. The strain7rate sensitivity (m) was found to increase with strain up to 300% on elongation (. 35 -*-. 5)-parallel to the rolling . direction. and it was also found to be anisotropic in-the plane of the sheet. The strain ratio r was also strain dependent and varied in the plane of the sheet. At 900 to the rolling direction, the strain ratio. increased from . 35 to . 75 after an elongation of 350%, that is, tending to unity (isotropy). Texture determination after straining showed a marked change and agreed qualitatively with the change in strain ratio. Grain growth occurred at room temperature, but was observed to be inhibited on superplastic deformation. Surface observations after deformation revealed that grainboundary sliding was taking place; fracture behaviour, though characteristically ductile in nature, varied with strain-rate. This alloy obeyed the Hall-Petch relationship above. a certain critical grain size, below which it was inapplicable, due to the occurrence of superplasticity. Thin-foil transmission-electron microscopy showed the importance of a dislocation recovery Mechanism in the interpretation. of this deformation behaviour, and calculations based on the current theories of volume and grainboundary diffusion, grainboundary sliding and dislocation climb/recovery, showed-that a grainboundary sliding/dislocation-climb recovery model could reasonably predict the observed. strain rate sensitivity and strain-rate. Biaxial tests confirmed the anisotropic properties observed in uniaxial. tests and also in punch-stretching the effect of-friction on cup height was contrary to that observed with workhardening metals. In the second investigation, measurements of. the-flow stress (af) and. strain-rate. sensitivity (m). over a wide range of strain- . rates (6)-and temperatures between -75-to 3000C have been made on a range of superplastic alloys, based on. the Zn - Al eutectoid, but with additions of up to 1% copper. These additions do not significantly affect af or m above about-1500C. The peak in the m. -ý curve is not displaced. by these-copper additions at temperatures above 1500C. Increasing the grain-size (L) increases af for. temperatures above about 600C but decreases. of-below this temperature.. With increasing-grain-size, the peak in m-value moves towards lower L, The dependence of af vs.. La showed that the exponent a. was strain-rate dependent and varied, from 0.6 to I at 2500C. The exponent b in the relation ý vs. 1 was independent F of stress and varied from 1.8 at 2500C to 3 at L 200C. The activation energy was grain-size and stress-dependent, and for the smallest grain size (. 55 jim), a value. of about 14 k. cal/mole was obtained in the superplastic region, while a value of near 20 k-cal/mole was obtained at the low 6 region. Creep-rate - measurements-at room-temperature showed that the secondary creep- rate decreased with increasing copper. content,, by a factor-of about 120 between 0 and 1.0% copper. . Increasing the grain size from 0.55 Um to 1.75 Um decreased the creep-rate further by a-factor varying from 10-50 times and thus an overall gain in creep resistance of 1200 times can be obtained. Uniaxial tension, torsion and_camplastometer tests were. used to cover strain-rates between. 10 3. to 104'. -mirCl in order experimentally to determine the multistage. af -e curve. Hot-totsion stress-strain curves were typical of those shown in previous published work on hot working, and showed that a steady-state stress was obtained during superplasticity. . In uniaxial tension, elongations of greater than 1000% were obtained at the very high initial strain-rate of 1.6 x 101 min-1. Grain coarsening occurred during deformation and was found to be strain-rate and strain dependent. Thin-foil transmission electron microscopy showed the extensive activity. of dislocations and diffusional processes. Dislocation-free structures and rounded interphase boundaries-were observed under . superplastic. conditions. Also, though many of the grains appeared equiaxed after deformation, a variety of odd-shaped grains were observed, particularly in hot torsion, where there was evidence of accelerated spherodization. Fracture. behaviour was dependent on grain size, temperature and strain-rate sensitivity. Calculated of curves,. from current theories, suggested that a dislocation-climb-recovery/grainboundary sliding model, based on grainboundary diffusivity was the operating mechanism during superplasticity.
Open Access
The warm forming of aluminium/magnesium alloy sheet
(Cranfield University, 1979-08) Shehata, Farouk; Pearce, Roger
The desire to reduce the overall motor vehicle weight, and so use less fuel, means that aluminium alloys are now being considered for car bodies. Unfortunately, increase in strength generally leads to a decrease in ductility, because of the alloying additions. Warm forming however , of the Al/Mg series of alloys restores and enhances ductility to a remarkable degree. Cont/d
Open Access
Creep Fatigue Analysis of a Nickel Superalloy over the Range 750-1040°C
(Cranfield University, 1979-09) de Abreu e Antunes, V. T.; Hancock, P.
After the review of the predictive methods in the high temperature fatigue field the characterization of the low cycle fatigue behaviour of a nickel superalloy, t4ARMOO2, is carried out using one of those predictive methods, the Strainranqe Partitioning method. The basic concepts and procedures of this method are reviewed and applied to NARt"O02 over the range 750° - 1040 C. -These'procedures invol ed the determination of the four basic life relationships at P50 C and 1040°C and their use in conjunction with a damage rule were then employed to assess the degree of insensitivity of the four basic strainrange versus life relationships to test temperature. Three damage rules and the assumptions behind them are discussed within the context of their application with the Stra i nrange Partitioning approach. An alternative analysis based on Ostergren's method is studied in a separate chapter and proved to be an easy and helpful method in predicting high temperature lot., cycle fatigue of several superalloys. The characterization of the creep-fatigue behaviour of 1,4F. RP"002 was completed by separation of initiation and propagation periods within two temperature intervals. A situation of earl formation of cracks at the higher temperature intervaa 950°- l040 C with accelerated growth. at lower tennperatures 750 - 250oC showed that great care is necessary when applying MAPP"002 isothermal results to cases where temperature varies.
Open Access
Cavitation of superplastic alloys: a study using a hot microhardness technique
(Cranfield University, 1980-01) Sohal, Gurnam Singh; Pearce, Roger
This thesis is concerned with the study of cavitation behaviour of two-phase superplastic alloys, using mainly a hot microhardness technique. Cavitation is a serious problem in copper and iron base alloys, it drastically limits the elongation to failure and may affect the service properties of superplastically formed components. There is some empirical evidence to suggest that, for cavitation to occur, the two phases involved must be 'incompatible' that is, they show marked differences in certain properties. Ideally, this phenomenon would be investigated directly by an in-situ study of the deformation behaviour of each phase separately in the microduplex alloy at the superplastic temperature and hence pinpointing the phase incompatibilities, but existing techniques do not allow for this. Here, a hot microhardness tester was commissioned and used to determine the hardness and activation energy of each phase in-situ in a duplex alloy in thc superplastic temperature range. Zn/Al eutectoid and 60/40 brass were here used as models to represent a non-cavitating and cavitating class of superplastic alloys. In addition, a series of alloys were produced of compositions corresponding to those of the individual phases in these systems over a supcrplastic temperature range. These alloys were hot tensile. tested to find the ductility and ten'fle strength of each phase of superplastic alloy. The hot hardness data was correlated with the hot tensile data for the alloys over the whole temperature range from 0.4 to 0.84 Tm. Variation of Young's modulus with temperature was determined by a vibration technique and activation energy calculated form LnH versus Tm plots for all the alloys. In 60; 40 brass, the amount E of -T cavitation decreased with an increase in temperatur% and this alloy gave a maximum elongation of ti 110 pct at 250°C 1,0.45 Trrj, but it still exhibited extensive cavitation. In the Zn/Al eutectoid, no cavitation was observed apart from that associated with a few large inclusions. The hardness values of the two phases in a/ß brass were very different at the superplastic temperature, as were the load extension curves from the tensile tests and the calculated activation energies. In. the Zn/Al eutectoid however, the mechanical properties of the two phases were similar, though the activation energies were different. Finally, an attempt was made to explain the occurrence of cavitation in Supral 150 and certain steels, in some cases experimentally and in others from data available in the literature.
Open Access
Fracture toughness testing of a weldable steel
(Cranfield University, 1981-08) Al-Hadithy, Nabil Abdul-Jalil; Hancock, P.
The mechanical anisotropies of two varieties of BS 4360 50D steel were demonstrated for tensile, Charpy V impact and COD testing. The detrimental effect of sulphide inclusions for through thickness behaviour was related to the total inclusion length per unit area and the interaction of inclusions within the plastic zone. Sulphide inclusions in the through thickness orientation were found to increase crack tip constraints, reduce the plastic zone size and the post-yield load bearing capacity of the specimen ligament. This was achieved by the ease of movement of the growing crack tip to various planes containing suitable clusters of inclusions. COD at maximum load was shown to decrease exponentially with increasing inclusion content. For acceptable through thickness toughness it was shown necessary to limit the inclusion density to 1 to 1.5mm/mm2, according to the constraints in its application. For plate or pipe material made from highly rolled steel, low sulphur steel melts must be used. Even rare-earth-modified steels will show unacceptable inclusion densities after high rolling strains in the mill. The inclusion density would increase both in the ZR and ZT through thickness directions. Notches along the rolling plane gave lower toughness levels due to inclusion interactions out-of-plane facilitated by the added length of the inclusion caused by hot rolling. A computer program was included which uses a polynomial fitting technique relating COD to inclusion density to predict through thickness toughness for any given inclusion content. A method was devised for through thickness testing of thin plate materials. Valid maximum load COD values were obtained by friction welding of extensions to undersized specimens. The effect of free surfaces that interacted with the plastic zone at the crack tip were found to be beneficial to crack tip deformations. For these reasons thin plates were shown to be unsusceptible to through thickness failures, such as, lamellar tearing, unless the effects of the free surface were removed by welding attachments to the surface. At upper shelf temperatures for ductile structural materials, it was shown that the measured toughness was related to the size of the plastic zone and, hence, to specimen geometry. The measured toughness related more to the absolute length of uncracked ligament rather than to crack length or crack length to width ratio. To -achieve geometry independence, the ligament length was required to be greater than the characteristic plastic zone size for the specimen thickness and testing temperature. The extensive plastic zone and the small highly strained zone sizes were shown to be dependent on temperature. At high temperatures the crack tip strains increased which resulted in crack blunting and stress dissipation. The work hardened material ahead of the crack tip showed evidence of small crack fissuring which led to stable crack growth. At low temperatures, where brittle fracture occurred, the highly strained region and extensive plastic zone were much smaller in size. Crack blunting was greatly reduced which allowed brittle fracture stresses to be achieved at the crack tip. At intermediate temperatures the crack tip blunting was extensive and it was shown that the amount of ductile cracking required to increase the constraint necessary to achieve brittle fracture decreased with decreasing temperature. Large specimen sizes resulted in high stored energy which, at transition temperatures, drove the ductile crack to catastrophic failures. This resulted in narrower transition regions which effectively shifted the transition to higher temperatures. The transition from ductile to brittle behaviour was considered, from the experimental evidence supplied, not to represent a shift in the state of stress. The through-thickness strain decrease associated with this transition was a result'of the associated decrease in COD. As the COD was shown to vary with specimen geometry independently of specimen thickness and, hence, independ- ently of the state of stress, then the associated change in through thickness strains were also not indicative of a change in the state of stress. A shift in the state of stress was considered to occur only when the through thickness strains varied with respect to COD. The method of load application was shown to have a significant effect on the measured toughness. Generally yielded specimens were shown to be under greater crack tip constraints when the specimen was loaded in bending rather then in tension.
Open Access
The Characteristics and Structure of High Pressure (1-42 bars) Gas Tungsten Arcs
(Cranfield University, 1982) Allum, C. J.; Apps, R. L.
The last decade has seen a considerable growth in the exploitation of deep sea mineral reserves. Accompanying these developments has come the need for suitable underwater repair and uainten-nce techniques. one such technique involves the use of fusion welding processes in localised dry high pressure environments created around weldments. Pressure chambers at Cranfield have been employed to simulate this sitiu. ation. These have been used to investigate the influence of ambient pressure (1 to 45 bars) on gas-tungsten arcs. The study has been of a basic nature with emphasis on arc characteristics and arc structure. Special attention is given to the argon TIG arc although helium TIG arcs and constricted argon-tungsten arcs have also been examined. Arc characteristics are reported in terms of arc appearance and modes, electrical characteristics and weld bead studies. The investigation of arc structure is concerned with gaining an understanding of observed characteristics. This has involved experimental and theoretical developments. Experimental techniques used include, electrostatic probes, calorimetry and the measurement of total power radiated from an arc. Models developed here have successfully explained many of the experimental findings and special emphasis has been directed at understanding gas flow in the column and arc stability. Much of the work included in this thesis has implications for the development of underwater welding procedures. Results presented should also contribute to gaining a better understanding of arcs operating under normal ambient conditions. However, these aspects are not discussed in any detail as the main emphasis has been placed on documenting and explaining the influence of pressure on gas-tungsten arcs.
Open Access
Laboratory experimentation for the statistical derivation of equations for soil erosion modelling and soil conservation design.
(Cranfield University, 1982-04) Quansah, C.; Morgan, R. P. C.
Since Ellison (1947) described the process of erosion as comprising a) the detachment of soil particles from the soil mass by raindrop impact, b) detachment by runoff, c) the transport of the detached particles by raindrop impact, and d) transport by runoff, research has been directed into the mechanics of each of these four phases and how the phases might be linked together in the form of a soil erosion model, such as the Meyer-Wischmeier (1969) model. From a literature review, it became evident that in spite of this work, gaps in knowledge still exist and that i) most studies on soil erosion tend to lump the processes together; ii) whilst a considerable amount of investigation has been carried out on splash erosion, the other processes have received very little attention; iii) there is no explicit study on the effects of factor-interactions on the processes and the role of the laboratory as a place for studying interactions by controlling factors has not attracted much attention; iv) equipment and techniques for the separate evaluation of the detachment and transport of soil particles by overland flow are not available; and v) studies on the hydraulic characteristics of overland flow in relation to the detachment and transport of soil particles in such flows are scarce. This study was therefore specifically aimed at establishing a sounder research base for modelling the subprocesses and ultimate~ for soil conservation design b,y: i) evaluating separate~ each of the above subprocesses; ii) assessing the influence of the factors affecting the processes, particular~ their interactioDS; and iii) examining the hydraulics of soil particle detachment and transport by overland flow with and without rain. As a means to achieve these objectives, a factorial experiment vas set up in the laboratory to examine both the individual effects of rainfall intensity (50, 80, 110, 140 mm h- 1 ) , soil ~ (standard sand, ISIUld, clay loam and clay) and slope steep:1.8Ss (3.5, 7.0, 10.5 and 14.0 per cent) and their interactions on each of the above subprocesses. Additionally, the effects of four rates of runoff (1.0, 1.6, 2.2 and 2.8 ~min) on the hydraulic characteristics of flow such as velocity, depth, Reyuolds number, Froude number and friction factor were examined and used in characterizing the detachment and transport of soil particles in these flows. For each subprocess, these variables were replicated four times. Splash detachment and transport were determined by simulating rainfall from a nozzle simulator over a target soil placed in a rectangular soil tray (10 x 20 x 4 cm) which being set in the centre of a catching tray (90 x 80 x 30 cm) allows for the separate determination of ups lope and downslope splash. The separate measurement of the detachment and transport of soil particles by overland flow with and without rain was carried out b,y using a specially designed rainfall simulator - bed flume facility with runoff and sediment input and measuring devices. The results were analysed by analysis of variance to show the Significance of soil type, rainfall in tensi ty, flow rate t slope steepness and their first and second order interactions in influencing the processes studied. Multiple correlation techniques were used to search for the best associations between the erosion influencing variables and soil loss. RegreSSion analySis was used for establishing predictive equations for detachment and transport rates. Detachment of the test soils by splash can be placed in rank order of standard sand, sand, clay and clay loam with increasing resistance. For splash transport the order is standard sand ) clay > sand > clay loam. For each soil type there are significant increases in splash detachment and transport with increasing rain intensity and slope steepness. The most significant interactions influencing the two splash processes are soil x intensity and slope x intensity for detachment and transport respectivel,J. Significant interactions show that the factors are not independent of each other; the simple effects of a factor differ, and the magnitude of any simple effect varies according to the level of the other factors of the interaction term. The factors influencing detachment by flow without rain rank in ~ order of importance as soil type, slope steepness and discharge. The corresponding order for flow with rain is discharge, slope steepness and soil type. The order of soil detachability for both flow with and without rain is standard sand , sand ~ clay loam> clay. There are also significant increases in detachment rate as slope steepness and flow rate increase. It is further shown that the first and second order interactions of the above factors Significantly influence detachment by flow. On a relative basis, the second order interaction is small and the importance of the first order interactions can be placed in an increasing order of slope x soil, slope x discharge t and discharge x soil for flow without rain. For flow with rain, they rank as slope x soil, discharge x soil, and slope x discharge. The slope x soil interaction showed that as slope steepens the influence of each Boil on detachment rates increases with the proportionate increase being greater for sand and standard sand than for clay and clay loam. The slope x discharge interaction revealed significant increases in detachment rate for all slopes as discharge increased. The magnitude of the response is however greater at the lower than higher slopes. As slope steepness increases, detachment rates by flow with and without rain are also enhanced. The increase was proportionately more for the 1.0 and 1.6 J/min than 2.2 and 2.8 J/min flows. The Boil x discharge interactiC?n also indicated that, for flow without rain, detachability increases more for clay and clay loam than for the sand and standal'd sand as discharge increases. In the presence of rain however, the response of the soils did not differ much. Detachment by flow without rain is predominantly by rilling. In the presence of rain, detacbment rates by flow are increased about three fold and relatively even removal of soil particles from the eroding bed is characteristic. Raindrop impact thus appears to inhibit rill formation by overland flow especially on small slope steepnesses. There is a critical slope steepness at which both raindrop impact and overland flow contribute equally to total detachment. At slopes lower than the critical value, raindrop impact is the main detaching agent whilst flow predominates the detachment process at steeper slopes. The critical slope steepness is soil specific and decreases in the order of clay ~ clay loam ) sand ~ standard sand. The transport of soil particles by combined flow and rain is significantly influenced by soil type, slope steepness, flow rate and their first and second order interactions. Transport rates decreased in the order of sand > standard sand ) clay ) clay loam. Increases in discharge and slope steepness significantly increased transport capacity. For a discharge range of 1.0 - 2.8 l/min, transport capacity increased four fold. The most significant interaction that influences transport capacity is slope x soil. Where factors interact significantly, interpretation of results based solely on the main effects of the influencing factors m&1 result in loss of vital information and lead to wrong conclusions. For example, examination of the slope x soil interaction showed that at lower slopes (3.5 and 7.0 per cent) combined flow and rain has a greater transport capacity for the larger clay and clay loam aggregates than for the fine grains of sand and standard sand. This is obscured when effects are averaged over all the slopes as is the case when only main effects are considered.
Open Access
Static and Dynamic Fracture of Structural Steel.
(Cranfield University, 1983-11) Smith, Paul; Hancock, P.; Spurrier, J.
The present study is concerned with the assessnent of structural steel fracture toughness, as close to real service loading conditions as practically possible in the laboratory, using small scale specimens. The effects of stored strain energy content is evaluated for slow-static and dynamic COD tests for maximum load and cleavage instability. The literature reviews elastic-plastic fracture mechanics and goes on to study the effect of stored strain energy, the COD technique and dynamic testing procedures presently available. Static and dynamic fracture toughness testing using the COD technique is carried out on BS4360 - 50D structural steel in its normalised state. The testing procedures used closely relate to either the BS5762 COD standard or BS5447 plane strain standard. The specimen size tested is 2B =U= 24 mn, with a fatigue notch size of approximately a/W between 0.48 and 0.57. Photographic-macros and SEM fractography were carried out after the specimens were tested to assess the micromechanism processes operative during a fracture test. It is believed the present work is of special significance to determinate structural design using structural steel, for example with liquefied gas pressure vessels. The resulting test data available from this thesis is envisaged to be the closest approach to real service "true limit severity", and consequently is beneficial to fracture prevention technology.
Open Access
Phenomenological investigation of the influence of Cathodic protection on corrosion fatigue crack propagation behaviour, in a BS 4360 50D type structural steel and associated weldment microstructures, in a marine environment.
(Cranfield University, 1984-06) Thompson, J. W. C.; Hockenhull, B. S.
The influence of Cathodic Protection potential upon corrosion fatigue crack propagation rates in a medium7strength ferritic-pearlitic structural steel (ES 4360 grade 50D) and associated weldment microstructures in simulated sea-water was studied and the results were presented in bi-modal da/dN vs AK curves. Above transition propagation rate data was satisfactorily described by the Paris relationship da/dN = C. AKm and a relationship of the formin = Aln C+D between Paris exponent m and constant C was confirmed. In all microstructures the influence of cathodic protection on crack propagation rate was found to be dependent upon the level of cathodic potential applied and crack depth. A. critical crack depth of approximately 5.0mm was identified. Optical crack monitoring combined with graphical data processing, was found to be particularly effective for the characterisation of corrosion fatigue crack propagation behaviour and resulted in minimal data scatter. The phenomena of transition which was evident in the bi-modal da/dN vs LK curves was found to be associated with secondary or branched-crack activity. Back-extrapolation of below transition data was used to estimate Arm values and showed that the weldment beat-affected zone microstructure was a major potential source of fatigue or corrosion fatigue fracture. The effect of a single cycle of simulated overload, to stormload levels, on both fatigue and corrosion fatigue crack propagation behaviour in parent plate material was studied and the phenomenon of retardation was confirmed.
Open Access
Methanol dehydrogenase biofuel cells and enzyme-based electrodes
(Cranfield University, 1984-12) Aston, W. J.; Higgins, I. J.; Turner, Anthony P. F.
This thesis describes the linking of enzymes to electrodes and their application in biofuel cells and as analytical devices. Methanol dehydrogenase, an NAD independent enzyme was purified by two phase aqueous partition. The enzyme incorporated into a biofuel cell was capable of producing a current in the presence of either a soluble or insoluble mediator. Optimisation of the current was carried out and a variety of alternative membranes, mediators and electrodes were investigated for possible use in the biofuel cell. Although laboratory studies involved the use of platinum electrodes and the soluble mediator N,N,N',N' tetramethyl-p-phenylenediamine, other configurations were investigated, including modified membranes and electrodes. The ability to detect methanol coulometrically in solution led to the construction of a homogeneous poised potential sensor. The device was capable of detecting methanol at concentrations in solution as low as 0.02uM. the sensor was unaffected by many potential interfering compounds present in water supplies and was used in the analysis of water samples. The retention of the enzyme in the presence of the insoluble mediator 1,1'-dimethylferrocene allowed the construction of a probe. The probe was unaffected by fluctuations in the oxygen tension and was capable of detecting methanol in the range 0.9 uM to 0.1 mM. Covalent immobilisation of glucose oxidase in the presence of 1,1'-dimethylferrocene enabled the amperometric determination of glucose in the range 0.01 - 30 mM. The device was independent of pH in the normal physiological range with a temperature coefficient of 4.0% degrees-1. The electrode was used to assay both buffered glucose samples and preliminary work was carried out on untreated samples from diabetic and non-diabetic patients.
Open Access
Removal of internal porosity in Supral 150 by hot isostatic pressing
(Cranfield University, 1985) Ahmed, Hamayun Kabeer; Pearce, Roger
In recent years, considerable concern has been shown about the effects SPF cavitation has on the mechanical properties of superplastic alloys. This investigation was undertaken to ascertain whether Hot Isostatic Pressure (HIP) eliminated this cavitation in Supral 150 and correspondingly brought about an improvement in the mechanical properties. It was found that the density increased with various isothermal anneals; the activation energy for this process was close to that for grain boundary diffusion in aluminium (61.93 KJ mol-1). The rate of cavity sintering was seen experimentally to be enhanced by the application of pressures greater than 7 HPa, and had an activation energy of 62.42KJ mol-1. Complete cavity closure occurred when the external pressure was greater than the flow stress of the material at thaý temperature and strain-rate; the ratio of external pressure (Pe) to flow stress (of) increased with falling HIP temperature. The activation energy at constant strain-rate (Q-) associated with plastic flow under conditions of hole closure was found to be 53.54KJ mol-1; giving a corresponding activation energy at constant stress (Qa), which is close to that for lattice diffusion in aluminium. The alloy used contained a high level of hydrogen which caused blistering on heat treatment, and was also responsible for the reappearance of porosity in subsequently heat-treated material previously returned to theoretical density; the extent of which was decreased by the use of higher temperatures and pressures or by vacuum degassing the material prior to HIP. Post SPF room temperature ductility was enhanced by HIP. The scatter in the 0.2% PS and UTS values found in as-received SPF specimens was not altered by the use of low pressure HIP (up to 35 MPa), although higher pressures (100 NPa) did slightly enhance these values and drastically reduced the scatter. Room temperature fracture of as-received Supral was by a 450 ductile shear mechanism. In the SPF cavitated material, the external characteristics Of fracture had a more jagged appearance, as the cavitation alters the route of the propagating crack. SPF material which has been HIPped to remove cavitation, fails in a manner similar to the as-received material.
Open Access
An investigation into the mechanics of powered rotary tillage tools
(Cranfield University, 1985-01) Thakur, Tara Chandra.; Godwin, R. J.
A prediction model based upon Mohr-Coulomb soil mechanics theory has been developed to predict the itneraction between the soil and a rotary tiler blade with horizontal axis of rotation by neglecting the quasi-static reaction and the dynamic soil reactions due to acceleration of the deformed soil slice and sinkage of the chamfered back face of the blade as a special case. The quasi-static force prediction model is dependent upon the passive general shear failure of the soil slice towards the curved free surface of a previous cut and the lateral local shear failure towards the undeformed soil due to the effect of the tip. Cont/d.
Open Access
Soil Compactability
(Cranfield University, 1985-08) Seig, D. A.; Spoor, Gordon
Subsoiling and deep loosening are widely used to alleviate soil compaction but little is known about the mechanics of the compaction process. Further information is required on the process that soil goes through during compaction, along with the effect on the amount of soil compaction of various tyre configurations. Such information will allow more confident recommendations to farmers on the suceptability of their soil to compaction. Experimental work was conducted where the soil deformtions of a light textured soil were monitored throughout the whole soil mass. The deformations in the soil were caused by a loaded pneumtic tyre on the surface. In the experimental work, both the process of soil compaction and the final state of the soil following the passage of a wheel were monitored. The experiments showed that soil compaction on light textured soils is caused by a punch failure of the soil, therefore most of the compaction is confined to the area directly below the wheel. The experimental monitoring of soil deformations was a slow and complex process, drawing firm conclusions from the work was further complicated by the interactions of the input variables, such as load and contact length. In order to monitor the effect of individual inputs on soil compaction a thre dimensional mathematical model of the process was developed from Theories of Elasticity and a confined compression soil test. The model predicted the subsurface deformations in the three principle directions due to surface loads. Once the model was modified to account for the support capability of the soil it proved it could, with resonable accuracy, predict the defomations and hence soil canpaction due to a tyre on the soil surface. The model was used to predict the effect of various tyre configurations on soil ccrnpaction. From a number of these runs it was possible to find the sensitivity of soil to compaction due to that input. The results showed that the sensitivity of soil to ccmpaction is not a linear relationship and significant reductions in the amount of soil, canpacted and the level of ihe compaction can be achieved by the right tyre configuration.
Open Access
An Investigation into the Grade Dynamics of Drainage Implements
(Cranfield University, 1985-08) Magalhäes, Paulo Sergio Graziano; Godwin, R. J.
The use of the trenchless plough drainage implement has increased in the past few years due to its efficiency and cost advantages over other methods. However, the performance of these machines when working in fields with irregular soil conditions is not yet satisfactory. It is important therefore to study the soil parameters and conditions which could affect the implement behaviour under these circumstances. Therefore, a detailed investigation of the soil reaction forces acting upon a scale model of the trenchless plough was conducted under controlled conditions in a soil laboratory. The model was tested first under restricted conditions of movement, in order to observe and determine all the possible soil reaction forces. The tine, due to its geometric characteristics, was classified as a very narrow tine, and an existing model to predict the soil reaction force acting on the front face of these tines was extended to predict the forces on the sides. Since the length of the failure plane ahead of the tine is often required in the investigation of the soil reaction forces, a mathematical solution based on the Coulomb principle of Passive Earth Pressure was presented to estimate the soil failure pattern. There was good agreement between the values of the angle of the shear plane predicted by this method and the experimental data obtained from the glass sided tank tests. Dynamic tests were conducted with the implement assembled with a long floating beam arrangement assisted by a small link (free-link), used between the hitch-point and the pivoted end of the beam. These tests revealed that, when working over irregular soil conditions a better grade control can be obtained if the hitch-point is kept at constant level in reference to a desired line. In the case where field irregularities persist for long (step inputs), corrections in the hitch-point height might be necessary. These tests show that the implement depth changes in different proportion in relation to the hitch-point height. Where no control is imposed on the hitch-point, the path of the implement is attenuated in relation to the hitch-point position, where better results are obtained for high frequency of the hitch-point. A mathematical solution based on these findings and on the dynamic balance of the forces acting on the system was presented. Since it is an interactive method and requires long and repetitive calculations, a computer programme was developed and used to predict the response of the implement under these uneven conditions. Good agreement between data and estimated values suggested that the method is acceptable.
Open Access
Corrosion Fatigue Crack Propagation Behaviour of a High Strength Low Alloy Steel in a Synthetic Sea Water Environment.
(Cranfield University, 1986-12) Millar, Peter G.; Hockenhull, B. S.
The corrosion fatigue crack propagation behaviour of a high strength low alloy steel, N-A-XTRA 70, in a synthetic sea water solution was tested using S. E. N. specimens subjected to a loading frequency of 0.1 Hz and a load ratio of 0.6. In order to simulate the conditions encountered by a thumbnail type crack several specimens from each of the microstructural types tested, namely parent plate, heat affected zone and heat treated material, had their crack sides covered by transparent plastic covers. Severe overprotection and slight underprotection conditions were produced using cathodic protection potentials of -1400, -1300, -1200 and -700 mV (S. C. E. ). The Paris relationship da/dN = CLKm was found to be a useful tool in describing the crack propagation rate data. Results obtained, presented in the form of plots of log da/dN against log AK, show that for parent plate, H. A. Z. and heat treated material, covering the crack sides of specimens produces enhanced corrosion fatigue crack propagation rates, at cathodic protection potentials of -1400 and -1300 mV (S. C. E. ), when compared to non covered specimens. This trend was also true for H. A. Z. specimens at a potential of -700 mV (S. C. E. ). For parent plate specimens, however, covering the crack sides at a potential of -700 mV (S. C. E. ) produced reduced crack propagation rates over non covered specimens. It is believed restriced oxygen access may account for these results. Plots of the Paris exponent m and constant C for the three microstructures tested produced three lines of the form m= alnC +b where a and b were found to be dependent upon material parameters. Comparison of results with BS 4360: 50D revealed that N-A-XTRA 70 exhibited superior fatigue performance when tested in air but behaved worse under conditions of free corrosion.
Open Access
The development and application of a simulation approach to advanced manufacturing systems planning
(Cranfield University, 1987-07) Mills, R. I.; Rathmill, K.
In the competitive field of metalworking industry, the planning of manufacturing systems so as to maximise their performance is crucial. The relatively new field of Flexible Manufacturing Systems presents a new set of planning challenges to the production engineer. This is due to the integrated nature of the these systems and the resultant effects upon their performance. This thesis presents a structured approach to the planning of materials flow within these systems and develops it by the analysis of several proposed manufacturing systems. The approach is based upon the use of mathematical and discrete event simulation techniques. The thesis gives the background to the need for a structured approach, investigates the parallel development of simulation languages and related techniques as applied to manufacturing facilities planning; and of the Flexible Manufacturing Systems themselves. The approach is then detailed and some specific types of planning tool are identified as suitable for use at each project stage. The effects upon the system of the integration of separate units, especially in low work in progress environments, are discussed in some detail. The methodology developed is then used in the context of three projects, specifically developing the theme of automated tool handling and the requirements that it places upon other aspects of a manufacturing system. The projects cover the analysis of pooling strategies, a key factor in determining tool magazine sizes and handling capacity/frequency demands; an academic analysis of a system with both component and tool handling systems; and an advanced Flexible Manufacturing System, also with both automated component and tool handling, which is currently being installed. Conclusions are presented at each stage, and these are drawn together to form a foundation for the planning of materials flow within Flexible Manufacturing Systems in general. Finally, suggestions are made for future work to develop the analysis.
Open Access
A study of fatigue crack propagation in quenched and tempered and controlled rolled HSLA steels.
(Cranfield University, 1987-09) Callister, D. R.; Billingham, J.; Hockenhull, B. S.
A range of HSLA steels reflecting the two major processing routes, quench and tempering and controlled rolling, have been tested in fatigue to assess their potential wider application in the offshore Industry. The six steels chosen have a wide range of yield strenghts (470 to 690Nmm-2), fracture toughness (31 to 260J at -40°C) and carbon equivalent values (0.19 to 0.33). Fatigue testing has in general been carried out at low frequency (0.5Hz) and high load ratio (0.6) however some tests have been conducted at very low frequency (0.1Hz) and low load ratio (0.1). An in-air study was first used to assess the fatigue performance of all six parent plates. Five steels were welded by the Submerged Arc Welding process at high heat input (1.5kJmm -1) to evaluate the Heat Affected Zone (HAZ) fatigue performance. A new test was devised to grow a fatigue crack through a single pass, bead on plate-, HAZ whilst maintaining a constant stress intensity range. The surface crack length was continuously monitored and recorded to an accuracy of 0.01mm. A corrosion fatigue study evaluated the performance of one controlled rolled and one quenched and tempered steel at three levels of impressed current cathodic protection. Extensive metallographic examination was made to study the influence of microstructural features and types on fatigue crack propagation. Techniques used include optical microscopy, scanning electron microscopy, fatigue crack and surface replication and crack profile digitising. These techniques give an assessment of crack path deviation and branching, the influence of precipitates and inclusions, and an indication of the mode of fatigue crack propagation. The wide range of microalloyed HSLA steels tested have shown a significant improvement in fatigue crack propagation resistance over structural steels conforming to BS 4360 grade 50D. Typically an improvement by a factor of two has been observed. Whilst the observed increase in fatigue life was slightly reduced by high heat input welding the slope of the Paris curves remained unaffected thus indicating a similar stress intensity range sensitivity in the HAZ to that shown by the parent plate. The newly developed crack monitoring system coupled to a computer controlled fatigue testing machine has shown a wide variation in fatigue crack propagation rates through a heat affected zone microstructural gradient. Growth rates have increased by a factor of ten in localised coarse grained microstructural regions compared to the adjacent weld metal and outer heat affected zone. The corrosion fatigue study has also indicated that in general HSLA steels retain their superiour fatigue resistance compared to structural steels and in particular respond more favourably to cathodic protection. Both in-air and corrosion fatigue studies have indicated that the controlled rolled steel microstructures developed mainly for line pipe application has the greatest potential for increased use offshore.
Open Access
The Development of A mathematical Model to Predict Runoff From A micro-catchment under High Water Application Rates
(Cranfield University, 1988-05) Abo-Ghobar, Hussein Mohammed Ali; Kay, M. G.
Current trends in sprinkler irrigation to improve application uniformity and reduce energy requirements haste led to problems of water application and potential surface runoff, which in turn have highlighted the importance of the soil and cultivation practice in making best use of irrigation water. The objective of this study was to begin the development of a mathematical model, which will simulate the operation of current sprinkler-soil-crop system, in order to provide a means of predicting surface runoff and so provide a more effective approach to system design. A model has now been developed which will predict runoff from a small simple agricultural catchment in the form of a ridge and furrow ciltivation system. The model is based on the kinematic wave theory involving the continuity equation and the simplified momentum equation. A four-point implicit finite difference scheme is used to solve numerically the kinematic wave equations. The model (SROFF) may be used to predict the runoff at various times from a simple catchment with different slopes, water application rates and soil infiltration rate. A further development of the model was made by the introduction of the interception loss model (INCEPT) to predict the amount of water intercepted by the crop canopy during irrigation. The validity of the model was tested and supported by the results of laboratory experiments conducted on two soil samples with different infiltration rates, using three different application rates. The performance of the model was also evaluated by statistical test. There was good agreement between experiment and model results. The results indicated that this model can provide valuable information for the effective design of sprinkler systems, particularly where runoff may be a potential problem. This is particularly the case with current low pressure irrigation systems but equally the problem is common with high pressure systems when applied to soils with low infiltration rates.
Open Access
Railway management : an evaluation of management cybernetics in a public enterprise
(Cranfield University, 1989-03) Paradissopoulos, Iordanis K.; Seaton, R. A. F.
Two are the objectives of this thesis: To identify structural and cultural causes of ineffectiveness in a state-owned railway enterprise in the light of the management cybernetics area of knowledge. To assess the capacity of this area of knowledge, especially in its abstract and coded form (Beer's Model of the Viable System), to provide adequate explanations of organizational performance and organizational failure. The objectives are sought in the analysis of an actual enterprise, the Greek Railways Organization (OSE). An 'ethnographic type' pilot study is initially undertaken, to highlight organizational problems under a management cybernetics perspective. The study, though demonstrating structural problems associated with a certain organizational culture, is assumed in itself inadequate, as it reflects a subjective interpretation of reality. A 'survey within the case study' is therefore undertaken aiming at deriving the real dimensions of organizational problems from an analysis of managerial responses. Responses are designed to provide a picture of both the actual way in which the enterprise organizes in the pursuit of its tasks, and the organizational culture. The first subtheme (organizational structure) is examined in terms of the cybernetic model of the viable organization. The findings, in general, validate the assumptions of the ethnographic study. Numerous structural problems are identified. The second subtheme (culture) is examined in terms of managerial cohesiveness, defined as the agreement between managers on key issues of the identity of the enterprise. The overall conclusion is that though managers are, in general, in agreement, the content of this agreement tends rather to reflect a shared pessimistic view of the future than cohesiveness facilitating viability and development. The conclusion, as regards the enterprise, is, that though many problems are reflected in the organizational structure, proper modifications of this structure may not suffice to guarantee improved performance, unless considerable attention is paid in the building of a relevant organizational culture, quite difficult under the specific circumstances. The conclusion, as regards the adopted methodology, is that though Beer's model of the viable system assists in a diagnosis of many organizational deficiencies, it may not suffice to promote organizational change, especially when narrowly perceived, i. e., when results to a concentration on structural arrangements in the expense of the building of a corporate culture. Certain methodologies should develop, which, while making use of the advantages of the model, will not underestimate other significant aspects of organizational reality.
Open Access
An investigation into the mechanics of agricultural discs
(Cranfield University, 1989-07) Al-Ghazal, Abdullah Ali; Godwin, R. J.
A prediction model based upon Mohr-Coulomb soil mechanics theory has been developed to predict the interaction between the soil and agricultural discs of different geometries and operating angles to both vertical and tilted discs. The model is based on two forms of soil failure. The magnitude of each form of failure is depen- dent upon a passive reaction on the concave side of the disc and a vertical bearing reaction on the convex side of the disc. The predicted results are in close agreement with the results of the experimental studies. Disc geometry is one of the most important factors to be considered in evaluating the soil reaction acting upon a disc tool. A theoretical analysis of the disc geometry was therefore carried out. The analysis of the disc geometry makes it possible to determine the factors required for the predicted forces acting on a disc tool. The experimental studies were conducted in a sandy loam soil at a moisture content in the friable range, under controlled soil bin conditions. The work was carried out at full-scale with 3 dimensional force measuring apparatus developed primarily for this investigation. The discs studied had a range of disc angles between 150 and 600 and a range of tilt angles between 0 and 35. The depth of cut ranged from 80 mm to 140 mm and at speeds between 0.75 m/s and 1.5 m/s. The disturbance area of the soil caused by the rotating soil cutting disc is calculated to define the disturbed area for any combination of disc angle, disc diameter, gang spacing and depth of work in order to accurately calculate specific resistance. Disturbance and soil inversion were investigated using transparent discs and soil tracers, with a variety disc and tilt angles in order to quantify inversion and mixing.