Showing papers by "Cranfield University published in 1980"

Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding I. Fiber motion and viscosity measurement

Abstract: A study has been made of the fiber orientation in short glass fiber-filled thermoplastics resulting from convergent, divergent and shear flows. Convergent flow results in high fiber alignment along the flow direction, whereas diverging flow causes the fibers to align at 90° to the major flow direction. Shear flow produces a decrease in alignment parallel to the flow direction and the effect is pronounced at low flow rates. Non-linear Bagley plots have been observed, under some conditions, during rheological measurements. The data are consistent with a pressure dependent viscosity.

Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding. II. The effect of material parameters

Abstract: The effect of fiber concentration, fiber length, and temperature on the shear viscosity and die swell of several short glass fiber-filled thermoplastics has been determined. In addition, a study of the injection molding behavior of these materials has been performed. At low shear rates, viscosity increases appreciably with both fiber length and fiber concentration, but at high shear rates the effect is much less pronounced. A qualitative explanation is proposed for these effects in terms of the fiber orientation studies reported in Part I of this paper (1). The die swell is an important parameter in determining the method of mold filling of these materials, and depends strongly on fiber length.

Hot plate welding of plastics: Factors affecting weld strength

Abstract: Welded joints were made under a range of conditions in polypropylene, glass fiber reinforced polypropylene and poly (methylmethacrylate) bars. Melt flow in the weld was investigated by microscopy and by contact microradiography, and weld strengths were measured by tensile tests. The fracture toughness of the weld zone was determined by tests on double edge notched specimens. The study shows that weld strength is strongly affected by hot plate temperature, heating time and melt flow during welding. Insufficient heating or melt flow results in incomplete bonding. Excessive melt flow produces strong transverse orientation. Both reduce strength, but in different ways, which can be distinguished by fracture mechanics tests.

The effects of thermal history on the density and mechanical properties of poly(methyl methacrylate)

Abstract: The purpose of this work was to show that physical aging effects in poly(methyl methacrylate) (PMMA) could be correlated with the nonequilibrium state of the glassy polymer, as measured by dilatometry. Specimens were annealed at a series of temperatures within the glass transition region (90, 95 and 100°C) and quenched or slowly cooled to the test temperature (40 or 60°C). Volume recovery was monitored throughout the experiment by accurate dilatometry, and low strain tensile creep compliance measurements were made simultaneously on specimens subjected to identical thermal treatments. At both test temperatures, creep behavior and volume recovery showed a similar dependence on annealing temperature and time. However, the specific volume alone was not sufficient to characterize the aging behavior of glassy PMMA: it was also necessary to define the path by which the state of the glass was reached. This memory effect, which has a direct parallel in volume recovery, is attributed to the presence of a distribution of retardation times, and accounts for, the seemingly paradoxical observation that the creep compliance can initially increase on aging at a temperature below Tg if the specimen has previously been stored for a long period at a lower temperature.

Ignition and flame quenching of quiescent dust clouds of solid fuels

Abstract: Experiments have been carried out to study the influence of particle size, dust concentration, pressure, mass transfer number and oxygen/nitrogen ratio on quenching distance and minimum ignition energy of dust clouds of solid fuels. The solids chosen were aluminium, magnesium, titanium and carbon. Ignition was accomplished by using sparks whose energy and duration could be varied independently. A separate series of tests was also conducted to ascertain optimum spark duration. The results of these tests show that particle size has a strong influence on the minimum ignition energy, the quenching distance and the optimum spark duration. To a lesser extent pressure, dust concentration, mass transfer number and oxygen/nitrogen ratio also affect ignition and quenching of dust clouds. A detailed comparison of results for the dust clouds and the liquid mists studied previously shows a strong similarity between the two. It appears that both solid and liquid fuels may be treated as members of a single family. Thus it is found that the formulae for quenching distance and minimum ignition energy derived previously for liquid fuel mists also satisfactorily predict the experimental results obtained for dust clouds of metals and carbon. Further, a typical calculation shows that for aluminium, for example, the critical particle Sauter mean diameter below which the formulae become invalid is around 6 μm.

A Fiber-Optic Laser-Doppler Probe for Vibration Analysis of Rotating Machines

Abstract: The problem of obtaining vibratory information from remote, rotating, components within a machine has been overcome by means of a laser-Doppler fiber-optic probe. Laser light is transmitted down the fiber-optic and scattered light is returned for analysis in the same way. The Twyman-Green mode of operation of the laser-Doppler system has been shown to have serious shortcomings for this type of work and a new mode has been produced, and used successfully, in conjunction with Bragg cells for frequency shifting. The use of a single set of Bragg cells to compensate for the average velocity of a rotating system, limits the allowable speed of rotation to about 1000 rpm. However, other techniques for frequency shifting are available. An experimental investigation is reported in which a rotating system, consisting of a disk carrying flat cantilever blades, was rotated at about 1000 rpm while one of the blades was excited at 163 Hz. The measured frequency of the vibrating blade was 162.8 Hz and similar accuracy was obtained for the amplitude measurements.

The Influence of a Flameholder on a Plane Flame, Including Its Static Stability

Abstract: The plane pre-mixed flame adjacent to a coplanar porous-plug type of burner is analysed with the aid of large-activation energy asymptotics. It is shown that there is a unique relation between the mass flux of reactants through the holder and the burnt-gas temperature for a given value of the mixture equivalence ratio. A simple linear heat-flux-temperature model of the flameholder introduces a constant of proportionality called the conductance of the holder. The conductance has a strong influence on the details of flame behaviour; in particular the heat flux from the preheat regions of the flame into the flameholder is governed by the conductance, as is the stand-off distance between the face of the holder and the flame-sheet. It is also shown that, despite the foregoing facts, the heat flux that must be provided at the holder to or from some outside agency, such as a coolant, is actually independent of the conductance. A detailed and general analysis of the flame-flameholder system identifies a critical value for the conductance (that depends upon the mixture equivalence ratio). In addition a dimensionless number, called $\alpha$~, that is equal to the specific heat multiplied by the mass flux of the reactants divided by the conductance, has an important bearing on the type of equilibrium that exists between the flame and the flameholder. If ~$\alpha 1$ the equilibrium mass flux must exceed the adiabatic value, and the 'coolant' must supply heat to the system. A plot of inlet flow speed against equivalence ratio for several fixed values of the heat-loss to the coolant per unit area per unit time shows that there are either two equilibrium inlet speeds for a given equivalence ratio or none at all. This result is in accord with the experimental observations of Botha & Spalding (1954). The existence of a distinguishable spatial origin (the flameholder surface) means that the static stability of the flame, considered as a single plane sheet, can be defined. Domains of static stability and instability are identified, and help to explain observations of flame behaviour on a coplanar holder. Static stability or instability complements diffusional instabilities; however, static stability boundaries are not affected by the Lewis number, as are those of the diffusional mechanism. Despite the fact that most of the flames in streams the mass flux of which exceeds the adiabatic value at a given equivalence ratio are statically unstable, and are therefore not to be found in practice, the analysis predicts that plane flames can be stabilized on a holder in some circumstances at flow rates greater than the adiabatic if the flow speed exceeds a calculable minimum.

The application of optical fibres as witness devices for the detection of plastic strain and cracking

Abstract: Low cost optical fibres have recently become readily available for telecommunications purposes. Silica fibres are characterised by high elastic strains to failure. The feasibility of using these fibres for structural integrity monitoring particularly for off-shore structures is investigated. The basis of the technique is that a fibre may be bonded to a critical part of a structure and provides an optical path which will be broken if the fibre fails due to plastic strain or crack opening in the critical area. Groups of fibres which have been given predetermined fracture strains by surface etching were encapsulated in special packs. These packs were bonded to steel and concrete tensile specimens. Strain transfer occurred successfully between the specimens and individual fibres. The distribution of strain to fibre fracture appeared to be uniform along the fibre. The use of several fibres with a range of fracture strains caused fibres to break progressively with increasing strain. For applications to offshore structures it has been found possible to use water-repellent adhesives which can be applied and cured in sea water and suffer no deterioration. The advantages of this system include versatility, relatively low cost, adaptability to continuous monitoring and the possibility of being fitted retrospectively and refitted after repair operations.(a)

Materials for Machine Tool Structures

Abstract: A review is made of the most common machine tool structural materials Their properties are compared, including modulus of elasticity, specific stiffness, damping, long term dimensional stability, coolant resistance, wear rate, frictional properties, thermal conductivity and lead time for manufacture. Also described is ‘epoxy concrete’, a new material specifi- cally developed for high precision machine tool structures, with high damping, high specific stiffness and high dimensional stability. Using patented moulding techniques, structures are finish cast to a high precision at low cost. Precision slideways can be replicated into the structure, thus eliminating the need for slideway grinding, scraping and stabilisation heat treatment, etc..

The efficiency of aerial spraying

Abstract: Nobody would deny that a major objective of the peoples of the world is to improve standards of health and hygiene and an essential part of this must be to increase the quantity of food produced. To do this it is essential to use supplementary nutrients and exercise effective pest management. It has been shown that the yields of basic foods, such as rice, can be doubled by using the right seed strains, fertilisers and crop protection techniques. Crop yield losses because of insects alone are estimated at 5% in Europe where insecticides are used widely and as much as 21% in Asia where insecticides are used only in a few of the better organised cultural areas.

The effects of tyre type on driving speed and presumed risk taking

Abstract: The effects of tyre type on drivers choice of speed and implied risk taking were examined in a test-track lane-change manoeuvre, and on rural public roads. In the test-track situation at speeds requiring skill, older, presumably more skilful drivers, drove more quickly than younger drivers when the vehicle was fitted with crossply tyres. No differences were observed with radial ply tyres fitted. Subjective risk was assessed from the difference between mean test-track speeds and drivers' own estimates of the maximum safe speed for the manoeuvre. It was found that younger drivers, while driving more slowly than older drivers in some conditions, still drove with greater subjective risk. The implications of this finding are discussed with reference to the 'constant risk' hypothesis, which states that the benefits of improved safety equipment will be offset by the tendency of drivers to drive faster and so maintain a constant level of subjective risk. The implications for lyre design are also discussed. No spe...

Theory of a Hydrogen-Oxygen Diffusion Flame Part I: Profiles from a Large Damkohler Number Model

Abstract: A streamwise laminar diffusion flame in a boundary layer flow is modelled for a hydrogen-oxygen system with six step reaction kinetics. The method of matched asymptotic expansions, based on the existence of a large value of the Damkohler number, provides first order inner and outer temperature and concentration solutions from which composite series are constructed for a range of fresstream reactant concentrations, some of which are chosen to coincide with experimental situations. In these cases comparisons between theoretical and experimental results are made

World Energy Resources and Consumption

Abstract: Throughout the thousands of years prior to the industrialisation of societies, mankind’s requirements for energy have been met primarily by muscular effort, wind and water currents, fuel wood, direct solar warming and other ‘renewable’ sources, punctuated only occasionally by the use of minor outcrops of coal and oil for the high-temperature fires needed to make terracotta and similar materials. However, the tempo of industrialisation has reversed this pattern, with major withdrawals on the irreplaceable ‘capital’ resources of time-stored solar energy, in the form of fossil fuels derived from vegetable and animal organisms, and minor contributions only from the renewable energy ‘income’. In the absence of some virtually inexhaustible capital resource, it would appear that the world will eventually have to return to an energy income basis, and that it would be wise to invest some of the present ‘capital’ for research in anticipation of this event. The immediate concern therefore centres on the time scale still available for all the necessary preparations to be made, the vital question being the likelihood or otherwise of some energy deficiency arising before the full exploitation of the income flow. This in turn depends on both the overall extent of the remaining fossil fuel reserves, and the rate at which they are being consumed.

Automation of the EDM Process

Abstract: The paper describes work at Cranfield on progress towards automation of the electro-discharge machining process.

The Asymptotic Expansion of Solutions of the Differential Equation u $^{\text{iv}}$ + $\lambda ^{2}$ [(z $^{2}$ +c)u $^{\prime \prime}$ +azu $^{\prime}$ +bu] = 0 for Large $|z|$

Abstract: The asymptotic expansion of solutions of the fourth order differential equation u iv + λ 2 [( z 2 + c ) u " + azu 9 + bu ] = 0 are investigated for | z | -> oo where the parameters a, b, c and λ are supposed to be arbitrary complex constants with λ, b ^ 0. Exact solutions in the form of Laplace and Mellin-Barnes integrals, involving a Whittaker function and a Gauss hypergeometric function respectively, are used to define a fundamental system of solutions. The asymptotic expansion of these solutions is obtained in a full neighbourhood of the point at infinity and their asymptotic character is found to be either exponentially large or algebraic in certain sectors of the z -plane. The expansions corresponding to certain special values of the parameters a and b which yield logarithmic expansions are also treated. Linear combinations of these fundamental solutions which possess an exponentially small expansion for | z |->oo in a certain sector are discussed.

Weld defect distributions in offshore platforms and their relevance to reliability studies, quality control and in-service inspection

Abstract: The paper presents analyses of NDT data from a total of more than 250 m of welding in node connections in tubulars in different structures The weld defect information has been analysed in terms of type, size, position and distribution A system for coding NDT information and storing it in a data bank has been devised The analyses show that the distribution of defect size can be described by an exponential or a weibull distribution It is concluded that it is possible to define the weld defect pattern in an offshore platform in a suitable way for reliability analysis

Career Development: Meeting Individual and Organisational Needs

Abstract: In our experience there very often seems to be a discrepancy between the avowed aims of many management training programmes and the reality of the organisation in which participants are based. In some cases the organisation even appears to militate against objectives being achieved. The main causes of this are the different definitions of the aims of programmes that are held by all interested parties. These often contradict each other. This article will examine these later in more detail together with our approach both in theory and in practice.