A rationale for the optimisation by computer methods of the efficient use of metals and materials

The aim of the research project was to gain d complete and accurate accounting of the needs and deficiencies of materials selection and design data, with particular attention given to the feasibility of a computerised materials selection system that would include application analysis, property data and screening techniques. The project also investigates and integrates the three major aspects of materials resources, materials selection and materials recycling. Consideration of the materials resource base suggests that, though our discovery potential has increased, geologic availability is the ultimate determinant and several metals may well become scarce at the same time, thus compounding the problem of substitution. With around 2- to 20- million units of engineering materials data, the use of a computer is the only logical answer for scientific selection of materials. The system developed at Aston is used for data storage, mathematical computation and output. The system enables programs to be run in batch and interactive (on-line) mode. The program with modification can also handle such variables as quantity of mineral resources, energy cost of materials and depletion and utilisation rates of strateqic materials. The work also carries out an in-depth study of copper recycling in the U.K. and concludes that, somewhere in the region of 2 million tonnes of copper is missing from the recycling cycle. It also sets out guidelines on product design and conservation policies from the recyclability point of view.

Investigation of the effects of low energy high dose ion bombardment in metals and compound semiconductors

The effect of low energy nitrogen molecular ion beam bombardment on metals and compound semiconductors has been studied, with the aim to investigate at the effects of ion and target properties. For this purpose, nitrogen ion implantation in aluminium, iron, copper, gold, GaAs and AIGaAs is studied using XPS and Angle Resolve XPS. A series of experimental studies on N+2 bombardment induced compositional changes, especially the amount of nitrogen retained in the target, were accomplished. Both monoenergetic implantation and non-monoenergetic ion implantation were investigated, using the VG Scientific ESCALAB 200D system and a d. c. plasma cell, respectively. When the samples, with the exception of gold, are exposed to air, native oxide layers are formed on the surfaces. In the case of monoenergetic implantation, the surfaces were cleaned using Ar+ beam bombardment prior to implantation. The materials were then bombarded with N2+ beam and eight sets of successful experiments were performed on each sample, using a rastered N2+ ion beam of energy of 2, 3, 4 and 5 keV with current densities of 1 μA/cm2 and 5 μA/cm22 for each energy. The bombarded samples were examined by ARXPS. After each complete implantation, XPS depth profiles were created using Ar+ beam at energy 2 ke V and current density 2 μA/cm2 . As the current density was chosen as one of the parameters, accurate determination of current density was very important. In the case of glow discharge, two sets of successful experiments were performed in each case, by exposing the samples to nitrogen plasma for the two conditions: at low pressure and high voltage and high pressure and low voltage. These samples were then examined by ARXPS. On the theoretical side, the major problem was prediction of the number of ions of an element that can be implanted in a given matrix. Although the programme is essentially on experimental study, but an attempt is being made to understand the current theoretical models, such as SATVAL, SUSPRE and TRIM. The experimental results were compared with theoretical predictions, in order to gain a better understanding of the mechanisms responsible. From the experimental results, considering possible experimental uncertainties, there is no evidence of significant variation in nitrogen saturation concentration with ion energy or ion current density in the range of 2-5 ke V, however, the retention characteristics of implantant seem to strongly depend on the chemical reactivity between ion species and target material. The experimental data suggests the presence of at least one thermal process. The discrepancy between the theoretical and experimental results could be the inability of the codes to account for molecular ion impact and thermal processes.

Conformational analysis and dielectric relaxation of polycarbosilanes and related materials

The conformational characteristics of poly(dimethylsilmethylene), poly(dimethylsilethene), poly(dimethylsilethane) and a related material, poly(2,2,5,5-tetramethyl-1-oxa-2,5-disilapentane), have been investigated using the method of molecular mechanics. In this method, a quantitative analysis of the factors affecting the nature and magnitude of the bond rotation potentials governing their conformational behaviour has been undertaken. Along with their structural data, the results obtained were employed to calculate a variety of conformationally-dependent properties for these polymers, including the characteristic ratio, the dipole moment ratio and the mean-square radius of gyration. In addition, the dielectric relaxation behaviour of two samples of poly(2,2,5,5-tetramethyl-1-oxa-2,5-disilapentane) with molar masses Mw = 28000 and Mw = 46000 respectively, have been studied as a function of temperature (179K-205K) and frequency (100-105Hz). Activation energies for the α-relaxation process and Davidson-Cole empirical distribution factors have been calculated.

Some aspects of the microbiological properties of polymers and composite materials

The interaction of microorganisms with glass-reinforced polyester resins(GRP), both under laboratory and simulated operating conditions, has been examined following reports of severl! fungal biodeterioration. Although GRP was not previously associated with substantial microbial growth, small amounts of microbial activity would pose problems for products associated with comestible materials. The microbiology of the raw materials was investigated, two ingredients were supportive to microbial populations whilst five materials were biostatic or inhibitory in their action. Production laminate was not susceptible to microbial deterioration or inhibitory to microbes. Incorporation of zinc stearate, one of the supportive ingredients, at 300% manufacturing level or drastic undercuring produced laminate capable of supporting microbial growth but only after a non-biotic stage of degradation. Study of the long-term population dynamics of cisterns of GRP and competitive materials under conditions simulating in-service conditions, monitoring microbial numbers within the experimental vessels and comparing with the populations of the supply water, suggests that the performance of GRP cisterns is slightly superior to conventional competitive materials. An investigation of the biological performance of GRP cisterns in an isolated area of known microbiological hazard was conducted. Severe biodeterioration had been experienced with Preform GRP articles moulded using different production techniques, but substitution of current GRP articles resulted in no recurrence of the problem. All attempts to establish the fungal isolate responsible for the phenomena in cisterns under controlled conditions failed. Scanning Electron Microscopy of GRP surfaces showed that although differences exist between current and Preform laminates, these could not satisfactorily explain the differences in service behaviour. These results and the results of the British Plastics Federation Expert Working Group interlaboratory study are discussed in relation to the original report of gross fungal biodeterioration and, to the design of future testing programmes for the products of industrial concerns.

The influence of composition, temperature and strain rate on the deformation of F.C.C. metals and alloys

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Sewers and water mains in England and Wales; materials, manufacture and capital expenditure

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Tensile properties of as fabricated, aged, and stretched SiC whisker and particle reinforced 2009 aluminium alloy

Tensile tests were carried out using specimens of 2009 aluminium alloy reinforced by either SiC whiskers or particles. The size distributions of the whiskers and particles in the matrix were obtained by image analysis. It was found that failure was a result of uniform void nucleation and coalescence in the as fabricated composites, or a result of fast crack propagation initiated by a flaw developed at clusters of SiC in the aged or stretched and aged composites. The strengths of the as fabricated composites were estimated based on the results of image analysis using continuum mechanics and dislocation theories. The estimation indicated that the tensile strengths are largely contributed to by composite strengthening, supplemented by residual dislocation strengthening and work hardening. Owing to the flaw controlled failure, the tensile strengths of the aged or stretched and aged composites were independent of aging time, aging temperature, and the amount of stretching. The elastic moduli of the composites were estimated using the Halpin-Tsai model and a good correlation was found between the measured and estimated moduli. © 1996 The Institute of Materials.

Advances in femtosecond micromachining and inscription of micro and nano photonic devices

This thesis has focused on three key areas of interest for femtosecond micromachining and inscription. The first area is micromachining where the work has focused on the ability to process highly repeatable, high precision machining with often extremely complex geometrical structures with little or no damage. High aspect ratio features have been demonstrated in transparent materials, metals and ceramics. Etch depth control was demonstrated especially in the work on phase mask fabrication. Practical chemical sensing and microfluidic devices were also fabricated to demonstrate the capability of the techniques developed during this work. The second area is femtosecond inscription. Here, the work has utilised the non-linear absorption mechanisms associated with femtosecond pulse-material interactions to create highly localised refractive index changes in transparent materials to create complex 3D structures. The techniques employed were then utilised in the fabrication of Phase masks and Optical Coherence Tomography (OCT) phantom calibration artefacts both of which show the potential to fill voids in the development of the fields. This especially the case for the OCT phantoms where there exists no previous artefacts of known shape, allowing for the initial specification of parameters associated with the quality of OCT machines that are being taken up across the world in industry and research. Finally the third area of focus was the combination of all of the techniques developed through work in planar samples to create a range of artefacts in optical fibres. The development of techniques and methods for compensating for the geometrical complexities associated with working with the cylindrical samples with varying refractive indices allowed for fundamental inscription parameters to be examined, structures for use as power monitors and polarisers with the optical fibres and finally the combination of femtosecond inscription and ablation techniques to create a magnetic field sensor with an optical fibre coated in Terfenol-D with directional capability. Through the development of understanding, practical techniques and equipment the work presented here demonstrates several novel pieces of research in the field of femtosecond micromachining and inscription that has provided a broad range of related fields with practical devices that were previously unavailable or that would take great cost and time to facilitate.

The detection and identification of extraneous metals in material conveyance systems

The aim of this work was to design and build an equipment which can detect ferrous and non-ferrous objects in conveyed commodities, discriminate between them and locate the object along the belt and on the width of the belt. The magnetic induction mechanism was used as a means of achieving the objectives of this research. In order to choose the appropriate geometry and size of the induction field source, the field distributions of different source geometries and sizes were studied in detail. From these investigations it was found the square loop geometry is the most appropriate as a field generating source for the purpose of this project. The phenomena of field distribution in the conductors was also investigated. An equipment was designed and built at the preliminary stages of thework based on a flux-gate magnetometer with the ability to detect only ferrous objects.The instrument was designed such that it could be used to detect ferrous objects in the coal conveyors of power stations. The advantages of employing this detector in the power industry over the present ferrous metal electromagnetic separators were also considered. The objectives of this project culminated in the design and construction of a ferrous and non-ferrous detector with the ability to discriminate between ferrous and non-ferrous metals and to locate the objects on the conveying system. An experimental study was carried out to test the performance of the equipment in the detection of ferrous and non-ferrous objects of a given size carried on the conveyor belt. The ability of the equipment to discriminate between the types of metals and to locate the object on the belt was also evaluated experimentally. The benefits which can be gained from the industrial implementations of the equipment were considered. Further topics which may be investigated as an extension of this work are given.

Influence of macroscopic residual stress fields on fatigue crack growth measurement in SiC particulate reinforced 8090 aluminium alloy

The effect of residual stresses, induced by cold water quenching, on the morphology of fatigue crack fronts has been investigated in a powder metallurgy 8090 aluminium alloy, with and without reinforcement in the form of 20 wt-%SiC particles. Residual stress measurements reveal that the surface compressive stresses developed in these materials are significantly greater than in conventional metallurgy ingot 8090, because surface yielding occurs on quenching. The yield stresses of the powder route materials are greater than those of ingot produced 8090 and hence greater surface stresses can be maintained. In fatigue, severe crack front bowing is observed in the powder formed materials as a result of the reduction of the R ratio (minimum load/maximum load) by the compressive residual stresses at the sides of the specimen, causing premature crack closure and hence reducing the local driving force for fatigue crack growth ΔKeff. This distortion of the crack fronts introduces large errors into measurements of crack growth rate and threshold values of ΔK.

Failure in composite materials

The economic and efficient exploitation of composite materials in critical load bearing applications relies on the ability to predict safe operational lives without excessive conservatism. Developing life prediction and monitoring techniques in these complex, inhomogeneous materials requires an understanding of the various failure mechanisms which can take place. This article describes a range of damage mechanisms which are observed in polymer, metal and ceramic matrix composites.