This thesis applies Smoluchowski's coagulation-fragmentation equations to model the mechanical alloying process. Mechanisms operating during the milling process are reviewed. In the first instance, models are developed that predict the size distribution of a single milled powder while ignoring mixing phenomena. A methodology is developed that allows experimentally measured sieve-fractions to be converted into volumetric cluster size distributions. Model parameters describing the rate of aggregation and fragmentation are obtained by fitting the model's predicted average particle size data over time to that measured in experiments. Different size-dependent aggregation and fragmentation rates are tested in many milling scenarios and the most realistic size-dependence of rates is found. In the second part of the thesis, the best size-dependent rates are generalised and used with a two-component version of \Smol's system of equations. This model also includes binary mixing phenomena by considering clusters that have two types of component. The two-component models are applied to experimental situations using the methods developed for one-component models. Comparing these multi-component models to experimental measurements verifies the modelling method and gives reasonable agreement. An improved fragmentation rate is suggested to enhance the model's accuracy in the prediction of mixing rates.

This thesis aims to develop a rock mass classification system for UK Coal Measure strata such that the output from the classification system may provide a means by which the strength and stiffness properties of Coal Measure strata encountered within UK coal mines may be predicted. The development of the Coal Mine Classification system is described within this thesis. A structured methodology utilising a database of information obtained from 118 different rock mass classifications, together with consideration of the typical mechanisms of strata deformation within coal mines, was employed to determine the parameters of the Coal Measure strata that have the greatest influence on the engineering properties of the strata. These identified parameters have formed the basis of the Coal Mine Classification system. By comparison to a series of conceptual models of strata deformation that occur within the roof ,floor, ribs of roadways and within the region of the coal face, relative importance weightings and rating scales for the identified classification parameters have been proposed. The anisotropic nature of the UK Coal Measures is characterised within the Coal Mine Classification by the calculation of separate ratings for directions parallel to and perpendicular to bedding. An appraisal of the optimum method of using the classification ratings, determined by the Coal Mine Classification, to predict the strength properties of individual strata units was undertaken. Rock mass failure criteria that utilise outputs from existing rock mass classification systems to determine the rock mass strength, have been reviewed. Utilising published triaxial data the rock mass failure criterion that best predicts the failure characteristics of UK Coal Measure strata was identified. From this study the Hoek-Brown rock mass failure criterion was identified as the optimum existing criterion for predicting the intact strength and rock mass strength of Coal Measure strata. However this criterion was still found not to produce a close fit in many cases to the intact failure strength of the strata. A modified Coal Measure Failure criterion has been developed, which for a wide range of Coal Measure rock types was found to produce a better prediction of the intact strength of Coal Measure strata than any of the existing rock mass failure criteria. To determine the efficacy of the Coal Mine Classification system as a means of predicting the strength and stiffness properties of the rock mass the Coal Mine Classification was applied to the strata at case study localities within rock bolted roadways within three UK mine sites. Numerical models of the case study localities were developed using the FLAC finite difference code utilising a ubiquitous jointed elastic-perfectly plastic material model to simulate strata behaviour. The output from the modelling included predicted roof and rib side displacements, and these displacements were compared to the actual monitoring data for the case study localities. The results of the numerical modelling indicate that the predictions produced by the numerical models reflected the pattern and scale of deformations actually measured in-situ within the coal mine roadways, thus indicating that the Coal Mine Classification system provides a means of predictively determining the engineering properties of the in-situ Coal Measure strata. The modelling also indicated that time delays related to the installation of the roof extensometers may under predict that actual roof deformation that occurs within the roadway roof.

The thesis is a study of the stability, closure behaviour and rock fracture development associated with mine tunnels with particular reference to Coal Measures conditions. A detailed survey has been carried out of relevant theories and mathematical concepts which relate to tunnel stability and the effects of in situ stresses. Of special importance has been identifying appropriate mathematical theories which relate to the field of scholarship undertaken. The literature survey has found useful application especially in giving guidance on those areas needing further investigation. The author discusses mathematical theories in relation to the research undertaken. The major area of investigation has been the effect of different in situ stress fields on various aspects of tunnel design and geometrical configuration. Attention has focussed on available research methods which allow ease of investigation of the parameters governing mine tunnel stability. After careful consideration, the author selected physical modelling using small scale sand plaster models of different mine tunnel and geological conditions. Much research effort has been directed at establishing the properties of such physical modelling materials, mathematical scaling aspects and the type of test rig for carrying out the investigations. Time was spent on establishing the accuracy and suitability of the research method employed. A range of experiments were carried out whereby the horizontal and vertical components of the in situ stress field were varied. The tests were repeated using the common range of mine tunnel profiles which exist in UK coal mines, namely arch, circular, square and rectangular. The research enabled the fracture pattern to be observed in association with the different tunnel profiles tested under the various stress field conditions employed. Closure of the model tunnels was observed in relation to the increasing stress field. Discussion has focussed on how various combinations of horizontal to vertical components of in situ stress influence mine tunnel stability. The results are discussed in relation to the choice of support type. In particular, the merits of standing support types such as square sets, steel arches and concrete linings are discussed in relation to the results of the research. The thesis draws attention to the practical application of the research method to investigate various mining situations as encountered in UK coalfields and in the Datong coalfield in North China, of which the author has particular experiences regarding rock mechanics and mine tunnel stability.

Structural and kinetic aspects of precipitation in the systems Mg-Th and Mg-Nd , with various ternary additions, have been studied, using electron microscopy and electrical resistivity techniques. The sequence of precipitation in the Mg-Th alloy is solid solution → β" → β. Small additions of manganese and silver have little effect on the precipitation process but additions of zirconium and zinc alter the process significantly. The β” reaction is completely suppressed by an addition of 0.3% zinc and a phase not present in the binary system, β’ Mg2Th, is formed as two polymorphs in the zirconium containing alloy. The sequence of precipitation in the Mg-Nd system is completely changed by the zinc addition. Alloys containing Mg 2.8% Nd 1.3% Zn have the following precipitation sequence Solid solution → low temperature reaction → plates γ”││ (0001) → rods on γ (0001) in <1120> & <1010> The low temperature reaction has not been elucidated but it occurs with an activation energy approximating to that of vacancy migration in magnesium, and may possibly be associated with short range order. The structures of these various alloys have been correlated with their creep and mechanical properties. In particular, the creep properties of the Mg-Nd-Zn alloy have been shown to be superior to those of the binary Mg-Nd alloy and the improvement has been attributed to the γ" phase restricting dislocation motion on the {1011} planes.

The effects of copper and magnesium on the precipitation characteristics of Al-Li-Mg, Al-Li- Cu, and Al-Li-Cu-Mg alloys have been investigated during isochronal and isothermal ageing. In AI-Li-Mg alloys, increasing the magnesium concentration results in stimulation of δ'precipitation by a shift of the α/δ'solvus boundary to higher temperatures. It was shown that for each wt%Mg present in the alloy the α/δ'solvus boundary shifts by 7.0°C. In Al-Li-Cu alloys the concentration of copper has no effect on the position of the α/δ'solvus boundary. The significant stimulation of δ' observed in Al-Li-Cu alloys was shown to be due to the formation of GPCu zones that act as heterogeneous nucleation centres. TEM analysis showed that this heterogeneous nucleation produced composite precipitates consisting of an inner plate of GPI zone and an outer cylindrical shell of δ'. At high copper concentrations (Cu>2.0%) and long ageing times at 150°C, significant retardation of δ' precipitation takes place due to precipitation of the equilibrium T1 and T2 phases. The mechanisms by which copper and magnesium affect the precipitation characteristics of Al- Li-Cu-Mg alloys are different than those operating in the ternary AI-Li-Mg alloys and Al-Li-Cu alloys. In 1.7Lil. 2CuXMg alloys, increasing the magnesium concentration beyond 1.2% causes significant stimulation of δ'precipitation through the formation of Li-Cu-Mg clusters (mechanism referred to as CL δ') that are capable of rapidly developing into δ'. It is proposed that in 1.7Lil. 2CuXMg alloys the initial 1.2%Mg added is consumed in the formation of GPB zones that have very little effect on δ' precipitation. As the magnesium concentration increases to levels higher than 1.2%, the magnesium is free in the matrix to gather both copper and lithium thus forming Li-Cu-Mg clusters which are extremely effective at nucleating δ' In 1.7Li1.2MgXCu alloys the mechanisms by which stimulation of δ' precipitation takes place are again by formation of Li-Cu-Mg clusters (CL δ'), and by nucleation on GPB zones (mechanism referred to as GP δ'). During ageing at 70 and 100°C, and for copper concentrations in the range 0-1.2%, the dominant precipitation mechanism is GP δ'. For higher copper concentrations (1.2<Cu<3.0) the dominant process is CL δ'. Increasing the ageing conditions to 150°C causes precipitation of δ' through classical nucleation and growth for low copper concentrations. For high copper concentrations, the precipitation of δ'comes about through the GP δ'mechanism. Using Kissinger's method, it was found that the activation energy for a' formation in AI-Li-Cu-Mg is equal to 62 kJ/mol, suggesting that the kinetics of the δ'precipitation process are also controlled by the presence of excess vacancies quenched-in from solution heat treatment. It is likely that the Li-Cu-Mg clusters that develop in the alloy also gather excess vacancies thus making the clusters vacancy-rich. For all the alloy systems (Al-Li-Cu, Al-Li-Mg, and Al-Li-Cu-Mg alloys) and independently of the concentrations of copper and magnesium, the largest volume fraction of δ' precipitates form during ageing at 100°C where there is an optimum combination of thermodynamics and kinetics. Ageing the alloys at 150°C (standard heat treatment for lithium containing alloys) and subsequently exposing at 70°C (to simulate service conditions for an aerospace alloy) resulted in embrittlement due to precipitation of additional (fine) δ'. This embrittlement was shown to be closely related to the volume fraction of δ' that precipitates during exposure. In Al-Li-Mg and AI-Li-Cu ternary alloys, increasing the concentration of magnesium and copper respectively, resulted in increased volume fractions of δ' precipitated during exposure and hence increased degrees of embrittlement. For Al-Li-Cu-Mg alloys the maximum volume fraction of δ' precipitated during exposure occurred in the 1.7Li1.2Cu1.2Mg alloy. It was shown that this alloy composition also showed the maximum degree of embrittlement.

The increasing depth, distance from surface connections and falling quality of coal mined are factors that increase the risk of spontaneous combustion in working areas. The trend towards high capital investment, high output faces significantly raises the economic consequences of spontaneous combustion. Much work has been directed towards methods of identifying the liability of a coal to spontaneously combust under given conditions. The cost of prevention and combat of spontaneous combustion underground is high, however this work is carried out with little knowledge of the likely location of a heating in a coalface waste. This thesis investigates the airflow patterns in a coalface waste, with a view towards improving the use of prevention and combat methods. The factors that affect the liability of a coal to spontaneously combust, and the methods of prevention and combat are discussed to provide a background to the subject area. An investigation into the flow of nitrogen that was injected from one hole into a coalface waste as a combat measure was conducted. The results of this showed how the amount of nitrogen entering the waste depended on the rise and fall of the atmospheric pressure. An attempt was made to develop a method of sampling gas from deep within the coalface waste. It proved impossible to sample further than 15m behind the face line. The results from this exercise are presented. The finite element method was used to model the pressure distribution in the waste under differing boundary pressure and waste permeability conditions. A suggested area at risk from spontaneous combustion is presented.

Novel aspects of solid state laser spot melting of aluminium using a pulsed solid state laser were investigated. After a thorough characterisation of the performance of the solid state laser, an initial series of ranging trials were performed to identify parameters which produced cosmetically satisfactory consistent melt spots on the surface of a commercially available aluminium alloy. These melt spots demonstrated a number of features of interest, including symmetrical concentric ring structures on the surface of the spots. A review of published literature on the use of laser beams as an intense radiation source for pulsed laser surface melting was carried out which confirmed that these phenomena have not been researched or reported in any depth. Experimental work identified the conditions under which they could be reliably reproduced, and these conditions are very close to laser parameters used commercially for pulsed laser welding. Further investigations to understand their origin involved using modified aluminium surfaces and temporally shaped laser pulses. Experimental details are included which will allow reliable reproduction of this effect in the future. Specific thresholds were identified for these phenomena and this has led to an improved understanding of solid state laser spot melting on aluminium. It appears that these rings are part of a continuum of irradiance which leads to melt expulsion due to reactive vapour pressure.

Thesis (M.S.)--Ohio University, November, 1987. / Title from PDF t.p.

Thesis (M.Eng. (Mechanical and Aeronautical Engineering)) -- University of Pretoria, 2007. / Includes bibliographical references (p. 103-108)

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1899. / 1899 determined to be year of publication from the "1874-1990 MSM-UMR Alumni Directory". The entire thesis text is included in file. Holograph [Handwritten and illustrated in entirety by author]. Title from title screen of thesis/dissertation PDF file (viewed )