The development over the last decade of the reference stress method for estimating the deformation of structures composed of time dependent Maxwell material is reviewed, together with the implications of recently derived energy theorems based on idealized material models. Experiments are described which confirm predictions implicit in two energy theorems which extend the concepts of a plastic limit load and a plastic shakedown state to situations involving time hardening creep. The influence of constitutive relationships on stress redistribution effects which in turn affect the deformation of structures subjected to both constant and cyclic histories of loading are considered, and it is argued that the two energy theorems derived for time hardening materials provide conservative bounds which permit the designer to estimate deformation of structures composed of a wider class of materials with related constitutive relationships. An empirical method is proposed for estimating structural creep deformation due to cyclic loading. The method applies to structures composed of materials whose creep law for constant uniaxial stress is known, but knowledge of the form of the creep law for time varying stress is not required, as use is made of data obtained from a single cyclic creep test and results are obtained from a weighted time hardening calculation. In order to check the proposed procedure calculations were performed for a two-bar structure in which stress redistribution effects were particularly severe. At worst the errors in the predicted deformation rate corresponded to a 2% error in the applied load. The results also suggest that in most practical situations the actual solution is likely to correspond to an optimal upper bound provided by one of the energy theorems. The method also permits this optimal bound to be applied to structures composed of a wider class of materials with related constitutive relationships.

The thesis describes the design, calibration and use of a floating element skin friction meter in smooth wall boundary layers under favourable and adverse pressure gradients. The results of an experimental investigation in turbulent, fully developed duct flow are combined with those obtained by BROWN and JOUBERT (1) to give a secondary force contour map for element Reynold's numbers (dm ur/v) between 500 and 4000 and element Euler numbers between -16 and +20. It is shown that these meters can be used in favourable pressure gradient rough wall flows and that the secondary force characteristics are similar to those obtained over smooth walls. Simple physical and mathematical models for the secondary forces are developed which show good qualitative agreement with experiment. A strongly non-equilibrium boundary layer (-1.2 > delta*/tw dp/dx > 2.6) is investigated in detail and tabulated results given. A modified form of COLE'S (4) method for establishing the skin friction coefficient (Cf) from the velocity profile is developed and used to show the sensitivity of log-law methods to the coefficients assumed. It is also shown that the effects of changes in duct cross-sectional area seriously affect the relationship between wall shear stress and pressure gradient in fully developed flows.

The main topics of research are in the sub-areas of neurophysiology that are concerned with measurement of the electrical activity arising from contracting muscle (EMG) and from the surface of the scalp (EEG). Investigations are restricted to the surface-recorded interference pattern EMG, and to the EEG waveform recorded in response to sensory stimulation, known as the evoked potential (EP). The EMG and EP are representative of two important classes of signal commonly encountered in engineering, namely random noise-like and deterministic non-stationary. The thesis describes work on the development of a variety of new techniques and methods of analysis for application in neurophysiology and electrodiagnosis. A general purpose signal processing computer has been built which incorporates a high level of user-machine ergonomics. Turning Points Spectral estimation of the interference pattern EMG is simulated on this computer to demonstrate its flexibility for constructing analysis and control applications. Some emphasis is placed on methods of improving the quality of acquired EMG data for use in the analysis of the dynamics of the neuromuscular system. In this respect, the author describes the design of a fully controllable muscle loading system which uses dc electromagnetic suspension technology. The above computer can be used to control this muscle load for accurate loading protocols in EMG-Force modelling experiments. Techniques involved in the design and construction of the computer lead to higher-level program and data analysis specifications which employ Artificial Intelligence (AI) computing methods. These AI methods, in conjunction with some of those techniques which were used for EMG analysis, are applied to the investigation of single-trial EPs. A suite of adaptive EP analysis procedures, which include a prototype fuzzy expert system, facilitate the extraction of EP component latency variability estimates, and also provide automatic selective single-trial averaging. The latter selective averaging facility, can be used to enhance underlying activity and to examine the relationships that might exist between different components in the EP.

This thesis relates to the use of knowledge based signal processing techniques in the decomposition of EMG signals. The aim of the research is to fully decompose EMG signals recorded at fairly high force levels (up to twenty percent maximum voluntary contraction) automatically into their constituent motor unit potentials to provide a fast and accurate analysis routine for the clinician. This requires the classification of non-overlapping motor unit action potentials (MUAPs) and superimposed waveforms formed from overlapping MUAPs in the signal. Firstly, digital filtering algorithms are used to reduce noise in the signal. A normalisation and compression of the filtered signal is then performed to reduce the time of the analysis. Non-overlapping MUAPs are classified using a statistical pattern recognition method. The method first describes the MUAPs by a set of features and then uses diagonal factor analysis to form uncorrelated factors from these features. An adaptive clustering technique groups together MUAPs from the same MU using the uncorrelated factors. The decomposition of superimposed waveforms is divided into two sections. The first section is a procedural method that finds a reduced set of all possible combinations of MUAPs which are capable of forming each superimposed waveform. The second section is a knowledge based analysis of the selected MUAP combinations forming each superimposed waveform. An expert system has been designed to decide which combination is the most probable by studying the motor unit firing statistics and performs uncertainty reasoning based on fuzzy set theory. The decomposition method was tested on real and simulated EMG data recorded at different levels of maximum voluntary contraction. The different EMG signals contained up to six motor units (MUs). The new decomposition program decomposed all MUAPs in the EMG signals tested into their constituent MUs with an accuracy always greater than ninety five percent. The decomposition program takes about fifteen seconds to classify all non-overlapping MUAPs in an EMG signal of length one second and on average, an extra nine seconds to classify every superimposed waveform. Hardware limitations did not enable the testing of EMG signals containing more than six MUs. The results also show that the computer analysis can simulate the reasoning of a human expert when studying a complex EMG signal.

The physiological origins and physical characteristics of sounds from the thorax have been reviewed briefly. This thesis presents some signal processing algorithms and classification techniques which have been developed for the extraction and classification of those sounds. In order to evaluate the recording equipment and signal processing algorithms two simulators were constructed: a laboratory simulator generating lung sounds in a variable background noise environment and a heart sound simulator written such that the generated sound was defined by a set of variables. Four conventional transformation algorithms for the transient extraction process were evaluated. Their considerable user intervention and inconsistent transformed signal led to the development of the "signal's envelope" algorithm. The signal's envelope method was used to extract transients of interest which were then used for the classification stage. It is shown that, due to the numerical nature of the features used for the classification process, the nearest neighbour clustering algorithm could not correctly classify all the extracted transients. The numerical features were therefore converted into linguistic terms and a fuzzy logic technique was developed to classify the transients. The fuzzy inference engine was robust enough to cope with the small numerical variation in features such that the correct classification was achieved. The other classification method tried was the fuzzy "min-max" clustering algorithm. This also used numerical features for the classification process and was therefore not able to classify all of the extracted transients correctly. A lung sound analyser was constructed using the signal's envelope and fuzzy inference engine. The system was able to extract and classify individual heart sounds, crackles and wheezes from recorded phonograms. In about 4% of cases, the heart sounds were so indistinct that only a partial classification was achieved. It was concluded that by using simple transducers and sophisticated signal processing and classification algorithms it was possible to construct a chest sound classifier which may be of use in a clinical environment.

This study uses Computational Fluid Dynamics (CFD) to predict the thermal comfort and the flow field in an average family house in Iraq under natural cross-ventilation in a hot climate. The study is performed on the effects of different building parameters, such as the inlet openings position, external boundary wall, wind speed and outdoor temperature, furniture and heat loads on the human thermal comfort indices and the flow field. Although the study showed that the flow rate through openings located near the centre of the building is higher and steadier than the flow rate of openings located near the sides of the building, these positions of the openings have only slight effects on the thermal comfort indices at both the seated and the standing levels. It was also observed that the external boundary wall created well-distributed indoor airflow and improved the indoor environment regarding the mean velocity inside the building. Also, increasing the height of the wall by 20% did not offer a noticeable improvement on the mean velocity distribution. This study has also predicted the range of wind temperatures that would allow for all rooms in the building to be of acceptable thermal comfort. The results of the study suggest that acceptable thermal conditions can be maintained with the external wind speeds ranging from 2 to 5 m/s at the temperature of 25°C. In addition, the results showed that the heat dissipated from electrical appliances found in daily life only have a small effect on the thermal comfort indices at both the seated and the standing levels because they use only relatively small amounts of energy, whereas these indices are increased remarkably at these two levels when an additional heat source was operated in conjunction with these appliances. Lastly, no significant differences between the empty building and the furniture-filled building were observed at the two levels when comparing the air velocity, temperature, and thermal comfort indices.

In this thesis, the solidification behaviour and microstructure evolution of Ta-Al-Fe, Nb-Al-Co, Nb-Al-Fe, Ta-Al-Ti and Nb-Si-Ti alloys rapidly solidified via arc melting, suspended droplet alloying and additive manufacturing techniques were examined. Loss of interfacial equilibrium resulted in an extended solute solubility with significant undercooling due to nucleation constraints, leading to unexpected phases. For Ta-Al-Fe alloys, when Al < 10 at.% and Fe < 4 at.%, the peritectic reaction, L+A2 → σ, is suppressed and the eutectic, L → A2 + μ, occurs with formation of a halo of μ on primary σ phase. For Co-rich Nb-Al-Co alloys, when Nb > 20 at.%, the quasi-peritectic reaction, L+Co2AlNb → C36+CoAl does not occur, C36 and CoAl phases form through solid-state precipitation. A halo of C14 forms on primary CoAl but limited vice-versa. In Nb-Al-Fe alloys, failure to initiate coupled growth of NbAl3+C14 leads to a two-phase halo of C14+Nb2Al. The quasi-peritectic reaction, L+Nb2Al → (Nb)+μ is suppressed, forming the eutectic Nb2Al+μ instead. The ternary eutectic, L+C14+Nb2Al → μ, is limited with μ forming primarily. For Ti-Al-Ta alloys, the quasi-peritectic reactions, L+β → α+σ and L+σ → α+κ, occur at a very narrow window; good agreement for γ and ε phases is found with non-equilibrium formation of ε. For additive manufactured Nb-Si-Ti alloys, an increase in scanning speed led to microstructure refinement. Due to elemental additions, Nb3Si is suppressed with formation of Nbss+Nb5Si3. C15 Laves phase formed when Cr > 5 at.%, with HfO2 when Hf is added. For Ti > 22 at.% and SI > 18 at.%, a Ti-rich Nb5Si3 forms due to rejection of Ti solute. Hot isostatic pressing and heat treatment led to crystal structure changes, densification and phase coarsening. Diffusion and local super-saturation led to the split of Nbss into an energetically stable and homogeneous Tiss phase.

The effort dedicated to developing the material properties of engineering ceramics has not been accompanied by a similar effort in developing design methods that would allow engineers to make full use of these materials. In particular the high temperature creep behaviour of engineering ceramics has received little attention. In this thesis two parallel approaches, one theoretical and one practical, have been taken towards the final aim of constructing design codes for the creep of ceramic materials. In the theoretical work the principles developed for modelling creep and failure in metals were employed and adapted where necessary to provide new models that describe the behaviour of ceramics under multiaxial stresses. Important changes were made to account for differences in microstructure between these two classes of materials. In the practical work equipment was developed to provide suitable multiaxial creep test data with which to verify and further construct models. This involved the construction of a tension/torsion creep testing machine featuring a radio-frequency heating furnace, cooled grip heads, extensometry equipment, biaxial loading system and a temperature measurement and control system. The machine was capable of operating for at least 300 hours at a temperature of at least 1400 °C. Nine creep tests were conducted on reaction bonded silicon nitride specimens including two unique tests under pure torsion and combined tension/torsion. Four tests were conducted on aluminium oxide specimens including a unique test under combined tension/torsion. Tensile test results showed good agreement with previously published data for both materials confirming the equipment accuracy. Results from the multiaxial tests indicated that reaction bonded silicon nitride fails in response to the value of the effective stress. In addition reasonable agreement was obtained between the test data and predictions from the new models.

Electrodeposited metal matrix nanocomposites (MMNCs) offer improved mechanical properties for tribological coatings. The development of nanotechnology in the last 25 years means there are now a multitude of nanoparticles, nanowires and nano-tubes available in an ever- increasing range of materials and hence the scope for new nanocopmosites coatings by electrodeposition is greater than ever, with the potential to develop a coating with functional performance equivalent to hard chrome. Recent work on pulse reverse deposition of MMNCs by Weston, et al has suggested the capability to control the co-deposition of metals and particulates. The technique includes the use of a surfactant and pulse reverse plating (PRP). In the present work, the suggested mechanism investigated on cobalt matrix nanocomposites with a number of particles including SiC, Al2O3, and PTFE with different particles loading and size. The produced nanocomposites assessed microstructurally and mechanically by different analysis: Field emission gun scanning electron microscopy FEGSEM cross section and surface topography, Energy Disperse X-ray EDX, image analysis, X-ray diffraction XRD, and transmission electron microscopy TEM. The microstructural results indicated the applicability of PRP for Co-SiC with different particle loadings, and for Co-SiC with 5 g l-1 Al2O3. The mechanical properties of the produced coatings suggests an increase in microhardness with increasing the particles volume fraction with 8.7 vol. % of SiC increasing the hardness by up to 25 % and 9.1 vol% of Al2O3 raising it by up to 31 % beyond the hardness of the pure Co coatings. No significant effect attributed to the reduction of the grain size was observed. A predictive model for the main controlling strengthening (dispersion strengthening) of the nanocomposites with low surfactant content 0.2 g l-1 of SDS was found. The model is applicable on both nanocomposites electroplated cobalt coatings Co-Al2O3 and Co-SiC.

The applications of composite materials have been increasing significantly in recent decades. The major effect limiting the use composite materials is the lack of understanding of their response and their structural integrity under dynamic loads. Delamination under dynamic load is particularly recognised as the most critical damage process in laminated composites. The objective of this thesis is to experimentally and numerically investigate the fundamental phenomena associated with delamination. This is important develop a further knowledge of the response and damage mechanisms of composite materials under low-velocity impact and static load. Various parameters that affect the delamination of composite material have been studied in this work, including the diameter of the hemi-spherical indenter and the type of load at the same energy level. The difference between the shape and size of delamination area between different plies has been examined using x-ray commutated tomography. Cohesive elements have been used in the ABAQUS finite element modelling to determine failure criteria that correspond with the experimental work. It is found that the main delamination area occurs on the tension side of laminates subjected to bending, and that it also depends on the difference in angle between adjacent plies. The effect of the indenter radius to thickness of plate ratio on the relation between force and damage evolution have been studied numerically for different thickness of plate. This analytical study was repeated for both isotropic and anisotropic materials to show the effect of material type on the previous relation. It is found that the initiation of the delamination can be assessed from the existence of a delamination threshold load in a force-displacement curve under quasi-static load or in a displacement-time curve under dynamic load.