Thesis (M. Phil.)--University of Hong Kong, 2000.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 174-184). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 91-92).

Automotive and aerospace industries consume a significant amount of Al alloys in structures and framing. There is, however, a significant challenge to join the alloy components by laser welding. A key problem is the presence of large amount of porosity in the welds. This research work aimed to understand factors affecting porosity formation in laser welding of AA6014 Al alloy and identification and verification of a suitable method for the porosity reduction and elimination. AC-170PX (AA6014) Al alloy was welded, for the first time, using a 5 kW disk laser in two different configurations: fillet edge and flange couch joints using a number of different filler wires. The experimental results showed that laser power (2-5 kW) and welding speed (20-50 mm/s) had a significant influence on porosity generation. Also, the introduction of a 0.2 mm gap between the sheets significantly reduced porosity for the fillet edge joint while it had a marginal effect for the flange couch joint. The effect of the chemical composition of the filler wire on the AA6014 weld quality was also evaluated for the first time by using different filler wires (AA3004, AA4043, AA4047 and AA5083) over a range of laser powers and welding speeds. The increase in Mg and Mn content in the filler wire's composition was found to reduce porosity in comparison with high silicon content filler wires. Nanosecond pulsed Nd:YAG laser cleaning was investigated as a surface preparation method for laser welding for AA6061, and its effect on porosity at various welding parameters was examined. The effect of laser cleaning on porosity reduction during laser welding using a filler wire has not been reported before. The surface characteristics before and after laser cleaning were analysed. The results showed that laser cleaning played an essential role in significantly reducing porosity in both the fillet edge and flange couch joints at different levels of power and laser welding speed. The developed surface preparation technology as a method for porosity reduction in laser welding has been successfully implemented in one of the largest UK/international car manufacturers. To study the laser cleaning process, a novel Smoothed particle hydrodynamics (SPH) meshless model has been implemented using a new 3-D multi-phase transient model. For the first time, a study was conducted to validate the temperature field distribution predicted in SPH method under nanosecond pulsed laser heating. The need for special surface treatment of the kernel truncation was also investigated. The proposed model accurately predicted the laser ablation depth and the crater shape and was validated using a significant number of experimental and numerical data reported in the literature. Moreover, a primitive laser welding model has been created to predict the material flow inside the welding pool. The research work has resulted in four publications in peer-reviewed journals. The research highlighted that future work should include the development of a more advanced SPH model for the prediction of porosity in laser welding and to fully describe the relationship between laser cleaning and porosity reduction in laser welding.

<p> Electric Vehicle (EV) has become an increasingly important topic in recent years due to energy and environmental concerns. Governments started to focus on remedies to the upcoming climate change threat and seek solutions through policies and regulations. The negative impact of carbon emissions along with pressure from governmental and social organizations force automotive manufacturers to shift to alternative energy sources. However, EV transition is a complex problem because its stakeholders are very diverse including governments, policy makers, EV manufacturers, and Non-Government Organizations (NGOs). Consequently, the barriers to EV adoption are not only consumer oriented, rather exist under many categories. The literature has yet to offer a comprehensive, quantified list of barriers to EV adoption. Although the enacted policies are known, the effectiveness of these policies in mitigating EV adoption is not known. </p><p> The objective of this research is to assess policy alternatives for mitigation of EV adoption barriers by developing a comprehensive evaluation model. Barriers are grouped under Social, Technical, Environmental, Economic and Political (STEEP) perspectives that are perceived by decision makers as important for adoption process. The decision model of research links the perspectives to barriers, and policy alternatives. The research implements the hierarchical decision model (HDM) to construct a generalized policy assessment framework. </p><p> Data for EV adoption barriers were collected from the abovementioned stakeholders. </p><p> Experts&rsquo; qualitative judgments were collected and quantified using the pair-wise comparison method. The final rankings and effectiveness of policy alternatives were calculated. This research&rsquo;s results showed that the most important perspective is Economic. The top three most important barriers to EV adoption were identified as Initial Cost, Battery Cost, and Entrenched Technology Resistance, respectively. The most effective policy in mitigating EV adoption barriers is R&amp;D Incentives. The research also extended the policy effectiveness research with Policy Effectiveness Curves by reaching out to additional experts. These curves helped determine the effectiveness of each of the 6 policies at different implementation levels. Based on these results, 25 scenarios were applied by combinations of policies at different implementation levels to investigate how the effectiveness of policies can change compared to today&rsquo;s conditions.</p><p>

The focus of the work in this thesis is concerned with the investigation and development of indirect measurement techniques. The methodology adopted is a combination of practical experimental, analytical deductive reasoning and simulation studies. This has led to proposals for a number of indirect tyre pressure monitoring systems, which are able to detect pressure loss under specific circumstances. The outcome overall is a proposal for a new supervisory system comprising of a modular framework, allowing various algorithms and techniques to be implemented in a complementary manner as they emerge and data sources become available. A number of contributions to the field have been made, which to the knowledge of the author, provide potential for further algorithm development and are imminently applicable given the above. The methods include a tyre pressure diagnosis via a wheel angular velocity comparator, the development of a model-based tyre pressure diagnosis via application of an unknown input observer and a parameter estimation scheme, a model-based tyre pressure diagnosis approach via an enhanced Kalman filter configured to estimate states including the input, a model-based tyre pressure diagnosis via cautious least squares, an investigation and critique of the effects of the choice of sampling interval on discrete-time models and estimation thereof. It is considered, that the extensive literature review provides a valuable historic insight into the tyre fault detection problem. It is clear, from the development and testing of the algorithms (and also the literature), that no single indirect pressure detection method is able to reliably detect changes in all driving scenarios which the regulations typically stipulate (depending on jurisdiction). In the absence of any information about the road input, the majority of the detection work must be shouldered by the wheel angular velocity comparator algorithm. As image recognition and sensor technology develops, it becomes possible to make estimates about the road surface and this removes some of the uncertainty on the input of the model-based parameter estimation approaches. Further work is detailed which goes some way towards realising the next steps in a development cycle suitable for a vehicle manufacturer to take through to the implementation stage.

The cyclical nature of the automotive industry has been blamed for many dealership closures as well as thousands of retrenchments. Macro environmental changes like the recent spike in oil prices and the sub-prime debacle can have a detrimental effect on the automotive retailers and be partially blamed for the closures and retrenchments. This results in a continuously changing external environment which might necessitate subsequent internal changes. These changes might involve physical resources like people, demographics, products and materials or non-tangible resources like policies, procedures and the way business is conducted and personnel are treated. The management style and methodologies of automotive retail are predominantly based on control of annual budgets and are therefore not pro-active and unable to cope with sudden and drastic changes like the recent global economic decline. The primary aim of this research is to do an explanatory study to determine whether senior managers in the automotive retail sector has identified their key resources and if they can leverage the application thereof to enable a sustainable competitive advantage. The secondary aim is to determine if these resources or the application thereof change during an economic decline. The research was conducted by means of multiple and in-depth semi-structured case studies of twelve dealers in the Gauteng area. This method is generally accepted as a technique to properly diagnose the current scenario and to evaluate the situation according to relevant theory. The results of this research shows that the automotive retail sector has not yet embraced the resource based view, can not recognise all their key resources, and do not actively cultivate resources for future utilisation. By creating resource awareness the recognition and application of resources might become more dynamic which can make the industry more resilient in future economic downturns which might result in less closures and retrenchments during future economic declines. / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted

Electromechanical position actuation systems typically consist of an electric motor, driven by a set of power electronics, effecting output through a mechanical transmission. Whilst an optimal fully integrated actuator design from first principles could be considered, this is often not a cost-effective option. It is common to construct designs utilising commercially available subcomponents – the Cummins variable geometry turbocharging application detailed in this thesis provides a typical example. The design problem studied in this work is therefore one of meeting requirements through careful subcomponent selection. Electromagnetic, mechanical and thermal equations are developed to model actuator performance. These may be parameterised based on datasheet values or sample component test data. A set of tests is proposed to extract the required information from example motors; this is demonstrated using five different sample motors. Validation is performed to assess the accuracy of the parameterised models for the sample motors. A process is then developed to use the validated models to assess actuator design performance against a set of requirements. A key contribution of this work is the derivation of a computationally efficient motor model, which may be used with an integrated low-order lumped-parameter thermal model to investigate actuator performance at elevated temperatures – since this is often the limiting factor in machine rating. This allows a user to select the appropriate modelling fidelity, allowing accuracy to be traded against simulation performance. The overall process is demonstrated through the assessment of a full actuator design. The models and design process developed in this work allow a candidate actuator design to be appraised through calculations and simulations at a range of different fidelities, and using only a minimal set of subcomponent parameters. This allows designs that cannot meet the performance requirements to be quickly identified and excluded. Satisfactory designs may then be modelled and evaluated in detail to optimise other requirements, such as cost or volume.

In-car communication systems (ICCS) are becoming more frequently used by drivers. ICCS are used in order to minimise the driving distraction due to using a mobile phone while driving. Several usability studies of ICCS utilising speech user interfaces (SUIs) have identified usability issues that can affect the workload, performance, satisfaction and user experience of the driver. This is due to current speech technologies which can be a source of errors that may frustrate the driver and negatively affect the user experience. The aim of this research was to design a new multimodal interface that will manage the interaction between an ICCS and the driver. Unlike the current ICCS, it should make more voice input available, so as to support tasks (e.g. sending text messages; browsing the phone book, etc), which still require a cognitive workload from the driver. An adaptive multimodal interface was proposed in order to address current ICCS issues. The multimodal interface used both speech and manual input; however only the speech channel is used as output. This was done in order to minimise the visual distraction that graphical user interfaces or haptics devices can cause with current ICCS. The adaptive interface was designed to minimise the cognitive distraction of the driver. The adaptive interface ensures that whenever the distraction level of the driver is high, any information communication is postponed. After the design and the implementation of the first version of the prototype interface, called MIMI, a usability evaluation was conducted in order to identify any possible usability issues. Although voice dialling was found to be problematic, the results were encouraging in terms of performance, workload and user satisfaction. The suggestions received from the participants to improve the system usability were incorporated in the next implementation of MIMI. The adaptive module was then implemented to reduce driver distraction based on the driver‟s current context. The proposed architecture showed encouraging results in terms of usability and safety. The adaptive behaviour of MIMI significantly contributed to the reduction of cognitive distraction, because drivers received less information during difficult driving situations.

In 1844 Charles Goodyear obtained U.S. Patent #3,633 for his “Gum Elastic Composition”. In a published circular, which describes his patent for the sulfur vulcanization of gum elastic composition, he stated: “No degree of heat, without blaze, can melt it (rubber)… It resists the most powerful chemical reagents. Aquafortis (nitric acid), sulphuric acid, essential and common oils, turpentine and other solvents… …” Goodyear's sulfur vulcanization of rubber fueled much of the industrial revolution and made transportation possible, as it exists today. In doing so, Goodyear created one of the most difficult materials to recycle. Rubber will not melt, dissolve, or lend itself to the usual methods of chemical decomposition. Ironically, Goodyear recognized this problem and in 1853 he patented the process of adding ground rubber to virgin material, now currently known as regrind blending. Today, scrap tires represent one of the most serious sources of pollution in the world. Studies estimate that there are roughly 2 billion scrap tires in U.S. landfills and more are being added at a rate of over 273 million tires per year. Current methods of recycling waste tires are crude, ineffective, and use rubber powder as a low cost filler instead of a new rubber. The groundwork for a very simple and effective method of producing high-quality rubber goods using 100% scrap rubber was discovered in 1944 by A. V. Tobolsky et al. This application, however, was not recognized until recently in our laboratory. The process as studied to date represents a method of creating quality, high-value added rubber goods with nothing other than heat and pressure. High pressure is required to obtain a void-free compaction of the rubber particles by forcing all of the free surfaces into intimate contact. High temperature then activates the chemical rearrangement, scission, and reformation of the chemical bonds thus providing new bridges between the once fractured interfaces. This occurs both within and between particles. The technique of high-pressure high-temperature sintering has worked on all types of thermoset materials. Typical mechanical properties for sintered SBR powder rubber are as follows: 1.3 MPa 100% Modulus, 12.0 MPa Tensile Strength and 300% Elongation at Break. The goal of this research is two-fold. First, to gain an understanding of the variables that control the process of high-pressure high-temperature sintering. Second, to study the factors governing the mechanism of fusion with the hope of controlling and exploiting this process so that tires can be recycled to produce high quality and high-value added products.