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Within the aerospace industry there is an increasing requirement to investigate the structural integrity of the new composite materials that are now being used frequently in the manufacture of aircraft. The complexity of the material manufacture necessitates that evaluation is required prior to final production and it is the development of a novel approach to this testing that constitutes the focus for the work of this Thesis. Existing techniques frequently utilise ultrasonic signals to interrogate the sample under investigation, however, these are cumbersome and scan speed is invariably slow when testing of large samples is considered. This is because large samples are normally tested using a through transmission approach, where narrow jets of water are used to couple the ultrasonic signal through the propagation channel. The fundamental basis of the proposed approach is the removal of the water couplant, enabling a receiver array to be employed, and thus scan large areas more quickly. Flexibility would also be increased with this technique due to a capability to scan moisture sensitive parts. In order to achieve this, however, the considerable problem of the acoustic impedance mismatch at each solid/air boundary would have to be overcome. Firstly, a narrowband, relatively low frequency approach is selected. It is concluded however, that in order to maximise the scan speed benefit, parallel data acquisition from the receiver array elements must be achieved and no signal averaging must be performed. A small array element pitch and focussing are deemed necessary in the pursuit of adequate defect detection resolution. It is important to select the most appropriate transducer technology for coupling in air and a comprehensive comparison of two relevant technologies (piezocomposite and electrostatic) is carried out. Piezocomposites are found to be superior in terms of sensitivity, robustness and focusing capability. A novel acoustic matching layer is developed to improve coupling from the transducers to the air load. This is investigated microscopically and acoustically and a linear model is developed to enable the design for the most successful operation. Prototype air-coupled systems are produced and scan results compared favourably with the results using water-coupled techniques.

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Mode of access: Internet via World Wide Web. Available at http://hdl.handle.net/1947/4681. / "November 2005"

This dissertation examines the effect that the introduction of an advanced manufacturing technology, specifically robotics, has on the work force of an aerospace defense company. In this endeavor, there are two main objectives. First, this study determines whether workers feel that their jobs are threatened by the introduction of robotic technology. Secondly, the research compares the degree to which workers from different labor types feel this threat. A review of the literature reveals that the technical factors involving manufacturing technology have been thoroughly examined and discussed, but the effect that they have on the work force has been somewhat neglected. This dissertation develops ten hypotheses to ascertain the perceived threat to job security for workers within an aerospace defense company. This study is based on an employee survey that examined the employee's perceived threat to job security by the introduction of robotics. The primary research was obtained from employees within an aerospace defense company through the use of questionnaires in a three phase approach. The first phase utilized a pretest that sampled the questionnaire prior to the company-wide solicitation. The second phase administered the questionnaire to the three labor types within the work force. Phase three consisted of data reduction and the comparison of the primary data to the research hypotheses. The results of the study concluded that workers closer to the robotic technology (hands-on employees) felt more threatened about their job security than workers more removed from the technology (support personnel and management). It was further found that the hands-on workers felt that the major factor that lead to the introduction of robots was the desire to lower labor costs while support personnel and managers felt that the major factor that lead to the introduction of robots was due to increasing productivity. Additional hypotheses tested in this study include the effect that robots have on the perceptions of the work force toward the company's employment level, worker apprehension and reaction, training, safety, health, and competition.

An autonomous vehicle is a vehicle that is capable of navigating and driving with no human intervention whatsoever through the utilization of various sensors and positioning systems. The possible applications of autonomous vehicles are widespread, ranging from the aerospace industry to the mining and military sectors where the exposure of human operators to the operating conditions is hazardous to their health and safety. Automobile accidents have become the leading cause of death in certain segments of the world population. Removing the human driver from the decision-making process through automation may result in significantly safer highways. Although full autonomy may be the ultimate goal, there is huge scope for systems that aid the driver in decision making or systems that take over from the driver under conditions where the human driver fails. The aim of the longitudinal control system to be implemented on the Land Rover test vehicle in this study is to improve the vehicle’s safety by controlling the vehicle’s longitudinal behaviour. A common problem with sports-utility-vehicles is the low rollover threshold, due to a high centre of gravity. Rather than modifying the vehicle to increase the rollover threshold, the aim of the control system presented here is to prevent the vehicle from exceeding speeds that would cause the vehicle to reach its rollover threshold. In order to develop a control system that autonomously controls the longitudinal degree of freedom, a model of the test vehicle (a 1997 Land Rover Defender 110 Wagon) was developed in MSC.ADAMS/View and validated experimentally. The model accurately captures the response of the test vehicle to supply forces as generated by the engine and demand forces applied through drag, braking and engine braking. Furthermore, the model has been validated experimentally to provide reliable simulation results for lateral and vertical dynamics. The control system was developed by generating a reference speed that the vehicle must track. This reference speed was formulated by taking into account the vehicle’s limits due to lateral acceleration, combined lateral and longitudinal acceleration and the vehicle’s performance capabilities. The control system generates the desired throttle pedal position, hydraulic pressure in the brake lines, clutch position and gear selection as output. The MSC.ADAMS\View model of the test vehicle was used to evaluate the performance of the control system on various racetracks of which the GPS coordinates were available. The simulation results indicate that the control system performs as expected. Finally, the control system was implemented on the test vehicle and the performance was evaluated by conducting field tests in the form of a severe double lane change manoeuvre. The results of the field tests indicated that the control system limited the acceleration vector of the vehicle’s centre of gravity to prescribed limits, as predicted by the simulation results. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Mechanical and Aeronautical Engineering / unrestricted

Polymer nanofibers have attracted a lot of industrial interest in the past decade. In general, these fibers need to be thermally stable for many applications, such as in the aerospace industry. However, most of these polymer nanofibers suffer from low temperature degradation, limiting their use in many potential applications. Graphene, which is one sheet of graphite, has unique properties such as high conductivity, and high thermal stability. This exceptional material can be incorporated into the polymer nanofibers as nanofillers in order to enhance their thermal properties. The aim of this dissertation is to investigate the effect of adding graphene nanofillers into the polymer fiber on the resulting fibers’ thermal properties. For that purpose, polyvinyl alcohol (PVA), a non-conductive polymer and a different source of graphene, namely graphene foam, expendable graphite and graphite powder were used. The growth technique was the electrospinning technique which offers a variety of parameters that need to be optimized. For this includes, the amount of PVA in the water solvent, the flow rate, the applied voltage, the growth time, and the tip/collector distance. In summary, it has been optimized that the best conditions for growth of fibers will be as follows: PVA concentration will be fixed at 10 wt%, flow rate will be 3 ml/h, applied voltage will be 30 kV, growth time of 60 s and tip/collector distance will be fixed at 12 cm. The resulted PVA fibers from these conditions were smooth continuous and hollow with diameter ranging between 190-340 nm, while PVA/graphene nano-fibers are much thinner with diameter ranging between 132 - 235 nm when the same parameters were used with only graphene concentration varied. The fiber obtained with PVA showed a hollow structure which is desirable for incorporation of graphene nanofillers. The dispersion of the different source of graphene sheets in the starting PVA solution showed enhanced thermal stability compared to the PVA fibers alone. Furthermore, an increase in the thermal stability is observed with increasing concentration of graphene nanofillers. This work shows the promising use of graphene as nanofillers for PVA fibers. This can be expended to other non-conductive and conductive polymers in order to broaden the application of these fibers in the industries, where thermal stability is a prerequisite. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Physics / unrestricted