Friction Stir Spot Welding (FSSW) has been developed from the conventional Friction Stir Welding (FSW) process, developed at The Welding Institute (TWI). FSSWs have been done without the keyhole being eliminated. Elimination of the keyhole would result in the process being more commercially viable. This dissertation focuses on an attempt of eliminating the keyhole using a retractable pin tool as well as a comparison of the weld integrity of a FSSW to that of a conventional Resistance Spot Weld (RSW). Welds were conducted on aluminium alloy 6063 T4. Comparisons between different weld procedures were done. Further analysis of the weld integrity between FSSW and RSW were conducted, comparing tensile strengths, microstructure and hardness. For the above welding procedure to take place, the current retractable pin tool, patented by PE Technikon, was redesigned. Problems associated during the welding process and the results obtained are documented. Reasons for the keyhole not being eliminated as well as recommendations for future work in the attempt to remove the keyhole are discussed.

Friction stir welding is a relatively new joining process. The heat transfer involved is crucial in determining the quality of the weld. Experimenrtal data, though important, does not provide enough information about the heat transfer process and experiments can be costly and time consuming. A numerical model, using the finite element method, was developed to stimulate the heat transfer in the workpiece in which the heat generation due to friction and plastic deformation was modelled as a surface heat flux boundary condition. This model was applied to Aluminium AL6082-T6 and Titanium Ti6A1-4V for different welding condiitions. Results were validated with experimental results. The model was shown to give better predictions of the maximum temperatures at locations in the workpiece than the overall temperature trend. A parametric study was also performed on the Aluminium model in order o predict temperature fields of the workpiece for welding conditions that were additional to those undertaken experimentally. It was found that rotational speed had a larger effect on the change in temperature than the feed rate. From the parametric study it was also clear that lower rotational speeds (300 to 660 rpm) had a greater effect on the change in temperature than the higher rotational speeds (840 to 1200 rpm). It was concluded that the model was well suited for the estimation of temperatures involved in the FSw of Aluminium Al6082-T6 but was not as accurate when applied to the FSW of Titanium.

This research project was conducted to increase weld gap tolerance in Friction Stir Welding (FSW) of 8 mm thick aluminum alloy 6082 – T6. Investigation was done on I-STIR PDS platform and a Johnford milling machine. The research project involved tool-pin design with varying re-entrant features and varying parameters as a method of weld gap closing to produce successful welds. Direction of spindle rotation and dwell time were established as part of a preliminary study. Clockwise spindle rotation with 20 seconds dwell time allows sufficient plasticity and improved material flow which assisted in achieving welds with prior 30 percent weld gap of the plate thickness. Final welds were made using three rotational speeds and feed rates with sufficient plunging to prevent root defects. Analysis of the results were detailed which include vickers microhardness test, tensile test and metallographic observation to access the suitability of the weld structure. From the set of tool-pins designed, the flare tool-pin gave a well-defined weld nugget with improved stirring at the weld root. Also, with a concave shoulder, right hand threaded tool-pin and counterclockwise flutes undergoing a clockwise spindle rotation, plasticized material flow was upward which was beneficial in reducing the amount of plate thinning. The right hand thread counter clockwise flute with a flute machined in the foot exhibited superior tensile strength for welds containing 30 percent weld gap.

Friction stir welding was used to join 3 mm Ti-6Al-4V alloy in a butt joint configuration. This research focused on optimization of a tool geometry and the interaction between process parameters and static performance of welded joints. The main parameters varied were tool travel speed and tool rotational speed. The results showed a relationship between heat input as a function of process parameters and static strength. Improved tensile properties correspond to high heat input. The hardness plots revealed an increase in hardness on both the stir zone and heat affected zone despite the small defects on the weld root. The weld microstructure was also evaluated, which showed a variation in microstructure on both the heat affected zone and stir zone in comparison to the parent material. It was also found that the use of MgO as a heat barrier on the backing plate was detrimental to the weld tensile properties of butt-welded plates compared to bead-on-plate welds of which MgO had no influence.

Friction Stir Welding (FSW) is a solid state welding process invented and patented by The Welding Institute (TWI) in 1991, for joining ferrous and non-ferrous materials1. The FSW of Aluminium and its alloys has been commercialised; and recent interest is focused on joining dissimilar materials. However, in order to commercialise the process, research studies are required to characterise and establish process windows. This research work through material characterisation of the welded joints establishes a process window for the Friction Stir welding of 5754 Aluminium Alloy and C11000 Copper. Furthermore, preliminary studies83,85 on the FSW of aluminium and copper have revealed the presence of intermetallic compounds which are detrimental to the weld qualities. This research work is also aimed at establishing process parameters that will result in limited or no intermetallic formation in the weld. The joint integrity of the resulting welds will also be correlated with the input process parameters. Based on the preliminary investigations conducted, a final weld matrix consisting of twenty seven welds was produced by varying the rotational speed between 600 and 1200 rpm, and the feed rate between 50 and 300 mm/min using three different shoulder diameter tools – 15, 18 and 25 mm to compare the heat input into the welds and to achieve the best results. The welds were characterised through microstructural evaluation, tensile testing, microhardness profiling, X-Ray Diffraction analysis, electrical resistivity and statistical analysis – in order to establish the interrelationship between the process parameters and the weld qualities. viii Microstructural evaluation of the weld samples revealed that the interfacial regions are characterised by mixture layers of aluminium and copper; while 33 percent of the tensile samples are within the acceptable range (> 75 percent joint efficiency). High Vickers microhardness values were measured at the joint interfaces, which corresponded with the intermetallic compounds. The Energy Dispersive Spectroscopy analysis revealed the presence of thin layers of intermetallics in nanoscale at the interfacial regions. The diffractograms of the X-Ray Diffraction analysis showed small peaks for intermetallics in some of the welds. Low electrical resistivities were measured at the joint interfaces. The statistical analysis showed that the downward vertical force, (Fz) can significantly influence the resulting weld qualities. An overall summary of the analysis of the weld qualities - with respect to the shoulder diameter tools employed showed that the 18 mm shoulder diameter tool is most appropriate among the three shoulder diameters considered, and a process window of medium spindle speed of 950 rpm and low-to-medium feed rate between 50 and 150 mm/min is established for FSW of Aluminium and Copper. Welds produced at 1200 rpm and 300 mm/min with low heat input did not have intermetallics formed at the joint interface.

The linear friction welding process is currently commercially used solely to produce titanium alloy aeroengine bladed disks (blisks). The process can, however, be potentially used to produce welds in non-aeroengine materials for non-aeroengine applications. The aim of this thesis was therefore to demonstrate the capabilities of the process to join materials not commonly used in the aeroengine industry and to develop understanding of the process. The focus of this thesis has been on the linear friction welding of 316L stainless steel and the linear friction welding of dissimilar materials: aluminium to copper, aluminium to magnesium and aluminium to steel. For all of these studies it was seen that weld line and near weld line microstructure could be altered by the use of different welding parameters. This property of linear friction welding was used to advantage to optimise microstructures in dissimilar welds. Intermetallic formation is usually a major challenge to the achievement of welds with good mechanical properties, and for work in this thesis welding parameters were optimised to allow welds with limited intermetallic formation. The welding of 316L and the dissimilar welding of aluminium to copper proved viable. For the welding of 316L and aluminium to copper, fracture during tensile testing occurred in the parent material (aluminium parent material for aluminium to copper). The welding of aluminium to magnesium and aluminium to steel showed promising results, with weld strength comparable to the aluminium parent material for aluminium to steel and comparable to the parent materials in O temper for aluminium to magnesium. However, repeatability of mechanical properties was poor for these dissimilar welds, which would be a significant barrier to commercial exploitation. Further work needs to be conducted to improve repeatability. Weld microstructures were characterised using optical and scanning electron microscopy as well as electron backscatter diffraction and X-ray diffraction techniques.

The phenomenon of urban identity escapes narrow definition. Its relevance to the interior design context arises as a tool for regeneration where it can assist to capitalize on the potential of particular places and social relations that distinguish one location from another. The city is a constant interplay of human actions. Small moments and rituals that take place with human activity give rise to the everyday interaction between people with one other and with their environment. It is specifically on this human scale that interior design offers the possibility to explore the physical manipulation of space and form to influence interaction. Circulation and interior elements become a means to promote socialisation across different cultural groups and generations. Social friction represents the traditional societal aspect when considering interaction. Here its importance is not diminished but is put on par with the tactile dimensions of the physical as well as the visual. The interrelatedness of the social, physical and visual elements is set against the emerging topic of neighbourhood regeneration. Identity is here considered to be part of the core essence of a sense of place and belonging, which ensures that the regeneration is driven by the local residents, both as individuals and collectively as a community. In the specific context of Sunnyside and Trevenna, which is an area that has undergone many demographic and physical changes, the possibility of a built space as a platform for different people to engage with one another and their surroundings is investigated. Such as intervention aims to instil a sense of ownership, to define the desired atmosphere and to provide a space where collective values for the shifting neighbourhood can be navigated. The design explores this relation between formal design and informal activities through the proposal of a new morphology in form of a public space and café on the ground floor, and a youth aftercare centre on the upper two floors that incorporates desirable aspects of the original structure’s functions. / Dissertation MInt(Prof))--University of Pretoria, 2012. / Architecture / MInt(Prof) / Unrestricted

This thesis reports an investigation of the generation of heat on, and the prediction of temperature of high-speed, dry-film lubricated, stainless steel bearing balls.

In this dissertation, a freight train suspension system is presented for all possible types of motion. The suspension system experiences impacts and friction between wedges and bolster. The impacts cause the chatter motions between wedges and bolster, and the friction will cause the stick and non-stick motions between wedges and bolster. Due to the wedge effect, the suspension system may become stuck and not move, which cause the suspension lose functions. To discuss such phenomena in the freight train suspension systems, the theory of discontinuous dynamical systems is used, and the motion mechanism of impacting chatter with stick and stuck is discussed. The analytical conditions for the onset and vanishing of stick motions between the wedges and bolster are presented, and the condition for maintaining stick motion was achieved as well. The analytical conditions for stuck motion are developed to determine the onset and vanishing conditions for stuck motion. Analytical prediction of periodic motions relative to impacting chatter with stick and stuck motions in train suspension is performed through the mapping dynamics. The corresponding analyses of local stability and bifurcation are carried out, and the grazing and stick conditions are used to determine periodic motions. Numerical simulations are to illustrate periodic motions of stick and stuck motions. Finally, from field testing data, the effects of wedge angle on the motions of the suspension is presented to find a more desirable suspension response for design.

Regenerative braking in conjunction with friction braking represents one of the most common braking strategies employed in electric and hybrid vehicles. As the friction brake accounts for about 5 to 85% of total braking in these “blended scenarios”, this warrants for more research into the development of new lightweight, wear resistant, and sustainable friction materials and also for reviewing the existing testing procedures.This research primarily focuses on generation of new knowledge related to development of environmentally friendly, lightweight friction material for vehicles with regenerative braking systems. A sample formulation was initially developed from knowledge gained by literature review and analysis of existing commercially available brake linings. Design of experiments based on Taguchi method and other statistical analysis tools were used to optimize the sample formulation. The density, porosity, shore D hardness, thermal stability, damping capacity of these pads were measured and compared with commercially available friction material. Pads were tested against commercially available rotors (ASTM A48 C30 gray cast iron) coated with ceramic material. Friction performance tests were completed using Universal Mechanical Tester (Tribolab by Bruker) and the scaled-down ISO SAE J2522 procedure. Friction surfaces of pads and rotors were analyzed in order to understand their surface chemistry and morphology, as well as their impact on performance of the tested friction material. The final optimized pad based on design of experiments (DOE 9) showed high and stable friction levels in high temperature sections (Section 9, Section 12.2 and Section 14 in ISO/SAE J2522 testing procedure) and excellent recovery capabilities at lower temperatures (Section 10, Section 13 and Section 15). This pad material was compatible with coated rotors, had low wear, and meets all the industry specifications and standards. SEM and EDX analysis showed that the pads developed stable friction layer on the friction surfaces and this capacity to develop friction material contributed towards overall friction stability of the material.