Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 87-91). Also available on the Internet.

Determining bumpiness and inclination of surfaces is very important in many different areas, such as airports and at constructions sites. In this study, a surveying trolley and a remote controlled (RC) car were used to determine the bumpiness of two different surfaces. The aim with this study was to test the accuracy of a surveying trolley and an RC car to see how the accuracy can be increased with different observation methods. Total station, GPS and laser scanner surveying equipments were used, and all observations obtained by them were analysed. The laser scanner data was found to have the best precision. For that reason, it was accepted as the “true” data and it was used for comparing and evaluating other methods. It was found that the trolley and the RC car provided good height information with total stations and they were corresponding to the laser scanner data. When they were used with GPS, the accuracy was much lower. It was concluded that using two total stations is not increasing the accuracy, the RC car and the trolley are good measuring methods but not capable to inspect 1,2 mm tolerance for the floors, and finally, 2-3 cm positioning accuracy is obtainable when using GPS.

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<p> The effect of strain hardening rate and material strength on the development of surface roughness in AA6111 was investigated. No measurable change in the rate of roughening, or in the surface morphology was observed due to altering the strain hardening rate by using different test temperatures. Changing the material strength and strain hardening rate by altering the precipitation state also gave no significant change in either roughening rate or morphology with respect to strain. The development of surface roughness is also independent of strain history. Samples subjected to an intermediate polish after 20% true strain resumed roughening at the same rate regardless of amount of previous tensile strain. The development of surface roughness is dependent on only the strain level to which the sheet is deformed. The surface morphology seems to be controlled by the combination and distribution of texture components on the surface. The rate of roughening is grain size dependent and the surface grain size may provide a key to controlling roughening. </p> / Thesis / Master of Applied Science (MASc)

As the existing steel infrastructure inevitably continues to age and deteriorate, engineers are increasingly looking for innovative and effective methods for repairing and maintaining existing structures. Structural steel components can degrade due to the surrounding environmental conditions, and are susceptible to corrosion damage when exposed to aggressive environments and deicing salts. The conventional methods for repairing steel structures can be labor-intensive and time-consuming, and add considerable weight to the existing structure. One alternative is utilizing carbon fiber reinforced polymers (CFRP). Many studies have documented the ability of CFRPs to enhance the strength of existing structures. Furthermore, CFRP offers the benefits of being non-corrosive and having a high strength-to-weight ratio. Most studies on steel strengthening have focused on the bond behavior of CFRP to steels having a smooth surface condition, which are not representative of deteriorated structures in greater need of retrofitting. Further research has examined the durability of CFRP-steel bonds relative to environmental conditions that do not reflect the service life conditions for typical applications. In this work, a comprehensive study is conducted on the effects of the surface condition and environmental exposure on the bond between CFRP and steel. The influence of corrosion and simulated corrosion pitting is evaluated to determine whether structures with non-uniform surfaces are adequate for CFRP retrofits. In addition, the durability of CFRP-steel bonded systems is investigated through laboratory hygrothermal aging and in-situ environmental conditioning to multiple environments in Virginia. The research can be useful in the development of guidelines that will assist engineers determine if a CFRP retrofit solution is applicable in a given environmental setting and appropriate for the level of deterioration of the structure. / Doctor of Philosophy / As steel structures continue to age, engineers are looking for innovative and effective methods for repairing and maintaining the existing steel infrastructure. Steel components in structures can degrade due to the surrounding environmental conditions. The conventional methods for repairing steel structures can be labor-intensive and time-consuming, and add considerable weight to the existing structure. One alternative is utilizing carbon fiber reinforced polymers (CFRP). The ability of CFRPs to enhance the strength of existing structures has been widely documented. Furthermore, CFRP offers the benefits of being non-corrosive and avoids adding considerable weight to the structure. Most studies on steel strengthening have focused on the bond behavior of CFRP to steels having a smooth surface condition, which are not representative of deteriorated structures in greater need of retrofitting. Further research has examined the durability of CFRP-steel bonds relative to environmental conditions that do not reflect the service life conditions for typical applications. In this work, a comprehensive study is conducted on the effects of the surface condition and environmental exposure on the bond between CFRP and steel. The influence of corrosion and simulated corrosion pitting is evaluated to determine whether structures with non-uniform surfaces are adequate for CFRP retrofits. In addition, the durability of CFRP-steel bonds exposed to laboratory and field conditions is investigated. The research can be useful in the development of guidelines that will assist engineers determine if the application of CFRPs retrofit solution is suitable in a given environment and appropriate for the level of deterioration of the structure.

In the past decade, the condensation on superhydrophobic surfaces has been investigated abundantly to achieve dropwise condensation. There is not a specific approach in choosing the size of the roughness of the superhydrophobic surfaces and it was mostly selected arbitrarily to investigate the behavior of condensates on these surfaces. In this research, we are optimizing the size of the roughness of the superhydrophobic surface in order to achieve dropwise condensation. By minimizing the resistances toward the transition of the tails of droplets from the cavities of the roughness to the top of the roughness, the size of the roughness is optimized. It is shown that by decreasing the size of the roughness of the superhydrophobic surface, the resistances toward the transition of the tails of droplets from Wenzel state to Cassie state decrease and consequently dropwise condensation becomes more likely.

In this study the author reports the effects of surface roughness on dynamic behavior of water droplets on different types of rough structures. First, the influence of roughness geometry on the Wenzel/ Cassie-Baxter transition of water droplets on one-tier (solid substrates with Si micropillars) surfaces is studied (Chapter 3). In order to address distinct wetting behaviors of the advancing and receding motions, the author investigates the Wenzel/ Cassie-Baxter transition of water droplets on one-tier surfaces over a wide range of contact line velocities and droplet volumes in both advancing and receding movements. The discussions are strengthened by experimental results. According to the author’s analysis, the advancing contact zone tends to follow the Cassie-Baxter behavior for a wider range of geometric ratios than the receding contact zone. Physical phenomena such as advancing contact line rolling mechanism and the pinning of the receding contact line are introduced to justify distinct transition points of the advancing and receding movements respectively. Based on the analysis provided in Chapter 3, the author experimentally investigates the contact line fluctuations and contact line friction coefficients of water droplets on smooth, one-tier, and two-tier (with carbon nanotubes (CNTs) grown on Si micropillars) surfaces in Chapters 4 and 5. Both the advancing and receding contact line fluctuations/friction coefficients have been measured, analyzed and compared on smooth, one-tier, and two-tier surfaces over a wide range of contact line velocities and droplet volumes. A comprehensive analysis is provided to explain the experimental observations.

Surface roughness exists at many length scales-from atomic dimensions to meters. At sub-micron scale, the distribution of roughness is largely dependent on the process that generates the surface through the mechanisms of material removal/addition involved and the process parameters. The focus of the research is to quantitatively characterize the evolution of sub-micron scale surface roughness in the mechanical, chemical and electrochemical material removal techniques and study the influence of roughness on the mechanical behavior of surfaces. High purity aluminum surfaces are subjected to surface dissolution techniques such as electropolishing, chemical etching and anodization. Owing to the lack of sufficient lateral resolution in conventional roughness measurement techniques and appropriate scale independent roughness characterization techniques, the effect sub-micron scale electrochemical inhomogeneities present on the surfaces have on the roughness evolution at various length scales has not been understood. In this work, the power spectral density method of roughness characterization is used to quantitatively evaluate the roughness length scales affected in the surface generation processes as a function of time. Results indicate that in the case of electropolishing, roughness is not uniformly reduced at all length scales. Further, cut-off frequencies are suggested to optimize the electropolishing process. In chemical etching, the nature of roughness produced is found to be dependent on the nature of the starting surface. The nature of surface and sub-surface structures produced in the initial stage of the anodization process, and the transition from a disordered to an ordered structure are studied. In order to study the mechanical behavior of surfaces as a function of surface roughness, a single asperity indentation is modeled using nanoindentation of micropillar produced by focused ion beam machining of aluminum surfaces. Load-displacement curves are constructed to show the transition from a single asperity deformation to bulk deformation as function of indentation depth. Additionally, indentation responses of polymer coated surfaces with varying degree of roughness that were produced by the aforementioned surface generation processes are studied. it is shown how high interface roughness gives rise to high scatter both in loading and unloading portions of the load-displacement curves. Finally, porous alumina surface generated by the anodization process discussed above is indented to simulate a multi-asperity interaction.

The purpose of this study was to develop a composite manufacturing process that would be able to deliver Class A surface finished products in the context of mould manufacturing methods. The problem required solving was to overcome the time needed to prepare Class A surfaces, by developing a composite manufacturing process that will deliver Class A surface finished products straight from the mould. The process was aimed at the entire development process, from mould and plug design up to the finished product. A literature study and a factory mould survey were conducted with a view to obtain the necessary insights into surface finishing and composite manufacturing. These surveys were followed by seven constructional tests which determined the most appropriate solutions for the proposed manufacturing processes. Test 1 was used to determine a quality finish standard for composites from the sanding grits used to finished composite surfaces versus surface roughness values used in other industries. The standard determined that a P800 finish has a roughness between 0.200 and 0.150 um and constitutes a Class A3 finish. P1000 to P1200 have a roughness between 0.150 um to 0.100 um and constitutes a Class A2 finish. Finally a P2000 and higher have a roughness of 0.100 um and lower and constitutes Class A1 surface finish. After the standard was set, the tests for finishing of the moulds, plugs and parts commenced. Test 2 was conducted on the CNC manufacturing of plugs out of Nuceron651 tooling board. Tool path parameters were varied in a matrix. The samples with the best surface finish value were cut with a step-over of 0.5 and feed of 800 mm/min. These parameters were found to be the most influential. Test 2 and 4 revealed that the plug surface finishing should commence with conventional 2K paint finishing, with a possibility of acrylic split surface. This process produced projected mould surfaces between 0.150 um and 0.200 um, which can be categorised as Class A-3. Test 5 and 6 determined methods for improving the mould surface quality and durability. It was established that the tooling gelcoat should be applied whilst being heated and backed with at least two layers of glass veil and a steady increase of GSM of structural glass fibres to prevent print-through. Test 3 determined that the mould corners could be strengthened with rovings pressed into the corner. It was also established that the moulds surfaces will require finishing after demoulding. The final moulds were manufactured from a fibreglass composite structure with tooling gelcoat surface. A number of guidelines and a set process were developed in order to produce moulds with a surface finish of average 0.9 um, equivalent to Class A1. Release agents were tested in Test 7, and the Loctite Frekote 770-NC release system was deemed appropriate for use with In Mould Coating (IMC) of 2K Paint. These elements were all synthesised into plug, mould and part manufacturing processes. The proposed processes were validated by the manufacturing of a JS instrument panel, which delivered a Class A2, 0.175 um, finish with IMC of 2K paint. With only a minor sanding of P3000 grit and polishing, the part was made into a Class A1 surface, measured at 0.63 um. The study proved that it is possible to produce Class A finished part with IMC. This method can provide a solution aimed at the elimination of P600 and lower finishing of composite parts manufactured with IMC. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014