To achieve efficient planarization with reduced device dimensions in integrated circuits, a better understanding of the physics, chemistry, and the complex interplay involved in chemical mechanical planarization (CMP) is needed. The CMP process takes place at the interface of the pad and wafer in the presence of the fluid slurry medium. The hardness of Cu is significantly less than the slurry abrasive particles which are usually alumina or silica. It has been accepted that a surface layer can protect the Cu surface from scratching during CMP. Four competing mechanisms in materials removal have been reported: the chemical dissolution of Cu, the mechanical removal through slurry abrasives, the formation of thin layer of Cu oxide and the sweeping surface material by slurry flow. Despite the previous investigation of Cu removal, the electrochemical properties of Cu surface layer is yet to be understood. The motivation of this research was to understand the fundamental aspects of removal mechanisms in terms of electrochemical interactions, chemical dissolution, mechanical wear, and factors affecting planarization. Since one of the major requirements in CMP is to have a high surface finish, i.e., low surface roughness, optimization of the surface finish in reference to various parameters was emphasized. Three approaches were used in this research: in situ measurement of material removal, exploration of the electropotential activation and passivation at the copper surface and modeling of the synergistic electrochemical-mechanical interactions on the copper surface. In this research, copper polishing experiments were conducted using a table top tribometer. A potentiostat was coupled with this tribometer. This combination enabled the evaluation of important variables such as applied pressure, polishing speed, slurry chemistry, pH, materials, and applied DC potential. Experiments were designed to understand the combined and individual effect of electrochemical interactions as well as mechanical impact during polishing. Extensive surface characterization was performed with AFM, SEM, TEM and XPS. An innovative method for direct material removal measurement on the nanometer scale was developed and used. Experimental observations were compared with the theoretically calculated material removal rate values. The synergistic effect of all of the components of the process, which result in a better quality surface finish was quantitatively evaluated for the first time. Impressed potential during CMP proved to be a controlling parameter in the material removal mechanism. Using the experimental results, a model was developed, which provided a practical insight into the CMP process. The research is expected to help with electrochemical material removal in copper planarization with low-k dielectrics.

This study focuses on the wear of piston rings in a hydraulic radial piston motor. The piston ring has to satisfy increasing demands for reliability and longer service life. It has two contacting surfaces, the face and the flank, and operates under a boundary lubrication state. This first part of the project aimed to detect and characterise piston ring wear. Measurement by weighing gives an overall value for wear defined as loss of mass. Two-dimensional form and surface roughness measurements show the distribution of wear on the piston ring face in contact with the cylinder bore and the piston ring flank in contact with the piston groove. Three-dimensional analyses, both quantitative and qualitative, allow the wear mechanisms to be identified. The wear of piston rings from an actual hydraulic motor was characterised. As well, rig testing was performed in two different test rig set-ups, one simulating the sliding movement of the piston ring and the other the tilting movement at the end of the strokes. Wear during the running-in period was investigated, and the findings indicate that the period when this takes place is of short duration. In the long term, mild wear makes the surfaces smoother than they were when new, resulting in a very low wear coefficient. Significant levels of wear were measured on both contacting surfaces of the piston ring. In cases in which the flank exhibits more wear than the face, the wear on the flank can be reduced by proper design of the piston groove. The second part of the project aimed to evaluate use of a textured surface for the cylinder bore counter surface and a coated surface for the piston ring. Three modelling experiments were performed to characterise the friction and wear properties under lean boundary lubrication conditions. Under such conditions, textured surfaces have the advantage of retaining more lubricant and supplying it over a longer time. Stable friction was also a distinctive feature of the textured surface. Use of a coating could also possibly reduce the amount of wear. Though a smooth surface, like a polished one, is hard to beat for a working texture, a coated surface is far ahead of a smooth uncoated one. Different manufactured and commonly used cylinder bore surfaces, including textured ones, were evaluated in the sliding movement test rig. That allowed favourable wear properties, such as lowest wear coefficient, to be determined with the use of a roller burnished surface. A final part of the research involved simulating wear on the piston ring face throughout the entire service life of a hydraulic motor. This allowed us to determine the roles of surface roughness and coating in prolonging service life and achieving acceptable and secure piston ring operation. The model is simple and realistic, but still needs to be refined so as to correspond even better to reality. / QC 20101007

The effect of freestream turbulence on generation of crossflow disturbances over swept wings is investigated through direct numerical simulations.  The set up follows  the  experiments  performed  by Downs  et  al.  in their  TAMU  experi- ment.  In this experiment the authors use ASU(67)-0315 wing geometry which promotes  growth  of crossflow  disturbances.   Distributed  roughness  elements are locally placed near the leading edge with a span-wise wavenumber, to ex- cite the corresponding crossflow vortices.  The response of boundary layer to external disturbances such as roughness heights, span-wise wavenumbers, Rey- nolds numbers and freestream turbulence characteristics are studied.  It must be noted that the experiments were conducted at a very low level of freestream turbulence  intensity  (T u).   In this  study,  we fully  reproduce the  freestream isotropic homogenous turbulence through a DNS code using detailed freestream spectrum data provided by the experiment. The generated freestream fields are then applied as the inflow boundary condition for direct numerical simulation of the wing. The geometrical set up is the same as the experiment along with application of distributed roughness elements near the leading edge to precipi- tate stationary crossflow disturbances.  The effects of the generated freestream turbulence are then studied on the initial amplitudes and growth of the bound- ary layer perturbations.  It appears that the freestream turbulence damps out the dominant stationary crossflow vortices. / <p>QC 20130604</p>

The effects on heat transfer of piston crown surface finish and use of a metal based thermal barrier coating (TBC) on the piston crown were studied in an SI engine. Measured engine parameters such as power, fuel consumption, emissions and cylinder pressure were used to identify the effects of the coating and its surface finish. Two piston coatings were tested: a baseline copper coating and a metal TBC. Reducing surface roughness of both coatings increased in-cylinder temperature and pressure as a result of reduced heat transfer through the piston crown. These increases resulted in small improvements in both power and fuel consumption, while also having measurable effect on emissions. Oxides of nitrogen emissions were increased while total hydrocarbon emissions were decreased. Improvements attributed to the TBC were found to be small, but statistically significant. At an equivalent surface finish, the TBC performed better than the baseline copper finish.

The effects on heat transfer of piston crown surface finish and use of a metal based thermal barrier coating (TBC) on the piston crown were studied in an SI engine. Measured engine parameters such as power, fuel consumption, emissions and cylinder pressure were used to identify the effects of the coating and its surface finish. Two piston coatings were tested: a baseline copper coating and a metal TBC. Reducing surface roughness of both coatings increased in-cylinder temperature and pressure as a result of reduced heat transfer through the piston crown. These increases resulted in small improvements in both power and fuel consumption, while also having measurable effect on emissions. Oxides of nitrogen emissions were increased while total hydrocarbon emissions were decreased. Improvements attributed to the TBC were found to be small, but statistically significant. At an equivalent surface finish, the TBC performed better than the baseline copper finish.

Geomembranes are one of the most widely used geosynthetics in various civil engineering applications. Their primary function is as a barrier to liquid or vapour flow. Smooth Geomembranes are frequently used in combination with different soils, and due to their low surface roughness, are challenging to design to ensure adequate shear strength along the smooth geomembrane-soil interface. It is important to use the appropriate values of interface shear strength parameters in the design of slopes incorporating one or more geomembranes in contact with soils. The parameters are determined by conducting direct shear test on the geomembrane-soil interface. Laboratory tests of interface shear strength for geomembranes and soil are typically carried out with no provision for measurement of pore pressures at the soil/geomembrane interface. <p>This thesis deals with study of smooth geomembrane-soil interfaces, particularly under unsaturated conditions. The various factors that affect the interface shear behaviour are also studied. The tests were conducted using a modified direct shear box with a miniature pore pressure transducer installed adjacent to the surface of the geomembrane. Geomembranesoil interface shear tests were carried out with continuous measurement of suction in close proximity to the interface during the shearing process thus making it possible to analyze test results in terms of effective stresses. The method was found to be suitable for unsaturated soils at low values of matric suction. <p>Results of interface shear tests conducted using this method show that it is quite effective in evaluating interface shear behaviour between a geomembrane and an unsaturated soil. The results suggest that soil suction contributes to shearing resistance at low normal stress values. At lower normal stress values, the interface shear behaviour appears to be governed only by the magnitude of total normal stress. <p> At high normal stresses, the failure mechanism changed from soil particles sliding at the surface of geomembrane to soil particles getting embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane soil interface. It was found that placement water contents near saturated conditions results in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.

When designing a new fuel management system for a spark ignition engine the amount of air that is fed to the cylinders is highly important. A tool that is being used to improve the performance and reduce emission levels is engine modeling were a fuel management system can be tested and designed in a computer environment thus saving valuable setup time in an engine test cell. One important part of the modeling is the throttle which regulates the air. The current isentropic model has been investigated in this report. A throttle body and intake manifold has been simulated using Computational Fluid Dynamics (CFD) and the influence of surface heating and surface wall roughness has been calculated. A method to calculate the effective flow area has been constructed and tested by simulating at two different throttle plate angles and several pressure ratios across the throttle plate. The results show that both surface wall roughness and wall heating will reduce the mass flow rate compared to a smooth and adiabatic wall respectively. The reduction is both dependent on pressure ratio and throttle plate angle. The effective area has showed to follow the same behaviour as the mass flow rate for the larger simulated throttle plate angle 31 degrees, i.e. an increase as the pressure drop over the throttle plate becomes larger. At the smaller throttle plate angle 21 degrees, the behaviour is completely different and a reduction of the effective area can be seen for the highest pressure drop where a increase is expected. / När ett nytt bränslesystem ska designas till en bensinmotor är det viktigt att veta hur stor mängd luft som hamnar i cylindrarna. Ett verktyg som är på frammarsch för att förbättra prestanda och minska emissioner är modellbaserad simulering. Med hjälp av detta kan ett bränslesystem designas och testas i datormiljö och därigenom spara dyrbar tid som annars måste tillbringas i en motortestcell. En viktig del av denna modellering är spjället eller trotteln vilken reglerar luften. I denna rapport har studier gjort på den nuvarande isentropiska modellen. Ett spjällhus och insugsgrenrör har simulerats med hjälp av Computational Fluid Dynamics (CFD) och påverkan av värme samt ytjämnhet på väggen har beräknats. En metod att beräkna den effektiva genomströmmade arean har konstruerats och testats vid två olika spjällvinklar samt flertalet tryckkvoter över spjället. Resultaten visar att både en uppvärmd vägg och en vägg med skrovlighet kommer att minska massflödet jämfört med en adiabatisk respektive en slät vägg. Minskningen har både spjällvinkel samt tryckkvots beroende. Den effektiva genomströmmade arean har visats sig följa samma beteende som massflödet vid den större simulerade spjällvinkeln 31 grader, det vill säga öka med ökat tryckfall över spjället. Vid den mindre vinkeln 21 grader, är beteendet helt annorlunda jämfört med massflödet och en minskning av den effektiva arean kan ses vid det största tryckfallet där en ökning förväntades.

As a result of manufacturing processes, real surfaces have roughness and surface curvature. The real contact occurs only over microscopic contacts, which are typically only a few percent of the apparent contact area. Because of the surface curvature of contacting bodies, the macrocontact area is formed, the area where microcontacts are distributed randomly. The heat flow must pass through the macrocontact and then microcontacts to transfer from one body to another. This phenomenon leads to a relatively high temperature drop across the interface. Thermal contact resistance (TCR) is a complex interdisciplinary problem, which includes geometrical, mechanical, and thermal analyses. Each part includes a micro and a macro scale sub-problem. Analytical, experimental, and numerical models have been developed to predict TCR since the 1930's. Through comparison with more than 400 experimental data points, it is shown that the existing models are applicable only to the limiting cases and none of them covers the general non-conforming rough contact. The objective of this study is to develop a compact analytical model for predicting TCR for the entire range of non-conforming contacts, i. e. , from conforming rough to smooth sphere-flat in a vacuum. The contact mechanics of the joint must be known prior to solving the thermal problem. A new mechanical model is developed for spherical rough contacts. The deformation modes of the surface asperities and the bulk material of contacting bodies are assumed to be plastic and elastic, respectively. A closed set of governing relationships is derived. An algorithm and a computer code are developed to solve the relationships numerically. Applying Buckingham Pi theorem, the independent non-dimensional parameters that describe the contact problem are specified. A general pressure distribution is proposed that covers the entire spherical rough contacts, including the Hertzian smooth contact. Simple correlations are proposed for the general pressure distribution and the radius of the macrocontact area, as functions of the non-dimensional parameters. These correlations are compared with experimental data collected by others and good agreement is observed. Also a criterion is proposed to identify the flat surface, where the influence of surface curvature on the contact pressure is negligible. Thermal contact resistance is considered as the superposition of macro and micro thermal components. The flux tube geometry is chosen as the basic element in the thermal analysis of microcontacts. Simple expressions for determining TCR of non-conforming rough joints are derived which cover the entire range of TCR by using the general pressure distribution and the flux tube solution. A complete parametric study is performed; it is seen that there is a value of surface roughness that minimizes TCR. The thermal model is verified with more than 600 data points, collected by many researchers during the last 40 years, and good agreement is observed. A new approach is taken to study the thermal joint resistance. A novel model is developed for predicting the TCR of conforming rough contacts employing scale analysis methods. It is shown that the microcontacts can be modeled as heat sources on a half-space for engineering applications. The scale analysis model is extended to predict TCR over the entire range of non-conforming rough contacts by using the general pressure distribution developed in the mechanical model. It is shown that the surface curvature and contact pressure distribution have no effect on the effective micro thermal resistance. A new non-dimensional parameter is introduced as a criterion to identify the three regions of TCR, i. e. , the conforming rough, the smooth spherical, and the transition regions. An experimental program is designed and data points are collected for spherical rough contacts in a vacuum. The radius of curvature of the tested specimens are relatively large (in the order of m) and can not be seen by the naked eye. However, even at relatively large applied loads the measured joint resistance (the macro thermal component) is still large which shows the importance of surface out-of-flatness/curvature. Collected data are compared with the scale analysis model and excellent agreement is observed. The maximum relative difference between the model and the collected data is 6. 8 percent and the relative RMS difference is approximately 4 percent. Additionally, the proposed scale analysis model is compared/verified with more than 880 TCR data points collected by many researchers. These data cover a wide range of materials, surface characteristics, thermal and mechanical properties, mean joint temperature, directional heat transfer effect, and contact between dissimilar metals. The RMS difference between the model and all data is less than 13. 8 percent.

This work was carried out to study the effect of shot-peening on the fatigue behaviour of carbon steels. Differently heat treated medium and high carbon steel specimens were selected. Medium carbon steels, AISI 1141 and AISI 1151, were respectively air cooled and quenched-tempered. A high carbon steel, C70S6 (AISI 1070), was air cooled. The other material was a powder metal (0.5% C) steel. Each group of steels was divided into two. One was shot-peened. The other half remained in their original conditions. All were fatigue tested under fully reversed (R=-1) tension-compression loading conditions. Microhardness tests were carried out on both the grip and gage sections of selected non shot-peened and shot-peened specimens to determine the hardness profile and effect of cycling. Shot-peening was found to be deeper on one side of each specimen. Compressive residual stress profiles and surface roughness measurements were provided. Shot-peening increased the surface roughness from 0.26±0.03µm to 3.60±0.44µm. Compressive residual stresses induced by shot-peening reached a maximum of -463.9MPa at a depth of 0.1mm.The fatigue limit (N≈106 cycles) and microhardness profiles of the non shot-peened and shot-peened specimens were compared to determine the material behaviour changes after shot-peening and cycling. Also their fatigue properties were related to the manufacturing process including heat and surface treatments. Comparing the grip and gage microhardness profiles of each steel showed that neither cyclic softening nor hardening occurred in the non shot-peened condition. Cyclic softening was apparent in the shot-peened regions of all steels except powder metal (PM) steel. The amount of softening in the shot-peened region was 55.0% on the left side and 73.0% on the right in the AISI 1141 steel , 46.0% on the left side and 55.0% on the right in the C70S6AC steel and 31.0% on the right side in AISI 1151QT steel. Softening was accompanied by a decrease in the depth of surface hardness. It is suggested that although the beneficial effects of shot peening, compressive residual stresses and work hardening, were offset by surface roughness, crack initiation was more likely to occur below the surface. Surface roughness was not a significant factor in controlling the fatigue lives of AISI 1141AC and C70S6 steels, since they were essentially the same for the non shot-peened and shot-peened conditions. Shot-peening had very little effect on the push-pull fatigue limit of C70S6 steel (-2.1%), and its effect on AISI 1141AC steel was relatively small (6.0%). However, the influence of shot-peening on the AISI 1151QT and PM steels was more apparent. The fatigue limit of the PM steel increased 14.0% whereas the fatigue limit of the AISI 1151QT steel decreased 11.0% on shot peening.

Geomembranes are one of the most widely used geosynthetics in various civil engineering applications. Their primary function is as a barrier to liquid or vapour flow. Smooth Geomembranes are frequently used in combination with different soils, and due to their low surface roughness, are challenging to design to ensure adequate shear strength along the smooth geomembrane-soil interface. It is important to use the appropriate values of interface shear strength parameters in the design of slopes incorporating one or more geomembranes in contact with soils. The parameters are determined by conducting direct shear test on the geomembrane-soil interface. Laboratory tests of interface shear strength for geomembranes and soil are typically carried out with no provision for measurement of pore pressures at the soil/geomembrane interface. <p>This thesis deals with study of smooth geomembrane-soil interfaces, particularly under unsaturated conditions. The various factors that affect the interface shear behaviour are also studied. The tests were conducted using a modified direct shear box with a miniature pore pressure transducer installed adjacent to the surface of the geomembrane. Geomembranesoil interface shear tests were carried out with continuous measurement of suction in close proximity to the interface during the shearing process thus making it possible to analyze test results in terms of effective stresses. The method was found to be suitable for unsaturated soils at low values of matric suction. <p>Results of interface shear tests conducted using this method show that it is quite effective in evaluating interface shear behaviour between a geomembrane and an unsaturated soil. The results suggest that soil suction contributes to shearing resistance at low normal stress values. At lower normal stress values, the interface shear behaviour appears to be governed only by the magnitude of total normal stress. <p> At high normal stresses, the failure mechanism changed from soil particles sliding at the surface of geomembrane to soil particles getting embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane soil interface. It was found that placement water contents near saturated conditions results in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.