In the past several years, the Defense Advanced Research Projects Agency (DARPA) has sponsored two Grand Challenges, races among autonomous ground vehicles in rural environments. These vehicles must follow a course delineated by Global Positioning System waypoints using no human guidance. Airborne LIDAR data and GIS can play a significant role in identifying barriers and least cost paths for such vehicles. Least cost paths minimize the sum of impedance across a surface. Impedance can be measured by steepness of slope, impenetrable barriers such as vegetation and buildings, fence lines and streams, or other factors deemed important to the vehicle's success at navigating the terrain. This research aims to provide accurate least cost paths for those vehicles using airborne LIDAR data. The concepts of barrier identification and least cost path generation are reviewed and forty-five least cost paths created with their performance compared to corresponding Euclidean paths. The least cost paths were found superior to the corresponding Euclidean paths in terms of impedance as they avoid barriers, follow roads and pass across relatively gentler slopes. / Master of Science

A direct, simple, and accurate way to measure skin friction by oil-film laser interferometry has been developed by various researchers. Equations and methods were developed to correct measurement errors arising from three-dimensional effects and pressure gradients. The oil-film, dual-beam laser interferometer was constructed to measure the skin friction around a wing-body junction in a three-dimensional, turbulent boundary layer with pressure gradients. The flow was dominated by the formation of a junction vortex generated at the nose of the wing-body. The oil-film skin friction results were compared with previous skin-friction measurements for the flow obtained by hot-wire measurements. The skin friction values agreed within approximately 8% between the two methods. The effects and benefits of scanning laser interferometry and alternative beam directions were investigated and discussed. The effect of dirt contamination on the data is also discussed. Methods to improve the data quality are presented. / Master of Science

High strength boron steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength boron steels are usually formed by press hardening at elevated temperatures with a view to facilitate forming and simultaneous hardening by quenching of complex shaped parts.The high strength steel sheets are used with an Al–Si coating with a view e.g. to prevent scaling of components during hot-metal forming. The Al-Si coated high strength steel can lead to problems with galling (i.e. material transfer from the coated sheet to the tool surface) which have a negative influence on the quality of the produced parts as well as the process economy. The available results in the open literature pertaining to high temperature galling are very scarce. With this in view, the friction and wear behaviours of different tool steel coatings and different roughness lay directions sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature reciprocating friction and wear tester at temperature of 900 °C.The results have shown that parallel sliding with respect to the surface roughness lay reduces the severity of galling compared to perpendicular sliding. None of the coatings included in this study have shown beneficial effects in view of galling. The DLC coating experienced less galling compared to the AlCrN and TiAlN. Post polishing of the coated tool steel has resulted in more severe material transfer with higher and more unstable friction. / <p>Validerat; 20111022 (anonymous)</p>

Joining of dissimilar metals is a process that is of interest in many fields, especially the automotive industry where lightweighting of the body structure is important. However, creating strong joints between dissimilar metals can be challenging. Friction bit joining (FBJ) is a solid-state method that uses a consumable bit to create a strong joint between dissimilar metals such as aluminum and steel. The purpose of this research is to gain understanding of how adjusting FBJ parameters affects the heating and pressure at the weld interface using a modeling approach, in order to better understand the bonding process. The questions guiding this research are: (1) What is the effect of spindle speed, plunge rate, and plunge depth on joint strength? (2) Can the proposed model be developed with enough fidelity to correlate the effect of these parameters on joint strength, within 10%? (3) What is the effect of the simulated vertical load profile on heating at the interface? (4) Does the load profile/heating relationship correlate to experimental joint strength to within 10%? A design of experiments approach found that the effect of spindle speed on joint strength is significant. Plunge rate did not have a significant effect, but the interaction between plunge rate and spindle speed was significant. A model was created, and multiple simulations were run to study these interactions. Initial simulations were run based on the input parameters used for the experiments. The simulation data was used to run a full second order regression was run which found that spindle speed had a significant effect on the experimental Z load. The data also revealed that spindle speed and plunge rate have a strong correlation between bonded area and temperature. Simulated versus experimental Z loads have a good correlation. Experimental bonded area had a slight correlation to joint strength trending in the correct direction. The shape of the simulated cross section did not fully match the experimental cross sections but was reasonable. Simulated bonded area and experimental bonded area also have a positive correlation. Despite some weaknesses, the current model does appear to be predictive enough that it can provide insight into other FBJ design configurations and material combinations in terms of temperature profiles and welding loads.

In HEV and EV, higher fuel economy is achieved by operating the ICE and electric motor in the most efficient region and by using regenerative braking. Such a braking system converts, transfers, stores and reuses kinetic energy which would otherwise be dissipated as heat through friction brakes to the environment. This research investigates the control of braking for a mixed-mode braking system in a these vehicles based on the proportion of braking energy that can be stored. Achieving mixed-mode braking requires the ‘blending’ of the two systems (regenerative and friction), and in brake blending, the electric motor/generator (M/G) and the hydraulic actuation pressure are controlled together to meet the driver’s braking demand. The research presented here has established a new robust dynamic modelling procedure for the design of combined regenerative and hydraulic braking systems. Direct torque control and pressure control were selected as the control criteria in both brakes. Two simulation models have been developed in Matlab/Simulink to generate analysis the performance of the control strategy in the blended braking system. Integration of the regenerative braking system with ABS has also been completed, based on two conditions, with and without the deactivation of the regenerative braking. Verification of the models is presented, based on experimental work on two EVs manufactured by TATA Motors; the ACE light commercial vehicle and the VISTA small passenger car. It is concluded that braking demand and vehicle speed determine the operating point of the motor/generator and hence the regenerative braking ratio.

Additive Friction Stir Deposition is an emerging solid-state additive manufacturing process that leverages severe plastic deformation to deposit fully dense metallic parts. This is of particular interest for high-strength aluminum alloys in which the addition of copper to the alloy chemistry makes them susceptible to hot cracking. This plagues traditional 3D printing of metals which is based on melting and solidification. This work looks at a particular high-strength aluminum alloy AA7050, one of the most widely utilized alloys for complex aerostructures. One of the key traits allowing for its widespread use is its low quench sensitivity, which enables it to be formed into thick sections and still achieve adequate strength. This work studies the feasibility of printing AA7050 and achieving full strength in thin cross sections as well as the influence of the zirconium dispersoid particle on quench sensitivity when applied to thicker sections. It was found that AA7050 after AFSD has significantly more quench sensitivity than traditionally processed material and through STEM, it was determined that this was due to the Al3Zr dispersoid particles providing heterogeneous precipitation sites. It was demonstrated that removing Zr alleviates the quench sensitivity in the case of printing with a featureless tool; however, the breakup of large constituent particles with a protrusion tool increases the number of interfaces for heterogeneous nucleation that induces sensitivity. This work shows that the dynamic recrystallization necessary to deposit material is detrimental to the fundamental performance of the alloy, making it challenging for thick AA7050 to achieve peak strength. A separate study is shown in which AFSD was utilized to successfully repair analogous corroded fastener holes in AA7050 commonly observed in service. After repairing with AFSD, the AA7050 outperformed the baseline material in R=0.1 and R=-1 fatigue, even outperforming pristine material in the R=0.1 case. This was determined to be due to the breakup of Fe-rich constituent particles serving as fatigue crack initiation sites which effectively delays the crack initiation process. / Doctor of Philosophy / Additive Friction Stir Deposition (AFSD) is an emerging additive manufacturing technique that utilizes severe plastic deformation instead of melting to 3D print metals. This work focuses on one of the most prominent aluminum alloys used in aerostructures (AA7050) and its performance after printing. It was found that printing AA7050 in thick sections has further challenges and that modifying the alloy chemistry can alleviate losses in strength. The understanding of AA7050 and AFSD was utilized for a specific application, the repair of corroded fastener holes on the coupon level. It was found that repairing the simulated corroded hole improved the fatigue performance of the coupon indicating a successful means for repairing components.

No description available.

Open-graded friction course (OGFC) is a porous mix primarily used to improve pavement safety. OGFC is characterized by air voids ranging from 15 to 20 percent which allows surface water to drain through its structure and then laterally from the pavement structure. The ability of OGFC to drain water quickly results in less water ponding on the pavement surface, thereby reducing hydroplaning, reducing vehicle spray, and providing improved skid resistance. Research objectives were to evaluate the use of OGFC mixes containing 100 percent gravel and 50 percent gravel/50 percent limestone and to determine specifications to be employed by the Mississippi Department of Transportation (MDOT). Specimens were prepared at design asphalt binder content and evaluated for permeability, durability, stability, and moisture resistance. Research findings show mixes containing 100 percent gravel and 50 percent gravel/50 percent limestone perform comparably in laboratory testing.

The last few decades have seen a significant development of complex heat transfer enhancement geometries such as a helicallyinned tube. The arising problem is that as the fins become more complex, so does the prediction of their performance. In addition to discussing existing prediction tools, this dissertation demonstrates the successful use of artificial neural networks as a correlating method for experimentally- measured heat transfer and friction data of helicallyinned tubes.

Friction stir welding (FSWing) is a solid state, thermo-mechanical process that utilizes a non-consumable rotating weld tool to consolidate a weld joint. In the FSW process, the weld tool is responsible for generating both the heat required to soften the material and the forces necessary to deform and consolidate the former weld seam. Thus, weld tool geometry, material selection, and process parameters are important to the quality of the weld. To study the effects of the weld tool geometry on the resulting welds, a previous study was conducted using varying degree taper, microwave-sintered tungsten carbide (WC) weld tools to FSW Ti-6Al-4V. Fully consolidated welds were down selected for this study to evaluate the resulting mechanical properties and to document the microstructure. X-ray diffraction (XRD) was used to compare the parent material texture with that in the weld nugget. The purpose of this study is to quantify the temperatures obtained during FSWing by interpreting the resulting microstructure. This information is useful in process optimization as well as weld tool material selection.