The contact patch of the tire is responsible for all of the transmission of a vehicle's motion to the road surface. This small area is responsible for the acceleration, stopping and steering control of the vehicle. Throughout the development of vehicle safety and stability control systems, it is desirable to possess the exact forces and moments at the tire contact patch. The tire is a passive element in the system, supplying no explicit information to vehicle control systems. Current safety and stability algorithms use estimated forces at the tire contact patch to develop these control strategies. An "intelligent" tire that is capable of measuring and transmitting the instantaneous forces and moments at the contact patch to the control algorithms in real-time holds promise to improve vehicle safety and performance. Using the force and friction information measured at the contact patch, an anti-lock braking control strategy is developed using sliding mode control. This strategy is compared to the performance of a current commercial anti-lock braking system that has been optimized by performing a threshold sensitivity analysis. The results show a definite improvement in control system strategy having known information at the tire contact patch. / Master of Science

This work is concerned with determining empirical parameters in stress and fiber orientation models required to accurately simulate the fiber orientation in injection molded composites. An independent approach aims to obtain the material parameters using a sliding plate rheometer to measure the rheology of fiber suspensions at increased fiber lengths subjected to transient shear flow. Fiber orientation was measured in conjunction with shear stress to determine the relationship between stress and fiber orientation. Using a compression molding sample preparation procedure, the transient shear stress response was measured for glass and carbon fiber suspensions up to a number average fiber aspect ratio (length/diameter) of 100. Increases in concentration or fiber aspect ratio caused the magnitude of the stress response to increase by as much as an order of magnitude when compared to the suspending matrix. The degree of shear thinning at low shear rates also increased with increases in aspect ratio and concentration. The compression molding sample preparation procedure provided poor control of the initial fiber orientation which led to the investigation of samples subjected to flow reversal and samples generated through injection molding. The samples prepared through injection molding provided improved repeatability in the measured shear stress response and fiber orientation evolution during the startup of flow compared to compression molded samples and samples subjected to flow reversal. From repeatable stress and orientation evolution data, models for stress and fiber orientation were assessed independently. Current theories for stress were unable to reflect the overshoot in the measured stress response and could at best capture the steady state. The transient behavior of the fiber orientation models were found to be highly dependent on the initial fiber orientation. The repeatable orientation data obtained from the injection molding sample preparation procedure provided material parameters in the strain reduction factor and reduced strain closure models. The injection molded samples provided evolution data from different initial fiber orientations to provide further scrutiny or validation of the material parameters. Orientation model parameters that provided reasonable agreement to multiple sets of fiber evolution data in simple shear flow should allow for a better assessment of the orientation models in complex flow simulations. / Ph. D.

This thesis presents the use of sliding mode control applied to a 1/10th scale robotic car to operate at a desired slip. Controlling the robot car at any desired slip has a direct relation to the amount of force that is applied to the driving wheels based on road surface conditions. For this model, the desired traction/slip is maintained for a specific surface which happens to be a Lego treadmill platform. How the platform evolved and the robot car was designed are also covered. To parameterize the system dynamics, simulated annealing is used to find the minimal error between mathematical simulations and physical test results. Also discussed is how the robot car and microprocessor can be modeled as a hybrid system. The results from testing the robot car at various desired percent slip show that it is possible to control the slip dynamics of a 1/10th scale automated robotic car and thus pave the way for further studies using scaled model cars to test an automated highway system. / Master of Science

Investigating the mechanical dynamics of bacterial motility has led to a deeper understanding of the behaviors and lifecycle of many bacterial species. We discuss chain driven sliding motility where the bacteria maintain connections between daughter cells following division, resulting in long chains that expand across the viscous substrate. These chains grow exponentially, suggesting the chain tips may accelerate to very fast speeds. We devise multiple mathematical frameworks encapsulating the key physical dynamics and interactions to investigate the dynamics of bacterial chains and the biological implications of this motility. Our first framework, the rigid rod model, provides a set of equations describing the chain growth dynamics. Analysis of these equations reveals the stress maintaining cell-cell linkages increases unsustainably at an exponential rate. We devise a perturbation analysis of the rigid rod model in order to predict the critical stress associated with mechanical failure of these linkages. A phenomenological population model reveals that repeated chain breakages limit the expansion of the entire population to linear growth. Through experimental observation and computer simulations, we identify two key mechanical instabilities that emerge in growing bacterial chains. The first is sharp localized kinking that leads to the chain breakage mentioned above. In the second dynamic, the chain buckles due to compressive drag forces resulting in the emergence of large curvatures throughout the chain. We devise a continuum mechanics framework to examine the curvature dynamics in the growing chain. Through linear stability analysis of the rigid rod model and the continuum mechanics framework, we predict the dominant instability dynamic based on the physical properties of the chain and its environment. We use rigid rod model simulations to investigate the biological implications of these dynamics. Lastly, we introduce a number of methods that extend the rigid rod model to allow for the investigation of interacting chains. We consider methods that implement forces due to the entanglement of cell body appendages as well as collision dynamics. In total these models provide generic frameworks for investigating mechanical dynamics of growing bacterial chains. Our models provide testable predictions and suggest biological motivations for the typical behaviors that are observed in these cell chains. / Doctor of Philosophy / Motility is crucial in the life of many bacterial species. Effective motility allows bacteria to obtain nutrients and avoid dangerous hazards. Since motility is such an important part of bacterial survival, understanding bacterial motility has strong implications in bacterial control and utilization. We consider a motility in which the bacteria move by forming long, often straight chains of many cell bodies that expand across the surface. This is known as chain-mediated sliding motility and can allow the bacteria to move at very high speeds. We present multiple physics based mathematical frameworks that provide the tools to investigate chain-mediated sliding motility. These frameworks are generic and can be applied to study any bacterial species that use chain growth as a means for motility. Using these tools, we learn the speed at which these chains can expand is limited by the mechanical strength of the linkages connecting adjacent cells with in the chain. This limitation means the chains will repeatedly break into shorter chains, a pattern that limits the speed at which the entire bacterial population can expand. Additionally, we discover two interesting behaviors exhibited by these bacterial chains, one in which the chain kinks before breaking into two shorter chains, and a second in which the chain buckles, resulting in curved chains. We apply our mathematical frameworks to determine how the physical conditions dictate which of these two behaviors will emerge and learn the chains may curve and bend as a means to avoid breaking. Lastly we introduce additional methods that extend these frameworks to allow for investigating the behavior of the bacteria when multiple chains interact with one another. The mathematical frameworks we present allow for investigation into the specific mechanical properties that make chain growth possible as well as the mechanics that limit its efficiency. The models also give insight into the biological impact of this motility, suggesting how it affects the growth-coupled spreading of an entire bacterial population.

No / This paper investigates the sliding wear performance of two types of co-electrodeposited cermet coatings com- posed of nano-sized tungsten carbide (WC) and combined tungsten carbide and alumina (Al2O3) particles incor- porated in a nickel matrix. For this purpose, the effects of alternating the ceramic particle concentration in the electrolyte solutions on microhardness of the coatings and also the effect of applied loads on wear performance of the coatings have been studied using ball-on-flat sliding wear tests. The wear track volumes and the progres- sion of wear depths as a function of time and at three applied loads were recorded and wear track morphologies were investigated using FE-SEM and microhardness testing. The results showed that microstructure, microhard- ness and wear performance of the coatings composed of WC improved when Al2O3 particles were introduced into the matrix. It was also found that the rule of mixtures for composite materials provides a good explanation for microhardness behaviour while Archard equation can explain the changes in wear performance due to the hardness and microstructural changes. / Alberta Innovates Future Technologies (Nanoworks) Canada

Structure-tribological property relations have been studied for five high entropy alloys (HEAs). Microhardness, room and elevated (100°C and 300°C) temperature sliding friction coefficients and wear rates were determined for five HEAs: Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4; Co Cr Fe Ni Al0.25 Ti0.75; Ti V Nb Cr Al; Al0.3CoCrFeNi; and Al0.3CuCrFeNi2. Wear surfaces were characterized with scanning electron microscopy and micro-Raman spectroscopy to determine the wear mechanisms and tribochemical phases, respectively. It was determined that the two HEAs Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4 and Ti V Nb Cr Al exhibit an excellent balance of high hardness, low friction coefficients and wear rates compared to 440C stainless steel, a currently used bearing steel. This was attributed to their more ductile body centered cubic (BCC) solid solution phase along with the formation of tribochemical Cr oxide and Nb oxide phases, respectively, in the wear surfaces. This study provides guidelines for fabricating novel, low-friction, and wear-resistant HEAs for potential use at room and elevated temperatures, which will help reduce energy and material losses in friction and wear applications.

Friction and wear have been observed m mechanical systems when there is a relative motion between two solid bodies Friction mainly results in loss of energy and wear results in matenal loss The proper understanding of friction and wear mechanisms provides practical solutions to tribological related problems Various models are available m tribology literature to calculate function coefficient and wear rate of matenals However, expenments suggest that these models are incomplete and fortuitous as the tnbological response is system dependent The objective of present investigation is to understand the tribological lesponse of commercially puie titanium and OFHC copper pins sliding on polyciystallme alumina discs Di\ shdm% tests were conducted in air, and vacuum (1 5 x 10~2Pa) at room tempeiatuie under different experimental conditions The normal load was vaned from 15 3 N to 76 0 N, sliding speed was vaned from 0 01 ms"1 to 1 4 ms"1, and tempeiatuie was varied from 293 K to 793 K It is found that the haidness of metals do not have any effect on their tribological response The experimental obseivations indicate that tribological response of metals mainly depends up on miciostructural evolution, oxygen activity and relative shear strength of metals and ceramics Chapter 1 starts with the background and concepts of tribology A brief literature survey is given with published work in relation with the present work In Chapter 2, the experimental proceduies of the dry sliding test and compression test are given Chapter 3 explains the tribological response of titanium during shdmg against alumina Different wear mechanisms such as oxidation, deformation and adhesion were identified Deformation wear mechanism is explained using strain rate response approach Chapter 4 explains the tribological response of copper during sliding against alumina The influence of environment and microstructural evolution on its tribological behavior are studied Chaptei 5 explains the dependence of tribological response of metals on micro structural evolution, oxygen activity and relative shear strength of metals and ceramics This thesis ends with the conclusions of the present investigation

The aim of this study is to evaluate a methodology for modeling the influence of crystallographic grain orientation on key parameters in normal and sliding contacts. The simulations of interfering cylindrical asperities, using finite element analysis, were conducted using two different plasticity models for copper: a conventional isotropic, homogeneous J2 plasticity model and a continuum crystal plasticity model. A normal contact study was conducted in which crystallographic orientation effects on different parameters were investigated. The model was then adapted for sliding contacts, which allowed other parameters such as energy dissipation to be investigated. Using crystal plasticity, the dependence of crystallographic orientation on plastic deformation and energy dissipation can be determined. The relative trends predicted using crystal plasticity are consistent with experiments that show friction depends on crystallographic orientation when plastic deformation is one of the primary energy dissipation mechanisms.

Robustness of the closed-loop system has repercussions on both stability and performance, making the study of robustness very important. Fundamentally, the performance and stability of closed-loop systems utilizing state-feedback are tied to that of the observers. The primary goal of this thesis is to develop a robust nonlinear observer and closely examine the usefulness of the observer in the presence of non-collocation and parametric uncertainty and as an integral component in closed-loop control. The usefulness of the observer being investigated depends on robustness, accuracy, computational burden, tunability, ease of design, and ease of implementation on an actual flexible motion system. The design and subsequent integration of the Kalman filter, an optimal observer, into a closed-loop system is well known and systematic. However, there are shortcomings of the Kalman filter in the presence of model uncertainty which are highlighted in this work. Simulation studies are conducted using the Simulation Module in National Instruments LabVIEW 8.5 and experiments are conducted on a physical system consisting of a single flexible link with non-collocation of actuators and sensors using LabVIEW Real Time 8.5. Simulations serve as a means to analyze the performance of the optimal observer and the robust observer by analyzing their dynamic behavior as well as that of the closed-loop system with each observer in place. The focus of experiments is on investigating implementation of the robust observer, including initialization and tuning of observer design parameters off-line and on-line. Simulations verify the robustness properties of the sliding mode observer while experiments show that the robust observer can be implemented at fast control rates and that replacing the Kalman filter with a robust observer has direct ramifications on closed-loop performance.

Ein Haupteinsatzgebiet der Großraummanipulatoren stellen Betonverteilermasten dar. Aufgrund der langen schmalen Armkonstruktionen fällt bei diesen Maschinen der Trend zum Leichtbau bezüglich der Dynamik besonders ins Gewicht. Um die Vorteile leichter Konstruktionen wie geringere Achslasten, geringerer Kraftstoffverbrauch und kleinere Antriebe nutzen zu können, werden Regelungen benötigt, die die Struktur stabilisieren und ein Schwingen der Mastspitze verhindern. Zur Systemanalyse und Regelungsauslegung wurde ein Mehrkörpermodell aus starren und elastischen Körpern sowie den notwendigen Hydraulikzylindern erstellt und durch Messungen validiert. Am Modell konnte gezeigt werden, dass die Regelung im letzten Gelenk die Schwingung an der Mastspitze maßgeblich beeinflusst und zur Schwingungstilgung eingesetzt werden kann. Hierfür wird die Bewegung des Verteilermastes durch eine Ausgleichsbewegung im letzten Gelenk kompensiert, sodass die Mastspitze keine starken Schwingungen ausführt. Die Schwingungen werden über Beschleunigungsmessung detektiert und nach entsprechender Filterung kann die Bewegung bestimmt werden. Mittels Sliding Mode Control erfolgt die Berechnung der schwingungsmindernden Zylinderkraft und garantiert somit Robustheit gegenüber Modellierungsungenauigkeiten und äußeren Störungen. Die Kraftregelung des Hydraulikzylinders wird anschließend über eine Integrator-Backstepping Regelung realisiert. Die resultierende Schwingungsminimierung beträgt in unterschiedlichsten Maststellungen bis zu 95%. / A special case of multi-link manipulators are truck mounted concrete pumps. Due to the lightweight design of the long and slender boom, it is vulnerable to vibrations. The advantages are smaller masses and therefore less actuation power which results in smaller actuators with less fuel consumption. In order to retain the advantages of lightweight design, special controllers are needed to stabilize the overall system and result in a vibration free motion of the boom tip. A multibody system with flexible bodies has been built in order to analyse the system's behaviour and to test and design appropriate control strategies. It could be demonstrated, that controlling only the last joint of the boom decisively effects the motion of the boom tip and is therefore suitable to suppress vibrations. The idea is to compensate the boom's motion by adjusting the last joint angle in a way, so that the boom tip stays at its initial position. In order to implement these findings and obtain a robust control three steps are necessary: the boom's motion must be measured and a vibration reducing force defined which has to be applied by the hydraulic actuator. The vibrations are detected by acceleration measurement and after appropriate filtering a joint angle trajectory can be determined. The cylinder force is found using Sliding Mode Control which guarantees robustness against modeling inaccuracies and external disturbances. A mathematical description of the last segment is necessary for the design of this nonlinear control strategy. The force control of the hydraulic cylinder is then implemented via backstepping control. The resulting vibration is minimized by this control by up to 95% at different boom positions.