Doctor of Philosophy, University of Akron, 2017, Polymer Engineering

Improved friction characteristics and reduced wear are desired in most of the contacting surface systems. With this motivation, our work is focused on two different applications. First application involves improving friction characteristics of automobile wet clutch system by exploiting `lubricant additive-friction material' interaction and material modification aspects. The second part is focused on reducing friction and wear in boundary lubrication using multiwalled carbon nanotube (MWCNTs) as a lubricant additive. Wet clutch is an integral part of a transmission system in automobiles. Positive slope of the friction coefficient versus sliding speed curve along with a high dynamic friction coefficient value indicate ideal friction characteristics for smooth clutch engagement between the friction material (FM – also called “friction paper”) and the reaction plate (steel) in the presence of automatic transmission fluid (ATF). The first part of our work involved adsorption analysis of ATF additives on friction material components (filler and fiber) using DSC and UV/VIS techniques. Adsorption behavior was further correlated with rheological and friction phenomena. Shear stress and strain rate obtained from rheological testing were correlated with friction and sliding speed, respectively, as obtained from friction characteristics testing. It was observed that ATF causes shear thickening while base oil causes shear thinning behavior when mixed with FM filler. Higher rate of increase of shear stress with shear rate (i.e., enhanced shear thickening) is expected lead to higher friction coefficient with sliding speed. Following up on this hypothesis, the filler component of the friction paper was found to show shear thickening behavior and improved friction characteristics, as compared to its fiber component. Further concentrating on the filler component, we used three different fillers (diatomaceous earth and a proprietary clay) to top-coat the friction paper. It was o (open full item for complete abstract)

Committee: Erol Sancaktar Dr. (Advisor); Sadhan Jana Dr. (Committee Member); Xiong Gong Dr. (Committee Member); Mesfin Tsige Dr. (Committee Member); Gary Doll Dr. (Committee Member); Rashid Farahati Dr. (Committee Member) Subjects: Engineering; Materials Science; Nanotechnology; Polymers

Doctor of Philosophy, The Ohio State University, 2008, Mechanical Engineering

This study examines the salient effects of sliding friction on spur and helical gear dynamics and associated vibro-acoustic sources. First, new dynamic formulations are developed for spur and helical gear pairs based on a periodic description of the contact point and realistic mesh stiffness. Difficulty encountered in existing discontinuous models is overcome by characterizing a smoother transition during the contact. Frictional forces and moments now appear as either excitations or periodically-varying parameters, since the frictional force changes direction at the pitch point/line. These result in a class of periodic ordinary differential equations with multiple and interacting coefficients. Predictions match well with a benchmark finite element/contact mechanics code and/or experiments. Second, new analytical solutions are constructed which provide an efficient evaluation of the frictional effect and a more plausible explanation of dynamic interactions in multiple directions. Both single- and multi-term harmonic balance methods are utilized to predict dynamic mesh loads, friction forces and pinion/gear displacements. Such semi-analytical solutions explain the presence of higher harmonics in gear noise and vibration due to exponential modulations of periodic parameters. This knowledge also analytically reveals the effect of the tooth profile modification in spur gears under the influence of sliding friction. Further, the Floquet theory is applied to obtain closed-form solutions of the dynamic response for a helical gear pair, where the frictional effect is quantified by an effective piecewise stiffness function. Analytical predictions are validated using numerical simulations. Third, an improved source-path-receiver vibro-acoustic model is developed to quantify the effect of sliding friction on structure-borne noise. Interfacial bearing forces are predicted for the spur gear source sub-system given two whine excitations (static transmission error and sliding frict (open full item for complete abstract)

Committee: Rajendra Singh (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, The Ohio State University, 2005, Mechanical Engineering

In this study, a general methodology is proposed for the prediction of friction-related mechanical efficiency losses of gear pairs. This methodology incorporates a gear contact analysis model and a friction coefficient model with a mechanical efficiency formulation to predict the gear mechanical efficiency under typical operating conditions. The friction coefficient model uses a new friction coefficient formula based on a non-Newtonian thermal elastohydrodynamic lubrication (EHL) model. This formula is obtained by performing a multiple linear regression analysis to the massive EHL predictions under various contact conditions. The new EHL-based friction coefficient formula is shown to agree well with measured traction data. Additional friction coefficient formulae are obtained for special contact conditions such as lubricant additives and coatings by applying the same regression technique to the actual traction data. These coefficient of friction formulae are combined with a contact analysis model and the mechanical efficiency formulation to compute instantaneous torque/power losses and the mechanical efficiency of a gear pair at a given position. This efficiency prediction methodology is applied to both parallel axis (spur and helical) and cross-axis (spiral bevel and hypoid) gears. In the case of hypoid gears, both face-milling and face-hobbing processes are considered, and closed-form expressions for the geometric and kinematic parameters required by the efficiency model are derived. The efficiency prediction model is validated by comparing the model predictions to a set of high-speed spur gear efficiency measurements covering several gear design and surface treatment variations. The differences between the predicted efficiency values and the measured ones are consistently within 0.1 percent. Influence of basic gear design parameters, tooth modifications, operating conditions, surface finish and treatments, lubricant properties, and manufacturing and assembly erro (open full item for complete abstract)

Committee: Ahmet Kahraman (Advisor) Subjects: Engineering, Mechanical

Master of Science, University of Akron, 2006, Mechanical Engineering

This thesis illustrates the application of a non-linear robust control to deal with friction variations in a hydraulic positioning system. The hydraulic system is modeled using analytical and experimental identification techniques considering both linear and nonlinear dynamics of the system. In the literature the friction is usually modeled as a function of velocity which has static, Coulomb and viscous friction components. However, there are several fascinating properties observed in systems with friction. This research is aimed at investigating the friction phenomenon and performing experiments on hydraulic positioning system to validate the identification of dynamic friction model (behavior in pre-sliding friction regime). The LuGre friction model which combines the pre-sliding behavior as well as the steady state characteristics is used to model and predict the friction for the controller design. A sliding mode controller is developed which has a feedback linearizing component plus additional terms that explicitly deal with system uncertainties due to friction and other unknowns. The sliding mode controller performed well during the experiments and simulations.

Committee: Celal Batur (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2024, Mechanical Engineering

The rise of electric vehicles (EVs) has led to new engineering challenges for electric motors and new design opportunities for lubricants and tribological elements like bearings and gears. High power density EV motors require dual fluids: a high heat capacity, low viscosity coolant fluid and a highly effective lubricant capable of protecting ultra-high-speed bearings and gears. This dual fluid practice requires two different fluid systems (sumps, pumps, pipes, and filters) adding cost, weight and complexity. Compared to combustion engines, EVs fluids (oils and coolants) do not require similarly extreme high temperature capabilities. Thus, the opportunity exists to consider new fluids (coolants/lubricants) to enhance EV system performance. Towards this end, low viscosity, high heat capacity fluids such as water-based lubricants (WBLs) have gained popularity, as they can cool electric components and lubricate moving parts fulfilling the single fluid approach. However, WBLs have limitations such as low viscosity, evaporation, freezing point, microbiological growth, oxidation, corrosion, and high electrical conductivity. To mitigate these limitations, different additives such as ionic liquids, bio-based oils, and nanoparticles have been incorporated into WBLs. This has resulted in significant improvements in coefficient of friction and wear reduction. Limited literature is available on the rheological and tribological behavior of WBLs in steels, and the wear mechanisms for these lubricants are not fully understood. The proposed work aims to test different WBLs by characterizing their rheological properties and conducting tribological tests such as fretting and sliding experiments. Posttest analyses will be performed via SEM/EDX, XRD, and AFM to characterize the tribofilms and surface morphology. The results will be compared with traditional lubricants to gain a better understanding of the mechanisms and propose adjustments to current modeling tools. The study unders (open full item for complete abstract)

Committee: Christopher DellaCorte (Advisor); Yalin Dong (Committee Member); Nicholas G. Garafolo (Committee Member); Manigandan Kannan (Committee Member); Weinan Xu (Committee Member); Richard L. Einsporn (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2015, Mechanical Engineering

This dissertation is divided into two categories based upon lubrication functionality and its application. The categories are: Dry film lubrication and Fluid film lubrication with thin film coatings. Thin film coatings examined in this work were deposited using closed field unbalanced magnetron sputtering and RF-DC coupled magnetron sputtering systems. In Dry/Solid film lubrication, the mechanical, structural and tribological properties of two Molybdenum disulphide (MoS2) based coatings are examined and evaluated. Among the two coatings, one coating is doped with Ti (Ti-MoS2) and the other is a combination of metal, lubricant and oxide (Sb2O3/Au - MoS2). These coatings are known to provide low friction in vacuum environments. The goal of this work was to evaluate friction and wear performance of MoS2 doped coatings in unidirectional and reciprocating sliding contact under different environmental conditions. Sliding contact results showed friction and wear dependence on temperature and humidity. The formation and removal of transfer films and the recrystallization and reorientation of basal layers on the steel counterface was observed as the mechanism for low friction. Structural analysis revealed a relationship between the microstructural properties and tribological performance. It was also observed that the addition of dopants (Ti, Au, Sb2O3) improved the mechanical properties as compared to pure MoS2 coatings. Further, the rolling contact performance of the coatings was measured on a five ball on rod tribometer and a Thrust bearing tribometer under vacuum and air environments. The rolling contact experiments indicated that life of the rolling components depend on the amount of material present between the contacts. Fluid film lubrication with thin film coatings investigates the possibilities to improve the performance and durability of tribological components when oils and thin films are synergistically coupled. In this work, the ability of a Diamond L (open full item for complete abstract)

Committee: Gary Doll (Advisor) Subjects: Aerospace Materials; Engineering; Experiments; Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2014, Mechanical Engineering

This research is motivated by the need to have a better understanding of the non-linear contact dynamics of systems with combined rolling-sliding contact such as cam-follower mechanism, gears and drum brakes. Such systems, in which the dominant elements involved in the sliding contact are rotating, have unique interaction among contact mechanics, siding friction and kinematics. Prior models used in the literature are highly simplified and do not use contact mechanics formulation hence the dynamics of the system are not well understood. The main objective of this research is to gain a fundamental understanding of the non-linearities and contact dynamics of such systems, for which a cam-follower mechanism is used as an example case. Specifically, the non-linearities, impact damping and coefficient of friction are analyzed in this study. The problem is examined using a combination of analytical, experimental, and numerical methods. First, the various non-linearities (kinematic, dry friction, and contact) of the cam-follower system with combined rolling-sliding contact are investigated using the Hertzian contact theory for both line and point contacts. Alternate impact damping formulations are assessed and the results are successfully compared with experimental results as available in the literature. The applicability of the coefficient of restitution model is also critically analyzed. Second, a new dynamic experiment is designed and instrumented to precisely acquire the impact events. A new time-domain based technique is adopted to accurately calculate the system response by minimizing the errors associated with numerical integration. The impact damping force is considered in a generalized form as a product of damping coefficient, indentation displacement raised to the power of damping index, and the time derivative of the indentation displacement. A new signal processing procedure is developed (in conjunction with a contact mechanics model) to estimate the (open full item for complete abstract)

Committee: Rajendra Singh (Advisor); Dennis Guenther (Committee Member); Ahmet Kahraman (Committee Member); Vishnu Baba Sundaresan (Committee Member); Jason Dreyer (Committee Member) Subjects: Engineering; Mechanical Engineering; Mechanics

Master of Science, The Ohio State University, 2010, Mechanical Engineering

This study presents an improved gear noise source model with surface undulation or roughness as the main excitation while taking into account the sliding frictional contacts between meshing teeth. This model extends the prior linear time-varying model that predicted the surface roughness-induced air-borne noise source. The structure-borne noise source is examined in this study by employing a six degree of freedom linear time-varying model. Gear contact mechanics is used to determine the mesh stiffness variation and also to relate the surface undulation to an equivalent static transmission error over a range of torques. Four alternate dynamic sliding friction models are also compared. Sound pressure radiated by the casing via structure-borne noise path is predicted using experimental partial pressure to acceleration transfer functions given pinion and gear accelerations in the line of action and the off-line of action direction. Linear time-invariant models are also developed by assuming that the mesh stiffness, moment arm and coefficient of friction do not vary with time. Sinusoidal, periodic and random tooth surface undulations are examined and sound pressures at gear mesh harmonics are predicted; the random undulation also generates off gear mesh frequency components. Both linear time-varying and linear time-invariant models are utilized to quantify the structure-borne noise sources and to understand the role of mesh stiffness, moment arm and coefficient of friction variations. The effects of torque, surface undulation amplitude, coefficient of friction and speed are also examined by using the linear-time varying model. Noise predictions (especially the trends) are compared with prior literature and some plausible explanations regarding the dominant sources are provided.

Committee: Dr. RAJENDRA SINGH (Advisor); Dr. AHMET KAHRAMAN (Committee Member) Subjects: Acoustics; Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2009, Mechanical Engineering

The ability to control the effective friction coefficient between sliding surfaces is a problem of significant interest in automotive applications. For reducing friction, lubricants or different material combinations are typically used. In this research, the role of ultrasonic vibrations on the friction coefficient between sliding surfaces is investigated, with the goal of being able to control the friction coefficient in an automotive seat belt system by modulating the vibrations at the interface between the D-ring and seat belt webbing. These ultrasonic vibrations are generated using piezoelectric materials that respond mechanically to an electrical input. To that end, a systematic approach is developed, with the help of experiments and models, to predict and characterize the frictional force between sliding surfaces in the presence of ultrasonic vibrations under various controlling parameters.The applied ultrasonic vibrations may be tangential, perpendicular or out-of-plane to the direction of sliding velocity. For rigid surfaces in contact, maximum friction reduction has been reported in the case of tangential vibrations. It has been shown that the extent of friction reduction depends on the ratio of the velocity of the ultrasonic vibrations to the sliding velocity. A series of experiments over a wide range of loads and speeds are designed to characterize the friction reduction effect between solid-solid contacts and Hertzian contacts in the case of seat belts. Using Coulomb and Dahl friction models, the mechanism of friction reduction in the presence of ultrasonic vibrations is studied. System level analytical modeling is presented which consists of a single degree-of-freedom model with LuGre friction at the sliding interface. By controlling parameters such as load, system stiffness, contact stiffness and the control force generated by the piezoelectric stack, characterization plots are obtained which can help optimize design parameters of ultrasonic lubricati (open full item for complete abstract)

Committee: Marcelo Dapino PhD (Advisor); John Yu PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2008, Materials Science and Engineering

The unlubricated sliding of metals is important in many mechanical devices covering a wide range of sliding velocities. However, the effect of sliding velocity on the tribological behavior of unlubricated metals has not been widely studied. Similarly, the relationship between microstructures developed at high sliding velocities and tribological behavior has not been studied in depth. The current research relates two aspects of the sliding friction of ductile metals, the effect of sliding velocity and the production of nanocrystalline tribomaterial. The project focused on the effects of sliding velocity on the frictional behavior of oxygen free high conductivity (OFHC) copper sliding against 440C stainless steel, Nitronic 40 stainless steel, and copper. Low velocity tests were performed with a pin on disk tribometer. High velocity tests were performed with a rotating barrel gas gun (RBGG) which combined impact with sliding. Surface and subsurface microstructures and chemical compositions of the worn samples were characterized with a wide range of instruments. In the case of self-mated copper the sliding velocity had little effect on the coefficient of friction and associated microstructural changes. An increase in the coefficient of friction for copper sliding against stainless steel in both the pin on disk and RBGG systems was observed. For the pin on disk tests the coefficient of friction was strongly influenced by material transfer from the copper to the steel pin. The increase in the coefficient of friction for the RBGG tests was correlated to an increase in subsurface plastic deformation. The growth of the nanocrystalline tribolayer in copper after sliding against 440C stainless steel at varying times was studied at sliding velocities of 0.05 and 1.0 m/s. The 0.5 m/s sliding velocity produced a consistent nanocrystalline layer in as little as 10 s. The thickness of the nanocrystalline layer grew continuously at sliding times of up to 10 ks. The 1.0 m/s sliding v (open full item for complete abstract)

Committee: David Rigney (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2005, Mechanical Engineering

The advent of micro/nanostructures and the subsequent miniaturization of moving components for various nanotechnology applications, such as micro/nanoelectromechanical systems (MEMS/NEMS), have ascribed paramount importance to the tribology and mechanics on the nanoscale. Most of these micro/nanodevices and components operate at very high sliding velocities (of the order of tens of mm/s to few m/s). Atomic force microscopy (AFM) studies to investigate potential materials, coatings and lubricants for these devices have been rendered inadequate due to the inherent limitations on the highest sliding velocities achievable with commercial AFMs (<250 μm/s). The development of a new AFM based technique, done as part of this research work, has allowed nanotribological investigations over a wide range of velocities (up to 10 mm/s). The impacts of this research on the design and development of nanotechnology applications are profound. Research conducted on various materials, coatings and lubricants reveals a strong velocity dependence of friction, adhesion and wear on the nanoscale. Based on the experimental evidence, theoretical formulations have been conducted for nanoscale friction behavior to design a comprehensive analytical model that explains the velocity dependence. The model takes into consideration the contributions of adhesion at the tip-sample interface, high impact velocity related deformations at the contacting asperities and atomic scale stick-slip. Dominant friction mechanisms are identified and the critical operating parameters corresponding to their transitions are defined. Wear studies are conducted at high sliding velocities for materials, coatings and lubricants to understand the primary failure mechanisms. A novel AFM based nanowear mapping technique is developed to map wear on the nanoscale and the interdependence of normal load and sliding velocity on sample surface wear is studied. This technique helps identify and classify wear mechanisms and determi (open full item for complete abstract)

Committee: Bharat Bhushan (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2004, Materials Science and Engineering

The dry sliding behavior of diamond-like carbon (DLC) based nanocomposite coatings has been examined in different environments, ranging from vacuum, high-purity nitrogen to ambient air using 440C stainless steel sliders. The test geometry of pin-on-disk allowed convenient collection of wear debris, measuring of the friction force and, using a Kelvin probe, in situ detection of structural and chemical changes incurred on wear tracks. It was found that WCS composite coatings have excellent tribological characteristics in all test environments, including low friction coefficient, negligible wear rate and extended lifetimes. Post-test characterization included TEM, Raman spectroscopy, SIMS, XPS, SEM and EDS. Examination of worn wear track and pin surfaces, cross-sections and debris confirmed the importance of mixing, material transfer and environmental interactions. Mixed components dominate the sliding behavior of WCS coatings. A single graphitic carbon or WS2 protective lubricating layer has not been found on wear tracks or pin surfaces. Instead, both components were identified to be present together in varied amounts depending upon the testing environment and loading. Thus, the lubrication mechanisms involved in different environments are far more complex than what has been reported previously. Synergistic effects contributed by both graphitic carbon and WS2 account for the extremely low frictional behavior of WCS coatings during dry sliding. Molecular dynamics (MD) calculations were implemented to simulate the behavior of soft and/or hard particles in a 2D 3-component composite system interacting via Lennard-Jones potentials. Sliding results showed that soft particles tended to mix with the base materials, and with increased sliding speed mixing proceeded even faster. The mixed materials formed a confined “weakened” zone at the sliding interface, where shear remained localized after a steady state was achieved. For the case of sliding of composites with hard particl (open full item for complete abstract)

Committee: David Rigney (Advisor) Subjects: Engineering, Materials Science

Doctor of Philosophy, University of Akron, 2007, Polymer Science

Friction and wear are important technologically. Tires on wet roads, windshield wipers and human joints are examples where nanometer-thick liquids are confined between flexible-rigid contact interfaces. Fundamental understanding of the structure of these liquids can assist in the design of products such as artificial joints and lubricants for Micro-electromechanical systems [MEMS]. Prior force measurements have suggested an increase in apparent viscosity of confined liquid and sometimes solid-like responses. But, these have not given the state of molecules under confinement. In the present study, we have used a surface sensitive, non-linear optical technique (infrared-visible sum frequency generation spectroscopy [SFG]) to investigate molecular structure at hidden interfaces. SFG can identify chemical groups, concentration and orientation of molecules at an interface. A friction cell was developed to study sliding of a smooth elastomeric lens against a sapphire surface. Experiments were done with dry sliding as well as lubricated sliding in the presence of linear alkane liquids. SFG spectra at the alkane / sapphire interface revealed ordering of the confined alkane molecules. These were more ordered than alkane liquid, but less ordered than alkane crystal. Cooling of the confined alkane below its melting temperature [TM] led to molecular orientation that was different from that of bulk crystal next to a sapphire surface. Molecules were oriented with their symmetry axis parallel to the surface normal. In addition, the melting temperature [Tconf] under confinement for a series of linear alkanes (n =15 - 27) showed a surprising trend. Intermediate molecular weights showed melting point depression. The Tconf values suggested that melting started at the alkane / sapphire interface. In another investigation, confinement of water between an elastomeric PDMS lens and sapphire was studied. SFG spectra at the sapphire / water / PDMS interface revealed a heterogeneous morphol (open full item for complete abstract)

Committee: Ali Dhinojwala (Advisor) Subjects: Chemistry, Physical; Chemistry, Polymer; Engineering, Materials Science; Physics, Condensed Matter; Physics, Optics