Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

The friction and wear properties of bilayer graphene on silicon substrate with diamond atomic force microscope tip were investigated using molecular dynamic simulation with three independent variables of tip velocity, temperature, and normal load. Based on isolated experimental results, it is determined that graphene friction is velocity, temperature, and normal load dependent. Velocity and normal load increase lead to positive friction correlations while temperature increase leads to negative friction correlations, thus leaving the mechanism to be determined. Combined studies reveal similar results, with each variable maintaining its isolated effect in chorus with the other utilized. Upon obtaining the contact area from these experiments it is evident that velocity and temperature change do not hold direct bearing on the contact area, rather that it is the normal load and size of the sliding surfaces that can fluctuate both contact area and friction in tandem. Hence, the mechanism with respect to velocity and temperature dependence of graphene friction is determined to be variation in interatomic potentials associated with interatomic interactions. Varying the contact area can increase or decrease the quantity of atoms in contact, therefore also having an impact on graphene friction.

Committee: Justin Ye (Advisor); Mark Sidebottom (Committee Member); Andrew Paluch (Committee Member); Timothy Cameron (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

PhD, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

A human's interaction with the outside world begins with the human skin and therefore, contact mechanics of human skin is an important area of research. The applications are all-encompassing, from medical technology in the form of drug delivery mechanisms and prosthetics to the digital world in the form of touchscreens or even personal care. The variations in morphological and physiological features in combination with the properties of counter surfaces make human skin contact a complex problem. There are several aspects of this complex tribological system that need to be addressed. These include characterizing the surface topography of human skin, enhancing the predictability of contact parameters, and understanding the mechanics at the interface of such interactions. In this study, as the first specific aim, a method is developed to characterize the directionality of skin tension lines using statistical methods of characterizing rough surfaces. The method is able to capture the increasing anisotropy of human skin with aging. The method can be applied to the surface coordinates of the skin and the pixel intensity data from skin images. The second specific aim is to predict the coefficient of friction considering the changes in the skin's morphological and physiological features. To achieve this, a fractal-based finite element model in combination with an interfacial condition-enhanced empirical method is used. Results show that the proposed approach can replicate several experimental findings from the literature. Human skin in general is a soft material. Therefore, the recent understanding of contact mechanics of soft materials is applicable to skin. The third specific aim is to understand the contact mechanics at the interface of skin interactions. To this end, we use finite element models to first extend the current single asperity studies to three-dimensional soft materials. Specifically, we investigate the role of surface roughness and mate (open full item for complete abstract)

Committee: Kumar Vemaganti Ph.D. (Committee Chair); Bhargava Sista Ph.D. (Committee Member); Manish Kumar Ph.D. (Committee Member); Woo Kyun Kim Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2022, Polymer Science

When a beam of light goes from a denser medium to a less dense medium, illuminates the interface of two mediums at an incident angle greater than the critical angle θ_C=sin^(-1)⁡(n_2/n_1 ), light is totally internally reflected to the denser medium. At this moment, an evanescent field is formed, and it propagates along the surface of the denser medium, attenuating exponentially away from the surface. When a 3rd dense medium is brought into the vicinity, a portion of light passes into it, attenuating the reflected intensity. This phenomenon, called frustrated total internal reflection (FTIR), has been utilized in visualizing contact dynamics. It also provides a means to understand adhesion and friction between surfaces because they are known to depend sensitively on actual contact area as well as magnitude and spatial distribution of gaps of near contact down to the nanoscale. However, quantitative conversion of the reflected signal to gap thickness has only recently been achieved by proper analysis of the Fresnel equation with consideration of multiple reflections, transmissions, and polarization of light. This thesis presents a study of applications of frustrated total internal reflection (FTIR). First, we present a quantitative optical method to characterize dynamics of contact formation between two mediums based on theory of FTIR. The method is first validated by measuring height profile of convex lens in contact with flat prism surface and comparing with Hertzian theory. The method is then used to track the evolution of contact between a soft hemisphere brought into contact with a hard surface under water, as function of hemisphere stiffness, and surface wettability. We find an exponential rate of water evacuation from hydrophobic–hydrophobic (adhesive) surfaces that is 3 orders of magnitude smaller than that from hydrophobic–hydrophilic (non-adhesive) contact. This counterintuitive result comes from adhesive surfaces to more tightly sealing puddles of trapp (open full item for complete abstract)

Committee: Hunter King (Advisor); Ali Dhinojwala (Committee Chair); Kwek-Tze Tan (Committee Member); Chunming Liu (Committee Member); Mesfin Tsige (Committee Member) Subjects: Fluid Dynamics; Materials Science; Polymers

Doctor of Philosophy, University of Akron, 2022, Polymer Science

Mechanics and dynamics of underwater soft contacts are critical in the field of biomaterials (adhesives and sealants), soft robotics, transportation (tires and seal design) and engineering (biomimetics). From wet tire traction to underwater adhesion, the evacuation of a thin layer of water between two surfaces is essential for contact formation and subsequent interactions. This dissertation explores the effect of roughness, elastohydrodynamics and thermodynamics on water entrapment. The fact that real surfaces possess roughness on scales ranging from size of an object to atomic cut off (few angstroms) makes it challenging to study. We perform quasi-static underwater adhesion measurements between soft-elastic polydimethylsiloxane (PDMS) hemispheres of varying stiffness and rigid polycrystalline diamond surfaces with topography characterized across all length scales. The results show that the adhesion energy is lower than that predicted using the Persson's model, indicating towards water entrapment. We developed a non-conformal contact adhesion model which requires the knowledge of real contact area and the new power spectral density (PSD) for PDMS after formation of partial contact. The real contact was determined using the Cassie-Baxter equation as the contact region is a composite of dry and water entrapment regions. We cannot measure the PSD for deformed PDMS directly and hypothesize that there exist a critical cut-off length-scale above which the surfaces are conformal, and the smaller length-scales contains entrapped water. This allowed calculation of elastic energy required to deform the PDMS and, hence, predictions of adhesion which are in excellent agreement with the experimental data. We also explored the effect of elastohydrodynamic deformation and thermodynamics/surface chemistry on contact formation. We determine the dependence of fluid evacuation on the surface wettability and elastomer modulus in underwater collision, as it is essential to any ob (open full item for complete abstract)

Committee: Ali Dhinojwala (Advisor); Mesfin Tsige (Committee Chair); Tevis DB Jacobs (Committee Member); Jutta Luettmer-Strathmann (Committee Member); Hunter King (Committee Chair) Subjects: Engineering; Mechanics; Physical Chemistry; Physics; Polymers

Doctor of Philosophy, The Ohio State University, 2021, Mechanical Engineering

Planetary gearsets are indispensable power transfer components in several mechanical systems and are preferred over counter-shaft gears due to their coaxial arrangement, high power density, minimal radial loads, and multiple possible kinematic combinations. In spite of their several benefits and widespread use, the complex arrangement of components in a planetary gear system makes them susceptible to noise and vibration issues. Analysis and design tools specific to planetary gear sets are sparse, accurate models that are available for detailed analyses of planetary gear sets require significant computational effort and expert users. In contrast, the computationally efficient lumped parameter models available in the literature are not very effective for root cause analysis because of the simplifications made in modeling the gear meshes. These challenges become multifold with the advent of electric drive units, not only due to their high operating loads and speeds but also due to the fact that there is no broadband noise from the engine to mask the transmission noise. Considering the aforementioned challenges with planetary gear design and lack of accurate and computationally efficient analysis tools, this dissertation presents a three-dimensional dynamic load distribution model for planetary gearsets. The proposed formulation uses a numerical integration scheme in conjunction with an iterative elastic contact algorithm to solve the multibody contact problem, and unlike previous models, can implicitly capture the influence of probable assembly and manufacturing errors in a planetary gear set. The developed dynamic load distribution model for planetary gears builds upon the quasi-static model of Hu et al. as its basis. Therefore to build trust in the fundamental framework, tightly controlled quasi-static planetary gear experiments were conducted to thoroughly validate the quasi-static model before developing the dynamic model. A unique experimental methodology, tha (open full item for complete abstract)

Committee: David Talbot (Advisor); Ahmet Kahraman (Committee Member); Carlos Castro (Committee Member); Manoj Srinivasan (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2020, Polymer Science

Understanding the mechanism of adhesion and friction in soft materials is critical to the fields of transportation (tires, wiper blades, seals etc.), prosthetics and soft robotics. Most surfaces are inherently rough and the interfacial area between two contacting bodies depends largely on the material properties and surface topography of the contacting bodies. Johnson, Kendall and Roberts (JKR) derived an equilibrium energy balance for the behavior of smooth elastic spherical bodies in adhesive contact that predicts a thermodynamic work of adhesion for two surfaces in contact. The JKR equation gives a reversible work of adhesion value during approach and retraction. However, viscoelastic dissipation, surface roughness and chemical bonding result in different work of adhesion values for approach and retraction. This discrepancy is termed adhesion hysteresis. Roughness is undermined as a cause of hysteresis in adhesion studies. Recently, a continuum mechanics model has been developed that predicts the work of adhesion on rough surfaces with known roughness in the form of power spectral density (PSD) function. To test the above mentioned theoretical model, we have conducted JKR experiments between highly cross-linked smooth polydimethylsiloxane (PDMS) of four different elastic moduli and diamond surfaces of four different crystal sizes and roughness.The rough diamond surfaces are characterized for topography using stylus profilometry, atomic force microscopy and in-situ transmission electron microscopy combined to give a comprehensive PSD. Results suggest that the observed work of adhesion during approach is equivalent to energy required to stretch the PDMS network at the surface and in the bulk to form the real rough contact area. However, in retraction work of adhesion is found to be proportional to the ratio of excess energy spent in the loading-unloading cycle and the true contact area obtained from topography indicating conformal contact matching fracture mechani (open full item for complete abstract)

Committee: Ali Dhinojwala Ph. D. (Advisor); Mesfin Tsige Ph. D. (Committee Chair); Tevis Jacobs Ph. D. (Committee Member); Jutta Luettmer-Strathmann Ph. D. (Committee Member); Hunter King Ph. D. (Committee Member) Subjects: Engineering; Mechanics; Physics; Polymers; Science Education

Master of Science, The Ohio State University, 2014, Mechanical Engineering

Variable displacement axial piston pumps are commonly found on a wide variety of off-highway vehicles and industrial equipment. Typically, these pumps employ a swash plate supported by a hydrostatic bearing to control the pump's volumetric displacement. Previous vibro-acoustical studies have identified the bearing interface between the swash plate and pump housing as a potential source of error in predicting vibration and structure-borne noise. A better understanding of the physics of this interface is necessary to improve pump noise prediction. Therefore, several experiments are first designed to measure the interfacial properties under static (force vs. deflection), modal (motion transmissibility), and transient (step-like) conditions. The results of the three experiments are then used to develop tractable linear viscoelastic models, with minimal parameters. Parallel force transmission paths (structural and fluid) are required to adequately describe the observed transmitted forces in time domain. The interfacial stiffness and damping properties of the main models are quantified with varying mean loads in the presence or absence of oil. Of the models examined, a combination of Kelvin-Voigt and Maxwell formulations yields a better fit for vibration (modal) and transient (step-like) experiments, especially in the presence of oil within the interface. Nevertheless, the linear visoelastic model parameters are effected by nonlinearities as their values depend on mean load, lubrication condition, and amplitude of excitation.

Committee: Rajendra Singh (Advisor); Mei Zhuang (Committee Member); Jason Dreyer (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2005, Engineering : Mechanical Engineering

Microslip friction plays an important role in determining vibratory response to external excitation of frictional interfaces. Surfaces in contact undergo partial slip prior to gross slip. This mechanism provides significant energy dissipation as a result of interface friction, thereby considerably reducing vibratory response of the system. Developing physics-based phenomological models for frictional contacts is the underlying aim of our study. Both analytical and numerical approaches have been employed for characterizing the interface friction behavior. Numerical approaches have traditionally employed bilinear hysteresis elements to simulate frictional contact. Single degree of freedom (SDOF) models that only include a single hysteresis element have been the focus of research in the past. Though these models capture the interface behavior qualitatively, they cannot be truly representative or predictive of the underlying physics of frictional joints. A multiple degree of freedom (MDOF) model built from a finite number of hysteresis elements can discretize the continuous friction interface, and is inclusive of the microslip approach. However, parameter estimation constitutes an important aspect of these models, and currently it is carried out using a calibration approach rather than physical motivation. We have developed a class of multiple degree of freedom (MDOF) model that account for microslip behavior of friction joints. The models take into account the damper mass, which was studied by very few models in the past. This adds significant dynamics to the phenomological model, thereby providing a more efficient tool to simulate friction joints using numerical models. These models are successful in capturing hysteresis behavior of frictional contacts. They also depict the exponential scaling of frictional energy dissipation with applied forcing level. As such, the richness of the frictional interface can be captured using these models. A complimentary analytical sol (open full item for complete abstract)

Committee: Dr. Edward Berger (Advisor) Subjects: Engineering, Mechanical

PhD, University of Cincinnati, 2004, Engineering : Mechanical Engineering

The dissertation is to address the need, in contact mechanics, of efficient and effective solutions to certain 3-D contact problems. The solutions developed here are based on underlying analytical solutions to pyramidal loading elements. This feature, along with other characteristics, distinguishes this method from other numerical solutions. The research work is logically divided into three subsequent parts, each of which addresses a particular aspect of the project: (1) Developed analytical solution sets in closed form to pyramidal loading profiles. First, a set of Boussinesq-Curruti equations to linear/bilinear distribution of normal and tangential loading over a triangular area are derived and evaluated. Second, solution sets to normal and tangential surface loading pyramids are constructed. The work provides a solution set to a basic loading element, which is the foundation of the development of effective and efficient semi-analytical solutions to 3-D contact problems with general geometry and loading profile. (2) Developed a semi-analytical approach (non-incremental algorithm) to 3-D normal contact problems with friction. This approach treats normal contact (indentation) phenomenon as a static problem. Based on fully coupled governing equations, the algorithm of contact detecting and stick/slip partitioning is designed as nested iterations, to fulfill contact boundary conditions. The computation shows that it is an efficient algorithm. Numerical examples are presented to show the accuracy and efficiency of the method.(3) Developed a semi-analytical approach (incremental algorithm) to 3-D contact problems with friction. This approach treats contact as a dynamic problem. The general dynamic models are simplified into quasi-static models in many practical cases that inertial force can be ignored. The incremental algorithm is designed to solve the quasi-static problems. The computation shows that the algorithm works very well for cases featuring both similar and di (open full item for complete abstract)

Committee: Dr. EDWARD BERGER (Advisor) Subjects: Engineering, Mechanical

PhD, University of Cincinnati, 2003, Engineering : Mechanical Engineering

This dissertation presents a new hybrid elasticity and finite element method for general non-conforming contact problems. It is an iterative numerical procedure, which has distinct advantage over classical theory of contact since general geometrical and loading profiles with friction can be treated. And over the traditional contact solution approach in finite element method, it eliminates the use of gap elements and therefore the non-linearity in the solution enhancing accuracy and efficiency of the solution. For the two dimensional problems the equations were derived for a triangular pressure element. While for three-dimensional problems, the analytical solution was derived from Boussinesq and Cerruti equations for conical pressure elements, from which a semi-analytical approach to three-dimensional contact problems with friction was evolved to find the extent of the contact area and the loading distribution over this area together with the extent of the stick and slip zones. The linear static finite element method was then used to find the displacements and stresses throughout the two bodies in contact, which were analyzed separately with the knowledge of the area of contact and the traction over such an area. The method was used for non-conforming bodies but it can be extended to include different kinds of contact problems. The basic theory was presented for both two and three-dimensional non-conforming contact problem, together with algorithm, and numerical examples that showed the accuracy, efficiency and robustness of the method.

Committee: DR. RONALD HUSTON (Advisor) Subjects: Engineering, Mechanical

PhD, University of Cincinnati, 2003, Engineering : Mechanical Engineering

The research work of this dissertation consists of two parts. The first part is the application of the finite element method (FEM) to nonlinear frictional contact stress analysis of full 3-D gear coupling models. To the author=92s best knowledge, no published work using the full 3-D finite element model of gear coupling is available in the literature. FEM models and processes have been developed in this thesis for the analysis of gear coupling with misalignment. The developed processes can be employed as a template to other gear models with different design parameters. They can also be expanded in more complex analyses such as fracture and thermo-elastic analyses. The second part of the research is on the development of two new boundary element algorithms for solving 3-D, frictional, and linear elastostatic contact problems. The main contribution of this research is that solving 3-D boundary element models with non-conforming discretizations becomes possible for the first time by using the proposed algorithms. These algorithms are implemented in a new 3-D boundary element code using C++ and verified using several numerical examples. For the models studied, the results using the new boundary element algorithms match well with the finite element results and clearly demonstrate the feasibility of the new boundary element approach for 3-D contact analysis.

Committee: Dr. Yijun Liu (Advisor) Subjects: Engineering, Mechanical

Master of Science, The Ohio State University, 2011, Mechanical Engineering

Wind energy has received a great deal of attention in recent years in part due to its minimal environmental impact and improving efficiency. Increasingly complex wind turbine gear train designs, well-known rolling element bearing failures, and the constant push to manufacture more reliable, longer lasting gear trains generate the need for more advanced analysis techniques. The objectives of this thesis are to examine the mechanical design of Orbital2 flexible pin, multi-stage planetary wind turbine gear trains using three dimensional finite element/contact mechanics models. These models are constructed and analyzed using software that specializes in elastic gear tooth contact. Computational results, such as gear tooth root strain, are compared to full system experiments. Root strain is calculated at multiple locations across the facewidth of ring gears from the computational models and compared to experimental data. Computational results for tooth load distribution and planet load sharing factor are compared to experiments. The computational models consider gear misalignment and carrier eccentricity and permit design recommendations for improving tooth load distribution and planet load sharing.

Committee: Robert Parker PhD (Advisor); Sandeep Vijayakar PhD (Committee Member) Subjects: Design; Energy; Engineering; Mechanical Engineering; Mechanics

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

Adhesion, friction/stiction and wear are among the main issues in magnetic storage devices, microelectromechanical systems (MEMS/NEMS), and other commercial devices having contacting interfaces with normal or tangential motion. Relevant parameters, i.e., layer thicknesses and their mechanical properties for the contact solid surfaces, the roles of meniscus and viscous forces for separation of surfaces from liquid films, need to be studied to provide a fundamental understanding of the phenomenon and the physics of the experienced problems. The simulation of contact mechanics and the modeling of separation of two surfaces with and without liquid mediated contacts are effective ways to investigate these issues. In the simulation of contact mechanics, a numerical three-dimensional (3D) rough multilayered contact model is developed to investigate the effects of roughness, stiffness, hardness, layer thicknesses, load, coefficient of friction, and meniscus contribution of elastic-perfectly plastic solid surfaces. The model is based on a variational principle in which the contact pressure distributions are those that minimize the total complementary potential energy. The quasi-Newton method is used to find the minimum. The influence coefficients of the displacements and stresses for a multilayered contact model are determined using the Papkovich-Neuber potentials with a Fast Fourier Transform (FFT) based scheme. Contact analysis of multilayered structures under both dry and wet conditions with and without sliding which simulates the actual contact situations of those devices is performed to identify and obtain optimum design parameters including materials with desired mechanical properties, layer thicknesses, and to predict and analyze the contact behavior of devices in operation. In the modeling of separation of two surfaces with liquid mediated contacts, numerical models of normal and tangential separation of smooth or rough surfaces are developed. The analyses for both (open full item for complete abstract)

Committee: Bharat Bhushan (Advisor) Subjects: Engineering; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2004, Mechanical Engineering

Belt vibration and slip are primary concerns in the design of serpentine belt drives. Belt-pulley coupling is essential for the analysis. This work investigates issues to advance the understanding of belt-pulley mechanics. Closed-form eigensolution approximations for an axially moving beam with small bending stiffness are given. This model is the first order approximation for the transverse vibration of each span in a serpentine belt drive. Perturbation techniques for algebraic equations and the phase closure principle are used. The eigensolutions are interpreted in terms of propagating waves. For a complete serpentine belt drive, a hybrid continuous-discrete model is built. Incorporation of belt bending stiffness introduces linear belt-pulley coupling. This model can explain the transverse span vibrations caused by crankshaft pulley fluctuations at low engine idle speeds where other coupling mechanisms do not. For the steady state analysis, a novel transformation of the governing equations to a standard ODE form for general-purpose BVP solvers leads to numerically exact steady solutions. A closed-form singular perturbation solution is developed for the small bending stiffness case. A coupling indicator based on the steady state is defined to quantify the undesirable belt-pulley coupling. A spatial discretization is developed to find the free vibration eigensolutions. In contrast to prior formulations, this discretization is numerically robust and free of missing/false natural frequency concerns. New dynamic properties induced by bending stiffness are characterized. Dynamic response calculations using the discretized model follow naturally. The effects of major design variables are investigated. This provides knowledge to help optimize structural design, especially to reduce large belt transverse vibration. Finally, to better predict the belt-pulley contact interactions applicable to serpentine belt drives an improved model is established for the steady state mechan (open full item for complete abstract)

Committee: Robert Parker (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, The Ohio State University, 2001, Mechanical Engineering

The deposition of layers is an effective way to improve the tribological performance of rough surfaces. The contact mechanics of layered rough surfaces needs to be studied to optimize layer parameters. Since 1995 a lot of progress has been made in the development of numerical contact models, which analyze the contact behavior of layered rough surfaces with no assumption concerning the roughness distribution as well as the effect of interfacial liquid film on the contact statistics. Based on the formulation of contact problems, these models are classified into three categories: direct formulation, weighted residual formulation, and minimum total potential energy formulation. The numerical methods applied in these models include Finite Difference Method (FDM), Finite Element Method (FEM), and Boundary Element Method (BEM). A 3-D BEM model based on a variational principle is developed for its capability to analyze the layered rough surfaces contact involving a large number of contact points. This model predicts contact pressure profile on the interface and contact statistics, namely fractional contact area, the maximum value of contact pressure, von Mises and principal tensile stresses, and relative meniscus force. The results allow the specification of layer properties to reduce friction, stiction, and wear of layered rough surfaces. Typical examples of layered rough surfaces contact simulated by this model are presented.The examples contain data for various surface topographies, elastic and elastic-plastic material properties, normal and tangential loading conditions, and dry and wet interfaces. Applications of this model to the magnetic storage devices and MicroElectroMechanical Systems (MEMS) are presented.

Committee: Bharat Bhushan (Advisor); Bernard Hamrock (Other); Shoichiro Nakamura (Other) Subjects: Engineering, Mechanical

Doctor of Philosophy, University of Akron, 2005, Polymer Engineering

In last 50 years, research on elastomer wear has produced qualitative and statistical data regarding wear debris and associated morphologies. However, the exact wear mechanism and the evolution of wear morphologies is not understood to the level where a quantitative prediction or description of wear is possible In this study a numerical analysis (FEA) has been used to understand mechanical interactions related to pattern wear. A blunt surface crack and it's interaction with a single penetrating asperity has been modeled for varying frictional, material and kinematic conditions. An interacting asperity creates a deformation field in an elastomeric body. This stress field is altered in the presence of a crack. The resulting stress relief is quantitatively estimated for varying geometric, material and friction parameters. Consequently, the energy available for a new crack to propagate in the vicinity of the existing crack decreases leading to a characteristic spacing between successive cracks. Energy release rate data from fracture experiments on thin rubber sheets is used to calculate the spacing between the cracks. The approach sheds some light on crack propagation characteristics in pattern wear. Other numerical experiments in this study analyze: (1) Elastomer response to dynamic asperity loading (2) Asperity loading at micro-scale where filled rubber has high degree of non-homogeneity (3) Effect of asperity loading at an angle on a rubber flap. As a result, we now better understand the evolution of wear related morphologies.

Committee: Arkady Leonov (Advisor) Subjects: