Master of Science in Engineering, University of Akron, 2019, Mechanical Engineering

With the rapid technology development these days, silicone rubber has become an important material to support our lives from house to industrial scale applications. Moreover, tire industries also considering the superior properties of silicone rubber in their product in applications that require high-temperature resistance to perform. This demand leads material science researchers to search for solutions by intensively studying the potential of nanotechnology to boost the mechanical performance of the materials to make them suitable to perform in extreme and specific conditions. Therefore, this research aims to explore an electrospinning method as a process to generate second phase materials with purpose to reinforce in a form of nanofibers into a room temperature vulcanized (RTV) silicone rubber together with study of the mechanical properties of reinforced RTV silicone rubber such as rolling resistance and the static friction of the material. The reinforcement process by electrospinning method was conducted by using polyether-based thermoplastic polyurethane as the reinforcement material that exhibits excellent temperature flexibility, abrasion resistance and strength to reinforce directly to the liquid silicone rubber to generate several specimens with a different composition ratio of matrix and reinforcement phase in the composite. Furthermore, the experiment was carried out by measuring the rolling resistance properties by using a wooden roller based device inspired by the invention of Dr. Alan Gent [1] and static friction of the material by using the inclined surface coefficient of friction tester to understand the influence of TPU on the RTV silicone rubber.

Committee: Shing-Chung "Josh" Wong (Advisor); Jiang Zhe (Committee Member); Kwek-Tze Tan (Committee Member) Subjects: Engineering

PhD, University of Cincinnati, 2014, Engineering and Applied Science: Mechanical Engineering

Friction and wear are two complex phenomena that occur at interfaces of contacting surfaces. The genesis of these phenomena is mapped down to adhesive forces and mechanical deformation of micro-asperities. The classical laws of friction hold for rigid bodies and deformable bodies undergoing small deformations but are not valid for materials that undergo large and time-dependent deformations. Usually, the large deformation of these materials at the micro-scale and the topography produced by different manufacturing processes introduce complex frictional behavior between the surfaces. This has led to investigations of the deformation of micro-asperities to capture friction and wear at micro-scale in order to predict the macroscale interfacial behavior. The overall objective of this study is to develop a micro-asperity-based model of friction in engineering surfaces. In this study, we present the development of a micro-asperity based model for friction between isotropic, Gaussian, elastoplastic surfaces. In order to do this, we present a statistical model that is Gaussian and isotropic in nature, to represent the surface micro-topography. We present a novel methodology for estimating scale-independent properties of the surface model from the measured surface profile. The normal and shear forces supported by a single asperity are then calculated using the micro-asperity model and the overall contact forces at macroscopic scale are calculated by using statistical homogenization. In this study, we assume the material behavior to be linearly elastic-perfectly plastic to model the frictional behavior between metallic surfaces. In particular, we develop the constitutive models of both friction force and coefficient of friction for Aluminum 6061 alloy surfaces with Gaussian, isotropic surface topography. We also study the effect of various entities such as surface roughness, material properties, normal load and adhesive forces on the overall friction behavior. We also p (open full item for complete abstract)

Committee: Kumar Vemaganti Ph.D. (Committee Chair); Kelly Anderson Ph.D. (Committee Member); Amit K. Kaushik Ph.D. (Committee Member); Jim Shepherd Ph.D. (Committee Member); Yijun Liu Ph.D. (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Mechanical Engineering

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

This thesis presents a mobility analysis of a simplified helicopter gearbox system focusing on structure-borne noise, based on linear time-invariant system theory. The internal gear dynamic system, with a unity spur gear pair, shafts and bearings, is modeled as an 8 degree of freedom linear time-invariant system with static transmission error and sliding friction as the primary excitations with assumed magnitudes that are uniform throughout the entire frequency range (5-20000 Hz). Natural frequencies are obtained and eigenvalue derivatives are used to identify variations in each natural frequency with respect to small changes in each system parameter using a Taylor's series approximation. Analytical expressions are derived through the mobility synthesis technique for the linear and rotational motions of the gear and pinion, dynamic transmission error and dynamic bearing and mesh forces in terms of the effective shaft/bearing stiffnesses, mesh stiffness, masses and inertias of the gears and shafts. These results are compared with the direct matrix inversion methods. The asymptotic trends in the frequency responses are compared with static forces. The gear motions predicted by this model are used to predict sound radiation from the casing by means of experimental pressure/acceleration transfer functions. Measured individually for line of action and off-line of action paths, these transfer functions are considered to be made up of separate transfer functions corresponding to the gear system response, bearing transmissibility, casing transmissibility and sound radiation efficiency. The variation of the overall transfer function for changes in internal sub-system parameters (mesh stiffness, bearing/shaft stiffness) is formulated assuming that the bearing and casing characteristics remain unaffected. These modified transfer functions are then employed to predict the effect of assumed variation in the internal parameters and source excitations on the radiated sound. Furthe (open full item for complete abstract)

Committee: Rajendra Singh PhD (Advisor); Ahmet Kahraman PhD (Committee Member) Subjects: Mechanical Engineering

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

Doctor of Philosophy, The Ohio State University, 2004, Industrial and Systems Engineering

While manufacturing is typically considered a high-volume industry, the necessity for small quantities of products and components exists for aerospace customers and those producers wishing to mass customize their products. Because of the high cost of tooling, injection molding processes are seldom used to produce only small quantities of parts. This, however, can be remedied if cost effective tooling methods are implemented. Rapid prototyping processes show great potential for such tooling applications because they generally require shorter lead times, produce less waste, and, in some cases, use less expensive materials. The research presented herein studies the feasibility of using injection mold inserts produced with additive methods by investigating ejection and friction. Through experimentation, the application of P-20 steel, laser sintered LaserForm ST-100, and stereolithography SL 5170 tools to produce limited quantities of a thin-walled cylindrical part are explored. A substantial amount of data and statistical analysis are provided that reveal conditions during the actual injection molding process, and comparisons are made among the three insert types. Experimental ejection forces from each tool type are compared with model-based calculations, and apparent coefficients of static friction are calculated and compared to standard test results. Based on the data and analyses, the benefits and limitations of using rapid tooled injection mold inserts are presented.

Committee: Blaine Lilly (Advisor) Subjects: Engineering, Industrial

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: