Master of Science in Engineering, University of Akron, 2021, Mechanical Engineering

The viscoelastic properties of rubber have allowed compounds to be utilized across many different industries. Rubber is a very unique material, and the chosen manufacturing process can result in numerous variations of the polymer. With many potential outcomes, it is crucial to accurately determine the physical attributes of the polymer. For many applications, but specifically for the tire industry, one of the standard methods for determining viscoelastic properties is through dynamic mechanical analysis (DMA). The raw data from DMA is adjusted through the Williams, Landel, and Ferry (WLF) shift equation to create a master curve for the rubber specimen. This study investigates methods for the calculation of friction coefficient, and suggests a new code to predict the friction coefficient. Several discussions in the paper will be for validation of the code and its range of applications. We then implement a parametric analysis to determine which factors critically affect the friction factor results. By finding the sensitivity of the inputs to the new code for friction coefficient, the critical inputs can be identified. The parameters that are studied are the storage modulus, loss modulus, surface asperities heights, the surface asperities wavelength, and the adhesive contribution to friction. The adhesion and hysteresis contributions to the friction coefficient are also discussed in this paper. It is shown that the adhesive contribution plays a large role in determining the friction coefficient. The data from the study will determine the effect that direct DMA testing has on the friction coefficient as well as tire performance indicators. The indicators that the direct testing affects the most are the wet traction indicator, the snow traction indicator, and the ice traction indicator.

Committee: Siamak Farhad (Advisor); Alex Povitsky (Committee Member); Shing-Chung (Josh) Wong (Committee Member) Subjects: Automotive Materials; Materials Science; Mathematics; Polymers

Doctor of Philosophy, University of Akron, 2019, Mechanical Engineering

Mechanical connection of parts through jointed connections are prolific throughout modern engineering applications; however, precision analysis and design of these systems remains difficult. Experimental findings have revealed a myriad of nonlinear properties of these systems such as nonlinear damping, hysteresis, etc., and these complex effects lead to extreme difficulties in the characterization and modeling of these common structural elements. To exacerbate matters, high-fidelity numerical analysis of these systems is often impractical due to disparate length and time-scales between microslip in the joint and macro-scale effects of interest. In this dissertation, original research on the analysis of damping of jointed structures is presented. This includes theoretical work in advancement of reduced-order modal models as well as practical development of Abaqus subroutines to implement cutting-edge damping models into finite element models. This work culminates in the study of a practical problem of interest to Sandia National Labs involving a jointed structure under blast loading, and important conclusions are draw about the nature of jointed structures under complex loads.

Committee: Donald Quinn (Advisor); Graham Kelly (Committee Member); Xiaosheng Gao (Committee Member); Ernian Pan (Committee Member); Kevin Kreider (Committee Member) Subjects: Aerospace Engineering; Applied Mathematics; Mathematics; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2017, Welding Engineering

Inertia Friction Welding (IFW), a critical process to many industries, currently relies on trial-and-error experimentation to optimize process parameters. Although this Edisonian approach is very effective, the high time and dollar costs incurred during process development are the driving force for better design approaches. Thermal-stress finite element modeling has been increasingly used to aid in process development in the literature; however, several fundamental questions on machine and material behaviors remain unanswered. The work presented here aims produce an analytical foundation to significantly reduce the costly physical experimentation currently required to design the inertia welding of production parts. Particularly, the work is centered around the following two major areas. First, machine behavior during IFW, which critically determines deformation and heating, had not been well understood to date. In order to properly characterize the IFW machine behavior, a novel method based on torque measurements was invented to measure machine efficiency, i.e. the ratio of the initial kinetic energy of the flywheel to that contributing to workpiece heating and deformation. The measured efficiency was validated by both simple energy balance calculations and more sophisticated finite element modeling. For the first time, the efficiency dependence on both process parameters (flywheel size, initial rotational velocity, axial load, and surface roughness) and materials (1018 steel, Low Solvus High Refractory LSHR and Waspaloy) was quantified using the torque based measurement method. The effect of process parameters on machine efficiency was analyzed to establish simple-to-use yet powerful equations for selection and optimization of IFW process parameters for making welds; however, design criteria such as geometry and material optimization were not addressed. Second, there had been a lack of understanding of the bond formation during IFW. In the present research, a (open full item for complete abstract)

Committee: Wei Zhang (Advisor); John Lippold (Committee Member); David Phillips (Committee Member) Subjects: Engineering; Materials Science

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

In this thesis, a mathematical model of an automotive powertrain featuring a wet dual clutch transmission is developed. The overall model is comprised of models that describe the dynamic behavior of the engine, the transmission mechanical components, the hydraulic actuation components, and the vehicle and driveline. A lumped-parameter model, that incorporates fluid film dynamics and a simplified thermal model, is used to describe wet clutch friction. The model of the hydraulic actuation system includes detailed models of the clutch and synchronizer actuation subsystems. A simulation of the dynamic powertrain model is built using AMEsim and MATLAB/Simulink. The powertrain simulator is used to demonstrate how changes in transmission parameters affect the quality of clutch-to-clutch shifts and the overall dynamic response of the powertrain. Based on this model, measurements of clutch pressure and the rotational speeds and estimated accelerations at the input and output sides of the clutch are used in the design of a friction parameter estimation scheme that can be implemented offline using past simulation data or online using current simulation signals. For both offline and online cases, simulation results demonstrate that friction parameters are estimated with reasonable accuracy. An integrated powertrain controller is developed with a model-based feedforward controller and multiple feedback loops. The feedforward controller, which generates a pressure command to either clutch, is developed by inverting a simplified model of the powertrain, and using a static friction model to relate clutch pressure to friction torque. The inputs to the feedforward controller are speeds and estimated accelerations of the engine and clutches. The feedforward controller adapts to changes in friction characteristics by updating the friction parameters used in the static friction model using the values generated by the estimation scheme. The feedback controller contains loops tha (open full item for complete abstract)

Committee: Krishnaswamy Srinivasan (Advisor); Shawn Midlam-Mohler (Committee Member) Subjects: Automotive Engineering; 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

Master of Science (MS), Ohio University, 1989, Mechanical Engineering (Engineering)

An alternative method to predict friction in metal forming

Committee: J. Gunasekera (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: