Doctor of Philosophy, The Ohio State University, 2015, Mechanical Engineering

Eulerian formulations of the equations of finite-deformation solid dynamics are ideal for numerical implementation in modern high-resolution shock-capturing schemes. These powerful numerical techniques -- traditionally employed in unsteady compressible flow applications -- are becoming increasingly popular in the computational solid mechanics community. Their primary appeal is an exceptional ability to capture the evolution and interaction of nonlinear traveling waves. Currently, however, Eulerian models for the nonlinear dynamics of rods, beams, plates, membranes, and other elastic structures are currently unavailable in the literature. The need for these reduced-order (1-D and 2-D) Eulerian structural models motivates the first part of this dissertation, where a comprehensive perturbation theory is used to develop a 1-D Eulerian model for nonlinear waves in elastic rods. The leading-order equations in the perturbation formalism are (i) verified using a control-volume analysis, (ii) linearized to recover a classical model for longitudinal waves in ultrasonic horns, and (iii) solved numerically using the novel space-time Conservation Element and Solution Element (CESE) method for first-order hyperbolic systems. Numerical simulations of several benchmark problems demonstrate that the CESE method effectively captures shocks, rarefactions, and contact discontinuities. The second part of this dissertation focuses on another emerging area of finite-deformation mechanics: magnetoelectric polymer composites (MEPCs). A distinguishing feature of MEPCs is the tantalizing ability to electrically control their magnetization, or, conversely, magnetically control their polarization. Leveraging this magnetoelectric coupling could potentially impact numerous technologies, including information storage, spintronics, sensing, actuation, and energy harvesting. Most of the research on MEPCs to date, however, has focused on optimizing the magnitude of the magnetoelectric coupling (open full item for complete abstract)

Committee: Sheng-Tao John Yu (Advisor); Marcelo J. Dapino (Committee Member); Daniel A. Mendelsohn (Committee Member); Amos Gilat (Committee Member); Kelly S. Carney (Committee Member) Subjects: Engineering; Mechanical Engineering; Polymers

Master of Science (MS), Ohio University, 2013, Mechanical Engineering (Engineering and Technology)

The purpose of this research was to evaluate the mechanical behavior of extruded (UNS-C12200) copper multi-channel tube for HVACR (heating, ventilation, air conditioning and refrigeration) systems. A model was developed to predict the burst pressure of the copper tube. The assumption for the model is based on plane strain plastic deformation to an instant of instability where differential internal pressure is equal to zero. Physical simulations were used to develop a relevant microstructure that is representative of the tube in a manufactured heat-exchanger. To this end, cold rolling was used to simulate post-extrusion straightening and sizing of the tube. A subsequent thermal treatment was performed in a tube furnace to simulate a brazing thermal cycle. Tensile tests were conducted to obtain material data, and to determine material constants for a Voce type constitutive equation. Burst tests were conducted to validate the predictive model. Burst pressures were predicted to within 6% of measured values. The effects from cold working and the simulated brazing cycle were also evaluated in this research.

Committee: Frank Kraft (Advisor) Subjects: Materials Science; Mechanical Engineering; Metallurgy

Master of Science, The Ohio State University, 2012, Mechanical Engineering

A wide range of advanced high strength steel (AHSS) sheets with nominal ultimate tensile strengths (UTS) from 590 to 1180 MPa and engineering strains to failure from 0.09 to 0.51 were tested to obtain the tensile flow stress under various combinations of strain, strain-rate, and temperature. Procedures were developed for selecting suitable constitutive forms corresponding to a generalized framework proposed in the literature by Sung et al. (Sung et al., 2010). Using the selected forms, the least-squares coefficients were obtained using an efficient optimization procedure that was also developed. The fit accuracy in all cases was similar to the test-to-test experimental scatter. Comparison with results from standard fitting schemes showed that the optimum coefficient values were found using the proposed, more time-efficient, methodology. The resulting constitutive models were compared with novel balanced biaxial bulge test measurements at strains up to several times larger than those accessible to tensile testing. The results show that constitutive models obtained by such procedures from standard tensile data can be extrapolated accurately to strain ranges of interest in bending-affected plastic localization (“shear fracture”).

Committee: Dr. Robert H. Wagoner (Advisor); Dr. Rebecca B. Dupaix (Committee Member) Subjects: Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2010, Mechanical Engineering

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Committee: Robert. H. Wagoner (Advisor); June Key Lee (Committee Member); Sudarsanam Babu (Committee Member); Rebecca B. Dupaix (Committee Member) Subjects: Mechanical Engineering

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

The overall goal of the research done in this dissertation is to develop next generation force feedback systems by combining novel Magnetorheological (MR) fluid based electromechanical systems with microstructural analysis and advanced control system design. Four MR fluid based systems are designed, prototyped and tested with medical applications: A two degree of freedom (2-DOF) force feedback joystick and a 5-DOF force feedback manipulator for telerobotic surgery application, a passive and a semiactive orthopedic knee brace for rehabilitation application. Furthermore, a force feedback steering wheel is modified using MR damper with application to steer-by-wire automobiles. The test results show the appropriate performance of MR fluid based systems used in haptic and force feedback applications.

Committee: Gregory Washington PhD (Advisor); Stephen Bechtel PhD (Committee Member); Vadim Utkin PhD (Committee Member); Giorgio Rizzoni PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2010, Mechanical Engineering

The objective of this research is to develop a constitutive model to predict the steady-state response of a rubber compound under cyclic loading. An MTS servo-hydraulic machine was used to obtain the dynamic hysteresis curves for a rubber compound in uniaxial tension-compression. The material tests were performed with mean strains from -0.1 to 0.1, strain amplitudes ranging from 0.02 to 0.1, and strain rates between 0.01 and 10s-1. Creep, the Payne effect and rate-dependence were observed from the experimental results. The uniaxial test results motivated the development of a three-dimensional constitutive model involving an equilibrium spring with temporary material set in parallel with a Maxwell element. A cornerstone of this constitutive modeling was to devise a scheme for evaluating a material set function for creep and a viscosity function for hysteresis. Material properties for the hyperelastic springs and viscous damper were identified from the uniaxial cyclic tension-compression test results. The constitutive equations were implemented into ABAQUS Standard via a user-defined material subroutine, UMAT. Numerical predictions of the cyclic hysteresis curves were found to be good agreement with the uniaxial test results. Cyclic torsion tests were also performed on the rubber cylinders to evaluate the accuracy of the proposed constitutive model and the UMAT was used to predict the response of the rubber cylinder under torsion. Good agreement with the torsion test results was also reported from the finite element analysis.

Committee: Michelle Hoo Fatt Dr. (Advisor) Subjects: Mechanical Engineering