Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

Rising concerns related to fuel consumption and greenhouse emissions are being addressed by the automotive industry through vehicle lightweighting. Hence to meet the stringent requirements for lightweighting, conventional steel body parts are being replaced with Al alloys, Mg alloys and composite materials. However, the use of dissimilar materials together poses a serious threat of galvanic corrosion leading to accelerated degradation of galvanically coupled body parts. Aiming to develop the automotive closure panels using carbon fiber reinforced plastics (CFRP) inner and an outer aluminum alloy sheet to replace what is now an all-steel design, corrosion studies are performed to determine effective qualification of materials. In the first part of this project, CFRP materials of two types, named as twill and random, coupled with aluminum alloys (AA) 6111 and 6022 in all combinations, are subjected to a Ford laboratory accelerated cyclic corrosion test (CETP: 00.00-L-467) and on-road testing with the help of OSU campus buses for a year. The ability of the laboratory accelerated test to predict the on-road corrosion behavior is assessed by comparing the material volume loss determined using optical profilometer, microscopic images of corroded regions, and measurements of galvanic currents of the coupons exposed to the cyclic test. Analysis of the test results indicated that the coupon combination AA6111 and CFRP-random exhibits the highest corrosion susceptibility whereas AA6022 coupled with CFRP-twill is least susceptible to galvanic corrosion among the combinations used in this study. In the second part of the study, electrochemical behavioral differences between CFRP-twill and -random contributing to the differences in activities when coupled to AA6xxx are evaluated. For this, a copper deposition technique was developed to quantify the extent of electrochemical activity and identify the exact location of electrochemically active sites on the CFRP. Optimization (open full item for complete abstract)

Committee: Gerald S. Frankel Dr. (Advisor); Narasi Sridhar Dr. (Committee Member); Jenifer Locke Dr. (Committee Member) Subjects: Atmosphere; Conservation; Energy; Engineering; Materials Science; Sustainability; Transportation

Master of Science, The Ohio State University, 2020, Mechanical Engineering

Magnetically geared machines perform gearing operations by utilizing magnetic force interactions between the rotors as opposed to mechanical force interactions. Many benefits of magnetic gears derive from the fact that there is no contact between the rotors. Contactless gearing allows for quieter operation, eliminates the need for lubrication outside the bearings, decreases the need for maintenance, and provides inherent overload protection. Another benefit is that the magnetic gear design lends itself to direct implementation in motors as opposed to having a separate mechanical gearbox. A magnetic gear has three fundamental components: a high speed rotor, a low speed rotor, and a flux modulator. These components work in tandem to generate magnetic field harmonics which scale the torque and speed of the input shaft. There are many magnetic gear designs that accomplish this task, but this thesis focuses on coaxial magnetic gears (CMGs) that utilize Halbach array magnet rotors and no back iron. In this design, the flux modulator is radially nested within the low and high speed rotors with the high speed rotor typically positioned at the inner most layer. Inherent to magnetic gear behavior is a 3D inefficiency known as end-effect loss. This loss causes flux to leak over the axial ends of the gear and back to its source. This flux never makes it to the flux modulator and never contributes to torque. End-effect losses can cause a significant decrease in output torque (10% to 40% depending on the design) and can only be modeled with large 3D simulations. The first aspect of this research involves the development of a reduced length modeling method which accounts for the axial variation of end-effect losses within the gear to shorten the computation time of magnetic gearing models. It has been shown for the models in this thesis that computation time can be cut in half while the torque results stay within 5% of their true value. Several magnetic gear design variable (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); Rebecca Dupaix (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

The development of new magnesium alloys with improved mechanical properties is important for lightweighting applications, since the current high pressure die cast (HPDC) magnesium alloys, i.e. AM50/60 (Mg-5/6wt.%Al-0.2wt.%Mn) and AZ91 (Mg-9wt.%Al-1wt.%Zn), have limited mechanical properties. Two magnesium alloy systems, Mg-Al-Sn (AT) and Mg-Al-Sn-Si (ATS), were investigated for potential automotive applications. A CALPHAD (CALculation of PHAse Diagrams) approach was used in the development of AT and ATS alloys and to aid in the design of heat treatment schedules. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and transmission electron microscopy (TEM) techniques were used to characterize the microstructure of the alloys in the as-cast and heat treated conditions. Mechanical testing was performed on cast specimens, as well as samples cut from thin-wall HPDC components to compare the strength and ductility of these alloys to currently used magnesium alloys. To expand the applications of HPDC components in the transportation industries, further development and optimization of the process is needed. The development of super vacuum die casting (SVDC) process for aluminum and magnesium thin-wall castings were explored using process simulation and experimental validation. Two experimental dies, i.e., a test specimen die and a fluidity die, were designed to evaluate the castability of several new aluminum alloys and optimize process parameters for these alloys. The process conditions were successfully validated in industrial castings such as an automotive door inner and a side impact beam.

Committee: Alan Luo (Advisor); Michael Mills (Committee Member); Glenn Daehn (Committee Member); Gary Kennedy (Committee Member) Subjects: Materials Science