Doctor of Philosophy, Case Western Reserve University, 2024, Macromolecular Science and Engineering

Traditionally, extrinsic approaches (e.g. blending and using additives) have been used to enhance the mechanical properties (e.g. toughness) of commercially available semicrystalline thermoplastics. In a continual search for economically scalable, scrapless, simple, and versatile manufacturing approaches, novel solid-state processes have a unique advantage over melt-processing methods alone. Cold-roll milling, or plastically deforming a workpiece by passing it through two counter-rotating rollers below its primary softening temperature, is well-established in the production of ductile metals. Roll-milling not only reduces thickness, but also cold-works the material improving its strength through microstructural refinement. In polymers, a crystalline network structure develops. The focus of this work is on biaxial cold-rolling (cross-rolling) which involves cross-passes alternately 90 ° apart, resulting in a sheet with planar isotropy. In the first part of this dissertation (chapter 2), the deformation of HDPE by cross-rolling is studied. Enhanced barrier properties (measured by oxygen permeability analyzer), increased visible light transmission (measured by spectrophotometer), and increased tensile fracture strength were observed after cross-rolling. A connection to discontinuous change in crystalline structure with thickness reduction (i.e. lamellar fragmentation) detected by density measurement, thermal analysis, and small-angle x-ray scattering (SAXS) is discussed. The second portion (chapters 3-5) focuses on the cross-roll pre-deformation of semicrystalline polymers below both the Tm and Tg at room temperature, and subsequently annealing at temperatures both below and above the Tg. In chapter 3, the Izod impact toughness of poly(p-phenylene sulfide), a notoriously low toughness high-temperature engineering thermoplastic, is found to increase by a factor of 10 after cross-rolling. The elongation to failure is enhanced by a factor of nearly 6 by cross- (open full item for complete abstract)

Committee: Gary Wnek (Committee Chair); Lei Zhu (Committee Member); Ica Manas (Committee Member); John Lewandowski (Committee Member) Subjects: Materials Science; Mechanical Engineering; Mechanics; Plastics

Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering

Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with and without blade profile contouring at the junction of the blade and endwall. The current work explores the loss production mechanisms inside the low pressure turbine cascade. Stereoscopic particle image velocimetry data, total pressure loss data and oil flow visualization are used to describe the secondary flow field. The flow is analyzed in terms of total pressure loss, vorticity, Q-Criterion, Reynolds' stresses, turbulence intensity and turbulence production. The flow description is then expanded upon using an Implicit Large Eddy Simulation of the flow field. The RANS momentum equations contain terms with static pressure derivatives. With some manipulation these equations can be rearranged to form an equation for the change in total pressure along a streamline as a function of velocity only. After simplifying for the flow field in question the equation can be interpreted as the total pressure transport along a streamline. A comparison of the total pressure transport calculated from the velocity components and the total pressure loss is presented and discussed. Peak values of total pressure transport overlap peak values of total pressure loss through and downstream of the passage suggesting that total pressure transport is a useful tool for localizing and predicting loss origins and loss development using (open full item for complete abstract)

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D. (Committee Member); Rory Roberts Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering