Master of Science (MS), Ohio University, 2006, Mechanical Engineering (Engineering)

Studies have proven hydrogen gas as a highly efficient, renewable and alternative energy source and it is expected to serve as a common fuel for all mobile and stationary applications. However, currently the on-board storage difficulties prevent the practical usage of hydrogen in automotive applications. A more efficient and innovative method of hydrogen storage for automotive fuel cell application is to compress hydrogen in minute hollow spherical bubbles incorporating the Hydrostatic Pressure Retainment (HPR) technology. In a HPR vessel, the material properties and the inner matrix structure are two critical design parameters that determine the hydrogen mass efficiency. The focus of this study is devoted to investigating the performance characteristics of one configuration; spherically shaped bubbles homogenously arranged in a simple cubic inner matrix packing structure for a HPR vessel, using Finite Element Analysis.

Committee: Hajrudin Pasic (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, The Ohio State University, 2021, Welding Engineering

Temper bead (TB) welding is often used as an alternative to PWHT when welding hardenable steels in the fabrication and repair process, commonly employed in the nuclear industry. Historically, qualification of TB welding techniques have employed Charpy V-notch testing to ensure acceptable HAZ fracture toughness; however, ASME Section IX (QW-290) included a provision, in 2004, that allows temper bead qualification through tensile, bend, and peak hardness without impact testing requirements. Previous work shows that for SA508, a common pressure vessel steel, tempered Martensite has the highest toughness of the microstructures present in the heat affected zone. This work looks to find a quantitative correlation between instrumented indentation, the newly found hardness drop parameter, and critical brittle volume fraction of the overall microstructure with impact toughness. These correlations will be the foundation for creating an alternative TB qualification criterion from just hardness indents but based on impact toughness properties, which supports the formation of tough Martensitic microstructures for pressure vessel steels, mainly SA508 but also SA387 Gr.22 Cl.2 (commonly referred to as F22). The idea of shifting these practices toward producing more Martensitic microstructures to improve impact toughness is a paradox when thinking about general steel metallurgy. Carbon partitioning to Austenite which is transformed to Martensite upon cooling can occur in heterogeneous structures embrittling the Martensite. However, in a fully Martensitic microstructure carbon partitioning does not occur and autotempering, tempering upon cooling, can be a toughening mechanism for untempered Martensite in pressure vessel steels. An investigation into carbon partitioning and autotempering was conducted which will further the field's fundamental knowledge on the impact properties of Martensite in pressure vessel steels.

Committee: Antonio Ramirez (Advisor); Boian Alexandrov (Committee Chair); Desmond Bourgeois (Committee Chair) Subjects: Engineering; Materials Science; Nuclear Engineering

Master of Science (MS), Ohio University, 2004, Mechanical Engineering (Engineering)

There is a great deal of attention being concentrated on reducing the weight of pressure vessels and fuel/oxidizer tanks (tankage) by 10% to 20%. Most efforts are focused at the use of new lighter weight high strength materials to achieve this goal. This author proposes another approach called Hydrostatic Pressure Retainment™ (HPR™) which has the potential of reducing tank weights by nearly 40% while simultaneously increasing safety and design versatility. HPR™ is an original invention of the author and his advisor, and represents a truly novel approach to light weight pressure vessel design. Described herein are the initial steps towards development of this new technology.

Committee: Bhavin Mehta (Advisor) Subjects: Engineering, Mechanical

Master of Science in Mechanical Engineering, Cleveland State University, 2008, Fenn College of Engineering

Stress analysis of a cone-cylinder pressure vessel was computationally simulated by a finite element method and probabilistically evaluated in view of the severaluncertainties in the performance parameters. Cumulative distribution functions and sensitivity factors were computed for overall Von Mises stresses due to the structural and thermodynamic random variables. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective. The analysis leads to the selection of the appropriate measurements to be used in structural and heat transfer analysis and to the identification of both the most critical measurements and parameters.

Committee: Rama Gorla Phd (Committee Chair); John Frater Phd (Committee Member); Earnest Poulos Phd (Committee Member); Majid Rashidi Phd (Committee Member) Subjects: Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2012, Materials Science and Engineering

Current production techniques for large diameter 6061 alloy seamless pressure vessels can lead to cylinder heads with regions of large (1mm+) grains that fracture in a low ductility intergranular fashion along the circumference of the head during proof tests. This phenomena and fracture mode was reproduced in commercially produced cylinders by a combination of slow strain rate (10-6/s) 4-point bending and controlled surface strain experiments. As-spun heads were commercially produced and given solution heat treatments at CWRU via either a salt bath or an induction coil, the former followed by quenching at rates from 180°C/s to 18°C/s. The effects of these different heat treatments on the resulting grain size, crack resistance and fracture mode were compared to the standard commercial treatments. Induction heated samples produced grain sizes below 150 µm and exhibited a significantly higher crack resistance, fracturing in a transgranular ductile manner.

Committee: John Lewandowski PhD (Advisor); Gary Michal PhD (Committee Member); David Schwam PhD (Committee Member); Henry Holroyd PhD (Other) Subjects: Aerospace Materials; Materials Science; Metallurgy