Engineering Commons^™

Interfacial Bonding Between Thermoset And Thermoplastic Polyurethane Reinforced Textile Grade Carbon Fiber: Structure Property Relationships, Surbhi Subhash Kore

Doctoral Dissertations

The research work focused on examining the interfacial adhesion of unsized, epoxy, and urethane-sized textile grade carbon fiber (TCF) reinforced in different classes of polyurethane (PU) thermoplastic (TPU) and thermoset (TSU) polyurethane (PU) through the structure-property relationship. The Carbon Fiber Technology Facility (CFTF) at Oak Ridge National Laboratory (ORNL) has produced TCF to reduce the cost of commercial-grade carbon fiber. The first part of the research examined the fundamental relationships between (a) soft segment thermoplastic polyurethane (S-TPU), (b) hard segment thermoplastic polyurethane (H-TPU), (c) thermoset polyurethane (TSU) and TCF reinforcement’s molecular behavior at the interface using the surface and thermal …

Fundamentals Of Cavity Formation In Α-Fe And Fe-Cr Alloys, Yan-Ru Lin

Doctoral Dissertations

Ferritic-martensitic steels are attractive candidate materials for fusion and advanced fission reactors primarily due to their low swelling characteristic, attractive thermo-mechanical properties, and the potential for development of nanostructured ferritic alloys. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. Several mechanisms have been proposed that may affect cavity swelling, but no general theory or model has received complete acceptance to explain these phenomena.

To better understand the formation of cavities in ferritic steels, we have performed multi-temperature (400-550°C) single-beam and simultaneous dual-beam irradiations (ex-situ and in-situ) on …

Development Of Density-Functional Tight-Binding Methods For Chemical Energy Science, Quan Vuong

Doctoral Dissertations

Density-functional tight-binding (DFTB) method is an approximation to the popular first-principles density functional theory (DFT) method. Recently, DFTB has gained considerable visibility due to its inexpensive computational requirements that confer it the capability of sustaining long-timescale reactive molecular dynamics (MD) simulations while providing an explicit description of electronic structure at all time steps. This capability allows the description of bond formation and breaking processes, as well as charge polarization and charge transfer phenomena, with accuracy and transferability beyond comparable classical reactive force fields. It has thus been employed successfully in the simulation of many complex chemical processes. However, its applications …

3d Printing Of Hybrid Architectures Via Core-Shell Material Extrusion Additive Manufacturing, Robert Cody Pack

Doctoral Dissertations

Biological materials often employ hybrid architectures, such as the core-shell motif present in porcupine quills and plant stems, to achieve unique properties and performance. Drawing inspiration from these natural materials, a new method to fabricate lightweight and stiff core-shell architected filaments is reported. Specifically, a core-shell printhead conducive to printing highly loaded fiber-filled inks, as well as a new low-density syntactic foam ink, are utilized to 3D-print core-shell architectures consisting of a syntactic epoxy foam core surrounded by a stiff carbon fiber-reinforced epoxy composite shell. Effective printing of test specimens and structures with controlled geometry, composition, and architecture is demonstrated …

Process-Structure-Property Relationships In 3d-Printed Epoxy Composites Produced Via Material Extrusion Additive Manufacturing, Nadim S. Hmeidat

Doctoral Dissertations

Extrusion-based additive manufacturing (AM) technologies, such as direct ink writing (DIW), offer unique opportunities to create composite materials and novel multi-material architectures that are not feasible using other AM technologies. DIW is a novel 3D-printing approach in which viscoelastic inks, with favorable rheological properties, are extruded through fine nozzles and patterned in a filament form at room temperature.

Recent developments in DIW of polymer composites have led to expanding the range of materials used for printing, as well as introducing novel deposition strategies to control filler orientation and create improved functional/structural composite materials. Despite these substantial advancements, the successful and …

Microscopic And Image Processing Characterization Of Aggregates To Predict Asr Expansion Potential Of Concrete, Ammar Elfatih Abdelssamd Elhassan

Doctoral Dissertations

Preventing ASR occurrence in new concrete structures requires reliable and quick methods to identify reactive aggregates and to evaluate proper mitigation alternatives. The current accelerated mortar-bar expansion tests (ASTM C 1260 or ASTM C1567) and the concrete prism expansion test (ASTM C 1293) have been reported to have several limitations. Assessment of the extend of ASR damage in existing affected structures requires more understanding on how ASR expansion and damage develop in field conditions such as under confinements and under relatively slow rate of ASR reaction.

The significance of ASR expansion rate and bi-axial restrain on concrete degradation has been …