Engineering Commons^™

Advancing Combinatorial Screening Of Refractory High Entropy Alloys Through Intrinsic Ductility Assessment Via Thin Film Fragmentation Testing, Taohid Bin Nur Tuhser

Theses and Dissertations--Chemical and Materials Engineering

High Entropy Alloys (HEAs), also known as Multiprincipal Element Alloys (MPEAs), represent a paradigm shift in alloy design. Unlike traditional practices that limit compositions to the edges of phase diagrams, HEAs exploit equiatomic mixing of five or more elements at the center of phase diagrams to maximize configurational entropy. This unconventional approach exponentially expands the spectrum of potential alloy compositions, rendering conventional experimental methods inadequate for exploring this extensive compositional space.

In response to these challenges, the scientific community has shown a growing interest in high-throughput techniques, encompassing both computational and experimental domains. Particularly, Refractory High Entropy Alloys (RHEAs) have …

Microstructural Investigation Of The Influence Of Geometry On The Mechanical Reliability Of Additively Manufactured Metals, Tracy Connor Varney

Theses and Dissertations--Chemical and Materials Engineering

The adoption of additive manufacturing across a wide range of fields is ever-increasing, allowing for solutions that were previously impossible to achieve. This dissertation demonstrates the wide range of macro- and micro- characterization techniques used to investigate several precipitation strengthened AM alloy systems. While AM allows for nearly unlimited design freedom, this brings along its own issues as the interplay between scan strategy and part geometry is less well known. In this work, a novel thin-wall dogbone geometry was utilized to study one type of complex geometry observed in a large portion of AM focused designs. The mechanical behavior of …

Optoelectrical Properties And Photostability Of Cspbbr3 Quantum Dots: Effects Of Dopants And Ligands, Md Shad Bin Salam

Theses and Dissertations--Chemical and Materials Engineering

Metal halide perovskite QDs have a great potential for displays and lighting because of their exceptional optoelectronic characteristics associated with quantum confinement effect. However, the stability in the environment during the applications of halide perovskite QDs remains a significant challenge, impeding their practicality and lowering their commercial scalability. High-temperature methods are well-established for producing doped perovskite QDs, the influence of room-temperature synthesis on thermal, size-dependent optical properties, and long-term stability remains inadequately understood. Also, there is a demand for strategies to increase the absorption of light, reduce trap states, and modify the energy levels of perovskite QDs.

In this study, …

Thermal Alteration Of The Mineralogy Of Calcium Sulfoaluminate Cements: Implications For The Performance Of Rapid Repair Materials, Jillian Cavellier

Theses and Dissertations--Earth and Environmental Sciences

Calcium sulfoaluminate (CSA) was developed in part to lessen the environmental impact of cementitious materials compared to traditional Portland cements. CSA was first put into production in the 1970s and has been undergoing various performance testing to investigate its durability. Yet to be evaluated is CSA’s response to a rapid, high temperature event. In this study, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectrometry and scanning electron microscope imaging were used to analyze alterations in the mineralogy due to such an event. As found in previous studies, after ~125°C, ettringite has been completely dehydrated. Ettringite decomposes into bassanite and calcium …

Mechanochemical Synthesis Of Halide Perovskite Microcrystals, Xuan Huang

Theses and Dissertations--Mechanical and Aerospace Engineering

Halide perovskites have emerged as a promising class of materials for various optoelectronic applications, including light-emitting diodes (LEDs), solar cells, photodetectors, and lasers, owing to their exceptional photophysical properties and ease of synthesis. Lead-based halide perovskites, despite their success, raise concerns regarding environmental toxicity, necessitating the exploration of lead-free alternatives. This thesis explores the synthesis and characterization of lead-free halide perovskites, focusing on tin-based variants, using a mechanochemical approach, which eliminates the use of toxic solvents and offers a sustainable synthesis route.

By employing a solventless mechanochemical method, lead-free tin-based halide perovskite microcrystals were successfully synthesized. This approach not only …

Matrix Stiffness Sensing By Nascent Adhesions And The Role Of Riam In Adhesion Assembly, Nikhil Mittal

Dissertations, Master's Theses and Master's Reports

Mechanical stiffness of the extracellular matrix (ECM) impacts many cellular functions such as proliferation, migration, and differentiation. ECM stiffness is sensed by a cell via integrin-based focal adhesions (FAs) by changing conformation and biochemical activities of molecules within FAs by the exchange of the force between the ECM and filamentous actin (F-actin). Cells in turn respond to this stiffness by generating traction force that plays an important role in many biological events such as tissue morphogenesis, stem cell differentiation, wound healing, and cancer cell metastasis. The stiffness of the extracellular matrix induces differential tension within integrin-based adhesions. Understanding stiffness sensing …

Liquid Metal Printing Of Ultrathin Conductive Metal Oxides, Andrew B. Hamlin

Dartmouth College Ph.D Dissertations

Widegap metal oxides are critical semiconducting materials in solar power generation, transparent electronics and displays. Ultrathin versions of these materials are poised to be at the forefront of next generation technology due to their high transparency, flexibility, and the capacity to advantageously use backchannel sensitivity and quantum confinement. Liquid metal printing is a novel deposition technique that fundamentally yields ultrathin oxide materials by exfoliating the self-limited oxide that exists on molten metals at low temperatures. Our work involves the invention of novel liquid metal printing techniques to deposit semiconducting 2D metal oxides with precise electrostatic properties. We investigate the electronic …

Halide-Assisted Growth Of Transition Metal Dichalcogenides, Vinaayak Sivam Balasubramaniam

Dissertations, Master's Theses and Master's Reports

Monolayers of transition metal dichalcogenides (TMDCs) have attracted significant attention as the rare two-dimensional (2D) semiconducting materials with a direct energy band gap. Chemical vapour deposition (CVD) is one of the scalable techniques to grow atomically thin TMDC monolayers in high quality, but it requires high growth temperature. Herein we report the growth of MoS2, WS2 and MoSe2 by a one-step halide-assisted CVD method using NaCl and KCl as the catalysts. These halides could reduce the growth temperature of TMDCS by reacting with the precursors (TMDC powders) to form volatile intermediate compounds as the growth species. We use optical microscopy, …

Fatigue Resistant Cast Steel Railcar Couplers Produced By Wire-Arc Additive Manufacturing (Waam), Samuel Vellequette

Dissertations, Master's Theses and Master's Reports

Every year, approximately 90,000 cast steel railcar coupler knuckles are replaced preemptively to avoid fatigue failure. The coupler geometry has been in service since the early 1930s, so geometry changes are restricted to maintain compatibility with the existing fleet. Defects from the casting process, decarburization during heat treatment, and in-service exposure to corrosive environments combine to promote fatigue crack nucleation in high-stress regions of the knuckle. Wire-arc additive manufacturing (WAAM), which uses traditional welding techniques to build material to near-net shapes, was employed to deposit higher-strength materials in critical regions. By replacing the cast steel in the high-stress region of …

Degree Of Dispersion/Exfoliation And Surface Functionalization Of 1d And 2d Carbon Nanostructured Materials: Interface Interactions And Effects On Mechanical Properties, Michail Margas

Material Science and Engineering Dissertations - Archive

The development of advanced cementitious nanocomposites relies heavily on understanding the interfacial interactions between carbon-based nanomaterials and the cement matrix, which significantly influence the material’s performance. The goal of this dissertation is to investigate the effect of dispersion/exfoliation and surface functionalization of 1D multiwall carbon nanotubes (MWCNTs), carbon nanofibers (CNFs), and 2D graphene nanoplatelets (GNPs) in aqueous suspensions on the interface interactions of nanoengineered cementitious composites. The first objective of this dissertation is to quantitatively evaluate the degree of nanomaterial dispersion for MWCNT and CNF suspensions, in a converging manner for cement-based materials applications using spectroscopic techniques, such as UV-vis …

Development Of Synthetically Accessible Glycolated Polythiophenes For High-Performance Organic Electrochemical Transistors, Bowen Ding, Vianna N. Le, Hang Yu, Guanchen Wu, Adam V. Marsh, Edgar Gutiérrez-Fernández, Nicolás Ramos, Martina Rimmele, Jaime Martín, Jenny Nelson, Alexandra F. Paterson, Martin Heeney

Chemical and Materials Engineering Faculty Publications

Four glycolated polythiophene-based organic mixed ionic-electronic conductors (OMIECs), PE2gTT, PE2gT, PT2gTT, and PT2gT are prepared by atom-efficient direct arylation polymerization, avoiding the need for toxic organometallic pre- cursors. PE2gT, PT2gTT, and PT2gT are operable in p-type accumulation mode organic electrochemical transistors (OECTs), with PT2gT displaying the best device performance with a μC* product figure-of-merit of 290 F cm−1 V−1 s−1 . A record volumetric capacitance among p-type glycolated polythiophene OMIECs of 313 F cm−3 is observed for PE2gT, ascribed to the high proportion- ality of polar components in its materials design. The good OECT performance of PE2gT with μC* = …

The Integrated Behavioral Model Of Mental Health Help Seeking (Ibm-Hs): A Health Services Utilization Theory Of Planned Behavior For Accessing Care, Joseph H. Hammer, David L. Vogel, Patrick R. Grzanka, Nayeon Kim, Brian T. Keum, Claire Adams, Sarah A. Wilson

Chemical and Materials Engineering Faculty Publications

This article introduces the integrated behavioral model of mental health help seeking (IBM-HS), a theoretical model for understanding the constructs (e.g., systemic, predisposing, and enabling factors; mental health literacy; illness perceptions; perceived need; stigma; shame; perceived benefits, motivation) that influence people’s decision making around seeking professional mental health care and their ultimate access to formal treatment. The IBM-HS is a help-seeking-specific adaptation of the empirically supported integrated behavioral model and integrative model, which are themselves evolutions of the theory of planned behavior and theory of reasoned action. The IBM-HS posits that help-seeking determinants (e.g., structural forces; cultural influences; past help-seeking …

Advanced Synthesis And Rational Design Of Support Structures For Nobel Metal Heterogeneous Catalysis: Towards Enhanced Activity And Continuous Processes, Brian R. Clark

Theses and Dissertations

The field of catalysis has a wide-ranging impact. Our group has identified the constant need for improved catalytic activity in high-impact applications such as hydrosilylation and cross-coupling reactions. For these reactions, precious metal catalysts often exhibit markedly better performance than their counterparts, but they can be a significant process cost that decreases overall economic efficiencies. To address this challenge, we explored support structures that can enhance catalytic activity at low metal loadings and improve precious metal recovery through simple filtration. We found that a platinum on graphene nanoplatelet catalyst (PtGNP) synthesized via strong electrostatic adsorption with microwave irradiation (SEA-MW) exhibits …

Passive Wireless Corrosion And Temperature Detection In High-Temperature Environments, Noah Lane Strader

Graduate Theses, Dissertations, and Problem Reports (ETD)

This work focuses on the theory and development of LC sensors for high temperature and corrosion measurement for stainless steel and copper surfaces with power industry and general corrosion detection applications. The LC resonators were fabricated via screen printing an Ag inductor on an alumina substrate. The LC design was modeled using the ANSYS HFSS modeling package. The LC passive wireless sensors operate with resonant frequencies centered at 85-110 MHz. The wireless response of the LC sensor was interrogated and received by a radio frequency signal generator and spectrum analyzer at temperatures from 50-800 °C for copper ground planes and …

Investigation Of Space Charge Effects On Co2 Electrocatalytic Reduction On Gd-Doped Ceria Via Scanning Kelvin Probe And Model-Based Bayesian Analysis, Alejandro Mejia

Graduate Theses, Dissertations, and Problem Reports (ETD)

In studying novel energy conversion and storage systems, such as high-temperature electrolysis, numerous underlying fundamental physical processes remain unclear or inadequately understood. Among these, the modeling and comprehension of surface reaction mechanisms, coupled with the intricate effects of space‑charge interfaces, remains an unclear and challenging area of research.

The work of this dissertation involves the development of a 2D finite element analysis model, leveraging the robust MOOSE framework from INL. This model, featuring inhomogeneous defect thermodynamics for near-surface chemistry, formulated through Poisson‑Cahn variational theory, has been exploited for studying the electrocatalytic reduction of CO₂ on gadolinia doped ceria. The …

Data-Driven Modeling Of Oxygen Kinetics In La0.6sr0.4co0.2fe0.8o3−Δ (Lscf) For High-Temperature Reduction Of Co2 In An Electrolysis Cell, Ferron Campbell

Graduate Theses, Dissertations, and Problem Reports (ETD)

Electrolysis systems are critical to several societal applications, particularly energy storage and conversion. Developing these systems requires a detailed knowledge of the chemistry and thermodynamics of the materials used in the electrolysis cell. This work focuses on using embedded scientific machine learning as an efficient way to build an interpretable model for the reaction and transport kinetics in the LSCF electrode, whose performance directly influences the electrolysis system’s performance. The models developed in this study are trained using the publicly available machine learning package, FoKL-GP. This package incorporates a robust Gibbs sampler that employs a forward variable selection process to …

Investigation Of Mechanically Fatigue Low-Frequency Energy Harvesting Effects On Isotropic Materials, Daniel J. Meade

College of Graduate Studies: Theses & Dissertations

This research project reports an exploratory investigation of energy harvesting effect on isotropic material that goes through low frequency mechanical fatigue. Energy harvesting is a growing field of study that can recycle ambient energy back into a system that would otherwise be lost. This is a significantly useful method for the ongoing energy crisis and provides an alternate route to design and upgrade systems to be more efficient and last longer than current system designs. However, it is time to investigate if there is any effect vibration-based energy harvesting has on the structure from which energy is being harvested. To …

Natural Convection Heat Transfer Characteristics Of Sierpinski Carpet Fractal Fins In Horizontal And Vertical Orientations, Ayomide Ayoola

College of Graduate Studies: Theses & Dissertations

This study investigates the thermal performance of fins with perforations inspired by the Sierpinski carpet fractal pattern under natural convection conditions in both vertical and horizontal orientations. The objective is to analyze the effects of fractal iteration levels on three primary performance metrics: efficiency, effectiveness, and effectiveness per unit mass. Experimental evaluations were conducted for fractal fins from iterations 0 through 4, utilizing aluminum material, with each fin heated to controlled conditions. The results reveal that efficiency generally decreases with higher fractal iterations, reflecting increased thermal resistance associated with greater porosity and complex geometry. However, effectiveness per unit mass improves …

Experimental Investigation Of Liquid Metal Embrittlement In Hot-Dip Galvanized Structural Steel, Amelia Mcnamee

College of Graduate Studies: Theses & Dissertations

This research investigated the liquid metal embrittlement (LME) of hot-dipped galvanized structural steel. The relationship between stress and failure time was analyzed to evaluate the potential presence of a critical stress threshold beyond which LME may occur. A testing apparatus to induce axial stress was designed and assembled in-house. A36 low carbon steel was tested in this study. Different deadweight loadings were applied to the testing sample along the axial direction. The test temperature was maintained by a programmable furnace while the sample gauge section was submerged in a molten zinc bath. Failure time and total displacement of the steel …

Processing-Microstructure-Properties Relationships In Additively Manufactured Zrb2-Sic Ceramics, Marharyta Lakusta

Doctoral Dissertations

"The study explores the pressure less sintering (PS) and chemical compatibility of ZrB₂-30 vol.%SiC produced by additive manufacturing (AM) with CO₂. The oxidation kinetics and scale microstructures were compared for ZrB₂-SiC made by hot pressing (HP) and by AM coupled with PS. All specimens exhibited parabolic oxidation kinetics. The difference in oxidation behavior becomes evident at temperatures of 1100-1400°C (200-900h). Oxidation rates increased as grain size increased. Similar oxide scale morphologies were observed in both CO₂ and air, with an outer borosilicate layer and an inner porous ZrO₂ layer containing partially oxidized …

Theoretical Investigations Of The Structural, Dynamical, Electronic, Magnetic, And Thermoelectric Properties Of CoMRhsi (M = Cr, Mn) Quaternary Heusler Alloys, Abdullah Hzzazi, Hind Alqurashi, Eesha Andharia, Bothina Hamad, M. O. Manasreh

Physics Faculty Publications and Presentations

The structural, dynamical, electrical, magnetic, and thermoelectric properties of CoMRhSi (M = Cr, Mn) quaternary Heusler alloys (QHAs) were investigated using density functional theory (DFT). The Y-type-II crystal structure was found to be the most stable configuration for these QHAs. Both CoCrRhSi and CoMnRhSi alloys possess a half-metallic behavior with a 100% spin-polarization as the majority spin channel is metallic. On the other hand, the minority spin channel is semiconducting with narrow indirect band gaps of 0.54 eV and 0.57 eV, respectively, along the Γ−𝑋 high symmetry line. In addition, both CoCrRhSi and CoMnRhSi alloys possess a ferromagnetic structure …

Effect Of Strain Profiling On Anisotropic Opto-Electronic Properties Of As2X3 (X =S, Te) Monolayers From First Principles, Eesha Andharia, Hind Alqurashi, Ihsan Erikat, Bothina Hamad, M. O. Manasreh

Physics Faculty Publications and Presentations

Strain Engineering is a widely adopted approach to modulate the opto-electronic performance of 2-Dimensional (2D) materials. Recently, anisotropic Van der Waals (vdW) based 2D As₂S₃ monolayer has gained significant attention within the scientific community due to its stability in ambient conditions. Similar compounds like As₂Te₃ have also been theoretically explored. However, its indirect bandgap nature limits its application in optical devices. In this study, a systematic study of compressive and tensile strain on three profiles–Uniaxial along a-axis, Uniaxial along b-axis and biaxial strain from −10% to +10%, is performed for As₂S_{3 …}

Ltspice Modeling For Gan-Git Hemt Including Cryogenic Temperature, Md Maksudul Hossain, Yuqi Wei, H. Alan Mantooth

Electrical Engineering Faculty Publications and Presentations

Highly efficient electrically driven avionics have led to a renewed interest in cryogenic propulsion systems with the goal of reducing carbon emission footprint. Although cryogenic converters promise better efficiency and improved power density, the successful design is incumbent upon the appropriate switching device selection and simulation-based analyses prior to initial prototyping. In this work, a datasheet-driven compact model for a gallium nitride (GaN) Gate Injection Transistor (GIT) has been proposed and implemented in LTspice, a versatile, high performance, and free circuit simulator in order to investigate the merit of the chosen device in a power electronic system.

Laser Deposition Additive Manufacturing Of Multi-Material And Metal-Ceramic Composite Structures, Manikanta Grandhi

Graduate Theses, Dissertations, and Problem Reports (ETD)

The increasing performance requirements of modern industrial systems, coupled with the imperative for decarbonization, necessitate a fundamental rethinking of metallic component design and manufacturing. Traditional materials, with their inherent limitations in property optimization, susceptibility to degradation, and weight constraints, are proving insufficient. Multi-material joining offers a potential solution, enabling designers to strategically integrate diverse materials with specific, tailored properties into single component. Functionally graded materials (FGMs) and oxide dispersion strengthened (ODS) materials are prime examples of this approach, delivering substantial improvements in wear resistance, thermal regulation, high-temperature resilience, and overall weight efficiency. However, conventional manufacturing approaches further exacerbate the limitations …

Processing, Stability, And High-Temperature Properties Of Doped Lacro3-Based Refractory Ceramics And Composites For Harsh Environments Sensing Applications, Javier A. Mena

Graduate Theses, Dissertations, and Problem Reports (ETD)

In order to test and monitor the operational stability and conditions of various energy, transportation, and manufacturing systems and their components, accurate sensors capable of operating at temperatures over 1000 °C in various environments for long durations are required. In addition, many of these harsh environmental systems do not permit sensors to be directly inserted into the environment, so the sensors need to be embedded into the surrounding support or thermal protective materials. Some technological and industrial applications that require the use of harsh environment conditions sensing include nuclear and chemical reactors, jet engines, heavyduty gas turbines, rotating bearings in …

Molecular Modeling Of Phenolic Resin For Carbon-Carbon Composites, Ivan Gallegos

Dissertations, Master's Theses and Master's Reports

One of the most difficult challenges associated with space exploration is terrestrial atmospheric reentry due to the high thermal loads generated. Carbon carbon (C/C) composites have been used as heat shielding materials due to their high strengthto- weight ratio and thermal properties and their applications include heat shielding for various high temperature environments. C/C composites are manufactured by polymer-infiltration pyrolysis (PIP) via cycles of curing and pyrolysis of a prepreg which can be costly and take up to several days. Thus, C/C composites ideal candidates for computationally-driven optimization techniques, such as a multiscale Integrated Computational Materials Engineering (ICME) approach, by …

F-Temper Vs O-Temper Brazing Of 3003 Aluminum Return Bends, Mieka R. Clark

Dissertations, Master's Theses and Master's Reports

As-extruded (F-temper) 3003 return bends can provide cost savings over annealed (O-temper) return bends in aluminum heat exchangers. To assess if F-temper return bends are an alternative to the baseline O-temper bends, the grain structure, bending performance, and melting behavior were assessed through:

• Quantifying the effect of dispersoids on recrystallization
• Tracking bending behavior through grain morphology and surface texture
• Measuring the number and volume fraction of the α-Al(Mn,Fe)Si intermetallic
• Inducing incipient melting through high temperature thermal exposure.

When homogenized at 620°C and 630°C, the F-temper bends had no orange peel texture, the grain size was equivalent to the annealed product, …

Improving Cast Steel Rail Coupler Fatigue Resistance Through Local Wire-Arc Additive Manufacturing, Andrew M. Bunge

Dissertations, Master's Theses and Master's Reports

Every year, thousands of cast-steel railcar couplers suffer from corrosion-initiated fatigue cracking in similar areas of the coupler’s knuckle; between 2015 and 2018 about 90,000 knuckles were replaced, otherwise these couplers would have been at risk for unexpected failures. These types of couplers have been common in industrial use as early as 1932, hence it is desirable for a countermeasure to the fatigue cracking that does not involve significantly altering the geometry or casting process. Wire arc additive manufacturing (WAM) is a developing technology which boasts the ability to produce complex near-net-shape components; however, less attention has been paid to …

High Temperature Strength Reduces Soldering In Aluminum High Pressure Die Casting, Jacob A. Belke

Dissertations, Master's Theses and Master's Reports

Die soldering, an adhesion defect in high pressure die casting (HPDC), is a symptom of localized sticking where a localized portion of the cast material is adhered to the tooling surface causing build up over time. This requires the tooling to be serviced which incurs additional costs to the process that gets passed on to the parts. Historically, soldering has been mitigated using lubricants, coatings, and alloy chemistry modifications but solder persists.

The Tresca friction thermomechanical model suggests soldering occurs when the local interfacial shear stress between the casting and die surface exceeds the local shear strength of the casting. …

Machine Learning For Electronic Structure Prediction, Shashank Pathrudkar

Dissertations, Master's Theses and Master's Reports

Kohn-Sham density functional theory is the work horse of computational material science research. The core of Kohn-Sham density functional theory, the Kohn-Sham equations, output charge density, energy levels and wavefunctions. In principle, the electron density can be used to obtain several other properties of interest including total potential energy of the system, atomic forces, binding energies and electric constants. In this work we present machine learning models designed to bypass the Kohn-Sham equations by directly predicting electron density. Two distinct models were developed: one tailored to predict electron density for quasi one-dimensional materials under strain, while the other is applicable …