Master of Science in Engineering, Youngstown State University, 2020, Department of Mechanical, Industrial and Manufacturing Engineering

Wind tunnels continue to be essential for testing aerodynamic systems and underlying flow physics required in research and industry for proper modeling and design. This study introduces the newly reconstructed low-speed, research-grade boundary-layer wind tunnel constructed at Youngstown State University and first measurements of performance to support computational modeling of experiments. The tunnel design is based on a facility that previously existed in the Fluid Mechanics Laboratory at the NASA Ames Research Center that contributed validation experiments for direct numerical simulation (DNS) of non-trivial flows in the 1990s. In this work, the newly-built tunnel was calibrated and a flow quality survey was conducted, which included measurements of cross-section uniformity, boundary-layer measurements, and turbulence intensity. Measurements were performed at operating speeds of 3, 7.5, 15, and 30 m/s. Prior to construction, computational modeling of the facility had been performed and estimated that a 40 hp blower would provide the desired operating speed envelope and maximum speed of 40 m/s. It was found that the top speed of the wind tunnel with an empty test-section was 35 m/s. The cross-sectional flow nonuniformity, measured with the Pitot-static tube, showed a maximum difference of 3% from the centerline velocity in the upper half of the speed range. The natural boundary-layer state was measured using a fine Pitot-tube and compared to 3-D, Reynolds-averaged flow calculations and well-known velocity profile benchmarks from laminar incompressible theory (Blasius solution for zero-pressure-gradient-flow) and the turbulent 1/7th power law. The results showed good agreement with the laminar profile at the lowest speeds tested (3 and 7.5 m/s). The highest speeds tested (15 and 30 m/s) showed good near-wall agreement with the turbulent calculations. The streamwise turbulence intensity measured with a hot-wire probe was 0.18% at test speeds above 7.5 m/s, agree (open full item for complete abstract)

Committee: Kevin Disotell PhD (Advisor); Hazel Marie PhD (Committee Member); Stefan Moldovan PhD (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Master of Science, University of Toledo, 2020, Mechanical Engineering

A MacCormack type artificial dissipation operator has been formulated based on the dissipation portion of a 2N storage MacCormack time marching scheme. This new dissipation operator will reduce to a standard even derivative dissipation operator on a uniform grid and will satisfy the metric invariants of transformation on a non-uniform grid. The MacCormack scheme is an inherent dissipation scheme which uses alternate biased spatial stencils in time marching stages to provide dissipation at the end of each time step. Unlike MacCormack scheme, MacCormack type artificial dissipation can be used in each stage of a time step with a central spatial differencing scheme. In this thesis, MacCormack dissipation is derived and modified for 2D Euler equations. Then the resulting dissipation scheme is validated on two dimensional unsteady inviscid fow problem which is taken from High Order CFD (HiOCFD) workshop problems.

Committee: Ray Hixon (Committee Chair); Sorin Cioc (Committee Member); Omid Amili (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science in Engineering, University of Akron, 2018, Mechanical Engineering

Nanostructured materials with superior physical properties hold promise for the development of novel nanodevices. Full potential applications of such advanced materials require study of vibrational analysis to reduce equipment downtime and maintenance cost of the unit by detecting the experimental faults when applied in industries, in general, it is a study concerning the system under oscillatory motion about a stable equilibrium position focusing on the analysis not the design of the systems. Which in turn necessitates the development of computer-based simulations along with novel experimental techniques. Since controlled experiments are difficult for nanoscale materials and atomic studies are computationally expensive, continuum mechanics-based simulations of nanomaterials and nanostructures have become the focal points of computational nanoscience and materials modeling. In this thesis, the free and forced vibrations of coupled coaxial carbon nanotube in the vicinity of graphene sheet using Euler Bernoulli beam model for free-free end conditions are studied. The multiwalled carbon nanotube can be studied by considering each of the nested nanotubes to be a Euler Bernoulli beam and coupled through the Van der Waals forces. Damping is also considered and modeled using a Kelvin-Voigt damping model. Using the estimated Van der Waals interaction energy potential using Lennard-Jones potential expressed as a function of interlayer spacing. Equilibrium distance affects the natural frequencies of the system and is calculated in the thesis. To study the forced response of coupled co-axial nanotube with damping a modal analysis is performed assuming graphene has a harmonic excitation. There is a necessity to develop a solution method to determine the response of a system for all times and even after the excitation is removed. Many excitations change form at the discrete time, so it is convenient to determine a unified mathematical form of response. In this Thesis, the solu (open full item for complete abstract)

Committee: Graham Kelly Dr. (Advisor); Alper Buldum Dr. (Committee Member) Subjects: Automotive Materials; Chemistry; Design; Engineering; Mechanical Engineering; Mechanics; Molecular Chemistry; Nanoscience; Nanotechnology

Master of Science, The Ohio State University, 2018, Mechanical Engineering

In this study, a two-dimensional model is proposed for determining theoretical contact lines, tooth separation, and approximated loaded transmission error with frequency spectra thereof, as well as various other output variables such as instantaneous center distance, operating pressure angle, and instantaneous contact ratio when circular runout error is applied to either or both gears in a spur or helical gear pair. As an addendum, a method for calculating off-line of action tooth separation using this model is described for spur gears. Additionally, a three-dimensional model is proposed for determining theoretical contact lines and tooth separation when any combination of circular runout or wobble error are applied to either or both gears in a spur or helical gear pair. Sample analyses are shown for spur and helical gear pairs with runout error applied using the two-dimensional model, and a helical gear pair with various combinations of runout and wobble error applied using the three-dimensional model. The results are discussed qualitatively with respect to the expected effects the applied errors would have on the tooth separation and related variables.

Committee: David Talbot (Advisor); Ahmet Kahraman (Committee Member) Subjects: Mechanical Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2017, Mechanical Engineering

Next generation aircraft (especially combat aircraft) will include more technology and capability than ever before. This increase in technology comes at the price of higher electrical power requirements and increased waste heat that must be removed from components to avoid overheating induced shutdowns. To help combat the resulting power and thermal management problem, a vehicle level power and thermal management design and optimization toolset was developed in MATLAB®/Simulink®. A dynamic model of a three-stream variable cycle engine was desired to add to the capabilities of the power and thermal management toolset. As an intermediate step to this goal, the dynamic mixed-flow turbofan engine model previously developed for the toolset was modified with an afterburner, a variable geometry nozzle, and a new controller to automatically control the new components. The new afterburning turbofan engine model was tested for a notional mission profile both with and without power take-off. This testing showed that the afterburning turbofan engine model and controller were successful enough to justify moving on to the development of the three-stream variable cycle engine model. The variable cycle engine model was developed using the components of the afterburning turbofan model. The compressor and turbine components were modified to use maps that incorporate the effects of variable inlet guide vane angles. The new engine model and components were sized by attempting to match data from a Numerical Propulsion System Simulation model with similar architecture. A previously developed heat exchanger model was added to the third stream duct of the new engine model. Finally, a new simplified controller was developed for the variable cycle engine model based on the controller developed for the afterburning turbofan model. The new variable cycle engine model was tested for a notional mission profile for five cases. The first case operated the engine model without power take-off (open full item for complete abstract)

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

Master of Science, The Ohio State University, 2017, Mechanical Engineering

Our current understanding of electrophysiological phenomena is limited by our ability to measure particular processes. There are a number of electrophysiological intracellular and extracellular measuring techniques which currently exist; however, they are not without limitations. These techniques, such as patch-clamping, involve the careful isolation of a singular cell (which removes the cell from its native environment) and subsequent puncturing or suctioning of the cell membrane (which can damage the cellular structure). This research focuses on the development of conducting polymer sensors for in vivo measurements of electrophysiological phenomena. The goal of this work is to create a system by which ion concentration dynamics can be directly measured and analyzed to quantify metrics of biological processes without harming tissues of the organism. Quasi-potentiostatic amperometric sensors were developed using polypyrrole doped with dodecylbenzenesulfonate (DBS) to form PPy(DBS). By applying a cyclic pulse voltage input to the conducting polymer measurement system, and measuring the resulting current response, system parameters can be correlated to deviations from an equilibrium concentration as a function of time. This research will lay the foundation for more complex measurement techniques, both in electrophysiology, as well as in energy storage technology.

Committee: Vishnu Baba Sundaresan (Committee Member); Daniel Gallego-Perez (Committee Member) Subjects: Biomedical Engineering; Cellular Biology; Engineering; Mechanical Engineering; Neurobiology; Neurology; Neurosciences

Master of Science in Mechanical Engineering, Cleveland State University, 2016, Washkewicz College of Engineering

Seal whiskers have been found to produce unique wake flow structures that minimize self-induced vibration and reduce drag. The cause of these wake features are due to the peculiar three-dimensional morphology of the whisker surface. The whisker morphology can be described as an elliptical cross section with variation of diameter in the major and minor axis along the length and, angle of incidence, rotation of the elliptical plane with respect to the whisker axis, α at the peak and β at the trough. This research provided a more complete morphology characterization accomplished through CT scanning and analysis of 27 harbor and elephant seal whisker samples. The results of this study confirmed previously reported values and added a characterization of the angle of incidence finding that the majority of angles observed fall within ±5° and exhibit a random variation in magnitude and direction along the whisker length. While the wake effects of several parameters of the whisker morphology have been studied, the effect of the angle of incidence has not been well understood. This research examined the influence of the angle of incidence on the wake flow structure through series of water channel studies. Four models of whisker-like geometries based on the morphology study were tested which isolate the angle of incidence as the only variation between models. The model variations in angle of incidence selected provided a baseline case (α = β = 0°), captured the range of angles observed in nature (α = β = -5°, and α = β = -15°), and investigated the influence of direction of angle of incidence (α = -5°, β = -5°). The wake structure for each seal whisker model was measured through particle image velocimetry (PIV). Angle of incidence was found to influence the wake structure through reorganization of velocity field patterns, reduction of recovery length and modification of magnitude of Tu. The results of this research helped provide a more complete understanding of the seal wh (open full item for complete abstract)

Committee: Wei Zhang PhD (Advisor); Ibrahim Mounir PhD (Committee Member); Shyam Vikram PhD (Committee Member) Subjects: Aerospace Engineering; Aquatic Sciences; Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science, The Ohio State University, 2016, Mechanical Engineering

The Ohio State University is participating in EcoCAR 3, which is a four-year long competition amongst 16 North American university teams to redesign the 2016 Chevrolet Camaro to reduce its environmental impact, while maintaining the muscle and performance expected from the iconic American car. To effectively assess and increase overall product quality and readiness of Ohio State's vehicle, this work defines and deploys a state of the art Model-Based Systems Engineering (MBSE) approach for managing engineering complexity as it relates to requirements management, traceability, and fulfillment. To demonstrate the effectiveness of the implemented approach, this work presents system safety development activities that have been conducted during the first two years of the competition. As EcoCAR 3 transitions into year-three, this work has already contributed to over a dozen awards by increasing overall documentation, traceability and workflow management as part of the overall engineering development process.

Committee: Shawm Midlam-Mohler (Advisor); Giorgio Rizzoni (Committee Member) Subjects: Automotive Engineering; Mechanical Engineering

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

Particle Image Velocimetry (PIV) has been of relevant discussions lately as the equipment used to obtain temporally and spatially resolved flow fields have advanced rapidly. Despite these advancements, the accuracy of evaluating these images have yet to exceed expectations. Current techniques typically utilize one method, either correlation based (frequently) or optical flow (non-frequently), and both are vulnerable to specific conditions incorporated in the PIV images. Only through the combination of two methods, cross correlation and optical flow, can a technique benefit from the strengths of each method while concealing the flaws each individual method contains. The Hybrid Particle Image Velocimetry method utilizes the fairly unrestricted cross-correlation method, which can process images that contain particles with relatively large displacements, and the high resolution analysis of the Optical Flow method. Susceptible to large displacements, the Optical flow method is restricted to images with particularly small displacements. Combining the two methods requires the constraints set forth on the Optical flow method to be conserved. Meaning that the Cross-correlation results have to be manipulated into a form applicable for the Optical Flow method. Thus steps such as interpolation, shifting the image, and filtering the image are crucial for transitioning cross-correlation results to optical flow analysis. Validating the accuracy of the Hybrid method was conducted through standard PIV images that encompassed various parameters encountered in PIV. Each set of images were analyzed by the hybrid method and three other commonly-used correlation techniques in order to compare the hybrid method's accuracy with current methods. Results confirmed that the Hybrid method is consistently more accurate than the other methods, especially near the boundaries. Additionally, for cases dealing with large particles or small displacement, the Hybrid method attains more accurate result (open full item for complete abstract)

Committee: Zifeng Yang Ph.D. (Advisor); Philippe Sucosky Ph.D. (Committee Member); Rory Roberts Ph.D. (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2016, Secondary Education

Few studies have focused on perceptions of creativity in engineering. Previous researchers have tended to focus on perceptions concerning the degree to which creative thinking is emphasized in the classroom, rather than on whether students value creativity as an important part of the engineering design process. Moreover, the relationship between students' perceptions of the importance of creative thinking in engineering design and their creative performance has not been investigated. Given the value placed on the ability of an engineer to think creatively, it is important to understand how engineering students perceive creativity as it relates to the engineering design process and whether such perceptions have the potential to influence their ability to think creatively during the engineering design process. In this mixed-methods study, perceptions related to four primary themes: students' perceptions of (a) the definition of creativity with respect to engineering design, (b) the importance of creativity during engineering design, (c) the extent to which creativity was developed throughout the engineering program, and (d) their own creative abilities. Themes were compared among eight engineering students who scored at the extreme ends of the Creative Engineering Design Assessment (CEDA). In addition, perceptions were gathered from 12 mechanical engineering faculty in order to compare their perceptions of creativity in the mechanical engineering program to those of the students. The findings of this study support predictions made by applying the expectancy-value theory, which holds that students who value creativity in engineering design and confidently believe they have the ability to be creative are more likely to be creative in various engineering design scenarios. Further, all students interviewed shared the perception that the mechanical engineering program did little to encourage and develop creative-thinking skills; however, students agreed the program (open full item for complete abstract)

Committee: Nidaa Makki Dr. (Advisor); Susan Kushner Benson Dr. (Committee Member); Wondimu Ahmed Dr. (Committee Member); Edward Evans Dr. (Committee Member); Francis Broadway Dr. (Committee Member) Subjects: Education; Engineering

Master of Science in Aerospace Systems Engineering (MSASE), Wright State University, 2024, Mechanical Engineering

The development of high order numerical schemes has been instrumental in advancing computational fluid dynamics (CFD), particularly for applications requiring high resolution of discontinuities and complex flow phenomena prevalent in high-speed flows. This thesis introduces the Pade-ENO scheme, a high-order method that integrates Essentially Non-Oscillatory (ENO) techniques with compact Pade stencils to achieve superior accuracy, up to 7th order, while maintaining stability in harsh environments. The scheme's performance is evaluated through benchmark tests, including the advection equation, Burgers' equation, and the Euler equations. For high Mach number flows, such as the sod shock tube the Pade-ENO method demonstrates its ability to resolve sharp gradients and discontinuities with no smoothing required. Numerical results highlight the scheme's robustness and its potential as a powerful tool for high-speed aerodynamic simulations, paving the way for future advancements in CFD modeling.

Committee: George Huang Ph.D., P.E. (Advisor); Jose Camberos Ph.D., P.E. (Committee Member); Nicholas Bisek Ph.D. (Committee Member); James Menart Ph.D. (Other) Subjects: Aerospace Engineering; Engineering; Fluid Dynamics; Mathematics; Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2024, Mechanical Engineering

The goal of this work is to analyze and characterize solid granular media in high temperature CSP applications. This work expands on commercially available Discrete Element Method (DEM) modeling software, Aspherix®, through development of two calibration templates designed to mimic both the experimental rigs for the slump test and rotary kiln discussed in this thesis. Whereas, designed experimental rigs were developed to isolate desired frictional behaviors in three different material types (CarboBead HSP, CarboBead CP, and Granusil) for temperatures varying from 25°C – 800°C. Additionally, improvements were made upon the previously constructed rotary kiln to facilitate high temperature testing experimentally.

Committee: Andrew Schrader Dr. (Advisor) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 1950, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2024, Mechanical Engineering

The design of transmission components must meet multiple performance requirements to ensure they are durable, efficient and quiet. In certain applications, weight reduction is an additional requirement especially for an aerospace system. Towards this goal, material is typically removed from the gear bodies, resulting in gear rims and webs that are rather flexible. Such flexible-rim gears might involve a class of dynamic behavior associated with the deformable-body vibratory modes. If the transmission is operated at resonances associated with these modes, it may result in adverse dynamic loading conditions. The main focus of this thesis is to develop an experimental means of quantifying such deformable-body behavior of high-speed gearing. A new test machine is developed to study the contributions of deformable-body modes of a flexible-rim spur gear to the overall dynamic behavior in a lab environment under realistic torque and speed conditions. Several measurements systems are designed and implemented to monitor key features of deformable-body motions such as accelerations, displacements and strains. Simple and repeatable methods of introducing manufacturing variations in the experimental set-up are developed in order to quantify the impact of such variations have on vibratory models of flexible-rim gears. The methodology is employed to establish a baseline (no-error) database and demonstrate the deviations from this baseline behavior due to manufacturing variations. These results indicate that the proposed methodology is effective in investigating flexible-rim behavior.

Committee: Ahmet Kahraman (Advisor); Isaac Hong (Committee Member); Carlos Castro (Committee Member) Subjects: Mechanical Engineering

Master of Science, Miami University, 2023, Mechanical and Manufacturing Engineering

Balancing creativity with a structured approach in engineering design poses a critical challenge, necessitating optimization of each stage to aid in efficiently creating superior products. Functional analysis, a systematic approach defining the design problem, enables comprehensive exploration of the design space. However, critics argue that it requires too many resources, restricts creativity, and imposes high demands on design teams. The goal of this research is to enhance the effectiveness of functional analysis by integrating theories from cognitive research and human-centered design. The proposed method, Natural Cognitive Flow Functional Analysis (NCFFA), aims to promote designers' creative freedom, maintain the quality of the function model, and be accessible to engineering students and professionals alike. A between-subject study involving novice engineers evaluated the effectiveness of NCFFA. Although determining the full effectiveness of NCFFA in terms of enhanced creativity and reduced effort proved challenging, the study found marginal improvement in designers' Flow State, suggesting the potential merit of the NCFFA method for enhancing the designer experience during functional analysis. The study highlights the benefits of incorporating cognitive research and human-centered design principles into functional analysis and paves the way for further research to refine the structured design process.

Committee: Jinjuan She (Advisor); Christopher Wolfe (Committee Member); Sk Khairul Hasan (Committee Member) Subjects: Cognitive Psychology; Engineering; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2022, Integrated Bioscience

Continuously expanding urban environments compete with and negatively impact natural ecosystems. Building processes consume numerous resources including materials which need to be extracted, transported, shaped, and disposed of. To reduce this negative impact and instead potentially positively affect natural ecosystems, the built environment needs to perform ecosystem services originally in place and sustainable building practices should be employed for their entire life cycle. The principle of biological growth has architectural potential including adaptation, resilience, dynamics, differentiation, and continuous functionality. Biotechnology and biomimicry serve as integrated bioscience methods to transfer biology into architecture by integrating living organisms into the manufacturing process and applying abstracted biological principles into technological systems. This PhD explores the solidification of aggregate materials through both methods to show their potential and limitations: growth of fungal mycelium on agricultural byproducts to produce building materials and design of foundation systems inspired by tree roots. Mycelium-based materials are of increasing interest for their potential in generating biodegradable building materials with tunable properties from waste products through clean manufacturing processes. Before their implementation into permanent buildings, numerous aspects have yet to be researched. This PhD primarily focuses on: the optimization of large-scale manufacturing processes, effects of the manufacturing process and material compositions on mechanical properties and outdoor durability, and utilization of local species. Root-inspired foundation systems can enhance traditional foundations by reducing resources utilized and integrating new functions to serve the built environment and natural ecosystems. Conceptual designs present how root strategies are abstracted and transferred towards the future of building foundations. Biolog (open full item for complete abstract)

Committee: Hunter King (Advisor); Petra Gruber (Committee Member); Jason Miesbauer (Committee Member); Nariman Mahabadi (Committee Member); Hazel Barton (Committee Member) Subjects: Architecture; Biology; Biomechanics; Civil Engineering; Materials Science

Doctor of Philosophy (PhD), Wright State University, 2022, Engineering PhD

High-power laser systems (HPLS) have wide-ranging applications in many prominent areas. HPLS use laser diodes to pump fiber gain media. Understanding the functionality of both components is critical for achieving effective HPLS operation. System optical efficiency is a function of diode junction temperature. As junction temperature changes, the wavelength spectrum of the diode output shifts causing optical power losses in the fiber gain media. Optical/thermal interactions of the dynamically coupled laser diodes and fiber gain media are not fully understood. A system level modeling approach considering the interactions between optical performance and component temperature is necessary. Four distinct models were created: Diode optical, diode thermal, fiber optical, and fiber thermal. Dynamically coupling these models together provided the capability to demonstrate how HPLS electro-to-optical efficiency changes when the laser diode pump spectrum shifts due to various levels of thermal management. Subsequent studies were done to determine which parameters across all four models had the most significant impact on laser performance from a designer's perspective. Next, a statistical surrogate model was created by varying these parameters to create a parameter space. Response variables of interest were then reduced to a single equation as a function of these important parameters across the parameter space, allowing for quicker exploration of the potential design space. Lastly, laser time to steady state and laser efficiency were employed to determine when a specific diode cooling method should be used to achieve the highest laser efficiency. Understanding the optical/thermal interactions of laser operation and exploring the impact of various thermal capabilities can provide better system design and optimization guidelines. Bridging the gap between the optical and thermal aspects of laser operation in pursuit of such understanding has been made possible by the re (open full item for complete abstract)

Committee: Rory Roberts Ph.D. (Advisor); Mitch Wolff Ph.D. (Committee Member); George Huang Ph.D. (Committee Member); Amir Farajian Ph.D. (Committee Member); Soumya Patnaik Ph.D. (Committee Member) Subjects: Mechanical Engineering; Optics

Master of Science in Mechanical Engineering, Cleveland State University, 2022, Washkewicz College of Engineering

Water main geothermal systems have the potential to bring geothermal heat pump systems to a larger scale and drastically reduce carbon emissions. Current research supports this by showing that the quality of water produced by these systems remains unchanged (Smith and Liu 2018). There have been studies that show some form of economic feasibility without an in-depth design, evaluation, and economic analysis (Ambort and Farrell 2020). This research will provide that analysis and help determine any next steps to achieve the feasibility of the design and implementation of these systems on a larger scale and the impact these systems will have on reducing carbon emissions. The main objective of this research is to design, evaluate, and provide an economic analysis of a water main geothermal system in a residential space using TRNSYS 18 with the TESS component library package. Provide concrete data that supports the economic feasibility of owning and operating this type of geothermal system. The water main geothermal system was designed using TRNSYS 18 with the TESS component library package. A detailed guide, explaining the procedure for using TRNSYS 18 with the TESS component library package is given. The guide will allow researchers to understand the overall system design including results. This research work will determine the economic feasibility of implementing a water main geothermal HVAC system in a residential space using TRNSYS 18 to simulate the performance.

Committee: Yong Tao Dr. (Advisor); Wei Zhang Dr. (Committee Member); Navid Goudarzi Dr. (Committee Member); Ungtae Kim Dr. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

The automotive industry wants to advance integrated computational materials engineering (ICME) approaches that combine models of joining processes and microstructural evolution for prediction of material property gradients and ultimately the mechanical performance of multi-sheet lap joints. Despite the increasing demand for computational optimization within vehicle structures and the increased use of low-density materials, modern integrated modeling frameworks of automotive lap joining are often limited to the resistance spot welding (RSW) of conventional steels. Moreover, important phenomena in steel weldments, like decomposition of austenite on-cooling, tempering of martensite, and microstructure-dependent flow stress and damage properties are too material-specific for universal application. In this research, generalized metallurgical and mechanical modeling strategies are investigated for increased applicability to a wider range of steels and joining processes. The study evaluates: the reliability of heat transfer predictions within state-of-the-art numerical models of RSW, the accuracy of existing austenite decomposition models, the readiness of steel time-temperature-transformation (TTT) diagram tools containing CALPHAD-calculated parameters, the generality of a recently developed martensite tempering model, and the determination of RSW fusion and heat-affected zone flow stress and fracture behavior. Results show that state-of-the art finite element models of RSW that are validated using experimental weld nugget dimensions have a propensity to underpredict cooling rates. A JMAK and additivity rule approach calibrated with experimental TTT diagram data exhibited the greatest accuracy when predicting AHSS austenite decomposition; however, calibrations using calculated TTT diagrams better facilitated material optimization. Generalized parameters within a JMAK-type model of martensite tempering successfully predicted HAZ softening within martensitic and dual-phase (open full item for complete abstract)

Committee: Antonio Ramirez (Advisor); Avraham Benatar (Committee Member); Boian Alexandrov (Committee Member) Subjects: Materials Science

Master of Sciences (Engineering), Case Western Reserve University, 2019, EMC - Mechanical Engineering

Shape memory smart materials that are self-fixing and auto-adaptive upon the application of a stimuli could play a key role in the manufacturing of next-generation intelligent technologies. In particular, the development of shape memory polymer composites that exhibit variable thermal conductivity upon straining requires an in-depth understanding of the material, mechanical, and thermal properties of the respective polymer and filler materials as well as the composite itself. For this work, a multi-block thermoplastic polyurethane co-polymer is used as the shape memory matrix with cellulose nanocrystals (CNCs) and carbon nanofibers (CNF) as fillers. The shape memory polymer composite is thermally characterized and its behavior explained using knowledge of filler alignment and crystallinity that vary upon straining.

Committee: Alexis Abramson (Committee Chair); Yasuhiro Kamotani (Committee Member); Chirag Kharangate (Committee Member); Steve Hostler (Committee Member) Subjects: Aerospace Engineering; Materials Science; Mechanical Engineering; Polymers