Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Explorations of Carbon-Nanotube-Graphene-Oxide Inks: Printability, Radio-Frequency and Sensor Applications, and Reliability(2022) Zhao, Beihan; Das, Siddhartha SD; Dasgupta, Abhijit AD; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon-Nanotube (CNT) is a novel functional material with outstanding electrical and mechanical properties, with excellent potential for various kinds of industrial applications. Additive manufacturing or 3D printing of CNT-based materials or inks has been studied extensively, and it is vital to have a thorough understanding of the fluid mechanics and colloidal science of CNT-based inks for ensuring optimum printability and the desired functionality of such CNT-based materials.In this dissertation, a custom-developed syringe-printable CNT-GO ink (GO: Graphene Oxide) is introduced and the fluid mechanics and colloidal science of this ink as well as the different devices (e.g., temperature sensor, humidity sensor, and RF antenna) fabricated with this ink are studied. The following topics are discussed in this dissertation: (1) the application and printability (in terms of the appropriate fluid mechanics and colloidal science) of CNT-based inks; (2) development of temperature sensors with CNT-GO inks; (3) development of humidity sensors with CNT-GO inks; (4) development of RF patch antenna with CNT-GO inks; and (5) evaporation-driven size-dependent nano-microparticulate three-dimensional deposits (CNTs serve as one type of nanoparticle examined in this part of the study). In Chapter 1 of this dissertation, a literature review is conducted on the application of CNT-based inks and the fluid mechanics and colloidal science issues dictating the printability and performance of such CNT-based inks. The problem statement and overall research plan are also introduced in this chapter. In Chapter 2, the development of our custom CNT-GO ink is introduced. Detailed material selection and the mechanism of shape-dependent arrest of coffee-stain effect, which ensured that the printable ink led to uniform deposition, are discussed in this chapter. Temperature sensor prototypes printed with the CNT-GO inks are also presented in Chapter 2. From Chapter 3 to Chapter 5, the performances of our CNT-GO based flexible temperature sensor, humidity sensor, and patch antenna prototypes are discussed. The ink printability on flexible thin PET films is studied, and a straightforward ‘peel-and-stick’ approach to use the CNT-trace (or patch)-bearing PET films on surfaces of widely varying wettabilities and curvatures as different prototypes is introduced. Excellent temperature and humidity sensitivity of our CNT-GO based sensors are presented in Chapter 3 and Chapter 4, and the potential of this CNT-GO material for fabrication of ultra-wideband (UWB) patch antennas is discussed in Chapter 5. Furthermore, the stability and reliability of these printed CNT-GO-based prototypes are also explored. In previous Chapters, the printed CNT-GO patterns were cured by evaporation-mediated deposition on flat substrates (i.e., 2D deposition spanning in x and y directions). This motivated the extension of the physics to the 3rd dimension and probing of particle deposition on a 3D substrate and particle deposition in all x, y, and z directions. Therefore, in Chapter 6, we perform an experiment to demonstrate this kind of possibility using three kinds of micro-nanoparticle-laden water-based droplets (i.e. coffee particles, silver nanoparticles, and CNTs). These droplets were first deposited at the bottom of an un-cured PDMS film; these droplets were lighter than the PDMS and hence, they rose to the top of the PDMS where they could have either attained a Neuman like state or simply remained as an undeformed spherical drop with the top of the drop breaching the air-liquid-PDMS interface. The calculations based on air-water, water-PDMS, and air-PDMS surface tension values confirmed that the Neuman like state was not possible, and the droplets were likely to retain their undeformed shapes as they breached the air-PDMS interface. The timescale differences between the fast PDMS curing and the slower droplet evaporation, led to the formation of spherical shape cavities inside the PDMS after completion of the curing, and allowed evaporation-driven deposition to occur in all x, y, and z directions inside the cavity, with the exact nature of the deposition being dictated by the sizes of the particles (as confirmed by the experiments conducted with coffee particles, silver nanoparticles, and CNTs). Finally, in Chapter 7, the major contributions of this dissertation and proposed future studies related to this dissertation work are listed.Item Assessment of FIDES Reliability Prediction Methodology(2021) Gaonkar, Aishwarya Prashant; Das, Diganta; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The FIDES Guide is a reliability prediction handbook published by a group of European defense and aerospace manufacturers under the supervision of the French Ministry of Defense. This paper evaluates the suitability of FIDES for predicting reliability based on the model used to calculate the failure rate, and the accuracy of its reliability predictions. The evaluation makes use of IEEE Standard 1413, titled, “IEEE Standard Framework for Reliability Prediction of Hardware.” The paper shows that FIDES is based on the erroneous assumption of a constant failure rate for electronics, and lacks key attributes (e.g., materials and geometry of components) required to make a prediction accurate or to be considered physics-of-failure based. FIDES predictions are not reproducible due to subjective factors, selection of which varies depending on who is making the prediction.Item EFFECTS OF GLASS/EPOXY INTERPHASES ON ELECTRO-CHEMICAL FAILURES IN PRINTED CIRCUIT BOARDS(2018) Sood, Bhanu Pratap; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Reduction in printed circuit board line spacing and via diameters and the increased density of vias with higher aspect ratios (ratio between the thickness of the board and the size of the drilled hole before plating) are making electronic products increasingly more susceptible to material and manufacturing defects. One failure mechanism of particular concern is conductive anodic filament formation, which typically occurs in two steps: degradation of the resin/glass fiber bond followed by an electrochemical reaction. The glass-resin bond degradation provides a path along which electrodeposition occurs due to electrochemical reactions. Once a path is formed, an aqueous layer, which enables the electrochemical reactions to take place, can develop through the adsorption, absorption, and capillary action of moisture at the resin/fiber interphase. This study describes the experimental and analytical work undertaken to understand the glass-resin delamination and the methods used for analyzing this critical interphase. This study shows that a smaller conductor spacing in reduces the time to failure due to conductive anodic filament formation and that the plated-through-hole to plated-through-hole conductor geometry is more susceptible to conductive anodic filament-induced failures than plated through hole to plane geometries. The results also show that laminates with similar materials and geometries with a 45-degree angle of weave demonstrate a higher resistance to conductive anodic filament formation compared with a 90-degree angle of weave. The study is the first of its kind conducted on FR-4 printed circuit board materials where the pathway formation due to breakage of the organosilane bonds at the glass/resin interphase was evaluated. Using techniques such as force spectroscopy, micro-Fourier transform infrared spectroscopy, scanning quantum interface device microscopy and focused ion beam, evidence of bond breakage and a pathway formation was revealed, poor glass treatment, hydrolysis of the silane glass finish (adsorption of water at the glass fiber/epoxy resin interphase) or repeated thermal cycling contribute to the bond breakage. The technique of applying in-situ resistance measurements during cross-sectioning analysis of printed circuit boards suspected of conductive anodic filament is the first time this method is described in the open literature. This solution addresses the potential problem in destructive physical analysis of grinding away the evidence of the CAF filament and ultimately loosing evidence at the failure site. By applying a subset of the evaluation criteria described in this research, an upfront evaluation of printed circuit board materials can be performed for susceptibility to electro-chemical migration and other failure causes in PCBs that are attributable to the glass/resin interfacial adhesion. Manufacturers can identify board suppliers based on answers to and validation of a series of questions. These questions focus on the necessary requirements of reliable board material manufacturing and are independent of the specifications of the product.Item SUBSCORE REPORTING FOR DOUBLE-CODED INNOVATIVE ITEMS EMBEDDED IN MULTIPLE CONTEXTS(2018) Li, Chen; Jiao, Hong; Measurement, Statistics and Evaluation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Reporting subscores is a prevalent practice in standardized tests to provide diagnostic information for learning and instruction. Previous research has developed various methods for reporting subscores (e.g. de la Torre & Patz, 2005; Wainer et al., 2001; Wang, Chen, & Cheng, 2004; Yao & Boughton, 2007; Yen, 1987). However, the existing methods are not suitable for reporting subscores for a test with innovative item types, such as double-coded items and paired stimuli. This study proposes a two-parameter doubly testlet model with internal restrictions on the item difficulties (2PL-DT-MIRID) to report subscores for a test with double-coded items embedded in paired-testlets. The proposed model is based on a doubly-testlet model proposed by Jiao and Lissitz (2014) and the MIRID (Butter, De Boeck, & Verhelst, 1998). The proposed model has four major advantages in reporting subscores— (a) it reports subscores for a test with double-coded items in complex scenario structures, (b) it reports subscores designed for content clustering, which is more common than subscores based on construct dimensionality in standardized tests, (c) it is computationally less challenging than the Multidimensional Item Response Theory (MIRT) models when estimating subscores, (d) it can be used to conduct Item Response Theory (IRT) based number-correct scoring (NCS, Yen, 1984a). A simulation study is conducted to evaluate the model parameter recovery, subscore estimation and subscore reliability. The simulation study manipulates three factors: (a) the magnitude of testlet effect variation, (b) the correlation between testlet effects for the dual testlets and (c) the percentage of double-coded items in the test. Further, the study compares the proposed model with other underspecified models in terms of model parameter estimation and model fit. The result of the simulation study has shown that the proposed 2PL-DT-MIRID yields more accurate model parameter and subscore estimates, in general, when the testlet effect variation is small, the dual testlets are weakly correlated and there are more double-coded items in a test. Across the study conditions, the proposed model outperforms other competing models in model parameter estimation. The reliability yielded from models ignoring dual testlets are spuriously inflated, the 2PL-DTMIRID produces higher overall score reliability and subscore reliability than models ignoring double-coded items, in most study conditions. In terms of model fit, none of the model fit indices investigated in this study (i.e. AIC, BIC and DIC) can achieve satisfactory rates of identifying the proposed true model as the best fitting model.Item Stress Response of Tall and Heavy Electronic Components Subjected to Multi-axial Vibration(2017) Sridharan, Raman; Dasgupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electronic assemblies often experience multiaxial vibration environments in use and tall, heavy components are more vulnerable when exposed to multiaxial vibration than are shorter, lighter assemblies. The added vulnerability comes from higher stresses that are a result of nonlinear dynamic amplification which large components are susceptible to under simultaneous multiaxial excitation, termed multi degree of freedom (MDoF) excitation. However, it is still common practice to conduct vibration durability testing on electronic assemblies one axis at a time – in what is termed sequential single degree of freedom (SSDoF) testing. SSDoF testing has been shown to produce lower fatigue damage accumulation rates than simultaneous MDoF testing, in the leads of tall and heavy electronic components. This leads to overestimating the expected lifespan of the assembly. This paper investigates the geometric nonlinearities and the resulting cross-axis interactions that tall and heavy electronic components experience when subjected to vibration excitation along two orthogonal axes – one direction is in the plane of the PWB and the other is along the normal to the PWB. The direction normal to the PWB aligns with the axial direction of the leads, while the in-plane direction aligns with the primary bending direction of the leads. Harmonic excitation was simultaneously applied to both axes to study the vibration response as a function of frequency ratio and phase “difference” along the two axes. The experimental observations were verified with a nonlinear dynamic Finite Element study. The effect of geometric nonlinearity on cyclic stresses seen in the vibrating component are analyzed.Item EFFECTS OF EXTERNAL PRESSURE ON SOLID STATE DIFFUSION OF LITHIUM IN LITHIUM-ION BATTERIES(2016) Williard, Nicholas Dane; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electrochemical-mechanical effects in lithium-ion batteries refer to the phenomena that give way to the piezo-electrochemical properties observed during intercalation of lithium into lithium-ion battery electrodes. By applying perturbations to the external pressure of a lithium-ion battery, the dynamics of lithium intercalation, in particular the diffusion rate of lithium-ions onto and out of battery electrodes, can be studied with respect to the open-circuit potential and the applied hydrostatic pressure. In this study, commercial thin film batteries were subjected to tests in a low-pressure chamber and in a dynamic materials analyzer simulating hydrostatic pressures between 0 and 115 KPa. Under each hydrostatic pressure condition, galvanostatic intermittent titration technique (GITT) was performed to measure and correlate lithium diffusivity to battery strain, open-circuit potential, and applied hydrostatic force. From the data a model was developed for lithium diffusivity as a function of open circuit potential and hydrostatic pressure. The implications of this work extend from the use of lithiated graphite for energy harvesting and actuation to policy and regulations for how batteries should be safely transported. To provide some insight into how this work can be applied to policy actions, current international regulations regarding the air transport of lithium-ion batteries are critically reviewed. The pre-shipping tests are outlined and evaluated to assess their ability to fully mitigate risks during battery transport. In particular, the guidelines for shipping second-use batteries are considered. Because the electrochemical state of previously used batteries is inherently different from that of new batteries, additional considerations must be made to evaluate these types of cells. Additional tests are suggested that evaluate the risks of second-use batteries, which may or may not contain incipient faults. Finally, this work is extended to supercapacitors through the development of a model to predict the oxidation of functional groups on the surface of graphite electrodes with respect to operational temperature and voltage. This model is used to predict the operational life of supercapacitors and validates the model on accelerated testing data. The final results are compared to previous models proposed in literature.Item Synergistic Configurable Ring Oscillator PUF: Design, Characterization, and Implementation(2014) Lai, Khai Vinh; Qu, Gang; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Silicon Physical Unclonable Function (PUF) is a novel hardware primitive that uses the intrinsic variation of integrated circuit manufacturing process for various security applications. Ring oscillator PUF (RO PUF) is one of the most popular silicon PUFs due to its ease of implementation on both ASIC and FPGA. However, RO PUF can have severe reliability issues when the operating environment deviates from the normal environment and security issues when it lacks an efficient anti-cloning mechanism. In this work, we propose a novel approach to build reliable RO PUF efficiently and enhance its resistance against physical cloning attack. The key idea of our approach is to construct ring oscillators with carefully selected inverters during the testing phase after the chip is fabricated. Our experimental results show that our configurable approach outperforms the traditional RO PUF and 1-out-of-8 PUF by generating more reliable bits that pass the NIST randomness tests. Our approach is also more hardware efficient than these RO PUFs. We also demonstrate that the configuration vectors can prevent physical cloning and have the potential usage in chip-dependent applications such as device authentication.Item Observing and Improving the Reliability of Internet Last-mile Links(2013) Schulman, Aaron David; Spring, Neil; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)People rely on having persistent Internet connectivity from their homes and mobile devices. However, unlike links in the core of the Internet, the links that connect people's homes and mobile devices, known as "last-mile" links, are not redundant. As a result, the reliability of any given link is of paramount concern: when last-mile links fail, people can be completely disconnected from the Internet. In addition to lacking redundancy, Internet last-mile links are vulnerable to failure. Such links can fail because the cables and equipment that make up last-mile links are exposed to the elements; for example, weather can cause tree limbs to fall on overhead cables, and flooding can destroy underground equipment. They can also fail, eventually, because cellular last-mile links can drain a smartphone's battery if an application tries to communicate when signal strength is weak. In this dissertation, I defend the following thesis: By building on existing infrastructure, it is possible to (1) observe the reliability of Internet last-mile links across different weather conditions and link types; (2) improve the energy efficiency of cellular Internet last-mile links; and (3) provide an incrementally deployable, energy-efficient Internet last-mile downlink that is highly resilient to weather-related failures. I defend this thesis by designing, implementing, and evaluating systems.Item Prognostics of Ball Bearings in Cooling Fans(2012) Oh, Hyunseok; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ball bearings have been used to support rotating shafts in machines such as wind turbines, aircraft engines, and desktop computer fans. There has been extensive research in the areas of condition monitoring, diagnostics, and prognostics of ball bearings. As the identification of ball bearing defects by inspection interrupts the operation of rotating machines and can be costly, the assessment of the health of ball bearings relies on the use of condition monitoring techniques. Fault detection and life prediction methods have been developed to improve condition-based maintenance and product qualification. However, intermittent and catastrophic system failures due to bearing problems still occur resulting in loss of life and increase of maintenance and warranty costs. Inaccurate life prediction of ball bearings is of concern to industry. This research focuses on prognostics of ball bearings based on vibration and acoustic emission analysis to provide early warning of failure and predict life in advance. The failure mechanisms of ball bearings in cooling fans are identified and failure precursors associated with the defects are determined. A prognostic method based on Bayesian Monte Carlo method and sequential probability ratio test is developed to predict time-to-failure of ball bearings in advance. A benchmark study is presented to demonstrate the application of the developed prognostic method to desktop computer fans. The prognostic method developed in this research can be extended as a general method to predict life of a component or system.Item A PROBABILISTIC MECHANISTIC APPROACH FOR ASSESSING THE RUPTURE FREQUENCY OF SMALL MODULAR REACTOR STEAM GENERATOR TUBES USING UNCERTAIN INPUTS FROM IN-SERVICE INSPECTIONS(2011) Chatterjee, Kaushik; Modarres, Mohammad; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)One of the significant safety issues in nuclear power plants is the rupture of steam generator tubes leading to the loss of radioactive primary coolant inventory and establishment of a path that would bypass the plant's containment structure. Frequency of steam generator tube ruptures is required in probabilistic safety assessments of pressurized water reactors to determine the risks of radionuclide release. The estimation of this frequency has traditionally been based on non-homogeneous historical data that are not applicable to small modular reactors consisting of new steam generator designs. In this research a probabilistic mechanistic-based approach has been developed for assessing the frequency of steam generator tube ruptures. Physics-of-failure concept has been used to formulate mechanistic degradation models considering the underlying degradation conditions prevailing in steam generators. Uncertainties associated with unknown or partially known factors such as material properties, manufacturing methods, and model uncertainties have been characterized, and considered in the assessment of rupture frequency. An application of the tube rupture frequency assessment approach has been demonstrated for tubes of a typical helically-coiled steam generator proposed in most of the new small modular reactors. The tube rupture frequency estimated through the proposed approach is plant-specific and more representative for use in risk-informed safety assessment of small modular reactors. Information regarding the health condition of steam generator tubes from in-service inspections may be used to update the pre-service estimates of tube rupture frequency. In-service inspection data are uncertain in nature due to detection uncertainties and measurement errors associated with nondestructive evaluation methods, which if not properly accounted for, can result in over- or under-estimation of tube rupture frequency. A Bayesian probabilistic approach has been developed in this research that combines prior knowledge on defects with uncertain in-service inspection data, considering all the associated uncertainties to give a probabilistic description of the real defect size and density in the tubes. An application of the proposed Bayesian approach has been provided. Defect size and density estimated through the proposed Bayesian approach can be used to update the pre-service estimates of tube rupture frequency, in order to support risk-informed maintenance and regulatory decision-making.
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