Title of dissertation: ANALYSIS OF THE LIFE-CYCLE COST AND CAPABILITY TRADEOFFS ASSOCIATED WITH THE PROCUREMENT AND SUSTAINMENT OF OPEN SYSTEMS
Date/time: March 19th at 9:00 AM
Location: 2164 DeWALT Conference Room, Glenn L. Martin Hall.
Zoom link: https://umd.zoom.us/j/6254630014?omn=99524160244
Committee members:
Professor Peter A. Sandborn, Chair
Professor Bilal M. Ayyub, Dean’s Representative
Professor Katrina Groth
Professor Jeffrey Herrmann
Professor William Lucyshyn
Author: Samuel Gigioli
Date: November 13th, 2023 at 10:00AM
Location: IREAP 1207
Committee Members:
Dr. Ashwani Gupta, Chair
Dr. Bao Yang
Dr. Kenneth
Title: DISSECTION AND MODELING OF AEDC WIND TUNNEL 9 CONTROL LAW AND FACILITY DURING BLOW PHASE
Abstract:
This work presents the progress towards a mathematical modeling of the Arnold
Engineering Development Complex (AEDC) Wind Tunnel 9 control law during the blow
phase of a given tunnel run, composing of electrical analog physics, ideal gas control
volume physics, incompressible fluid mechanics, and force balance kinematics. Tunnel 9
does not currently have a well-defined process for developing control law parameters for a
new tunnel condition. The modeled control law is developed based on electrical schematics
and theoretical analog circuitry. The model is further refined by analyzing historical data
through a two-factor interaction analysis of several run-condition factors. The primary goal
of this work is to provide enhanced support to the Tunnel 9 engineers with the ability to
model different run conditions. Key facility measurements can be estimated, aiding in the
determination if proposed non-standard run conditions will meet or maintain the facility
capabilities, and if the facility can be operated under safe operating limits. The secondary
goal of this model is to progress toward a digitally controlled valve system to replace the
current analog system. Such changes may enable considerably more advantages in facility
(1) performance, (2) health monitoring, (3) maintainability, and (4) sustainment.
Author: Gabriel Smith
Date: October 26, 2023 at 2pm EST
Location: EGR-2164, Martin Hall
Committee Members:
Title: DIRECT LASER WRITE PROCESSES FOR SPIDER-INSPIRED MICROHYDRAULICS AND MULTI-SCALE LIQUID METAL DEVICES
Abstract:
Direct Laser Write (DLW) through two-photon polymerization (2PP) empowers us to delve into the realm of genuine three-dimensional design complexity for microsystems, enabling features smaller than a single micrometer. This dissertation develops two novel fabrication processes that leverage DLW for functional fluidic microsystems. In the first process, we are inspired by arachnids that use internal hemolymph pressure to actuate extension in one or more of their leg joints. The inherent large foot displacement to body length ratio that arachnids can achieve through hydraulics relative to muscle-based actuators is both energy and volumetrically efficient. Until recent advances in nano/microscale 3-D printing with 2PP, the physical realization of synthetic complex ‘soft’ joints would have been impossible to replicate and fill with hydraulic fluid into a sealed sub-millimeter system. This dissertation demonstrates the smallest scale 3D-printed hydraulic actuator 4.9 × 10−4 mm^3 by more than an order of magnitude. The use of stiff 2PP polymers with micron-scale dimensions enables compliant membranes similar to exoskeletons seen in nature without the requirement for low-modulus materials. The bio-inspired system is designed to mimic similar hydraulic pressure-activated mechanisms in arachnid joints utilized for large displacement motions relative to body length. Using variations on this actuator design, we demonstrate the ability to transmit forces with relatively large magnitudes (milliNewtons) in 3D space, as well as the ability to direct motion that is useful towards microrobotics and medical applications. Microscale hydraulic actuation provides a promising approach to the transmission of large forces and 3D motions at small scales, previously unattainable in wafer-level 2D micro-electromechanical systems (MEMS).
The second fabrication process focuses on incorporating functionality through the use of liquid metals in 3D DLW structures. Room temperature eutectic Gallium Indium (eGaIn)-based liquid metal devices with stretchable, conductive, and reconfigurable behavior show great promise across many areas of technology, including robotics, communications, and medicine. Microfluidics provide one means of creating eGaIn devices and circuits, but these devices are typically limited to larger feature sizes. Developments in 3D printing via DLW have enabled sub-100 µm complex microfluidic devices, though interfacing microfluidic devices manufactured with DLW to larger millimeter-scale systems is difficult. The reduced channel diameter creates challenges for removing resist from the channels, filling microchannels with eGaIn, and electrically integrating them to larger channels or other circuitry. These challenges have prevented microscale liquid metal devices from being used more widely. In this dissertation, we demonstrate a facile, low-cost multiscale process for printing DLW microchannels and devices onto centimeter-scale custom fluidic channel substrates fabricated via stereolithography (SLA). This work demonstrates a robust interface between the two independently printed materials and greatly simplifies the filling of eGaIn microfluidic channels down to 50 µm in diameter, with the potential to achieve even smaller feature sizes of liquid metals. This work also demonstrates eGaIn coils with resistance of 43-770 mΩ and inductance of 2-4 nH. As a result, this process empowers us to manufacture interfaces that are not only low-temperature but also conductive and flexible. These interfaces find their application in connecting with sensors, actuators, and integrated circuits, thereby opening new avenues in the field of 3D electronics. Furthermore, our approach extends the lower limits of size-dependent properties for passive electronic components like resistors, capacitors, and inductors crafted from liquid metal, expanding the frontiers of possibilities in miniature electronic design.
Author: Upamanyu Ray
Date: October 4, 2023 at 1pm EST
Location: EGR-1131b, Martin Hall
Committee Members:
Title: Mechanics and thermal transport modeling in nanocellulose and cellulose-based materials
Abstract:
Cellulose, the abundantly available natural biopolymer, has the potential to be a next generation wonder material. The motivation behind this thesis stems from the efforts to obtain mechanical properties of two novel cellulose-based materials, which were fabricated using top-down (densified engineered wood) and bottoms-up (graphite-cellulose composite) approaches. It was observed that the mechanical properties of both the engineered wood (strength~596 MPa; toughness ~3.9 MJ/m3) and cellulose-graphite composite (strength~715 MPa; toughness ~27.7 MJ/m3) surpassed the equivalent features of other conventional structural materials (e.g., stainless steel, Al alloys etc.). However, these appealing properties are still considerably inferior to individual cellulose fibrils whose diameters are in the order of nanometers. A significant research effort needs to be initiated to effectively transfer the mechanical properties of the hierarchical cellulose fibers from the atomistic level to the continuum. To achieve that, a detailed understanding of the interplay of cellulose molecular chains that affects the properties of the bulk cellulosic material, is needed. Modeling investigations can shed light on such underlying mechanisms that ultimately dictate multiple properties (e.g., mechanics, thermal transport) of these cellulosic materials.
To that end, this thesis (1) applies molecular dynamics simulations to decipher why microfibers made of aligned nanocellulose and carbon nanotubes possess excellent mechanical strength, along with understanding the role of water in fully recovering elastic wood under compression; (2) delineates an atomistically informed multi-scale, scalable, coarse grained (CG) modeling scheme to study the effect of cellulose fibers under different representative loads (shearing and opening), and to demonstrate a qualitative guideline for cellulose nanopaper design by understanding its failure mechanism; (3) utilizes the developed multi-scale CG scheme to illustrate the reason why a hybrid biodegradable straw, experimentally fabricated using both nano- and micro-fibers, exhibits higher mechanical strength than individual straws that were built using only nano or microfibers; (4) investigates the individual role of nanocellulose and boron nitride nanotubes in increasing the mechanical properties (tensile strength, stiffness) of the derived nanocellulose/boron-nitride nanotube hybrid material; (5) employs reverse molecular dynamics approach to explore how the boron nitride nanotube based fillers can improve thermal conductivity (k) of a nanocellulose derived material.
In addition, this thesis also intends to educate the readers on two perspectives. The common link connecting them is the method of engineering intermolecular bonds. The first discussion presents a few novel mechanical design strategies to fabricate high-performance, cellulose-based functional materials. All these strategies are categorized under a few broad themes (interface engineering, topology engineering, structural engineering etc.). Secondly, another discussion has been included by branching out to other materials that, like nanocellulose, can also be tuned by intermolecular bonds engineering to achieve unique applications. Avenues for future work have been suggested which, hopefully, can act as a knowledge base for future researchers and help them formulate their own research ideas. This thesis extends the fundamental knowledge of nanocellulose-based polymer sciences and aims to facilitate the design of sustainable and programmable nanomaterials.
Author: Mohammed Ibaad Shareef Gandikota
Date: September 20th, 2023 at 12:00pm
Zoom Link: https://umd.zoom.us/j/9221913124
Location: AVW 1146 (ISR)
Committee Members:
Title:
Development and In-situ Characterization of Bi-layered Laminated Composites for Enhanced Moisture Barrier Performance
Abstract:
Silicone encapsulations are widely used in high-temperature electronic applications, providing excellent properties like thermal stability, high purity, and chemical resistance. However, silicone is susceptible to moisture-induced failures due to high moisture permeability. This study mainly focuses on improving the moisture ingression characteristics of the silicone encapsulation by adding a polyurethane moisture barrier layer. This study focuses on the effects of moisture ingression by adding polyurethane and testing with embedded relative humidity sensors at different environmental conditions. The diffusivity of both the bi-layered composites and the pure encapsulation materials was assessed using two distinct experimental methods for the calculation of diffusivity based on the principles of 1-dimensional Fick’s law of diffusion. The diffusivities were statistically analyzed to determine significant differences between the samples, and the experiment yielded a minimum of 65% reduction in diffusivity across the samples. Furthermore, a thermomechanical analysis was performed on two different GaN power MOSFETs by the application of different underfill and potting encapsulations to determine stresses and strains on the solder bumps.
Author: Gilad Nave
Date: September 13th, 2023 at 1:00pm
Zoom Link: https://umd.zoom.us/j/5095422567
Location: EGR-2164, Martin Hall
Committee Members:
Dr. Francis Patrick McCluskey, Chair
Dr. Mohammad Al-Sheikhly, Dean’s Representative
Dr. Hugh Bruck
Dr. Diganta Das
Dr. Abhijit Dasgupta
Dr. Peter Sandborn
Title: Electrical and Structural Formation of Transient Liquid Phase Sinter (TLPS) Materials During Early Processing Stage
Abstract:
The growing demands of electrification are driving research into new electronic materials. These electronic materials must have high electrical conductivity, withstand harsh environments and high temperatures and demonstrate reliable solutions as part of complete electronic packaging solutions. This dissertation focuses on characterizing the initial stage of the manufacturing process of Transient Liquid Phase Sinter (TLPS) alloys in a paste form as candidates for Pb-free high-temperature and high-power electronic materials.
The main objective of this dissertation work is to investigate the factors and decouple the multiple cross effects occurring during the first stage of TLPS processing in order to improve the understanding of material evolution. The work proposes, develops, and conducts in-situ electrical resistivity tests to directly measure material properties and analyze the dynamics at different stages of the material’s evolution. The research explores various factors, including alloying elements, organic binders, and heating rates, to understand their effects on the development of electrical performance in electronic materials. More specifically, the work examines the performance of Ag-In, Ag-Sn and Cu-Sn TLPS paste systems. Additionally, packing density and changes in cross-section are investigated using imaging techniques and image processing to gain insights into the early formation of the material’s structural backbone. An Arrhenius relationship together with Linear Mixed Models (LMM) techniques are used to extract the activation energies involved with each of the processing stages. The study then develops procedures to model different states of the TLPS microstructures at different heating stages based on experimentally observed data. Using these models, the study uses Finite Element Method (FEM) analysis to verify the experimental results and gain a better understanding and visualization into the involved mechanisms. This investigation not only sheds light on the material’s behavior but also has implications for robust additive manufacturing (AM) applications.
Author: Lokesh Sangepu
Date: Friday, July 28th, 2023, at 11:00 AM
Zoom Link:https://umd.zoom.us/meeting/register/tJYocuyprjwtHNdboK5kJ-r6O3ua_2WlLi3_
Location: EGR-2164, Martin Hall
Committee Members:
Thesis Title: PART SELECTION AND MANAGEMENT BASED ON RELIABILITY ASSESSMENT FOR DIE-LEVEL FAILURE MECHANISMS
Abstract:
Electronic part manufacturers often communicate part reliability information using metrics such as mean time between failures (MTBF) or failure per billion hours (FIT). However, these metrics, which rely on constant failure rate assumptions, do not adequately account for damage accumulation or wear-out phenomena leading to limitations in making informed decisions regarding the part selection and management for specific applications. This thesis addresses these limitations by proposing a physics-of-failure approach for developing a part selection methodology based on time-to-failure estimation of electronic parts.
The thesis contributes to the field by providing a comprehensive and physics-based approach to perform part selection and management. By moving beyond constant failure rate assumptions and considering wear-out phenomena, it offers a more accurate estimation of time to failure for electronic parts. The thesis begins by providing the challenges associated with manufacturers’ avoidance of sharing critical information, highlighting the impact on product quality, reliability, safety, and customer satisfaction. It describes that the insufficient information manufacturers provide hampers decision-making processes, necessitating an alternative approach for part selection.
The thesis focuses on four die-level failure mechanisms and investigates the extent to which industry-published documents discuss these mechanisms and their applicability to failure models. By understanding the specific failure mechanisms, the thesis aims to assist in selecting an appropriate failure model concerning the part and identify the required parameters for estimating the part’s time to failure. A methodology is developed to perform part selection utilizing the estimated time to failure. An application is created using MATLAB GUI to facilitate practical implementation, enabling designers, engineers, and procurement teams to make informed decisions when selecting electronic parts for specific applications. The methodology considers the susceptibility of parts to die-level failure mechanisms and identifies components with superior reliability performance. This approach enables informed decision-making, enhances product reliability, and improves customer satisfaction. The research findings and methodology presented in this thesis provide valuable insights for users to improve the reliability and performance of electronic systems through effective part selection.
Author: Eesh Kamrah
Date: Tuesday, July 25th, 2023, at 11:00 am
Location: EGR-2164
Committee Members:
Title of Thesis: EFFECTS OF DIVERSE INITIALIZATION ON BAYESIAN OPTIMIZERS.
Abstract: Design researchers have struggled to produce quantitative predictions for exactly why and when diversity might help or hinder design search efforts.
This thesis addresses that problem by studying one ubiquitously used search strategy – Bayesian Optimization (BO) – on a 2D test problem with modifiable convexity and difficulty.
Specifically, we test how providing diverse versus non-diverse initial samples to BO affects its performance during search and introduce a fast ranked-DPP method for computing diverse sets, which we need to detect sets of highly diverse or non-diverse initial samples.
We initially found, to our surprise, that diversity did not appear to affect BO, neither helping nor hurting the optimizer’s convergence. However, follow-on experiments illuminated a key trade-off. Non-diverse initial samples hastened posterior convergence for the underlying model hyper-parameters a Model Building advantage. In contrast, diverse initial samples accelerated exploring the function itself a Space Exploration advantage. Both advantages help BO, but in different ways, and the initial sample diversity directly modulates how BO trades those advantages. Indeed, we show that fixing the BO hyper-parameters removes the Model Building advantage, causing diverse initial samples to always outperform models trained with non-diverse samples.
These findings shed light on why, at least for BO-type optimizers, the use of diversity has mixed effects and cautions against the ubiquitous use of space-filling initializations in BO.
To the extent that humans use explore-exploit search strategies similar to BO, our results provide a testable conjecture for why and when diversity may affect human-subject or design team experiments.
The thesis is organized as follows: Chapter 2 provides an overview of existing studies that explore the impact of different initial stimuli. In Chapter 3, we explain the methodology used in the subsequent experiments. Chapter 4 presents the results of our initial study on the diverse initialization of BO (Bayesian Optimization) applied to the wildcat wells function. In Chapter 5, we analyze the conditions under which less diverse initial examples perform better and expand on these findings in Chapter 6 by considering additional ND continuous functions. The final chapter discusses the limitations of our findings and proposes potential areas for future research.
Author: Harsimranjit Singh
Date/Time/Location of defense: 07/20/2023, 10:00 am to 12:00 pm, Rm. 2164 in Martin Hall
Zoom link: https://umd.zoom.us/j/4473163587?pwd=ZDN6aDhQZGlWalJncDlsSEJIc1dxUT09
Committee Members:
-Dr. Michael Ohadi, Chair
-Dr. Bao Yang
-Dr. Patrick McCluskey
-Dr. Amir Riaz
-Dr. Ratnesh Tiwari
-Dr. Christopher Cadou, Dean’s Representative
Title: THERMAL MANAGEMENT OF HIGH-HEAT FLUX ELECTRONICS WITH INTERLACED FILM EVAPORATION AND ENHANCED FLUID DELIVERY SYSTEM (iFEEDS)
Abstract:
Author: Changsu Kim
Date/Time/Location of Defense: 7/21/2023 at 12:00 pm in EGR-2162
Committee:
-Professor Bongtae Han (Chair)
-Professor Patrick McCluskey
-Professor Peter Sandborn
-Professor Michael Osterman
-Professor Sung W. Lee (Dean’s Representative)
Title: Measurements of Effective Cure Shrinkage of Epoxy Molding Compound and Induced In-line Warpage during Molding Process
Abstract: Cure shrinkage accumulated only after the gel point is known as effective cure shrinkage (ECS), which produces residual stresses inside molded components. The ECS of an epoxy-based molding compound (EMC) is measured by an embedded fiber Bragg grating (FBG) sensor. Under a typical molding condition, a high mold pressure inherently produces large friction between EMC and mold inner surfaces, which hinders EMC from contracting freely during curing. A two-stage curing process is developed to cope with the problem. In the first stage, an FBG sensor is embedded in EMC by a molding process, and the FBG-EMC assembly is separated from the mold at room temperature. The molded specimen is heated to a cure temperature rapidly in the second stage using a constraint-free curing fixture. The ECS of an EMC with a filler content of 88 wt% is measured by the proposed method, and its value is 0.077%. The measured ECS can be used to predict the warpage caused by molding processes. The validity of the prediction can be verified only by measuring the warpage during molding. A point-based measurement technique utilizing uniquely-generated multiple beams and binarization-based beam tracing method is developed to cope with the challenges associated with the warpage measurement during molding. The proposed method is implemented successfully to measure the warpage of a bimaterial disk that consists of aluminum and EMC as a function of time during molding process. Measurements are repeated to establish the measurement accuracy of the proposed method.