Mechanical Engineering Commons^™

Developing Methods Of Obtaining Quality Failure Information From Complex Systems, Oladapo Olalekan Bello

Graduate Theses and Dissertations

The complexity in most engineering systems is constantly growing due to ever-increasing technological advancements. This result in a corresponding need for methods that adequately account for the reliability of such systems based on failure information from components that make up these systems.

This dissertation presents an approach to validating qualitative function failure results from model abstraction details. The impact of the level of detail available to a system designer during conceptual stages of design is considered for failure space exploration in a complex system. Specifically, the study develops an efficient approach towards detailed function and behavior modeling required for complex …

Chip-Package Interfacial Stress Analysis And Reliability Implications For Flip-Chip Power Devices, Jonathan Gh Treco

Mechanical Engineering Undergraduate Honors Theses

The solder in flip-chip assemblies experience high stress and strain because of thermal mismatch induced deformation. These deformations occur because of the differences of coefficient of thermal expansion between flip-chip assembly materials. The similarly in stress profiles between thermal induced and shear induced stress in solder joints enable the use of die shear testing as a representative technique for relating the max stress the flip-chip can withstand to cyclic thermal fatigue failures. In this work, two electronic device sample preparation types are evaluated: One set of samples are soldered together and other set of samples use epoxy as an adhesive. …

System-Layout-Dependent Thermally Induced Solder Stress & Reliability Implications, Ange C. Iradukunda

Mechanical Engineering Undergraduate Honors Theses

Electronic flip chip assemblies consist of dissimilar component materials, which exhibit different CTE. Under thermal cyclic operating conditions, this CTE mismatch produces interfacial and interconnect stresses, which are highly dependent on system layout. In this paper, sensitivity analyses are performed using ANSYS FEA to establish how the proximity and arrangement of neighboring devices affect interconnect stress. Flip chip alignment modes ranging from edge-to-edge to corner-to-corner are studied. Results of these FEA studies, demonstrated that closely packing devices together has the effect of making them act as one. This results in a significant increase in the thermomechanical stresses induced on peripheral …

Selective Resistive Sintering: A Novel Additive Manufacturing Process, Austin Bryan Van Horn

Graduate Theses and Dissertations

Selective laser sintering (SLS) is one of the most popular 3D printing methods that uses a laser to pattern energy and selectively sinter powder particles to build 3D geometries. However, this printing method is plagued by slow printing speeds, high power consumption, difficulty to scale, and high overhead expense. In this research, a new 3D printing method is proposed to overcome these limitations of SLS. Instead of using a laser to pattern energy, this new method, termed selective resistive sintering (SRS), uses an array of microheaters to pattern heat for selectively sintering materials. Using microheaters offers significant power savings, significantly …

4d Printing Dielectric Elastomer Actuator Based Soft Robots, Jiyu Cai

Graduate Theses and Dissertations

4D printing is an emerging technology that prints 3D structural smart materials that can respond to external stimuli and change shape over time. 4D printing represents a major manufacturing paradigm shift from single-function static structures to dynamic structures with highly integrated functionalities. Direct printing of dynamic structures can provide great benefits (e.g., design freedom, low material cost) to a wide variety of applications, such as sensors and actuators, and robotics. Soft robotics is a new direction of robotics in which hard and rigid components are replaced by soft and flexible materials to mimic mechanisms that works in living creatures, which …

Optical Analysis And Fabrication Of Micro And Nanoscale Plasmonically Enhanced Devices, Avery M. Hill

Physics Undergraduate Honors Theses

Plasmonic nanostructures have been shown to act as optical antennas that enhance optical devices due to their ability to focus light below the diffraction limit of light and enhance the intensity of the incident light. This study focuses on computational electromagnetic (CEM) analysis of two devices: 1) GaAs photodetectors with Au interdigital electrodes and 2) Au thin-film microstructures. Experiments showed that the photoresponse of the interdigital photodetectors depend greatly on the electrode gap and the polarization of the incident light. Smaller electrode gap and transverse polarization give rise to a larger photoresponse. It was also shown that the response from …

Cfd Model For Ventilation In Broiler Holding Sheds, Christian Heymsfield

Biological and Agricultural Engineering Undergraduate Honors Theses

Broiler production in Arkansas was valued at over $3.6 billion in 2013 (University of Arkansas Extension of Agriculture). Consequently, improvement in any phase of the production process can have significant economic impact and animal welfare implications. From the time poultry leave the farm and until they are slaughtered, they can be exposed to harsh environmental conditions, both in winter and in summer. After road transportation, birds are left to wait in holding sheds once they arrive at the processing plant, for periods of approximately 30 minutes to two hours. This project was interested in this holding shed waiting time during …

Optical Analysis And Fabrication Of Micro And Nanoscale Plasmonically Enhanced Devices, Avery M. Hill

Mechanical Engineering Undergraduate Honors Theses

Plasmonic nanostructures have been shown to act as optical antennas that enhance optical devices due to their ability to focus light below the diffraction limit of light and enhance the intensity of the incident light. This study focuses on computational electromagnetic (CEM) analysis of two devices: 1) GaAs photodetectors with Au interdigital electrodes and 2) Au thin-film microstructures. Experiments showed that the photoresponse of the interdigital photodetectors depend greatly on the electrode gap and the polarization of the incident light. Smaller electrode gap and transverse polarization give rise to a larger photoresponse. It was also shown that the response from …

Design, Fabrication, And Testing Of A 3d Printer Based Microfluidic System, Carlton A. Mcmullen

Graduate Theses and Dissertations

A pneumatically actuated PDMS based microfluidic devices were designed and fabricated by soft-lithography. Two types of molds were fabricated out of different material for this experiment. The first mold, (device 1), was fabricated from a sheet of Polymethyl methacrylate (PMMA) material, similar to Plexiglas. The device features were micro-engraved onto the face of the material. The second mold, (device 2), was fabricated from the use of fused deposition modeling (FDM) 3D printing. The pumping efficiency of the PDMS devices was analyzed through the characterization of the micro-pumps flowrate with respect to the pumps driving pressure and the actuation frequency. Tested …

Three Dimensional Simulations Of Tornado Sheltering Effect Of Man-Made Structures, Piotr Gorecki

Graduate Theses and Dissertations

A three dimensional computational fluid dynamics (CFD) model was utilized to investigate tornado-like vortex interactions with wide man-made structures. The tornado-like wind profile was approximated using Rankine vortex model. By utilizing the CFD model, it was explained why tornadoes exhibit less damage on leeward side of large structures. During the preliminary stage of this study, a perpendicular vortex-prism interaction was analyzed. The prism height and the length were equal to the vortex core radius. The prism was also 12 times wider than the vortex core radius. During the vortex-prism interaction, the near-ground portion of the vortex was blocked by the …

Computer Modeling Of The Influence Of Structure Plan Areas On Tornado Forces, Nashmi Hassan M Alrasheedi

Graduate Theses and Dissertations

The study of the conventional Straight Line (SL) wind flow dominates research into wind loads on structures. Most structure design takes into account only research into SL flow. Few researchers have studied tornado forces on buildings and attempted to distinguish between tornadic wind loads and SL flow loads. Using a computer simulation, this research addresses and distinguishes between the tornadic forces and SL forces on structures. In the numerical simulation, tornado forces and SL forces will be compared on large structure plan areas and on thin structure plan areas. Additionally this research investigates how the increase in the vortex strength …

Design Of Orbital Maneuvers With Aeroassisted Cubesatellites, Stephanie Clark

Graduate Theses and Dissertations

Recent advances within the field of cube satellite technology has allowed for the possible development of a maneuver that utilizes a satellite's Low Earth Orbit (LEO) and increased atmospheric density to effectively use lift and drag to implement a noncoplanar orbital maneuver. Noncoplanar maneuvers typically require large quantities of propellant due to the large delta-v that is required. However, similar maneuvers using perturbing forces require little or no propellant to create the delta-v required. This research reported here studied on the effects of lift on orbital changes, those of noncoplanar types in particular, for small satellites without orbital maneuvering thrusters. …

Atomic Force Microscope Imaging Of Dna And Multi Walled Carbon Nanotubes, Jacob Hohnbaum

Mechanical Engineering Undergraduate Honors Theses

The Micro and Nano System Laboratory at the University of Arkansas currently is equipped with an Atomic Force Microscope (AFM). This device can be used to measure objects with resolution on the nanometer scale, but there are a number of technical difficulties in performing scans of carbon nanotubes and DNA. The goal of this research is to successfully perform scans on both carbon nanotubes and DNA and to also establish laboratory processing protocols to re-perform such scans in the future. Previous works performed by other researchers in the laboratory provided basic protocols with which to begin the present research. These …