Digital Commons Network^™

Multi-Scale Modeling Of Selective Laser Sintering: From Manufacturing Process And Microstructure To Mechanical Performance In Semi-Crystalline Thermoplastics, Cameron Zadeh

All Dissertations

Selective laser sintering is an additive manufacturing process that opens many design possibilities but is limited in its reliability and reproducibility. Numerical simulations validated by experimental data yield insights into the process and resulting part properties, allowing users to make more informed decisions. In this dissertation, a model for the process and microstructure is developed and validated, followed by a coupling to mechanical models to predict part performance. Further developments include a new addition of a reaction kinetics model to the process model to describe the interplay between thermal degradation and melt pool properties, and an exploration of the parameter …

Investigating The Effects Of Sic Abrasive Particles On Friction Element Welding, Gaurav Awate

All Theses

The growing demands on reducing the harmful emissions from automobiles have forced automakers to reduce the weight of the vehicle. The increasing demands on improving the fuel economy also has challenged automotive manufacturers to make the vehicle as lightweight as possible. However, the challenge is also to ensure that the vehicle meets safety standards. For the vehicle to meet these standards, it needs to be of adequate strength as well. Automotive manufacturers have adopted a strategy of using multi-material construction to achieve the target. But with multi-material construction comes the requirement of advanced joining techniques that are capable of joining …

Deep Learning-Guided Prediction Of Material’S Microstructures And Applications To Advanced Manufacturing, Jianan Tang

All Dissertations

Material microstructure prediction based on processing conditions is very useful in advanced manufacturing. Trial-and-error experiments are very time-consuming to exhaust numerous combinations of processing parameters and characterize the resulting microstructures. To accelerate process development and optimization, researchers have explored microstructure prediction methods, including physical-based modeling and feature-based machine learning. Nevertheless, they both have limitations. Physical-based modeling consumes too much computational power. And in feature-based machine learning, low-dimensional microstructural features are manually extracted to represent high-dimensional microstructures, which leads to information loss.

In this dissertation, a deep learning-guided microstructure prediction framework is established. It uses a conditional generative adversarial network (CGAN) …

Material Properties Of Anderson Localizing Optical Fiber, Matthew Artus Tuggle

All Dissertations

Over half a century ago, the paper entitled “Absence of Diffusion in Certain Random Lattices” was published by P. Anderson and described a metal-to-insulator transition phenomenon where electron diffusion does not occur in disordered semiconductors. This phenomenon is now commonly referred to as “Anderson localization” (AL). Since the AL detailed in Anderson’s paper arose from the wave nature of electrons, similar behavior should be observed in other wave systems, more specifically in optics.

Given the utility of optical fibers, extensive theoretical treatment has been conducted on transverse Anderson localization (TAL, disorder in x- and y-directions, with the z-direction remaining invariant) …

Characterization And Modeling Of The High Strain Rate Response Of Advanced High Strength Steels, Rakan Alturk

All Dissertations

The push for lightweighting in the automotive industry has motivated metallurgist and steel manufacturers to produce new generations of steel that provide significant improvements over the conventional steels to allow them to compete with the introduction of low-density materials into the industry. To achieve this goal, metallurgist introduced different (stronger and more ductile) phases into the ferrite-dominant microstructure of conventional steels. This has led for generations of AHSSs with significantly improved properties. However, the complex microstructure led to increased complexities and unpredictability in the behavior of these materials, especially in their response to variations in the strain rate. This is …

Analysis Of Frozen Desserts Using Low-Temperature Scanning Electron Microscopy (Lt-Sem), Kinsey Elizabeth Macdonald

All Theses

Commercial vanilla ice cream and other frozen desserts from the United States were analyzed for ice crystal length using low-temperature scanning electron microscopy (LT-SEM). Average ice crystal length was determined using multiple micrographs of each sample/product. Out of the products tested, 11 out of 15 samples had an average ice crystal length above the consumer sensory threshold limit of 55 µm. Products containing stabilizers tended to have smaller average ice crystal lengths than products without stabilizers. With a few exceptions, lower fat products tended to have larger ice crystals because there was less fat to stabilize the ice crystals. Four …

Effect Of Strain Rate On The Tensile Behavior Of Cocrfeni And Cocrfemnni High Entropy Alloys, Mitra Shabanisamghabady

All Theses

High entropy alloys (HEAs) are a new class of alloys with the potential to be used in critical load bearing applications instead of conventional alloys. The HEAs studied in this research were CoCrFeNi and CoCrFeMnNi. Both were single-phase face-centered cubic materials. The focus of this study was on the tensile behavior of the two materials at quasi-static and dynamic strain-rates (〖10〗^(-4) to 〖10〗^3 s^(-1)) and the underlying microstructural phenomena driving the behaviors. Electron back-scatter diffraction was performed on both HEAs to study the microstructure before mechanical testing. To study the effect of strain rate, tensile experiments were performed at quasi-static …

Structural Evolution And Fatigue Performance Of Laser Welded 30mnvs6/Sae 045 Xlf Joints, Robert Trahern Houliston

All Theses

Characterization of microstructural evolution and fatigue performance of laser welded joints was studied between microalloyed 30MnVS6 and high strength low alloy SAE 045 XLF steels. These steel grades were selected for potential application in a prototype automatic gearbox to be utilized within automotive manufacturing. Parameters were varied using an Nd:YAG laser welding system which included laser power (1,670 – 1,730 W), workpiece speed (1,700 – 1,800 mm/min), and laser beam focal position (-0.05 – 0.05 mm). Based on the parameters selected, the welds were produced using an energy transfer of between 305 and 325 J/mm0.5·s0.5. A 3-level factorial design of …

Microstructure Modification Of Cu0.2ag2.8sbsete2 Through, Sloan Lindsey

All Theses

Cu0.2Ag2.8SbSeTe2 is new potential thermoelectric compound that exhibits very low thermal conductivity and a region of glass-like thermal conductivity. The compound phase segregates into AgSbTe2 and Ag2Te phases with Se and Cu acting as isoelectronic dopants. Backscatter SEM imaging is used to study the resulting microstructure. Normally cast samples exhibit cracks forming near the interfaces of the two phases. In this work we show that the cracks are caused by a low temperature monoclinic to cubic phase transition that occurs in the Ag2Te phase. We demonstrate that through rapid quenching we can control the size and shape of the phase …

Real-Time Raman Spectroscopy And Wide-Angle X-Ray Diffraction During Single-Layer And Multi-Layer Blown Film Extrusion, Giriprasath Gururajan

All Dissertations

Properties exhibited by blown films are controlled by the microstructure developed during their processing. Therefore, real-time measurement of microstructure during the blown film extrusion can help in better control and optimization of the process needed to obtain desired properties. The objectives of this research were (i) to conduct real-time microstructural measurements during single-layer and multi-layer blown film extrusion of polypropylene (PP) and low-density polyethylene (LDPE) using real-time Raman spectroscopy; (ii) to conduct real-time wide-angle X-ray diffraction (WAXD) during single-layer blown film extrusion of LDPE to obtain crystallinity and orientation values during the process; and (iii) to investigate the effect of …