Matching Items (92)
Description
The following is a report that will evaluate the microstructure of the nickel-based superalloy Hastelloy X and its relationship to mechanical properties in different load conditions. Hastelloy X is of interest to the company AORA because its strength and oxidation resistance at high temperatures is directly applicable to their needs in a hybrid concentrated solar module. The literature review shows that the microstructure will produce different carbides at various temperatures, which can be beneficial to the strength of the alloy. These precipitates are found along the grain boundaries and act as pins that limit dislocation flow, as well as grain boundary sliding, and improve the rupture strength of the material. Over time, harmful precipitates form which counteract the strengthening effect of the carbides and reduce rupture strength, leading to failure. A combination of indentation and microstructure mapping was used in an effort to link local mechanical behavior to microstructure variability. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) were initially used as a means to characterize the microstructure prior to testing. Then, a series of room temperature Vickers hardness tests at 50 and 500 gram-force were used to evaluate the variation in the local response as a function of indentation size. The room temperature study concluded that both the hardness and standard deviation increased at lower loads, which is consistent with the grain size distribution seen in the microstructure scan. The material was then subjected to high temperature spherical indentation. Load-displacement curves were essential in evaluating the decrease in strength of the material with increasing temperature. Through linear regression of the unloading portion of the curve, the plastic deformation was determined and compared at different temperatures as a qualitative method to evaluate local strength.
ContributorsCelaya, Andrew Jose (Author) / Peralta, Pedro (Thesis director) / Solanki, Kiran (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2015-05
Description
The main field of study research through this project is to study the effect of history of deformation in materials subjected to complex loading, useful for producing lightweight alloys and composites optimized for absorbing shock and impact. This is accomplished by creating a digital model of a system in which the material undergoes tension and compression through colliding bars. The results show that the system generated is accurate when compared to real tests, so the program used to create the model can be used in the future for simulated tests using different materials or applied loads.
ContributorsShoemaker, Bradley Dean (Author) / Oswald, Jay (Thesis director) / Solanki, Kiran (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
DescriptionHydrogen diffusion causes brittleness and cracking at stresses below the yield strength of susceptible metals. The effects of hydrostatic loading on the rate of hydrogen diffusion is relatively unknown. A study of these effects will provide a better understanding in the design process for accounting for the resulting hydrogen embrittlement.
ContributorsWalker, Jordan Scot (Author) / Solanki, Kiran (Thesis director) / Oswald, Jay (Committee member) / Adlakha, Ilaksh (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2013-05
Description
Fatigue damage accumulation under multiaxial loading conditions is an important practical problem for which there is a need to collect additional experimental data to calibrate and validate models. In this work, a sample with a special geometry capable of producing biaxial stresses while undergoing uniaxial load was fabricated and tested successfully and used, along with standard dogbone samples, to monitor the evolution of surface roughness development under cyclic loading using optical microscopy. In addition, a Michelson interferometer was successfully designed, built and tested that can be used to monitor surface roughness for lower levels of load than those used in this work. Results of testing and characterization in 2024-T3 samples tested at a maximum stress slightly below their yield strength and load ratio ~ 0.1 indicate that most of the surface roughness development under cyclic loads occurs on the second half of the fatigue, with the bulk of it close to failure. However, samples with load axes perpendicular to the rolling direction showed earlier development of roughness, which correlated with shorter fatigue lives and the expected anisotropy of strength in the material.
ContributorsMiller, Ryley J (Author) / Peralta, Pedro (Thesis director) / Solanki, Kiran (Committee member) / School of Earth and Space Exploration (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
A major concern in the operation of present-day gas turbine engines is the ingestion of hot mainstream gas into rotor-stator disk cavities of the high-pressure turbine stages. Although the engines require high gas temperature at turbine entry for good performance efficiency, the ingested gas shortens the lives of the cavity internals, particularly that of the rotor disks. Steps such as installing seals at the disk rims and injecting purge (secondary) air bled from the compressor discharge into the cavities are implemented to reduce the gas ingestion. Although there are advantages to the above-mentioned steps, the performance of a gas turbine engine is diminished by the purge air bleed-off. This then requires that the cavity sealing function be achieved with as low a purge air supply rate as possible. This, in turn, renders imperative an in-depth understanding of the pressure and velocity fields in the main gas path and within the disk cavities. In this work, experiments were carried out in a model 1.5-stage (stator-rotor-stator) axial air turbine to study the ingestion of main air into the aft, rotor-stator, disk cavity. The cavity featured rotor and stator rim seals with radial clearance and axial overlap and an inner labyrinth seal. First, time-average static pressure distribution was measured in the main gas path upstream and downstream of the rotor as well as in the cavity to ensure that a nominally steady run condition had been achieved. Main gas ingestion was determined by measuring the concentration distribution of tracer gas (CO2) in the cavity. To map the cavity fluid velocity field, particle image velocimetry was employed. Results are reported for two main air flow rates, two rotor speeds, and four purge air flow rates.
ContributorsJunnarkar, Nihal (Author) / Roy, Ramendra P (Thesis advisor) / Mignolet, Marc (Committee member) / Lee, Taewoo (Committee member) / Arizona State University (Publisher)
Created2010
Description
This paper investigates Surface Mechanical Attrition Treatment (SMAT) and the influence of treatment temperature and initial sample surface finish on the corrosion resistance of 7075-T651 aluminum alloy. Ambient SMAT was performed on AA7075 samples polished to 80-grit initial surface roughness. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were used to characterize the corrosion behavior of samples before and after SMAT. Electrochemical tests indicated an improved corrosion resistance after application of SMAT process. The observed improvements in corrosion properties are potentially due to microstructural changes in the material surface induced by SMAT which encouraged the formation of a passive oxide layer. Further testing and research are required to understand the corrosion related effects of cryogenic SMAT and initial-surface finish as the COVID-19 pandemic inhibited experimentation plans.
ContributorsDeorio, Jordan Anthony (Author) / Solanki, Kiran (Thesis director) / Rajagopalan, Jagannathan (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Surface Mechanical Attrition Treatment (SMAT) is a process used to coat metallic alloy surfaces with a nanocrystallized layer via mechanical abrasion. SMAT has garnered a significant amount of interest from the scientific community as a surface treatment technique due to the ability of this fine grain top layer to provide several benefits to its constituent alloy, namely significantly higher hardness, fatigue strength, and most pertinently, greatly improved corrosion resistance. Emerging research suggests that SMAT can also be used to apply powder coatings onto target substrates. A given substrate can be installed in a ball mill, where stainless steel balls coated with pure elemental powder deliver sustained impact onto the substrate, embedding the powders onto its surface. This paper will explore the process of coating aluminum 7075 coating with chromium powder via SMAT, and the effects doing so will have on the corrosion resistance properties of the aluminum 7075. Traditionally, high-strength alloys have been treated with chromium via the process of electroplating, where the alloys are subjected to a hexavalent chromium plating procedure that is known to risk releasing toxic carcinogens into the environment. Coating these alloys with SMAT could minimize such negative externalities, while yielding benefits unique to the SMAT coating process itself. Baseline corrosion testing reveals that the corrosion resistance properties of the aluminum 7075 improved marginally when exposed to SMAT without the addition of any chromium powder. A literature review conducted in this paper of select studies on SMAT coating also demonstrates that material properties intrinsic to aluminum 7075 and pure chromium powder, as well as interaction effects occurring between aluminum and chromium when subjected to mechanical alloying, could enable the SMAT coating of aluminum 7075 with chromium to result in greatly enhanced corrosion resistance properties. While this was not accomplished within the duration of the Honors Project due to logistical difficulties brought forth by the COVID-19 epidemic, the baseline corrosion testing performed, as well as the literature review of studies directly relevant to the matter, should hopefully provide some information of value in any future exploration of the topic.
ContributorsMcManus, Matthew Harada (Co-author, Co-author) / Solanki, Kiran (Thesis director) / Beura, Vikrant (Committee member) / School of Politics and Global Studies (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Mistuning is defined as the blade-to-blade variation of bladed disks caused by slight changes in material or geometric properties; mistuned blades can cause significant increases in vibrational response. The primary goal of this thesis is to describe the relationship between coupling index and amplification factors of mistuned bladed disks with various sets of parameters, targeting the veering zone. At around a coupling index of 0, the amplification factors tend to stay around 1. This is due to localization of energy, where no energy is "shared" between blades, and the response of mistuned blades remain at resonance. As coupling index increases, amplification factors reach a peak between coupling indices of 0.15 and 0.2, before experiencing a downward trend towards 1. As blade-to-disk interaction increases, more energy is "shared" across blades. This results in the upward trend of amplification factor as coupling index increases, until too much energy is "shared". Additionally, a reduced order model enriching-stripping process to match natural frequencies of Nastran simulations will be discussed. This thesis is a continuation of Saurav Sahoo's Master's thesis at Arizona State University, Approximate a-priori Estimation of the Response Amplification due to Geometric and Young's Modulus Mistuning.
ContributorsLiu, Gavin (Author) / Mignolet, Marc (Thesis director) / Murthy, Raghavendra (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
As technology increases in capability, its purposes can become multifaceted, meaning it must accomplish multiple requirements as opposed to just one. An example of said technology could be high speed airplane wings, which must be strong enough to withstand high loads, light enough to enable the aircraft to fly, and have enough thermal conductivity to withstand high temperatures. Two objectives in particular, topology and sensor deployment, are important for designing structures such as robots which need accurate sensor readings, known as observability. In an attempt to display how these two dissimilar objectives coincide with each other, a project was created around the idea of finding an optimum balance of both. This supposed state would allow the structure not only to remain strong and light but also to be monitored via sensors with a high degree of accuracy. The main focus of the project was to compare levels of observability of two known factors of input estimation error. The first system involves a structure that has been topologically optimized for compliance minimization, which increases input estimation error. The second system produces structures with random placements of sensors within the structure, which, as the average distance from load to sensor increases, induces input estimation error. These two changes in observability were compared to see which had a more direct effect. The main findings were that changes in topology had a much more direct effect over levels of observability than changes in sensor placement. Results also show that theoretical input estimation time is significantly reduced when compared to previous systems.
ContributorsLeaton, Andrew Griffin (Author) / Ren, Yi (Thesis director) / Mignolet, Marc (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The goal of this research is to compare the mechanical properties of CP-Ti and Ti-O and to understand the relationship between a material's microstructure and its response to fatigue. Titanium has been selected due to its desirable properties and applicability in several engineering fields. Both samples are polished and etched in order to visualize and characterize the microstructure and its features. The samples then undergo strain-controlled fatigue tests for several thousand cycles. Throughout testing, images of the samples are taken at zero and maximum load for DIC analysis. The DIC results can be used to study the local strains of the samples. The DIC analysis performed on the CP-Ti sample and presented in this study will be used to understand how the addition of oxygen in the Ti-O impacts fatigue response. The outcome of this research can be used to develop long-lasting, high strength materials.
ContributorsRiley, Erin Ashland (Author) / Solanki, Kiran (Thesis director) / Oswald, Jay (Committee member) / School of Art (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05