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Vuppu, Anil KumarStudy of carbon dioxide corrosion of carbon steel pipes in multiphase systems
Master of Science (MS), Ohio University, 1994, Chemical Engineering (Engineering)
Study of carbon dioxide corrosion of carbon steel pipes in multiphase systems

Committee:

W. Jepson (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Electrical Resistance Technique; Weightloss Technique; Scanning Electronmicroscopy

Smith, Craig EElectrical Resistance Changes of Melt Infiltrated SiC/SiC Subject to Long-Term Tensile Loading at Elevated Temperatures
Doctor of Philosophy, University of Akron, 2016, Mechanical Engineering
Melt infiltrated (MI) SiC fiber-reinforced SiC ceramic matrix composites (CMCs) are slowly replacing metals in the hot section components of turbine engines. The increasing application of these composites requires structural health monitoring techniques that are sensitive to transverse matrix cracks which form at elevated temperatures and limit the long-term durability of the material. Previous research has demonstrated a large increase in electrical resistance (ER) in response to transverse matrix cracks that formed in MI SiC/SiC during room temperature tensile loading. In this study, the ER response of slurry cast MI SiC/SiC CMCs at elevated temperatures (815°C and 1315°C), was explored under a wide range of applied tensile stresses. The results showed that the ER increased by up to 300% in response to tensile loading at the intermediate temperature of 815°C. Long-term stressed-oxidation tests at 815°C led to in-situ ER increases of more than 90% prior to sample break. The in-situ ER changes also directly correlated with measured crack density. Similarly, post-test inspection of the samples at room temperature showed ER increases greater than 100% for cracked samples after 100 hours. The room temperature inspection ER also correlated directly with the observed crack density. Thus, for all tests at 815°C, the ER was highly sensitive to the formation of matrix cracks. However, for the test temperature of 1315°C, the ER was less sensitive to damage. Resistance changes of the samples were an order of magnitude lower than they were at 815°C and there was no clear correlation between ER and crack density. The difference in results for the two test temperatures was explained by the decreasing sample resistivity at higher temperatures. Since the resistance was measured from the cold grips, the cooler (higher resistivity) regions had more effect on the sample resistance than the hotter (lower resistivity) regions.

Committee:

Gregory Morscher, Dr. (Advisor); Kwek-Tze Tan, Dr. (Committee Member); Wieslaw Binienda, Dr. (Committee Member); Erol Sancaktar, Dr. (Committee Member); Manigandan Kannan, Dr. (Committee Member); Tirumalai Srivatsan, Dr. (Other)

Subjects:

Mechanical Engineering

Keywords:

ceramic matrix composites; damage detection; health monitoring; electrical resistance

Almansour, Amjad Saleh AliUSE OF SINGLE TOW CERAMIC MATRIX MINICOMPOSITES TO DETERMINE FUNDAMENTAL ROOM AND ELEVATED TEMPERATURE PROPERTIES
Doctor of Philosophy, University of Akron, 2017, Mechanical Engineering
The room and high temperature mechanical properties of continuous ceramic fiber reinforced matrix composites makes them attractive for implementation in aerospace and nuclear applications. However, the effect of fiber content has not been addressed in previous work. Therefore, single tow composites with fiber content ranging from 3 to 47 % was studied. Single fiber tow minicomposite is the basic architectural feature of woven and laminate ceramic matrix composites (CMCs). An in depth understanding of the initiation and evolution of damage in various ceramic fiber reinforced minicomposites with different fiber volume fractions and interphases was investigated employing several non-destructive evaluation techniques. A new technique is used to determine matrix crack content based on a damage parameter derived from speed of sound measurements which is compared with the established method using cumulative energy of Acoustic Emission (AE) events. Also, a modified theoretical model was implemented to obtain matrix stress at the onset of matrix cracking. Room temperature tensile, high temperature creep rupture and high temperature oxidation degradation loading conditions were all considered and composites’ constituents were characterized. Moreover, fibers/matrix load sharing was modeled in creep and fiber volume fraction effect on load transfer was investigated using derived theoretical models. Fibers and matrix creep parameters, load transfer model results and numerical model methodology were used to construct minicomposites’ creep strain model to predict creep damage of the different fiber type and content minicomposites. Furthermore, different fiber volume fractions ceramic matrix minicomposites’ electrical resistivity temperature dependence isn’t well understood. Therefore, the influence of fiber content, heat treatment cycles and creep on electrical resistivity measurements of SiC/SiC minicomposites were also studied here. Next, minicomposites’ testing and characterization methodology was used to screen and characterize slurry-derived mullite bond coated minicomposites for enhanced oxidation and creep resistance. Finally, this study shows valuable testing methodologies and models approach for use in screening, developing and improving new generation ceramic matrix composites.

Committee:

Gregory Morscher, Dr (Advisor); Tirumalai Srivatsan, Dr (Committee Member); Craig Menzemer, Dr (Committee Member); Alper Buldum, Dr (Committee Member); Kwek Tze Tan, Dr (Committee Member); Robert Goldberg, Dr (Committee Member); Manigandan Kannan, Dr (Committee Member)

Subjects:

Acoustics; Aerospace Engineering; Aerospace Materials; Chemical Engineering; Chemistry; Electrical Engineering; Engineering; Experiments; High Temperature Physics; Materials Science; Mathematics; Mechanical Engineering; Mechanics; Metallurgy; Theoretical Mathematics; Theoretical Physics

Keywords:

Minicomposites,CMCs,Velocity of Sound, Creep, Creep Modelling, Creep Damage Characterization, Failure Analysis, Acoustic Emission, Electrical Resistance, Environmental Barrier Coating, EBC, CVI-SiC Creep, SiC Fibers Creep, Stress Dependent Matrix Cracking

Smith, Craig EdwardMonitoring Damage Accumulation In SiC/SiC Ceramic Matrix Composites Using Electrical Resistance
Master of Science, University of Akron, 2009, Mechanical Engineering
Ceramic matrix composites (CMC) are suitable for high temperature structural applications such as turbine airfoils and hypersonic thermal protection systems due to their low density, high thermal conductivity, and excellent mechanical properties. Specifically, silicon carbide-fiber reinforced silicon carbide (SiC/SiC) is a very creep resistant material with high temperature capability, that is being developed for such uses. Due to their brittle nature, one factor currently necessary for the implementation of these materials is the ability to accurately monitor and predict damage evolution. Current nondestructive evaluation methods such as ultrasound, x-ray, and thermal imaging are limited in their ability to quantify small scale, transverse, in-plane, matrix cracks developed over long-time creep and fatigue conditions. CMC is a multifunctional material in which the damage is coupled with the material’s electrical resistance, providing the possibility of real-time information about the damage state through monitoring of resistance. In this thesis, an electrical resistance-based nondestructive evaluation method is developed to detect the damages in SiC/SiC at room and high temperature. For undamaged samples, it was found that the resistivity is affected by composite constituent content and fiber architecture. Room temperature monotonic tensile tests of SiC/SiC composites were performed, coupled with modal acoustic emission and resistance monitoring. The results show excellent electrical sensitivity to mechanical damage. Room temperature experiments were able to correlate matrix cracking with resistance increases. Also, creep tests at 1315°C, coupled with resistance monitoring, were conducted. The high temperature creep tests also showed significant electrical resistance changes, although it is more difficult to isolate the specific causes since damage progression in creep is much more complicated. These experiments demonstrate that electrical resistance can be used both for in situ damage monitoring and also as a post-damage inspection method. A multi-physical model was also developed to explain and interpret the results as well as link the resistance change to the mechanical damage such as fiber breaks and matrix cracks. The predictions agree reasonably well with the experimental results.

Committee:

Zhenhai Xia, PhD (Advisor)

Subjects:

Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

Keywords:

SiC/SiC; ceramic matrix composite; NDE; electrical resistance

Appleby, Matthew P.High Temperature Damage Characterization Of Ceramic Composites And Protective Coatings
Doctor of Philosophy, University of Akron, 2016, Mechanical Engineering
Novel high-temperature experiments were conducted in ordered to address some of the most critical life-limiting issues facing woven melt-infiltrated, silicon carbide (SiC) fiber-reinforced SiC ceramic matrix composites (CMCs) as well as protective thermal and environmental barrier coatings (T/EBC). Heating of specimens was achieved using laser-based approaches that simulate the high heat-flux thermal gradient environments that these materials will be subjected to in service. Specialized non-destructive evaluation (NDE) and inspection techniques were developed to investigate damage modes and material response. First, in order to examine the capabilities of utilizing the emerging technique of electrical resistance (ER) measurement for use in high temperature mechanical testing in SiC/SiC CMCs, the temperature dependent ER response of several systems was determined. A model was developed to establish the contribution to overall ER from the individual composite constituents and applied thermal gradient. Then, elevated temperature tensile tests were performed to characterize the damage of composite materials to localized stress concentrations. Further experiments were done to assess the differences in damage mechanisms and retained tensile strength properties of uncoated SiC/SiC CMCs and EBC-CMC systems after prolonged exposure to high pressure, high velocity water vapor containing environments. Differences in damage modes were described using ER monitoring and post-test inspection. Localized strain fields were measured using a novel digital image correlation (DIC) technique and stress-dependent matrix crack accumulation was monitored using in-situ modal acoustic emission (AE). Coupled AE and thermography measurements were also used to describe failure of protective ceramic coatings due to the life-limiting case of thermal cyclic loading. Due to the complex nature of T/EBC failure, the decrease in coating life and durability due to thermal stress concentrations and degradation via molten calcium-magnesium-aluminosilicate (CMAS) infiltration was also examined. Finally, the use of ER measurements for damage characterization was extended to the complex case of creep and stress-rupture of damaged and undamaged composites as well as the dramatic increase in stress-rupture life to SiC/SiC CMCs from environmental barrier coatings. Post-test microscopy was performed to further explain differences in material response and damage morphology.

Committee:

Gregory Morscher (Advisor); Manigandan Kannan (Committee Member); Kwek Tze Tan (Committee Member); Craig Menzemer (Committee Member); Alper Buldum (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

ceramic matrix composites; environmental barrier coatings, thermal barrier coatings; non-destructive evaluation; electrical resistance; acoustic emission; digital image correlation

Deva, Yashika PoorviSlug flow induced corrosion studies using electrochemical noise measurements
Master of Science (MS), Ohio University, 1995, Chemical Engineering (Engineering)

Slug flow induced corrosion studies using electrochemical noise measurements

Committee:

W. Jepson (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Slug Flow; Electrochemical Noise Measurements; Conventional Corrosion Measurement; Linear Polarization Resistance; Electrical Resistance

Gordon, Neal AMaterial Health Monitoring of SIC/SIC Laminated Ceramic Matrix Composites With Acoustic Emission And Electrical Resistance
Master of Science in Engineering, University of Akron, 2014, Mechanical Engineering
Ceramic matrix composites (CMC) composed of Hi-Nicalon Type S™ fibers, a boron-nitride (BN) interphase, and pre-impregnated (pre-preg) melt-infiltrated silicon / silicon-carbide (SiC) matrix have been studied at room-temperature consisting of unidirectional and cross-ply laminates. Quasi-static, hysteretic and uniaxial tensile tests were done in conjunction with a variety of temporary, laboratory-based material health-monitoring techniques such as electrical resistance (ER) and acoustic emission (AE). The mechanical stress-strain relationship paired with electrical and acoustic measurements were analyzed to expand upon current composite knowledge to develop a more fundamental understanding of the failure of brittle matrix laminates, their constituents, and interactions. In addition, a simple but effective method was developed to allow visual confirmation of post-test crack spacing via microscopy. To enhance fidelity of acquired data, some specimens were heat-treated (i.e. annealing) in order to alter the residual stress state. Differences in location, acoustic frequency, and magnitude of matrix cracking for different lay-ups have been quantified for unidirectional and [0/90] type architectures. Empirical results shows complex hysteretic mechanical and electrical behavior due to fiber debonding and frictional sliding of which no general model exists to capture the essence of this CMC system. The results of this work may be used in material research and development, stress analysis and design verification, manufacturing quality control, and in-situ system and component monitoring.

Committee:

Gregory Morscher, Dr. (Advisor); Wieslaw Binienda, Dr. (Committee Member); Tirumalai Srivatsan, Dr. (Committee Member)

Subjects:

Aerospace Materials; Mechanical Engineering

Keywords:

Ceramic Matrix Composite,CMC;Aerospace;Non-Destructive Evaluation,NDE;Structural Health Monitoring,SHM;Composites;Acoustic Emission;Electrical Resistance