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Miller, Ian TimothyProbabilistic finite element modeling of aerospace engine components incorporating time-dependent inelastic properties for ceramic matrix composite (CMC) materials
Master of Science, University of Akron, 2006, Applied Mathematics
The research included in this abstract pertains to probabilistic finite-element creep analysis of a composite combustor liner. A composite combustor liner is an aerospace engine component that is subjected to very high temperatures, ranging between 1500 - 2100 degrees Fahrenheit. A creep analysis of this component is essential for rational design as creep (a slow time-dependent information under constant load) is prevalent at high temperatures. In a probabilistic analysis, many, if not all, of the state variables are represented by random variables with appropriate probability distributions incorporating relevant parameters. This formalism is much more realistic, as it more accurately describes the variability in properties and loadings that are inherent in the composition of aerospace materials and loadings encountered by aerospace components.

Committee:

Ali Hajjafar (Advisor)

Keywords:

Creep Analysis; Reliability Analysis; Aerospace Engine Components; Ceramic Matrix Composite Materials; Finite Element Analysis

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

Nowacki, Brenna M.Verification and Calibration of State-of-the-Art CMC Mechanistic Damage Model
Master of Science (M.S.), University of Dayton, 2016, Mechanical Engineering
Due to their low density, high toughness and elevated temperature performance, Ceramic Matrix Composites (CMCs) are attractive candidates for replacing metals in many high temperature applications, such as gas turbine engines and exhaust nozzles. While there are numerous benefits to CMCs, there are several limitations hindering the full-scale application within the aerospace industry. One significant limitation is the ability to accurately model and predict CMC damage behavior. A mechanistic approach to modeling the damage behavior in CMCs was previously developed by Structural Analytics. The damage model, CLIP (Ceramic Matrix Composite Life Prediction), is embedded in a software package that consists of an ABAQUS user-subroutine, as well as a standalone application. The current study verifies the model by calibrating it to a slurry melt-infiltrated SiC/SiC composite. A series of experimental tests were conducted at the Air Force Research Laboratory (AFRL) including montonic tensile tests at 23°C, 800°C and 1200°C, a creep test at 1200°C and a sequentially loaded tensile test at 23°C. The results from the experimental tests were used to calibrate the damage model. The calibration was concluded as successful when the model could produce matching stress-strain curves to the experimental data at the respective temperatures. Finally, the model was used to make predictions for intermediate temperature ranges of monotonic tension, sequentially loaded tension, and off-axis tension.

Committee:

Pinnell Margaret, Ph.D. (Advisor); Jefferson George, Ph.D. (Committee Member); Whitney Thomas, Ph.D. (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

ceramic matrix composite; ABAQUS; CLIP; damage model; calibration; SiC-SiC; material characterization

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