Microscale characterization of CMCs using 3D tomography techniques and machine learning algorithms to quantify and correlate initial microstructure to damage evolution

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Damage Evolution and Characterization of SiC/SiC Ceramic Matrix Composites Using Micro-Computed Tomography Techniques

In situ x-ray computed tomography was performed on melt infiltrated (MI) SiC/SiC ceramic matrix composites under tension in order to observe and quantify damage progression. The advanced light source (ALS) at Lawrence Berkeley National Lab was utilized to test two types of composite architectures, unidirectional and cross-ply, where each specimen was imaged at increasing tensile stress increments. Damage such as matrix cracking and fiber fragmentations were detected and measured for each specimen at each imaged stress increment. From the x-ray tomography observations, three different types of matrix cracks were observed including partial cracking, bifurcating cracks, and joining cracks. The onset of matrix cracking that was observed using in situ x-ray computed tomography was compared to mechanical model predictions. The comparison between the experimental observations and the mechanical models were similar, within the range of 100 MPa. The final matrix crack spacing was also compared to predicted debond lengths and shear lag distances. Fiber fragmentations were observed within the volume of each specimen and the breaks were quantified. The number of fiber fragmentations within a composite specimen continued to increase until the specimen broke. The opening height of each fiber fragmentation was qualitatively examined and two main observations were determined. First, as applied stress continued to increase, the initial fiber fragmentation opening also continued to increase. Second, fiber fragmentations that occurred at higher applied stresses have larger fiber fragmentation openings than ones that occurred at lower stresses. Using x-ray computed tomography allowed for the study of the relationship between fiber damage and the microstructure in terms of fiber locations and fiber clustering.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163149/1/amhilmas_1.pd

Microstructural changes in Beta-silicon nitride grains upon crystallizing the grain-boundary glass

Crystallizing the grain boundary glass of a liquid phase sintered Si3N4 ceramic for 2 h or less at 1500 C led to formation of gamma Y2Si2O7. After 5 h at 1500 C, the gamma Y2Si2O7 had transformed to beta Y2Si2O7 with a concurrent dramatic increase in dislocation density within beta Si3N4 grains. Reasons for the increased dislocation density is discussed. Annealing for 20 h at 1500 C reduced dislocation densities to the levels found in as-sintered materials

Method of Preparing a Solid Oxide Fuel Cell

A solid oxide fuel cell having a multichannel electrode architecture and method for preparing the same, the method including forming a first carbon laden composition, including a first thermoplastic binder, into a rod, applying a first zirconia laden composition, including a second thermoplastic binder, onto the rod to form a composite feed rod, extruding the composite feed rod to form a controlled geometry filament, bundling the extruded composite feed rod to form a multicellular feed rod, extruding the multicellular feed rod to form a multicellular rod, cutting the multicellular rod into multicellular discs, applying a zirconia laden material to one surface of a multicellular discs to form a multicellular structure, and heating processing the multicellular structure. The fuel cell is completed by adding anode and cathode materials to the multicellular structure

Dictyostelium discoideum\u27s 35-year Contribution to Growth of Biology: A Bibliometric Analysis

Biological Abstracts is a sufficiently adequate bibliometric tool for the analysis of the accumulated literature of certain organisms. Dictyostelium discoideum (Cellular slime mold) titles are scarce, yet literature growth parallels some of the same growth patterns as the whole of science. Relatively few (5 percent) biologists produce most (55 percent) of the literature on this organism. American authors predominate. The literature is grouped into various categories such as aggregation, cytology, growth, and genetics with the molecular-physiological works surpassing all other categories combined in the last 5 years (66 percent). Although the literature is scattered worldwide, most articles are found in relatively few journals. Biological Bulletin was the steady home for information for 22 years with 15 articles and the Journal of Bacteriology accumulated 16 articles in the last 4 years of the survey. The analysis begins with Raper\u27s discovery description of D. discoideum in 1935 and ends with 1970

Freeform Extrusion of High Solids Loading Ceramic Slurries, Part II: Extrusion Process Control

Part I of this paper provided a detailed description of a novel fabrication machine for high solids loading ceramic slurry extrusion and presented an empirical model of the ceramic extrusion process, with ram velocity as the input and extrusion force as the output. A constant force is desirable in freeform extrusion processes as it correlates with a constant material deposition rate and, thus, good part quality. The experimental results in Part I demonstrated that a constant ram velocity will produce a transient extrusion force. In some instances the extrusion force increased until ram motor skipping occurred. Further, process disturbances, such as air bubble release and nozzle clogging that cause sudden changes in extrusion force, were often present. In this paper a feedback controller for the ceramic extrusion process is designed and experimentally implemented. The controller intelligently adjusts the ram motor velocity to maintain a constant extrusion force. Since there is tremendous variability in the extrusion process characteristics, an on-off controller is utilized in this paper. Comparisons are made between parts fabricated with and without the feedback control. It is demonstrated that the use of the feedback control reduces the effect of process disturbances (i.e., air bubble release and nozzle clogging) and dramatically improves part quality.Mechanical Engineerin

Freeform Extrusion of High Solids Loading Ceramic Slurries, Part I: Extrusion Process Modeling

A novel solid freeform fabrication method has been developed for the manufacture of ceramic-based components in an environmentally friendly fashion. The method is based on the extrusion of ceramic slurries using water as the binding media. Aluminum oxide (Al2O3) is currently being used as the part material and solids loading as high as 60 vol. % has been achieved. This paper describes a manufacturing machine that has been developed for the extrusion of high solids loading ceramic slurries. A critical component of the machine is the deposition system, which consists of a syringe, a plunger, a ram actuated by a motor that forces the plunger down to extrude material, and a load cell to measure the extrusion force. An empirical, dynamic model of the ceramic extrusion process, where the input is the commanded ram velocity and the output is the extrusion force, is developed. Several experiments are conducted and empirical modeling techniques are utilized to construct the dynamic model. The results demonstrate that the ceramic extrusion process has a very slow dynamic response, as compared to other non-compressible fluids such as water. A substantial amount of variation exists in the ceramic extrusion process, most notably in the transient dynamics, and a constant ram velocity may either produce a relatively constant steady-state extrusion force or it may cause the extrusion force to steadily increase until the ram motor skips. The ceramic extrusion process is also subjected to significant disturbances such as air bubble release, which causes a dramatic decrease in the extrusion force, and nozzle clogging, which causes the extrusion force to slowly increase until the clog is released or the ram motor skips.Mechanical Engineerin