Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
Browse
3 results
Search Results
Item Fiber shape effects on the compressive strength of unidirectional carbon fiber composites: a computational study(Montana State University - Bozeman, College of Engineering, 2020) Clarke, Ryan; Chairperson, Graduate Committee: David A. MillerThe tensile strength tends to be much higher than the compressive strength for carbon fiber reinforced polymer composites because of a change in failure modes. Current research activities are looking at novel precursors for reducing overall costs of carbon fiber production. The potential cost savings in new precursor carbon fiber make it economically feasible to use in large structural components. Some fiber precursors and manufacturing methods produce carbon fibers that have a kidney-shaped cross-section whereas traditional carbon fiber is circular. The aim of this study is to investigate the differences in compressive failure responses between fiber shapes in carbon fiber composites. A finite element micromechanical model was developed in ABAQUS of a single carbon fiber embedded in a square matrix with periodic boundary conditions. Two fiber cross-sectional geometries were examined: circular and kidney shaped. Three factors that affect the compressive failure response of carbon fiber reinforced polymers were investigated. These include fiber misalignment, volume fraction, and multiaxial loading. The results showed negligible differences between the compressive failure response of fibers with different cross-sectional shapes. Compressive strength was shown to have a decaying sensitivity to increasing fiber misalignment. Decreasing the volume fraction did decrease the compressive strength but also increased the compressive failure strain. In addition, adding in-plane shear loads proved detrimental to the compressive load-carrying capacity of a composite structure. This research showed minimizing fiber misalignment in manufacturing processes is only beneficial for high tolerance processes. In addition, decreasing volume fraction could be beneficial for highly flexible structures. Finally, the results demonstrated the need to minimize multiaxial loading for optimal composite compressive response.Item Fabrication and assessment of anode supported SOFCS doped with aluminum titanate via electrochemical and non-destructive micro-indentation testing(Montana State University - Bozeman, College of Engineering, 2019) Kent, John Parker; Chairperson, Graduate Committee: Stephen W. SofieCeramic-metal (cermet) composites are the most promising electrochemical anodes for commercial implementation in solid oxide fuel cells (SOFC). Recent advances at MSU in cermet formulations utilizing aluminum titanate (ALT) dopants in nickel oxide (NiO)-yttria stabilized zirconia (YSZ) anodes has shown substantial performance gains in degradation rates as well as mechanical behavior when evaluated in low power density electrolyte supported cell (ESC) geometries and bulk anode forms through modulus of rupture and equibiaxial flexure. The benefits associated with ALT are due to the formation of secondary phases of nickel aluminate and zirconium titanate in NiO-YSZ cermets that form during processing. Cermet modulus of rupture studies are rigorous, can span multiple months, and requiring hundreds of samples when studying the effects of both thermal and redox cycling on SOFC anodes to achieve statistically significant results. The use of non-destructive methods such as micro-indentation to examine the strength and toughness of doped and differently processed cermet anodes can rapidly speed up the analysis of mechanical properties including the mechanical support characteristics of higher power density anode supported cell (ASC) geometries targeted by industrial SOFC developers. The aim of this study was to examine non-destructive micro-indentation testing in evaluating cermet anode materials in both oxidized and reduced state in direct contrast with traditional destructive methods. Extending the current state of ALT anode doping by utilizing these rapid assessment methods, this work examines mechanical properties degradation and fracture toughness under multiple thermal and redox cycles. Additionally, this work details the framework for cell fabrication methods that were developed to process ASCs with state of the art 5 micrometer electrolytes for the first evaluation of ALT doping of SOFCs in this high power cell configuration.Item Spectrum fatigue lifetime and residual strength for fiberglass laminates(Montana State University - Bozeman, College of Engineering, 2001) Wahl, Neil Kelly