Theses and Dissertations at Montana State University (MSU)

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Ice-templated ceramic-metal composites modified by interfacial metal aluminates
(Montana State University - Bozeman, College of Engineering, 2024) Marotta, Amanda Rose; Chairperson, Graduate Committee: Stephen W. Sofie; This is a manuscript style paper that includes co-authored chapters.
Interpenetrating phase (3-3) composites consists of two phases which are fully percolating throughout one system. Research efforts have been made towards routes to fabricate these composites that will allow for them to be utilized for applications like heat spreaders and leading-edge parts. Freeze-tape casting offers a potential avenue for developing 3-3 composites. The system can exhibit complete, long-range alignment through freeze-tape casting, in which both phases of the composite will be in constant periodicity of one another. To explore the potential of such ordering in 3-3 composites, ceramics, such as, yttria- stabilized zirconia (YSZ), alumina (Al 2 O 3) and zirconium diboride (ZrB 2) were freeze-tape casted and sintered to allow for second phase incorporation. Second phases, like copper (Cu) and silicon carbide (SiC) were utilized, so that ceramic-metal (cermet) freeze-tape casted composites and ultra-high temperature ceramic (UHTC) freeze-tape casted composites could be characterized. Initial composite property predictions were made using rule of mixtures (ROM). The work contained in this dissertation demonstrates that freeze-tape casted 3-3 composites can exhibit novel 3-axial anisotropic thermal behavior, and that, by ordering the percolating phases, high-temperature thermal behavior may be enhanced. This work, also, demonstrated that ceramic-metal interfaces are fragile, exhibiting thermal stress at the interface upon thermal cycling. Fostering interfacial adhesion between metal and ceramic phases is a primary tool for manipulating cermet properties. Common approaches to ceramic-metal joining include metallization and active brazing techniques. Though improvements in mechanical properties are notable, the functional capabilities can be sacrificed. To overcome these limitations, a novel approach, via a metal aluminate (copper aluminate), has been utilized to alleviate thermal stress along a ceramic-metal interface, and maintain adhesion of the ceramic-metal up to 100 psi. Mechanistically, it was not well- understood, as to what role copper aluminate played in modifying ceramic-metal interfaces. Chapter 5 of this work elucidates copper aluminate's role in fostering a ceramic-metal interface. By analyzing the surface and cross-sectional features of the cermet, it is discovered that through the formation of copper aluminate, porosity/roughness occurs to the bulk ceramic, allowing avenues for the metallic phase to penetrate through the thickness, fostering a mechanical interlocked joint.
Forming properties of stretch broken carbon fiber for aircraft structures
(Montana State University - Bozeman, College of Engineering, 2023) Nold, Dalton Bradley; Chairperson, Graduate Committee: Dilpreet S. Bajwa; Douglas S. Cairns (co-chair); This is a manuscript style paper that includes co-authored chapters.
Continuous carbon fiber is known to be a superior material for its strength, stiffness, and high strength-to-weight ratio and is often incorporated in aerospace composites. A challenge, however, is that it's not versatile in forming deep drawn geometries, which require convoluted manufacturing techniques resulting in expensive components. To overcome this, a type of carbon fiber with a random discontinuous fiber alignment called stretch broken carbon fiber (SBCF) is proposed. SBCF has potential to form parts with complex geometries with comparable or better mechanical properties to that of continuous carbon fiber. Montana State University (MSU) developed its own version of SBCF manufacturing processes, and research is being conducted to understand how SBCF prepreg tows react to stretch drawing at elevated temperatures using aerospace-grade epoxy resin systems. Currently, several new methods have been proposed to rapidly test these materials. This research revealed that SBCF forms with greater ease than continuous carbon fiber and is expected to substantially reduce manufacturing times for aircraft structures. To comprehend the material's behavior, simple tensile tests were coursed to understand how gauge length and temperature affected the peak loads when compared to continuous carbon fiber. It was discovered that on average, SBCF experienced stresses that were ten times less than continuous fibers. Additional tensile tests were conducted at elevated temperature to determine the true stress versus true strain. These tests are particularly important because they represent the material's most accurate mechanical properties. The results led to the discovery that SBCF experienced strain softening behavior. Furthermore, a series of forming tests using a novel "forming fixture" revealed that increasing the gap lowered the peak forming loads while the plunger geometry had little to no effect on peak forces at both room and elevated temperatures.
Application of functionalized cellulose nanocrystals to improve their dispersion in polymer matrix and enhance the thermo-mechanical properties of polymer composites
(Montana State University - Bozeman, College of Engineering, 2023) Chanda, Saptaparni; Chairperson, Graduate Committee: Dilpreet S. Bajwa; This is a manuscript style paper that includes co-authored chapters.
In the past few years, Cellulose nanocrystals (CNC) and its derivatives are exploited as potential bio-based nanofillers for functional polymer composites. The main challenge for manufacturing CNC-based composites is to disperse CNC uniformly in the hydrophobic polymer matrix. The hydrophilicity of CNC hindered their uniform distribution in the matrix and reduced the overall thermal, mechanical, and physical properties of the composite system. To overcome this challenge, several methods have been developed, such as physical and chemical modification of CNC. Also, polymer-based composites are highly flammable in nature and can cause severe life-threatening incidence. The flame-retardants available commercially should be added to the composite for a very high add-on% and toxic in nature, which is not eco-friendly and can be dangerous for humans. In this study, two critical research gaps are addressed: 1) uniform dispersion of CNC in a hydrophobic matrix, and 2) improving fire-retardancy of polymer composites by using non-toxic inorganic oxides. In the first part, a chemical compound, aminosilane was used as a dispersing agent for CNC in polyethylene oxide (PEO) based composite films and their thermo-chemical properties were analyzed. In the next part, the silanated CNCs are coated with nano ZnO and nano B2O3 and added as a functional filler to manufacture high density polyethylene (HDPE) based composites. The ZnO coated composites showed a significant improvement in thermo-mechanical properties of the composites even at a low add-on%, due to the smaller size and higher surface area of nano ZnO. The lignin containing CNC (LCNC) was also used as a functional additive along with nano ZnO and B2O 3. The hydrophobic character of lignin could not improve the dispersion of LCNC in the HDPE matrix because of the reduction of the aspect ratio and aggregate formation of LCNC/inorganic oxides during freeze drying. The role of the new age material graphene quantum dots (GQD) as a dispersing agent for CNC was also exploited. The CNC/GQD inclusion complex showed excellent dispersion behavior in HDPE matrix along with the significant improvement in thermo-mechanical properties of the composites, even at very low add-on% of GQD. The preliminary idea of using CNC/GQD inclusion complex as an energy storage device was also developed. Overall, the current work addresses the two main challenges which hindered the functional application of CNC based polymer composites and developed safe, effective, and eco-friendly methods to overcome those challenges. CNC based polymer composites have strong potential to be used in various industrial applications from fire-retardant material to energy storage device.
Forming evaluation metrics and methods for complex stretch broken and continuous carbon fiber parts
(Montana State University - Bozeman, College of Engineering, 2023) Dube, Madison Eve; Chairperson, Graduate Committee: Cecily Ryan
Carbon fiber composites are an ideal material for aircraft structures due to their light weight and high strength and stiffness. Traditional continuous carbon fiber composites are limited by their ability to form into complex geometric features as they have minimal abilities to stretch into a mold. Stretch broken carbon fiber is discontinuous which allows for the different tows of carbon fiber to slip relative to each other allowing for laminate displacements unattainable to continuous carbon fiber. In order to develop and improve stretch broken carbon fiber manufacturing processes, a method is developed herein to analyze the forming quality of a complex carbon fiber part. This method quantifies common qualitative forming metrics by measuring, evaluating, and scoring carbon fiber defects including: bridging, wrinkling, variation in thickness, forming depth, corner thinning and thickening, resin pooling, and additional texture defects. The scores produced from evaluating the various forming metrics on formed carbon fiber parts are assembled in a weighted matrix to produce an overall forming score. This forming evaluation method is demonstrated on three different geometric mold designs to assess that it is quantitative, repeatable, accounts for many carbon fiber defects, and accounts for discrepancies between the formed part and the designed part. This method was also tested on different carbon fiber prepreg materials: MSU SBCF/Cycom 977-3 resin from Solvay, MSU SBCF/Hexcel 8552, and Hexcel IM7/8552. Through testing, the method is found to have achieved the method design goals as well as ascertaining areas of improvement for MSU SBCF prepreg which is still under development. Results show that stretch broken carbon fiber and traditional continuous carbon fiber achieve similar overarching forming scores, but outperform one another in different category metrics. MSU SBCF has higher scores in corner thickening and resin pooling; continuous carbon fiber has higher scores in wrinkling and bridging. The method forms the foundation to evaluate layup practices and autoclave cure cycles when systematically applied in a process development setting. This method is also extendable to dissimilar geometric part types with modifications in suitable metrics.
Biodegradable composite hydromulches for sustainable organic horticulture
(Montana State University - Bozeman, College of Engineering, 2023) Durado, Andrew Dalton; Chairperson, Graduate Committee: Dilpreet S. Bajwa
In agriculture, mulch helps retain soil moisture and temperature while preventing weed growth. The most common material used for commercial mulching is low-density polyethylene (LDPE). At the end of the growing season, this plastic is typically buried or burned, causing a negative impact on the environment. This project aims to develop an alternative to LDPE mulch that is acceptable for organic farming and biodegradable. The tested hydromulch (HM) treatments contain a mixture of paper pulp, wood fiber, or hemp hurds combined with a tackifier and water. The tackifiers evaluated were guar gum, psyllium husk, and camelina meal, at various concentrations. These treatments were tested for tensile strength, puncture resistance, rain fastness, density, soil adhesion, porosity, and C:N ratio. The results have shown that samples containing tackifiers outperformed the control that contained no tackifier in the strength tests but not in the rain fastness or soil adhesion tests. Paper was the best fibrous material and guar gum was the top performing tackifier. When tackifier blends were considered, an interaction between two tackifiers occurred resulting in a decrease in strength. Blends containing wood fiber and hemp hurds did not show promising results. The puncture resistance of all mulches significantly decreased at 50% moisture level regardless of tackifier type. Some formulations performed well and could be promising in future field trials. The next step will be to examine these formulations outdoors in large-scale field studies.
Forming parameters and quantification of continous and stretch broken carbon fibers
(Montana State University - Bozeman, College of Engineering, 2021) Janicki, Joseph Charles; Chairperson, Graduate Committee: Dilpreet S. Bajwa; This thesis contains two articles of which Joseph Charles Janicki is not the main author.
Continuous carbon fibers are premium reinforcing material for aerospace composites. Carbon fiber reinforced polymers are five times stronger than steel and twice as stiff, making it an ideal candidate for structural aircraft components where weight is an important factor. The challenge with continuous carbon fibers is their difficulty to form deep drawn parts requiring intricate manufacturing techniques that increase manufacturing time, cost, and material waste. An alternative to continuous carbon fibers is stretch broken carbon fiber (SBCF). SBCF is a form of aligned discontinuous fiber, it has been proposed as an alternative to overcome this formability challenge. SBCF provides flexibility to form complex shapes while maintaining comparable strength and stiffness. A variety of testing methods have been developed to study both the ability of SBCF to form over traditional continuous carbon fiber and how different iterations of SBCF perform against each other. These include testing carbon fiber tows in tension on a universal test stand as well as designing and creating a forming tool that tests resin impregnated tows under different geometry conditions and temperatures. Tensile properties of both a continuous tow and a SBCF tow were evaluated at different gauge lengths and temperatures. It shows that SBCF tow maximum load increases as the gauge length decreases as well as elevated temperature has a clear effect on the tensile properties when fiber continuity is considered. Cross-sectional areas of continuous and SBCF tows were calculated using both areal weight and scanning electron microscopy showing that in general continuous fiber tows have a larger cross-section than SBCF. Using a forming fixture to test samples, results were statistically analyzed in order to display the significance of geometry and temperature on the maximum forming load of different fibers. The suite of testing and results indicate that in general SBCF maintains superior formability to that of continuous fibers. Overall lower maximum force is required for SBCF to form into deep drawn shapes. This supports their ability to be used more readily in complex aircraft structure while minimizing the disadvantages posed by traditional carbon composites.
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. Miller
The 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.
Developing a load acquisition system for a multiaxial test frame
(Montana State University - Bozeman, College of Engineering, 2019) Carpenter, Aaron James; Chairperson, Graduate Committee: David A. Miller
Material testing has traditionally been completed by using a uniaxial load frame which isolates a single stress component. Engineers however, design components for applications in a multi-axial world to withstand stress in multiple directions. The In-Plane Loader (IPL) at Montana State University expands the realm of material testing to three degrees of freedom within a two-dimensional plane. Applications of the IPL include composite material testing and experimental validation of constitutive models in multiple axes. The multi-axial test frame has been in place at MSU for several years. One of the primary challenges associated with the IPL is its ability to accurately measure multi-axial load components. The purpose of this work was to develop and validate an updated multi-axial load acquisition system for the IPL. The procedure included design, manufacture, implementation, and validation of the system. Validating the system in multiple axes required isolating single stress components along each of the planar axes. Tension tests were completed to isolate the vertical component, and shear tests were completed to isolate the horizontal component. Each of the results were compared to results of standardized test procedures designed to isolate their respective stress components. Digital image correlation was implemented as a non-contact method of measuring displacement for the testing procedures. The data collected in this study provides confidence in the ability to measure multi-axial loading in combination with digital image correlation to expand the capabilities of multi-axial testing. The system provides the ability to study load dependent failure of materials as well as displacement dependent failure. The information presented provides an understanding of challenges associated with multi-axial testing which hopes to assist in the development of future multi-axial test frames.
Investigation of the mechanical properties of aluminum titanate (Al 2TiO 5) doped NI-YSZ solid oxide fuel cell anodes
(Montana State University - Bozeman, College of Engineering, 2019) McCleary, Madisen Wynn; Chairperson, Graduate Committee: Roberta Amendola; Roberta Amendola was a co-author of the article, 'Effect of aluminum titanate (Al 2TiO 5) doping on the mechanical performance of solid oxide fuel cell Ni-YSZ anode' in the journal 'Fuel Cells' which is contained within this thesis.; Roberta Amendola was a co-author of the article, 'Investigation of the kinetics of the solid-state reduction process of undoped and aluminum titanate (Al 2TiO 5) doped NiO-YSZ anodes for solid oxide fuel cells' in the journal 'Ceramics international' which is contained within this thesis.; Roberta Amendola, Stephen Walsh and Benjamin McHugh were co-authors of the article, 'Analysis of the mechanical strength and failure mode of undoped and aluminum titanate (Al 2TiO 5, ALT) doped-Ni-YSZ solid oxide fuel cell anodes under uniaxial and biaxial strength testing conditions' submitted to the journal 'Materialia' which is contained within this thesis.; Roberta Amendola and Benjamin McHugh were co-authors of the article, 'Effect of redox cycling on the mechanical performance of undoped and aluminum titanate (Al 2TiO 5, ALT) doped NiO-YSZ solid oxide fuel cell anodes' which is contained within this thesis.; Roberta Amendola was a co-author of the article, 'Mechanical performance of aluminum titanate (Al 2TiO 5, ALT) doped NiO-YSZ SOFC half cells' which is contained within this thesis.
Recently, there has been growing interest in anode supported Solid Oxide Fuel Cells (SOFCs) because of improved single cell performance. In these systems, the anode layer is the thickest and provides the mechanical strength of the stack. Nickel-yttria stabilized zirconia (Ni-YSZ) composites are widely used as anode material but, in contrast to the vast amount of data available on their electrochemical properties, little data on the mechanical performance exists. This dissertation work focuses on the use of secondary materials added to traditional Ni-YSZ anodes to enhance SOFC anode mechanical performance. Small amounts of, aluminum titanate (Al2TiO5, ALT), added to the NiO-YSZ system during the manufacturing process, results in a material that is over 50% stronger than the native Ni-YSZ. Samples with different geometries have been fabricated and tested in uniaxial and biaxial strength testing apparatuses. Advanced microscopy techniques and Weibull statistical analyses have been used to properly characterize the mechanical performance, the failure mechanism and to elucidate chemical compositions. This work has found that the enhanced strength resulting from ALT is related to the development of secondary phases: Al2O3 reacts with NiO to form NiAl2O4 while TiO2 preferentially reacts with YSZ to form a solid YSZ framework defined as the 'rough phase' that add stiffness to the system and persists upon reduction. The mechanical behavior of reduced samples has been related to the partial reduction of NiAl2O4 which results in the formation of Ni nanoparticles within an Al2O3 matrix ('small particle phase'). This phase is characterized by a high strength interface while adding ductility and crack deflection ability to the system. ALT was also found responsible for changing the Ni-YSZ system failure mechanism from an intergranular to a transgranular fashion indicating the material toughness increased. During cyclic operational testing, ALT has potential for mechanical stabilization through porosity development with secondary phase formation. Testing of ALT anodes with YSZ electrolyte material showed increased strength over similar native assemblies. This dissertation work lays the foundation for future research into the effects of ALT doping on the SOFC system and how this material could be tailored for even further increases in strength.
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. Sofie
Ceramic-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.

Theses and Dissertations at Montana State University (MSU)

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