Theses and Dissertations at Montana State University (MSU)

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    Structure-performance relationship in sutured photopolymer composite films with tunable mechanical heterogeneity
    (Montana State University - Bozeman, College of Engineering, 2024) Darabi-Noferesti, Amir; Chairperson, Graduate Committee: Lewis M. Cox; This is a manuscript style paper that includes co-authored chapters.
    This dissertation investigates the structure-performance relationships of bioinspired materials using photopolymer films. Nature utilizes mechanical heterogeneity in a variety of design architectures to tune biological materials considering their environmental and loading conditions. Compliant interlayers within stiff matrices, often referred to as sutures, are prevalent in biological structures, offering enhanced mechanical performance often despite their weaker material properties. To mimic nature's architecture in engineering materials, understanding the mechanisms through which biological structures achieve their outstanding properties is necessary. Previous manufacturing processes were unable to replicate the complex designs of biological structures, and literature in this field was bound by this limitation. Advancements in the field of photopolymers have enabled the development of mechanical heterogeneity in a defect-free network, facilitating explorations into bioinspired structures, eliminating many of the challenges associated with previous additive manufacturing techniques. In this work, we employ a two-stage reactive polymer (TSRP) system to investigate the structure performance relationship of bioinspired sutured composites, but first, a thorough understanding of the material system is deemed necessary. Through thickness characterization of the photopolymer system demonstrated complexities in material properties, providing details on our control over the material system. The TSRP system is then used to incorporate compliant sutures into stiff matrices to study the impact of mechanical heterogeneity. First, we investigated composites embedded with a single suture joint of sinusoidal geometries. Variations in geometrical features of the sinusoidal wave were explored with respect to the applied tensile load and empirical relationships were developed to correlate the composite performance to the geometrical features of the embedded suture. Further analysis of the failure of suture composites revealed toughening mechanisms such as crack guiding and crack arrest that significantly enhance the composite toughness. Then, we explored composite films embedded with periodic patterns of stiff and compliant interlayers at various length scales. Additional discussion on the fracture toughness of composite films explained the differences observed for composite performance at different length scales. The findings of this research offer fundamental insights into the complexity of nature's architecture and enable a framework for engineering composites and bio-inspired structures in the future.
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    A mechanical investigation of flapping-wing flight through reduced-order modeling
    (Montana State University - Bozeman, College of Engineering, 2024) Reade, Joseph Elsmere; Chairperson, Graduate Committee: Mark Jankauski; This is a manuscript style paper that includes co-authored chapters.
    Micro air vehicles are a class of unmanned aerial vehicle far smaller than conventional vehicles. Due to their maneuverability and small form-factor, these craft show great promise in a myriad of applications, ranging from artificial pollination to mapping cave systems to search-and-rescue. When established platforms like multirotors are reduced down to these sizes, aerodynamic scaling effects has a deleterious impact on vehicle performance. To overcome this, we turn to insect flight for inspiration. Flying insects utilize flapping wings to achieve flight, and do so efficiently. Capable of migrating huge distances and performing advanced aerobatics, insects have many adaptations that help them fly. Highly- flexible wings yield aerodynamic and energetic benefits while reducing the reducing the weight the insect needs to carry. Potential energy storage in the thorax enables them to recoup effort spent driving their wings, and fly farther. Despite the benefits afforded by flapping wings, they are still not fully understood. Study of flapping-wing flight is challenging owing to the high-speed, large-amplitude wing motion and aeroelastic deformation of the wings, making measurement of aerodynamic forces difficult. Computational methods allow us to overcome these obstacles. High-fidelity modeling enables accurate prediction of the airflow and pressures acting on the wing, and of the fluid-structure interaction present, however the large computational cost makes them unsuited for parametric studies. In this work, a reduced-order model is developed to study the fluid-structure interaction in flexible flapping wing systems. Bulk aerodynamic forces are accurately predicted with short solutions times, enabling parametric studies to be conducted. The effect of variable rigidity is investigated in 2D and 3D wings, and results compared to high-fidelity methods. Thorax dynamics are added in order to study elastic energy recycling. We find that moderate levels of wing flexibility improve the performance of flapping wings by lowering the energetic requirements, and that optimized system parameters can reduce power consumption through elastic energy recycling and resonance excitation.
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    Multi-length scale mechanical investigation of the flying insect thorax
    (Montana State University - Bozeman, College of Engineering, 2024) Casey, Cailin Barrett; Co-chairs, Graduate Committee: Chelsea M. Heveran and Mark Jankauski; This is a manuscript style paper that includes co-authored chapters.
    Flying insects are small, efficient, and agile- all traits that engineers want to incorporate into designs for small flapping wing drones. Therefore, engineers study flying insects' adaptations to understand what makes them successful flyers. One such adaptation is indirect actuation. During indirect actuation, the flight muscles deform the thorax exoskeletal. Thorax deformations are translated into wing rotation via the wing hinge, where the wings attach to the exoskeleton. Indirect actuation may reduce the energetic cost of flight by allowing energy to be stored in the thorax during one part of the wing cycle and then used later. Researchers can model indirect actuation as a two-degree-of-freedom mechanical model where a parallel spring represents the combined stiffness of the thorax exoskeleton and indirect flight muscles, and a series spring represents the wing hinge stiffness. However, these stiffnesses have not been evaluated experimentally. Evaluating the thorax stiffness will help us better understand insect flight. I hypothesize that thorax stiffness depends on the flight muscle activation type. Insects with synchronous flight muscles convert one action potential into one wing flap, while those with asynchronous flight muscles can convert a single action potential into many wing flaps. In this thesis I compared the thorax stiffness of insects with synchronous and asynchronous muscle on multiple scales. On a microscale, I measured the elastic modulus of the thorax exoskeleton using nanoindentation. I found differences in the modulus gradient through the cuticle thickness and between thorax regions through between insects with synchronous and asynchronous muscle. On a macroscale, I first qualitatively compared the thorax stiffness for insects with synchronous and asynchronous. I found that insects with asynchronous muscle may rely more on their wing hinge for wing rotation. Next, I created a frequency response function to quantify the role of wing hinge resonance in flight. I found that both insects are flapping post-resonance. These studies improve our understanding of insect flight evolution by elucidating the connections between muscle activation, flight control, and flight energetics. With this knowledge, engineers can make informed decisions about which species they should mimic in their designs.
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    Design and fabrication of an automated soil-water micro-sampling system
    (Montana State University - Bozeman, College of Engineering, 2023) Collins, Daniel David; Chairperson, Graduate Committee: Stephan Warnat
    Sustainable management of soil nutrients is a challenge for food production to meet the nutritional demands of a growing population of humans, which has surpassed eight billion. Informed management decisions toward maintaining suitable availability of plant macronutrients in soils without excess fertilizer inputs is limited by the ability to collect and analyze water chemistry in small sample volumes extracted from intact soils over time. Additionally, the semi-arid climate and increasingly more frequent meteorological drought conditions in soil systems like the agricultural regions of the Northern Great Plains limit the practicality of conventional soil-water collection and analysis techniques due to the small amounts of water available in the shallow vadose zone during the growing season. In this work, I present progress toward a solution at the intersection of automation, microfabrication, and environmental monitoring systems. The Microfluidic Environmental Solute Analysis (MESA) system has the potential to allow multiple deployments providing enhanced spatial and temporal resolution compared to conventional soil-water collection techniques in measurements of soil water solutes critical to understanding the soil chemistry that supports agricultural production. Using only 100 microliters of water extracted from the soil, the MESA system provides onboard, real-time electrical conductivity analysis (future work will include temperature, pH, and nitrate sensing). The electrical conductivity (EC) sensor uses single-frequency electrochemical impedance spectroscopy (EIS) to measure the bulk fluid resistance within the measurement chamber of the MSM. Calibration of the MSM of EC ranging from 100 - 6440 microseconds cm -1 has shown that the cell constant is 9.530 cm -1, although this parameter is sensor and package dependent. In-situ conductivity measurements in engineered soil columns have revealed that the sand tested has an intrinsic conductivity of approximately 380 microseconds cm -1. The maintenance-free system is intended to be buried in the soil and provide automatic measurements throughout the Montana growing season without being disturbed. The deployment of the MESA system can provide researchers with new data that may enhance our understanding of biogeochemical cycling in dry-land agricultural settings.
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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.
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    Applying advanced materials characterization techniques for an enhanced understanding of firn and snow properties
    (Montana State University - Bozeman, College of Engineering, 2024) Schehrer, Evan Nicholas; Chairperson, Graduate Committee: Kevin Hammonds; This is a manuscript style paper that includes co-authored chapters.
    Understanding snow microstructure and stratigraphy is critical for enhancing modeling efforts and instrument validation for the polar regions and seasonal snow. Controlled laboratory experiments help with these efforts and are essential for enhanced comprehension of polar firn densification, snow metamorphism, avalanche mechanics, snow hydrology, and radiative transfer properties. This dissertation aims to characterize snow and ice as they relate to the mechanical and sintering properties of simulated firn subject to trace amounts of sulfuric acid (H 2SO 4). Studies were also developed to characterize faceted snow crystallographic orientation using electron backscatter diffraction (EBSD) and understand the observed reflectance of remote sensing instruments related to mapping changing snow microstructure. To investigate the effects of soluble impurities, 50 ppm H 2SO 4 and impurity-free ice grains were developed to simulate polar firn and then subjected to a series of unconfined uniaxial compression to monitor the effect in mechanical strength at different temperatures and strain rates. Meanwhile, the role of sintering is less defined for ice grains that contain impurities. Two experiments were developed to quantify sintering rates with H 2SO 4. One experiment tracked the changes in microstructure at isothermal conditions using X-ray computed microtomography over 264 days. A second experiment used angle of repose tests to characterize the subsecond sintering between H 2SO 4 and impurity-free ice grains. In addition, it is well known that snow has constantly changing microstructure once deposited during precipitation events. These changes have an immediate impact on the crystallographic and optical properties. Faceted snow crystals, collected from the field and artificially grown, were analyzed using EBSD to map vapor-deposited growth along the three ice (Ih) crystallographic planes. Moreover, validation of remote sensing techniques such as near-infrared hyperspectral imaging (NIR-HSI) and lidar is essential for accurate field measurements. In the laboratory, an intercomparison test was conducted for NIR-HSI and lidar to analyze bidirectional reflectance returns, mapping the effective grain size of snow under different microstructural conditions and during melt/freeze events and surface hoar growth.
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    Characterization of multi-physics aging effects on the thermomechanical viscoelastic response of ultra high molecular weight polyethylene fiber reinforced composites
    (Montana State University - Bozeman, College of Engineering, 2024) Weaver, Jonmichael Andrew; Chairperson, Graduate Committee: David A. Miller
    Ultra High Molecular Weight Polyethylene (UHMWPE) fiber reinforced composites have a high strength-to-weight ratio and are gaining attention as a material of choice for specialized applications subjected to extreme environmental conditions. Users value the water-repellent, lightweight, and flexible nature of the material for applications where weight is crucial. Marine, aerospace, and alternative energy sectors are exploring UHMWPE fiber reinforced composites for specialized applications in demanding environments where strength, flexibility, and weight efficiency are important design criteria. The viscoelastic and hydrophobic nature of UHMWPE makes it an attractive replacement for Kevlar® in ballistics protection shields and other industrial applications, providing similar performance while achieving upwards of 40% reduction in weight. However, the durability of UHMWPE composites under real-world aging conditions remains insufficiently examined. This research investigates how the viscoelastic properties of UHMWPE fiber reinforced composites, created through various manufacturing techniques, are altered after exposure to harsh conditions including immersion in water, temperature variations, humidity, and UV exposure. Additionally, the composites were irradiated with: X-rays, gamma-rays, and neutrons. After exposure to adverse environments, the thermomechanical viscoelastic response was characterized through Dynamic Mechanical Analysis (DMA). Surface morphology was evaluated using a field emission scanning electron microscope. DMA revealed an increase in the storage modulus with aging; however, elevated temperature creep tests showed that UV and hygrothermal aging had a higher creep compliance and decreased the ability of the composite to recover strain after unloading. Both single layer and pressed UHMWPE panels showed an increase in weight after submersion in water. Distilled water resulted in a faster rate of hydrolysis in the matrix than did salt water. The UV, gamma-ray, and neutron environments caused the composites to become brittle and yellow through chain scission and crosslinking, whereas the X-ray radiation exposure did not cause a measurable effect. Analysis on the surface of these composites after aging suggested the matrix protects these fibers from damage in harsh environments. Synthetic rubber matrix materials aged at a faster rate than the polyurethane rubber matrix materials. Increasing the strain rate showed an increase in moduli response during tensile DMA. These results quantify the limitations and strengths of this material for future models to accurately predict the lifespan and expand the application of this performance material in extreme environments to ensure safety for applications ranging from extreme sports to aerospace.
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    Stress wave propagation through cohesive snow using viscoelastic analysis
    (Montana State University - Bozeman, College of Engineering, 2024) Verplanck, Samuel Vincent; Chairperson, Graduate Committee: Edward E. Adams
    Many avalanches are triggered by dynamic loads. Previous avalanche-focused studies of snow's response to dynamic loading consisted of field-based observations and static, elastic models. In this dissertation, snow was modeled dynamically as a Maxwell-viscoelastic material using parameters determined from laboratory experiments which resembled the Compression Test (CT) and Extended Column Test (ECT) -- common stability tests used by avalanche practitioners. First, 1D homogenous tests, akin to the CT, determined relationships between observed snow properties and ascertained elastic moduli and viscosities. The snow was loaded with both shorter duration (~1 ms) and longer duration (~10 ms) impacts from a dropped mass. The model was then expanded to 2D and validated using laboratory tests which resembled the ECT. Lastly, layered snow was investigated. The cohesive snow, with densities ranging from 135 to 428 kg m -3 , exhibited elastic moduli between 1 and 100 MPa and viscosities between 5 and 40 kPa s. The shorter duration impacts resulted in higher wave speeds and greater damping coefficients. Furthermore, the laboratory's substantial concrete floor caused reflection and amplification of vertical-normal compressive stress -- a phenomenon both observed and modeled. This reflection had a dominating effect in the layered laboratory studies. The modeling effort was extended to infinite and semi-infinite domains. These simulations revealed that isolating a block of snow, as is done during a CT or ECT, creates a wave guide which leads to deeper transmission and different distribution of shear and normal stresses compared to a 2D half space. How cohesive layers of snow are positioned within the simulated snowpack are modeled to affect the dynamic stress distribution. In a softer-over-harder configuration, both vertical- normal compressive stress and shear stress are modeled to penetrate deeper below the layer interface. Above the interface, the vertical-normal compressive stress is modeled to be greater in a softer-over-harder configuration, while the shear stress is reduced. This result is attributed to how dilatational and distortional waves travel through layered materials. In conclusion, this study enhances our understanding of stress wave propagation through snow by dynamically modeling it as a Maxwell-viscoelastic material and validating the model with laboratory experiments.
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    Determining the impact of osteocyte lacunar-canalicular turnover on bone matrix quality
    (Montana State University - Bozeman, College of Engineering, 2024) Vahidi, Ghazal; Chairperson, Graduate Committee: Chelsea M. Heveran; This is a manuscript style paper that includes co-authored chapters.
    Bone fragility in aging is a major unsolved health problem. Existing treatments for bone fragility are effective for about 50% of the population who suffer from loss of bone mass in aging. However, bone fracture resistance is also determined by the quality of bone tissue, including microarchitecture and matrix properties of the bone. Recently-emerging therapeutics targeting bone matrix quality present new avenues for addressing bone fragility. New data suggests that osteocytes, the most abundant and longest-living bone cells, interact with bone matrix in ways that have been likely overlooked. Osteocytes interact with the bone matrix through resorbing and replacing the bone tissue in their expansive lacunar canalicular system, in a process called LCS turnover. Osteocyte LCS turnover might play an important role in maintaining matrix quality and bone fracture resistance throughout life. However, fundamental knowledge gaps persist regarding this process and its impact on bone matrix properties. In this dissertation, we investigated the impacts of aging on abundance, frequency, and dynamics of osteocyte LCS turnover. We also studied the impacts of osteocyte LCS turnover on the matrix properties of its surrounding tissue. Our findings revealed that osteocyte LCS turnover is a prevalent, frequent, and dynamic process but this process significantly declines with aging. The large decline in LCS turnover in aging can have significant implications for bone quality and fracture resistance. We also demonstrated that osteocyte LCS turnover impacts the matrix quality of its local bone tissue, including modulus and energy dissipation, with nanoscale gradations around lacunae and canaliculi. We adapted contact-resonance atomic force microscopy for mapping the viscoelasticity of hydrated bone at the nanoscale. Findings from this study demonstrate that bone viscoelasticity is highly variable at the nanometer-scale and is higher than bulk bone around some canaliculi. Our data highlight a need to revisit how osteocytes perceive strains, since bone properties differ near lacunae and canaliculi compared with bulk bone tissue. Our findings together demonstrate, for the first time, that the quality of a substantial amount of bone surrounding the LCS is influenced by the frequent and abundant osteocyte LCS turnover, and this process declines with aging. These findings motivate investigating the direct influence of the osteocyte on bone matrix properties in aging and disease.
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    Does bone-to-cartilage fluid transport exist and is it relevant to joint health?
    (Montana State University - Bozeman, College of Engineering, 2024) Hislop, Brady David; Chairperson, Graduate Committee: Ronald K. June II; This is a manuscript style paper that includes co-authored chapters.
    Osteoarthritis (OA) afflicts millions of people each year. The onset of OA has been associated with many factors including increased bone-cartilage fluid transport, yet a cure remains elusive. To implicate bone-cartilage fluid transport in the progression of OA, further studies are needed on fluid transport in health. Recent studies have challenged the assumption that no fluid transport occurs between bone and cartilage in healthy joints. However, many gaps remain in our understanding of bone-to-cartilage fluid transport, including 1) do fluid pressure gradients develop at the bone-cartilage interface, 2) do traumatic injuries impact subchondral bone stiffness, and synovial fluid metabolism 3) do larger molecules move from bone-to-cartilage and does cyclic loading enhance such movement, 4) what material properties influence bone-to-cartilage fluid transport 5) do distinct metabolism changes occur with osteoarthritis, evaluated using a novel clustering method. Our results showed the development of fluid pressure gradients at the osteochondral interface, and that cyclic compression enhances bone-cartilage fluid transport. Furthermore, our results showed that proteoglycan loss, and decreased subchondral bone stiffness increased bone-cartilage fluid transport. Finally, we showed that in the first week after traumatic joint injuries (e.g., ACL tears) subchondral bone volume decreases, and subchondral bone stiffness increases, while the synovial fluid metabolism shifts. In conclusion, we showed that osteochondral fluid transport is enhanced by cyclic compression for larger molecules than previously studied (3kDa dextran), and that material parameters changes associated with the progression of OA alter bone-cartilage fluid transport. These studies provide novel understanding of bone-to-cartilage fluid transport, leading us one step closer to understanding OA as a whole joint disease.
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