Browsing by Author "Ma, Kaka, committee member"
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Item Open Access A thermoplastic matrix continuous fiber reinforced composite impregnation method by direct polymer extrusion(Colorado State University. Libraries, 2018) Hedin, Kevin M., author; Radford, Donald W., advisor; Ma, Kaka, committee member; Heyliger, Paul, committee memberDuring component design, continuous fiber reinforced composite material systems are often chosen largely based on their structural efficiency. Their mechanical properties, such as specific strength and specific stiffness, are often cited as significant advantages over the use of other materials. However, composite component production often lacks the capability to provide the local variation necessary to ensure that 1) the reinforcing fibers are best aligned with anticipated loads, and 2) the ideal matrix composition and fiber volume fraction are found throughout the composite part. In practice, these limitations result in composite components that do not demonstrate the maximum possible efficiencies inherent to the fiber-reinforced composite material system. To further increase the flexibility of polymer matrix continuous fiber reinforced composites manufacturing methods, a new thermoplastic impregnation method was developed. This proposed method adds a thermoplastic matrix, which has previously been proven to allow significant variation of local fiber orientation, to the reinforcing fiber just prior to the consolidation of the composite. The increased independence of matrix and fiber addition should allow the local variation of volume and composition of the added matrix, while using less and simpler hardware than previous, similar efforts. In this work, the quality of material deposited from the proposed process is evaluated. The maximum possible quality of the proposed method and also that of a similar process that uses a commercially available material system were determined, primarily using short beam shear (SBS) testing. The material system of both methods consisted of E-glass continuous fiber reinforcement with a PETG matrix. It was found that both manufacturing processes are capable of producing samples with an SBS strength of approximately 53 MPa, and it was concluded that the proposed process has the capability to deposit material of comparable quality to that produced by the baseline method. Subsequent thermal analysis, fiber volume fraction/void content measurement, and metallographic imaging were conducted to investigate the effects of using two different PETG compositions on the SBS strength of composite material produced by the proposed process. It was found that, while using the proposed process, the PETG matrix with a lower glass transition temperature allowed better consolidation of the resulting composite part, ultimately increasing SBS strength. Each process parameter used in the proposed process was evaluated for the practical significance of its effects on SBS strength, which facilitated 1) an understanding of the underlying mechanisms of the process, and 2) a tenable simplification of the process that should reduce operating costs and also demonstrates its robustness via insensitivity to many of the possible process variations. Finally, it was established that the material inputs to the proposed process are relatively inexpensive: Using PETG and continuous E-glass fiber in the proposed process reduces material input cost by at least 52% compared to using commingled PETG and E-glass fibers in the baseline process, on a $/kg basis.Item Open Access A two-field finite element solver for linear poroelasticity(Colorado State University. Libraries, 2020) Wang, Zhuoran, author; Liu, Jiangguo, advisor; Tavener, Simon, advisor; Zhou, Yongcheng, committee member; Ma, Kaka, committee memberPoroelasticity models the interaction between an elastic porous medium and the fluid flowing in it. It has wide applications in biomechanics, geophysics, and soil mechanics. Due to difficulties of deriving analytical solutions for the poroelasticity equation system, finite element methods are powerful tools for obtaining numerical solutions. In this dissertation, we develop a two-field finite element solver for poroelasticity. The Darcy flow is discretized by a lowest order weak Galerkin (WG) finite element method for fluid pressure. The linear elasticity is discretized by enriched Lagrangian ($EQ_1$) elements for solid displacement. First order backward Euler time discretization is implemented to solve the coupled time-dependent system on quadrilateral meshes. This poroelasticity solver has some attractive features. There is no stabilization added to the system and it is free of Poisson locking and pressure oscillations. Poroelasticity locking is avoided through an appropriate coupling of finite element spaces for the displacement and pressure. In the equation governing the flow in pores, the dilation is calculated by taking the average over the element so that the dilation and the pressure are both approximated by constants. A rigorous error estimate is presented to show that our method has optimal convergence rates for the displacement and the fluid flow. Numerical experiments are presented to illustrate theoretical results. The implementation of this poroelasticity solver in deal.II couples the Darcy solver and the linear elasticity solver. We present the implementation of the Darcy solver and review the linear elasticity solver. Possible directions for future work are discussed.Item Open Access Bio-inspired design for engineering applications: empirical and finite element studies of biomechanically adapted porous bone architectures(Colorado State University. Libraries, 2020) Aguirre, Trevor Gabriel, author; Donahue, Seth W., advisor; Ma, Kaka, committee member; Heyliger, Paul, committee member; Simske, Steven, committee memberTrabecular bone is a porous, lightweight material structure found in the bones of mammals, birds, and reptiles. Trabecular bone continually remodels itself to maintain lightweight, mechanical competence, and to repair accumulated damage. The remodeling process can adjust trabecular bone architecture to meet the changing mechanical demands of a bone due to changes in physical activity such as running, walking, etc. It has previously been suggested that bone adapted to extreme mechanical environments, with unique trabecular architectures, could have implications for various bioinspired engineering applications. The present study investigated porous bone architecture for two examples of extreme mechanical loading. Dinosaurs were exceptionally large animals whose body mass placed massive gravitational loads on their skeleton. Previous studies investigated dinosaurian bone strength and biomechanics, but the relationships between dinosaurian trabecular bone architecture and mechanical behavior has not been studied. In this study, trabecular bone samples from the distal femur and proximal tibia of dinosaurs ranging in body mass from 23-8,000 kg were investigated. The trabecular architecture was quantified from micro-computed tomography scans and allometric scaling relationships were used to determine how the trabecular bone architectural indices changed with body mass. Trabecular bone mechanical behavior was investigated by finite element modeling. It was found that dinosaurian trabecular bone volume fraction is positively correlated with body mass like what is observed for extant mammalian species, while trabecular spacing, number, and connectivity density in dinosaurs is negatively correlated with body mass, exhibiting opposite behavior from extant mammals. Furthermore, it was found that trabecular bone apparent modulus is positively correlated with body mass in dinosaurian species, while no correlation was observed for mammalian species. Additionally, trabecular bone tensile and compressive principal strains were not correlated with body mass in mammalian or dinosaurian species. Trabecular bone apparent modulus was positively correlated with trabecular spacing in mammals and positively correlated with connectivity density in dinosaurs, but these differential architectural effects on trabecular bone apparent modulus limit average trabecular bone tissue strains to below 3,000 microstrain for estimated high levels of physiological loading in both mammals and dinosaurs. Rocky Mountain bighorn sheep rams (Ovis canadensis canadensis) routinely conduct intraspecific combat where high energy cranial impacts are experienced. Previous studies have estimated cranial impact forces up to 3,400 N and yet the rams observationally experience no long-term damage. Prior finite element studies of bighorn sheep ramming have shown that the horn reduces brain cavity translational accelerations and the bony horncore stores 3x more strain energy than the horn during impact. These previous findings have yet to be applied to applications where impact force reduction is needed, such as helmets and athletic footwear. In this study, the velar architecture was mimicked and tested to determine suitability as novel material architecture for running shoe midsoles. It was found that velar bone mimics reduce impact force (p < 0.001) and higher energy storage during impact (p < 0.001) and compression (p < 0.001) as compared to traditional midsole architectures. Furthermore, a quadratic relationship (p < 0.001) was discovered between impact force and stiffness in the velar bone mimics. These findings have implications for the design of novel material architectures with optimal stiffness for minimizing impact force.Item Open Access Dynamic mechanical analysis for quality evaluation of additively manufactured continuous fiber reinforced thermoplastic matrix composites subject to manufacturing defects(Colorado State University. Libraries, 2019) Rodriguez, Patrick A., author; Radford, Donald W., advisor; Ma, Kaka, committee member; Heyliger, Paul, committee memberContinuous fiber reinforced polymers (CFRP) have become integral to modern mechanical design as value-added alternatives to metallic, ceramic and neat polymeric engineering materials. Despite the advantages of CFRP, current methods of preparing laminated continuous fiber reinforced polymers are fundamentally limiting in that reinforcement is typically applied only in the plane of the mold or tool. Additionally, key operations inherent to all CFRP processing approaches require a variety of skilled labor as well as costly net-shape, hard tooling. As such, additive manufacturing has risen to the forefront of manufacturing and processing research and development in the CFRP arena. Additive manufacture of continuous fiber reinforced thermoplastics (CFRTP) exhibits the potential to relieve many of the constraints placed on the current design and manufacturing of continuous fiber reinforced structures. At present, the additive manufacture of CFRTP has been demonstrated successfully to varying extents; however, comprehensive dialogue regarding manufacturing defects and quality of the processed continuous fiber reinforced thermoplastics has been missing from the field. Considering the preliminary nature of additive manufacture of CFRTP, exemplary processed composites are typically subject to various manufacturing defects, namely excessive void content in the thermoplastic matrix. Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less-impactful on the results and overlooked. Hardware to facilitate additive manufacturing of CFRTP was developed and continuous fiber reinforced specimens, with high fiber volume fractions (~ 50 %), were successfully processed. Early efforts at evaluating the processed specimens using defect-sensitive Short-Beam Strength (SBS) analysis exhibited limited sensitivity to void content, coupled with destructive, inelastic failure modes. As a path forward, an expanded study of the effects of void content on the processed specimens was conducted by means of Dynamic Mechanical Analysis (DMA). Utilization of DMA allows for thermomechanical (i.e. highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus (E'), viscous loss modulus (E"), damping factor (tan δ) and the glass transition temperature (Tg) of the processed composite specimens. The results of this work have shown that DMA exhibits increased sensitivity, as compared to SBS, to the presence of void content in the additively manufactured CFRTP specimens. Within the relevant range of void content, non-destructive specimen evaluation by DMA resulted in a measured, frequency dependent, 5.5 – 5.8 % decrease in elastic storage modulus per 1 % increase in void content by volume. Additionally, quality evaluation by DMA realized a marked decrease in the maximum measured loss modulus in the additively manufactured composites, ranging from 7.0 – 8.2 % per 1 % increase in void content by volume. Effects of void content were also measured in both the damping factor and glass transition temperature, where an approximate 1.6 °C drop in Tg was recorded over the relevant range of void content. The results of this work indicate, firstly, that DMA is a superior evaluation method, as compared to SBS, in terms of sensitivity to void content in additively manufactured CFRTP. Additionally, the results of this work provide a clear expansion of the current state of the literature regarding additive manufacture of CFRTP materials in that the effects of prominent manufacturing defects have been assessed with regard to thermomechanical material performance. Furthermore, and finally, the results of this work establish a direct path forward to characterize long-term effects of manufacturing defects, by means of DMA, on the creep-recovery and stress relaxation behavior of the relevant composite material system.Item Open Access Elucidating structure-property-performance relationships of plasma modified tin(IV) oxide nanomaterials for enhanced gas sensing applications(Colorado State University. Libraries, 2017) Stuckert, Erin P., author; Fisher, Ellen R., advisor; Barisas, B. George, committee member; Prieto, Amy L., committee member; Krummel, Amber T., committee member; Ma, Kaka, committee memberThis dissertation examines structure-property-performance relationships of plasma modified tin(IV) oxide (SnO2) nanomaterials to successfully and efficiently create sensitive targeted gas sensors. Different project aspects include (1) materials characterization before and after plasma modification, (2) plasma diagnostics with and without a SnO2 nanomaterial, (3) sensor performance testing, and ultimately (4) elucidation of gas-surface relationships during this project. The research presented herein focuses on a holistic approach to addressing current limitations in gas sensors to produce desired capabilities for a given sensing application. Strategic application of an array of complementary imaging and diffraction techniques is critical to determine accurate structural information of nanomaterials, especially when also seeking to elucidate structure-property relationships and their effects on performance in specific applications such as gas sensors. In this work, SnO2 nanowires and nanobrushes grown via chemical vapor deposition (CVD) displayed the same tetragonal SnO2 structure as revealed via powder X-ray diffraction (PXRD) bulk crystallinity data. Additional characterization using a range of electron microscopy imaging and diffraction techniques, however, revealed important structure and morphology distinctions between the nanomaterials. Tailoring scanning transmission electron microscopy (STEM) modes and combining these data with transmission electron backscatter diffraction (t-EBSD) techniques afforded a more detailed view of the SnO2 nanostructures. Indeed, upon deeper analysis of individual wires and brushes, we discovered that despite a similar bulk structure, wires and brushes grew with different crystal faces and lattice spacings. Had we not utilized multiple STEM diffraction modes in conjunction with t-EBSD, differences in orientation related to bristle density would have been overlooked. Thus, it is only through methodical combination of several analysis techniques that precise structural information can be reliably obtained. To begin considering what additional features can affect gas sensing capabilities, we needed to understand the driving force behind SnO2 sensors. SnO2 operates widely as a gas sensor for a variety of molecules via a mechanism that relies on interactions with adsorbed oxygen. To enhance these interactions by increasing surface oxygen vacancies, commercial SnO2 nanoparticles and CVD-grown SnO2 nanowires were plasma modified by Ar/O2 and H2O(v) plasmas. Scanning electron microscopy (SEM) revealed changes in nanomaterial morphology between pre- and post-plasma treatment using H2O plasma treatments but not when using Ar/O2 plasmas. PXRD patterns of the bulk SnO2 showed the Sn4+ is reduced by H2O and not Ar/O2 plasma treatments. X-ray photoelectron spectroscopy (XPS) indicated Ar/O2 plasma treatment increases oxygen adsorption with increasing plasma power and treatment time, without changing Sn oxidation. With the lowest plasma powers and treatment times, however, H2O plasma treatment results in nearly complete bulk Sn reduction. Although both plasma systems increased oxygen adsorption over the untreated (UT) materials, there were clear differences in the tin and oxygen species as well as morphological variations upon plasma treatment. Given that H2O plasma modification of SnO2 nanomaterials resulted in reduction of Sn+4 to Sn0, this phenomenon was further explored. To develop a deeper understanding of the mechanism for this behavior, gas-phase species were detected via optical emission spectroscopy (OES) during H2O plasma processing (nominally an oxidizing environment), both with and without SnO2 substrates in the reactor. Gas-phase species were also detected in the reducing environment of H2 plasmas, which provided a comparative system without oxygen. Sn* and OH* appear in the gas phase in both plasma systems when SnO2 nanowire or nanoparticle substrates are present, indicative of SnO2 etching. Furthermore, H2 and H2O plasmas reduced the Sn in both nanomaterial morphologies. Differences in H* and OH* emission intensities as a function of plasma parameters show that plasma species interact differently with the two SnO2 morphologies. The H2O plasma gas-phase studies found that under most plasma parameters the ratio of reducing to oxidizing gas-phase species was ≥1. The final consideration in our holistic approach relied on sensor performance studies of SnO2 nanomaterials. Resistance was recorded as a function temperature for UT, Ar/O2 and H2O plasma treated nanoparticles and nanowires exposed to air, carbon monoxide (CO), or benzene (C6H6). Resistance data were then used to calculate sensor response (Rair/Rgas) and sensitivity (Rair/Rgas > 1 or Rgas/Rair > 1). Specifically, Ar/O2 and H2O plasma modification increase CO and C6H6 sensitivity under certain conditions, but H2O plasma was more successful at increasing sensitivity over a wider range of plasma parameters. In particular, certain H2O plasma conditions resulted in increased sensitivity over the UT nanomaterials at 25 and 50 °C. Overall, H2O plasma appears to be more effective at increasing sensitivity than Ar/O2 plasma. Furthermore, although certain treatments and temperatures for nanoparticles had greater CO or C6H6 sensitivity than nanowires, nanowire sensitivity was less temperature dependent than nanoparticle sensitivity. Prior materials characterization data were combined with resistance data to elucidate specific structure-property-performance relationships for the different UT and plasma treated materials.Item Open Access Enabling and understanding low-temperature kinetic pathways in solid-state metathesis reactions(Colorado State University. Libraries, 2020) Todd, Paul Kendrick, author; Neilson, James, advisor; Finke, Richard, committee member; Prieto, Amy, committee member; Henry, Chuck, committee member; Ma, Kaka, committee memberFor the kinetic pathway to influence the outcome of a solid-state reaction, diffusion barriers must be lowered or circumvented through low-temperature chemistry. Traditional ceramic synthesis use high temperatures to overcome diffusion, yet they result in the thermodynamically stable product. If the desired product lies higher in energy, they are unattainable at such temperatures. Extrinsic parameters, like pressure, can be used to change the stability of products (kinetic trapping), yet require extreme conditions. Another strategy involves kinetically controlling the energy barriers of the reaction to select for a given product. Here, we use solid-state metathesis reactions to understand and control kinetic pathways in the formation of complex oxides and binary metal sulfides. Through simple changes to precursor composition, three unique polymorphs of yttrium manganese oxide are synthesized, two of which are metastable phases. Using in situ diagnostics, the reaction pathways are characterized to identity intermediates and the temperature regimes at which they react. Using this information we identify why different polymorphs form using different precursors. Additionally, small functional organosilicon molecules are shown to catalyze the formation of iron(II) sulfide using metathesis reactions. Here we show that the Si-O functional group stabilizes intermediate species along the pathway to avoid forming more stable intermediates. The result is higher yields of FeS2 at lower temperatures and times. The included chapters will hopefully better inform future solid-state chemists when exploring new composition spaces and reaction pathways.Item Open Access Exploring phase selectivity and morphological control in Cu-Sb-Se nanoparticle synthesis(Colorado State University. Libraries, 2023) Kale, Amanda R., author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Ma, Kaka, committee memberNanoparticles are used in a variety of applications, such as optoelectronics, medicine, and energy generation and storage. Different applications necessitate different nanoparticle compositions and morphologies. Thus, developing fine synthetic control over composition, phase, and morphology is of interest to the field. Solution-phase nanoparticle synthesis allows control over particle shape and size, though phase purity is often an issue in ternary syntheses. Often precursor reactivity must be balanced to avoid binary sinks; however, in the Cu-Sb-Se system, the ternaries compete with one another. In this dissertation we explore the knobs of a hot-injection synthesis in oleylamine that can be tuned to favor different Cu-Sb-Se ternary phases and control particle morphologies. In Chapter I we begin with a discussion of the term precursor reactivity and how we define it here. We also address the common frameworks used to explain reactivity, and the specific challenges of balancing reactivity in multinary chalcogenide syntheses. We also discuss how these challenges manifest in the Cu-Sb-Se system, and why the structures and phase space of this material are interesting to study. In Chapter II we discuss a guide for fitting X-ray diffraction data for complex nanomaterial systems, outlining important considerations when working on the nanoscale as well as our sequential approach to refinements and recommended best practices. We also discuss a case study on the refinements of anisotropic, multiphase systems, which we use for the following chapter. The main synthetic work follows in the next two chapters, focusing first in Chapter III on the decomposition of metastable Cu3SbSe3 to thermodynamic CuSbSe2. We investigate how this can be manipulated through the addition of an amide base. In Chapter IV, we explore tuning morphology and specifically nanosheet branching in CuSbSe2, in which we show that we can induce twinning in CuSbSe2 and initial characterization suggests that this occurs in a different manner than in the very similar sulfide system. Finally, in Chapter V we reflect on the considerations and next steps for this work, including preliminary results on the use of soft base ligands to complex Cu, as well as on promising directions of field of nanoparticle synthesis as a whole.Item Open Access Hydroxyapatite structures created by additive manufacturing with extruded photopolymer(Colorado State University. Libraries, 2019) López Ambrosio, Katherine Vanesa, author; James, Susan P., advisor; Ma, Kaka, committee member; Prawel, David A., committee memberBone tissue has the ability to regenerate and heal itself after fracture trauma. However, this ability can be affected by different risk factors that are related to the patient and the nature of the fracture. Some of the factors are age, gender, diet, health, and habits. Critical-sized defects are particularly difficult, if not impossible, to heal correctly. Particularly in large defects, bone regeneration ability is impeded, disrupting normal healing processes, resulting in defective healing, integration, and non-union. To prevent and treat defective healing or non-union, surgical intervention is needed. Surgeons implant various forms of devices between the ends of the broken bone, usually with external fixation. Implants function by guiding and enabling new bone ingrowth while giving support to the healing tissue. Some of the most common implants are autografts, allografts, and metallic endoprostheses. Unfortunately, these common techniques have drawbacks such as the risk of infection and relatively poor biological or mechanical compatibility with host tissue, in addition to the limited source of donor tissue and high cost, often resulting from secondary surgical interventions. Critical defects are particularly problematic. Hence, there is a necessity for bone implant substitutes that diminish the risk of infection and incompatibility while also providing similar mechanical properties to real bone tissue. Hydroxyapatite (HAp) is a ceramic with a chemical composition similar to bone tissue that has shown biocompatibility and osteoconductive properties with host bone tissue, but it is difficult to manufacture into complex structures with mechanical properties comparable to bone tissue. Therefore, significant efforts are directed to produce materials and methods that could produce HAp synthetic implants to treat bone defects. This research aimed to create and characterize a hydroxyapatite photo-polymeric resin suitable for 3D printing, which could produce dense HAp ceramic parts in complex shapes without requiring support material. We created a HAp-based photopolymer slurry that achieved 41 vol% HAp loading in homogenous slurries. The HAp slurries presented a strong shear thinning behavior and dispersion stability over 20 days under dark storage conditions. The resultant rheological behavior of HAp slurries enabled 3D printing of HAp green bodies in complex shapes using a combination of viscous extrusion and layer-wise photo-curing processes. Complex structures with concave and convex forms and scaffolds with interconnected pores ranging from 130 µm to 600 µm pore sizes and 10% to 40% porosity were successfully built with high resolution and no support material. Moreover, HAp/PEGDMA green bodies presented complete layer cohesion. After 3D printing, sintering was used to densify HAp structures and eliminate the polymer matrix. The resultant HAp structures maintained their complex details, had a relative density of ~78% compared to fully dense HAp and a dimensional shrinkage of ~15% compared to its green body. Sintered HAp structures were found to be non-cytotoxic for ADSCs cells. Flexural properties of HAp green and sintered structures were also determined. It was found that green bodies had a flexural strength of ~30.42MPa comparable to trabecular bone. To summarize, a photopolymerizable resin with 41 vol% of HAp was created to produce ~78% dense HAp complex structures. This was achieved by using additive manufacturing that combined viscous extrusion and layer-wise photo-curing and a sintering process. HAp/PEGDMA showed flexural strength comparable to the trabecular bone, and HAp sintered structures demonstrated non-cytotoxic behavior.Item Open Access Interfacial modifications in fiber reinforced geopolymer matrix composites for improved toughness(Colorado State University. Libraries, 2017) Jackson, Patrick R., author; Radford, Donald, advisor; Heyliger, Paul, committee member; Kota, Arun, committee member; Ma, Kaka, committee memberGeopolymers have emerged in the recent decades as a potential matrix material for advanced composites. Geopolymers, or more generically inorganic polymers, extend the use temperature range over more common organic polymers, while retaining relatively low processing temperatures. In fact, some of the techniques used to process geopolymers are very similar to those developed for thermosetting polymers. This allows for processing of near net shape components without many of the complexities that would be associated with conventional ceramics or metals manufacturing technologies. To-date, fiber reinforced geopolymers have seen limited use, primarily in areas that emphasize high temperature resistance and good manufacturability over structural performance. The use of all-oxide geopolymer matrix composites (GMC) for high temperature structural applications remains uncertain due to limited toughness. Attempts to improve toughness in these materials through the use of an interphase material, such as those associated with ceramic matrix composites (CMC), have yielded mixed results. In some cases, an increase in toughness was observed, but at the expense of modulus and sometimes strength. The result was a composite that was less tough, or no tougher, than the composite with the untailored interface condition. Additionally, methods that would indicate differences between the tailored and untailored interface have not been employed leaving uncertainty as to what is providing improved toughness. This research examines the ability of weak interface concepts, often employed in ceramic matrix composites and created using fiber coatings, as means of producing greater toughness in GMCs exposed to elevated temperatures. This was accomplished through examination of composite mechanical properties and interfacial conditions. Geopolymer matrix composites reinforced with the 3M Nextel series of ceramic fibers were fabricated and exposed to elevated temperatures. From the fabricated composites, samples were prepared for testing in flexure, tension, short beam shear, and single fiber push-out. Microscopy techniques were employed to analyze fracture surfaces and results of push-out testing of composites. Both a model coating, carbon and thermally stable oxide coating known as monazite were applied to the surface of fibers and compared against a baseline condition to support the changes observed. The results of the research indicate the importance of ensuring adequate cure time of the geopolymer matrix, which enhances it properties. In GMCs using carbon coated fibers to achieve a weak interfacial condition, low mechanical properties of inadequately cured matrix produced composites with limited shear resistance and limited ability to transfer stresses to fibers. A moderate increase in the mechanical properties of the matrix via extended cure time from 1 to 5 hours resulted in a roughly 50% increase in modulus and 150% increase in strength for GMCs containing the interphase material. In all cases the use of fiber coatings resulted in a reduction of interfacial strength. This was revealed by fiber push-out testing, which constitutes the first known use of this technique in GMCs to directly analyze the strength of the bond between the fiber and the matrix. Analysis of the interfaces in specimens further revealed that simple reductions in bond strength are not sufficient for producing better toughness and mechanical properties in GMCs, but that there is a delicate interplay between the interface properties and improved mechanical behavior. Increased toughness was observed in the specimens containing the carbon coated and monazite coated fiber surfaces except in the instance where coating was degraded by the oxidizing environment. GMCs containing the monazite coated fiber demonstrated the greatest improvement in toughness. The improvement in toughness was the result of increased damage tolerance and also a roughly ~32 to 44% increase in strength as compared to GMCs without coated fiber surfaces. Both limited and elongated elevated temperature exposure did not limit greater toughness from being achieved in monazite coated fiber GMCs as compared to those composites without coatings. In general, the use of fiber coatings did improve the toughness of GMCs as result of weaker interfacial conditions and it was demonstrated that careful tailoring of the interfacial strength can result in retention of mechanical properties.Item Open Access Material validation and part authentication process using hardness indentations with robotic arm implementation(Colorado State University. Libraries, 2021) Weinmann, Katrina J., author; Simske, Steve, advisor; Chen, Thomas, committee member; Ma, Kaka, committee member; Zhao, Jianguo, committee memberIn today's global economy, there are many levels of validation and authentication which must occur during manufacturing and distribution processes to ensure sufficient cyber-physical security of parts. This includes material inspection and validation during manufacturing, a method of track-and-trace for the entire supply chain, and individual forensic authentication of parts to prevent counterfeiting at any point in the manufacturing or distribution process. Traditionally, each level of validation or authentication is achieved through a separate step in the manufacturing or distribution process. In this work, a process is presented that uses hardness testing and the resulting indentations to simultaneously provide three critical functions for part validation and authentication: (i) material property validation and material property mapping achieved by administering multiple hardness tests over a given area on the part, (ii) part serialization that can be used for track-and-trace through administering hardness tests in a specific 'barcode' pattern, and (iii) the opportunity for forensic-level authentication through use of high-resolution images of the indents. Additionally, a fourth manufacturing advantage is gained in the provision of improved bonding potential for adhesive joints provided by the increase in surface area and surface roughness resulting from the addition of indents to the adherend surface. A methodology for implementing this process using a robotic arm with an end-effector-mounted portable hardness tester is presented. Implementation using a robotic arm allows a high degree of customizability of the process without changes in setup, making this process ideal for additive manufactured parts, which are often custom or low-batch and require a higher level of material validation. As a whole, this work presents a highly-customizable, single-step process that provides multi-level quality control, validation, authentication, and cyber-physical security of parts throughout the manufacturing and distribution processesItem Open Access Method for creating functionally graded materials with spark plasma sintering and a continuous machine for future scalability(Colorado State University. Libraries, 2017) Colasuonno, Paul S., author; James, Susan, advisor; Ma, Kaka, committee member; Neilson, James, committee memberThis work develops a quantitative process to sinter functionally graded materials (FGMs) to specific porosity gradients using Spark Plasma Sintering (SPS). The powder densification in SPS is modeled using the Master Sintering Curve (MSC) calculated from shrinkage due to three different heating rates. The meaning of the apparent sintering activation energy is discussed along with the MSC's applicability to SPS. The MSC is adjusted for the additional sintering that occurs during cooling, such that porous materials can be produced by interrupting the heating schedule. The temperature in the powder is then spatially resolved by a constructed thermal-electric FEA model. Tooling is designed to apply a steady state temperature gradient (50°C/mm) on zirconia (+3% mol yttria) powder. The MSC, coupled to the thermal-electric model, is used to spatially predict densification in a temperature gradient. Resulting FGM microstructures and grain size distributions are discussed. Design problems found while attempting to scale the FGMs process to larger diameters are quantified. As an alternative to traditional SPS batch processes, a Continuous Electric Field Assisted Sintering (CEFAS) machine is developed to address these practical limitations from a new direction. The proof of concept CEFAS machine uses Joule heated rollers to continuously heat, compress, and extrude material under conditions analogous to SPS. Design considerations, lessons learned, and control variables for future iteration CEFAS machines are illustrated.Item Open Access Modeling deformation twinning in BCC transition metals(Colorado State University. Libraries, 2023) Faisal, Anik H. M., author; Weinberger, Christopher, advisor; Radford, Donald, committee member; Ma, Kaka, committee member; Heyliger, Paul, committee memberDeformation twinning is one of the important deformation mechanisms in body centered cubic (BCC) transition metals, especially under low temperature and high strain rate conditions. Plastic deformation via deformation twinning has been studied for decades both experimentally and computationally however, atomic level insights such as critical nuclei size, their local atomic structures and energetics which are important parameters in modeling twin nucleation has been lacking. In this work, deformation twins in BCC transition metals and their atomic level structures and energetics have been rigorously studied to reveal the full atomic level details of twin nucleation and propagation. As such, critical thickness of deformation twins in BCC transition metals have been a topic of debate with many computational and experimental studies accepting a three-layer twin thickness based on nucleation from a screw dislocation without proof whereas recent in-situ experiments suggest six-layer thick twin nuclei observed via High resolution transmission electron microscopy (HRTEM). In this study, we have determined the critical twin nuclei thickness in these metals using atomistic simulations to examine atomic structure and energetics of deformation twins under both zero and nonzero finite pure shear stresses. Our study reveals that twins in group VB BCC transition metals nucleate as two-layer thick nuclei under stress as opposed to the three-layer thick twin nuclei under zero stress. For group VIB BCC transition metals, for both zero and nonzero stresses, the critical twin nuclei thickness is two layer near reflection. As the twins grow and stress is relieved, twins under finite stresses adopt configurations that are much closer to the zero stress stability predictions. In addition to nucleation, growth of mechanisms of twins are explored and computational insights into the growth of twins in Tungsten bicrystals explaining multi-layer growth as opposed to layer-by-layer growth associated with small barriers. Free-end string simulations were used to investigate energy barrier associated with homogeneous twin nucleation using embedded atom method (EAM) potentials. Since homogeneous twin nucleation occurs near the ideal strengths of the material described by the potentials, energy barrier calculations were not possible for all BCC transition metals as some available potentials break down under large stresses. Moreover, density functional theory (DFT) simulations are known to be more accurate in describing atomic bonding but direct nucleation simulations in bulk crystals is prohibitively expensive. Hence, existing dislocation nucleation models are thoroughly analyzed to examine the behavior of these models near ideal strength of the material because spontaneous nucleation of dislocations occurs at high stresses. From there, a robust homogeneous twin nucleation model that includes elastic interaction among the twinning dislocation loops is developed which is able to replicate energy barrier data from free-end string simulations for multiple interatomic potentials. This model takes atomistic simulation inputs such as the concurrent twinning generalized stacking fault (GSF) energy curves and corresponding burgers vector of the twinning dislocations to compute the energy barriers as a function of applied stress. This model can be useful in modeling homogeneous twin nucleation all BCC transition metals and has the potential advantage of using DFT simulation inputs for accurate description of atomic bonding within the twin nuclei. Finally, nucleation stresses for twinning in bulk crystals have been studied to investigate whether the formation of twinning in experimental studies were initiated by homogeneous nucleation. Upper and lower bounds of stress values required for homogeneous twin nucleation has been computed and a semi-empirical model has been developed to predict homogeneous twin nucleation stresses as a function of temperature and strain rate. This analysis shows that reported critical resolved shear stress (CRSS) values in experimental studies are not associated with homogeneous twin nucleation despite some modeling studies claiming otherwise.Item Open Access Multiscale study of the pearlitic microstructure in carbon steels: atomistic investigation and continuum modeling of iron and iron-carbide interfaces(Colorado State University. Libraries, 2018) Guziewski, Matthew, author; Weinberger, Christopher, advisor; Heyliger, Paul, committee member; Kota, Arun, committee member; Ma, Kaka, committee memberWhile the behavior of carbon steel has been studied extensively for decades, there are still many questions regarding its microstructures. As such, classical atomistics is utilized to obtain further insight into the energetics, structure, and mechanical response of the various interfaces between iron and iron-carbides. Simulations were constructed for the commonly reported orientation relationships between ferrite and cementite within pearlite: the Bagaryatskii, the Isaichev, and the Pitsch-Petch, as well as their associated near orientations. Dislocation arrays are found to form for all orientation relationships, with their spacing and direction a function of lattice mismatch. Within each orientation relationship, different interfacial chemistries are found to produce identical dislocation spacings and line directions, but differing interfacial energies. This chemistry component to the interfacial energy is characterized and it is determined that in addition to the lattice mismatch, there are two structural factors within the cementite terminating plane that affect the energetics: the presence of like site iron pairs and proximity of carbon atoms to the interface. Additionally, an alternate method for determining the interfacial energy of systems in which there are multiple chemical potentials for a single element is developed and implemented, an approach which is likely valid for other similar systems. Atomistics finds the Isaichev orientation relationship to be the most favorable, while the "near" orientation relationships are found to be at least as energetically favorable as their parent orientation relationships. A continuum model based on O-lattice theory and anisotropic continuum theory is also applied to the atomistic results, yielding interfacial energy approximations that match well with those from atomistics and allowing for the characterization of the Burgers vectors, which are found to lie in high symmetry directions of the ferrite on the interface plane. The continuum model also allowed for the analysis of the system with changing lattice and elastic constants. This revealed that while most of the orientations had relatively small variation in their energetics with these changes, the Isaichev orientation was in fact very sensitive to variations in the lattice constants. The use of temperature dependent values for lattice and elastic constants suggested that while the Isaichev is most favorable at low tempertaures, other orientations may become more favorable at high temperatures. This combined atomistic/continuum approach was also applied to the austenite-cementite system and used to compare the proposed habit planes of both the Pitsch and Thompson-Howell orientation relationships. This analysis found the two orientation relationships to be unique, a point of previous contention, with the Pitsch the more favorable. Atomistic modeling was further used to investigate the mechanical response to compressive and tensile straining of the pearlitic orientation relationships. A range of interlamellar spacings and ferrite to cementite ratios are considered, and values for important mechanical properties including elastic modulus, yield stress, flow stress, and ductility are determined. Mechanical properties are shown to be largely dependent on only the volume ratios of the cementite and ferrite, with the interlamellar spacing having an increasing role as it reaches smaller values. Slip systems and Schmid factors are determined for a variety of loading states in both the transverse and longitudinal directions and were used to fit to simple elasto-plastic models. Transverse loading is observed to follow simple 1-D composite theory, while longitudinal loading requires the consideration of the strain compatibility of the interface. Orientation, and specifically the alignment of slip planes in the ferrite and cementite, was also determined to play a role in the mechanical response. Alignment of favorable slip planes in the cementite, notably the {100}θ and {110}θ, with high symmetry directions in the ferrite was found to greatly enhance the ductility of the system in longitudinal loading, as well as allow for lower flow stresses in transverse loading.Item Embargo Synthesis and discovery of mixed-anion nitride materials(Colorado State University. Libraries, 2023) Storck, Emily N., author; Neilson, James R., advisor; Ackerson, Chris J., committee member; Ma, Kaka, committee memberThe ability to synthesize heteroanionic (or mixed-anion) materials is an important area in solid-state chemistry research. Mixed-anion compounds offer the potential to provide more desirable functionality compared to single-anion systems. However, mixed-anion systems are underexplored compared to single-anions. This is especially true for nitride materials when compared to oxides, because nitrides are difficult to make. The ease of making most oxides is due to the reactivity of oxygen and the thermodynamic stability of metal oxides, whereas the strong triple bond of N2 leads to its low reactivity and therefore difficulty in making nitrides and oxynitrides. Therefore, improved synthetic routes to produce these mixed-anion compounds are needed to unlock the potential of this underexplored phase space. This thesis describes the use of solid-state metathesis reactions to produce heteroanionic ZrNCl through reaction between AyNCl (A = Zn, Mg, or Li) precursors and ZrCl4. This thesis also highlights the use of flux reactions in attempts to synthesize new oxynitride materials based on the hypothesis that alkali halide salts have the ability to solublize nitrogen and raise its chemical potential relative to the chemical potential of nitrogen in traditional solid-state reactions to produce nitrides and oxynitrides, allowing for incorporation into products to form an oxynitride material. Here, a eutectic flux mix, LiCl-KCl, was used in the reaction between V2O3 and Li3N to synthesize vanadium containing compounds along with preliminary experiments to ascertain their stiochiometry.Item Open Access The effects of point defects and microstructure on the pseudo-elasticity of ThCr2Si2-type crystals(Colorado State University. Libraries, 2018) Bakst, Ian Nathaniel, author; Weinberger, Christopher R., advisor; Ma, Kaka, committee member; Neilson, James R., committee member; Radford, Donald W., committee memberTernary intermetallic compounds with the ThCr2Si2-type structure, which are known for their high-temperature superconductivity, have recently garnered interest due to the discovery of a pseudo-elastic mechanical response to compression along the c-axis. However, the effects of point defects and doping on this response remain unknown. In this work, these effects are investigated with density functional theory (DFT) in conjunction with continuum-scale models. DFT simulations of hydrostatic and uniaxial compression of pure ThCr2Si2-type crystals were conducted. The magnetic phase transition of CaFe2As2 was reproduced, while LaRu2P2 exhibited a continuous transition into its collapsed tetragonal phase. The two-phase DFT data was used to build a continuum-scale, thermodynamically-driven composite model which predicts the pseudo-elastic response of a large sample under displacement control and load control scenarios. Strain along the c-axis was shown to be the critical parameter in predicting crystal collapse. Then, DFT simulations of defected or doped unit cells were conducted to investigate their energetics and mechanical responses to compression. In some cases, the addition of vacancies effectively suppressed the pseudo-elastic response of the crystals. Simulations of crystals doped with varying concentrations revealed alterations of the mechanical properties as well. Tunable variability of the phase change with respect to dopant concentration was predicted in disordered doped structures, while multiple phase changes were predicted in ordered doped structures. Composite models were then built with the DFT data to predict the response of a sample comprised of multiple microstructures. The models predict a wide range of variability in the mechanical behavior and provide insight into how impurities and defects can be used to tune the response of these materials.Item Embargo Thermally-assisted frontal polymerization for rapid curing of fiber-reinforced polymer composites(Colorado State University. Libraries, 2024) Naseri, Iman, author; James, Susan, advisor; Bailey, Travis, committee member; Herrera-Alonso, Margarita, committee member; Ma, Kaka, committee memberFiber-reinforced polymer composites (FRPCs) are widely used in a variety of applications owing to their excellent specific mechanical properties, chemical stability, and fatigue resistance. However, the state-of-the-art technologies for manufacturing FRPCs are intensive in terms of time and energy, generate a significant carbon footprint, and require costly resources. In addition, FRPCs lack key non-structural functionalities (e.g., de-icing, damage sensing) required for many applications. Despite the enormous efforts made to improve the manufacturability of FRPCs and address the shortcomings associated with the performance of FRPCs, there is still a pressing need for alternative manufacturing technologies to enable the rapid, energy-efficient, and low-cost manufacturing of multifunctional fiber-reinforced polymer composites. In this dissertation, a novel technique for rapid and cost-effective manufacturing of multifunctional fiber-reinforced polymer composites is developed by exploiting the frontal polymerization concept and joule heating of nanostructured materials. A nanostructured paper or fabric is integrated into the composite layup to supply the energy required to trigger frontal polymerization via the Joule heating effect. In addition, the nanostructured paper remains advantageous in in-service conditions and imparts new functionalities to the host composite structure. In the first chapter, the recent developments in material systems, as well as heating techniques reported for improving the manufacturability of FRPCs, are reviewed, and frontal polymerization (FP) as a rapid and energy-efficient technique for curing thermoset matrix composites is introduced. In the second chapter, frontal curing of multifunctional composites via a commercial nanostructured heater (buckypaper) is demonstrated, and the curing behavior of composite laminate is studied under various layup conditions. It is demonstrated that the through-thickness FP manufacturing strategy using an embedded buckypaper surface heater allows for rapid and energy-efficient manufacturing of fully cured composite panels using the conventional tooling materials utilized in the composite industry. However, the temperature profiles developed during the cure cycle, as well as the degree of cure of resin in produced composites, are greatly affected by the thermal properties of the tooling materials, where lower front temperatures and degree of cure are measured for composite panels manufactured using thermally conductive tooling materials such as aluminum. This issue can be effectively addressed by preheating the dry composite layup for a few minutes. Despite the relatively uniform heat generation in nanostructured buckypaper heaters, the infrared thermal imaging of the curing process reveals that the front initiates from multiple locations and propagates in both the through-thickness and in-plane directions. In addition, the de-icing functionality is demonstrated in the cured composite as one of the several possible functionalities imparted to composite structures due to the presence of a buckypaper layer. In the third chapter, a fabric heater is developed by writing laser-induced graphene on aramid fabric using a CO2 laser and used as an integrated heater for manufacturing FRPCs via the through-thickness FP manufacturing technique. A 10 cm × 10 cm composite panel is successfully cured within only 1 minute with a total energy consumption of 4.13 KJ, which is comparable to the time and energy required for producing a similar composite panel using a buckypaper heater. In addition to composite manufacturing, flexible heaters are prepared with the addition of silicone rubber to fabric heaters. Although the addition of electrically insulating rubber negatively affects the electrothermal performance of fabric heaters, it greatly improves the durability of fabric heaters. In the fourth chapter, a facile and rapid technique for the preparation of mechanically robust nanocomposite film heaters is developed based on a frontally polymerizable resin system. The mechanical and electrothermal properties of the nanocomposite film heaters are characterized, and the produced heaters are used for out-of-oven manufacturing composite laminates. In the final chapter, the main research findings are summarized, and the recommendations for future studies are presented.Item Open Access Toolless out of build plane manufacturing of intricate continuous fiber reinforced thermoplastic composites with a 3D printing system(Colorado State University. Libraries, 2019) Bourgeois, Mark Elliott, author; Radford, Donald, advisor; Ma, Kaka, committee member; Maciejewski, Anthony, committee memberContinuous fiber reinforced composite materials are manufactured using a variety of techniques ranging from manual layup to highly automated tape and fiber placement, yet all of the processes require significant tooling to act as a form which gives the composite the desired shape until processing is complete. Once processed and rigid, the composite is removed from the tooling and the tooling is, usually, then prepared and another composite component shaped on the tool. Manufacturing on such tooling has the advantage of offering a repeatable shape in a large batch production of fiber reinforced composite parts; however, the tooling itself can be a significant time to manufacture and cost challenge. It may take a large volume of composite parts to effectively amortize the cost of the tooling, which has a finite service life. Further, once the tooling is produced, making geometry changes during a production cycle is almost impossible. Geometry changes need either remanufacture of the tooling or the development of completely new tooling sets. Thus, technologies which could reduce the required tooling for composites production are highly desirable. With the advent of additive manufacture, it has become commonplace to expect the development of components of very complex geometry built from a simple surface. However, unlike continuous fiber reinforced composites, these complex geometry 3D printed components have material properties which are, for the most part, non-directional. While fiber reinforced composites are produced in a layer-by-layer additive fashion, the key to the performance of this material family is the positioning and orientation of the continuous fiber over complex contours, which has resulted in a need for substantial tooling. Thus, if concepts related to 3D printing could be mapped into the continuous fiber reinforced composite manufacturing space, the potential may exist for a radical reduction in the amount of tooling required and a corresponding increase in the flexibility of manufacture. The current research effort implements concepts common to 3D printing to investigate an approach to producing continuous fiber reinforced structures which require no tooling. Sandwich panels are commonly used as structure based on fiber reinforced composites, with the goal of high flexural stiffness and low mass. It is most common to separate two high performance composite laminates (facesheets) with a low-density core material, generally in the form of a foam of honeycomb. A recent concept has been to replace these traditional core materials with fiber reinforced truss-like structures, with the goal of further reducing mass; however, a manufacturable solution for these truss core sandwich panels has not been developed and those processes that do exist are tooling intensive. In this work, a system was developed and demonstrated that can radically reduce the amount of tooling required for truss core sandwich panels. Pyramidal truss core sandwich panels were manufactured to test the positional fidelity of out of build plane, unsupported space manufacturing. Laminates with different lamina counts were manufactured on a substrate and in unsupported space and tested for consolidation quality. Lap shear specimens were manufactured on a substrate and in unsupported space and tested for interlaminar bond quality. Individual continuous fiber reinforced composite strand specimens were manufactured in unsupported space at varying temperatures and tested for stiffness. These truss core panels, manufactured without tooling, were compared to similar truss core panels produced by more traditional techniques. The outcome of the research performed indicates that structures could be manufactured, unsupported, in free space with good precision. The void content of laminates manufactured in unsupported space decreased by 15% as the laminate was built up while the laminate manufactured on the substrate had no significant change in void content. Unidirectional laminates placed in space showed no statistical difference in strength when compared to laminates placed on a substrate. Crossply laminates had a 33% reduction in strength compared to similar laminates placed on a substrate. Composite truss core sandwich panels manufactured with the system developed in this work were more precise than composite truss core sandwich panels manufactured with compression molding and heat fusion bonding. Increasing the placement temperature of continuous fiber reinforced thermoplastic strands increases the quality of the strand by up to 44%. Improvements to the MAGIC system have increased the composite quality by 25%. Thus, manufacturing techniques were implemented to place fiber not only within the build plane, X-Y, but also to place continuous fiber out of the build plane, X Y Z. Intricate continuous fiber reinforced thermoplastic composites were manufactured without the use of tooling. While the composites produced with the new system were less stiff than composites made with compression molding further improvements to the manufacturing system have closed the stiffness gap between the two manufacturing methods.