Browsing by Author "Radford, Donald W., committee member"
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Item Embargo Advanced manufacturing of thermoset polymers and composites(Colorado State University. Libraries, 2023) Ziaee, Morteza, author; Yourdkhani, Mostafa, advisor; Radford, Donald W., committee member; James, Susan, committee member; Bailey, Travis, committee memberThermoset polymers and composites are lightweight materials extensively used in many industries from aerospace to automotive to prosthetics due to their excellent specific mechanical properties and high chemical resistance. However, these products are conventionally manufactured by labor-intensive processes using subtractive manufactured tooling or molds followed by thermal curing inside an oven or autoclave at elevated temperatures for several hours. Hence, conventional manufacturing approaches are energy- and time-consuming and require expensive equipment. Moreover, lack of design flexibility and poor repeatability are additional challenges, which limit the structural and functional capabilities of such products. In this dissertation, I present a novel approach to address the existing limitations in manufacturing thermosets and their composites by developing rapid curing resin systems and integrating them in additive manufacturing (AM) processes. In the first chapter, state-of-the-art manufacturing methods are reviewed and frontal polymerization (FP) as a promising curing strategy for rapid and energy-efficient manufacturing of thermosets and composites is introduced. In the second chapter, the effect of ambient conditioning and resin chemistry on thermal frontal polymerization of a high-performance resin system is explored. In the third chapter, FP is used to demonstrate, for the first time, simultaneous printing and curing of short carbon fiber-reinforced composites for high performance applications. In the following chapter, AM of a soft and stretchable elastomer with tunable thermomechanical properties manufactured via FP is discussed. In the fifth chapter, the printing process is further improved using an external localized heat source, instead of relying on the exothermic heat of polymerization of the resin, to accelerate the curing rate and make the printing process more robust and applicable to the manufacture of large-scale components. Finally in the last chapter, bubble-free frontal polymerization of polyacrylates is introduced for the developed 3D printing process.Item Open Access Development of biomass-derived furanic monomers for biorenewable polyesters and polyurethanes(Colorado State University. Libraries, 2019) Wilson, Jedediah Forrest, author; Chen, Eugene Y.-X., advisor; Reynolds, Melissa M., committee member; Ackerson, Chris J., committee member; Radford, Donald W., committee member; Crans, Debbie C., committee memberDevelopment of Biomass-Derived Furanic Monomers for Biorenewable Polyesters and Polyurethanes This dissertation describes the development of difuranic diol monomers through the N-heterocyclic carbene (NHC) catalyzed cross-coupling of the biomass-derived platform chemicals, 5-hydroxymethylfurfural (HMF) and furfural (FF), and their subsequent utilization in the synthesis of renewable polyesters and polyurethanes with tunable thermal and mechanical properties through the use of soft and rigid co-monomers. The resulting polymers can undergo reversible cross-linking with bis-maleimide cross-linkers through the thermally reversible Diels-Alder reaction involving both the internal and pendent furan rings. The ability to construct a thermally reversible cross-linked network, coupled with formation of a significant amount (up to 34%) of stable carbonaceous materials when heating the polymers to 700 °C, demonstrates some promising features of this class of new difuranic polymers. To address the need to enhance the molecular weight of the current furan-based polymers produced by the step-growth polycondensation process, alternative monomer structures have been designed to adopt the chain-growth mechanism. The first such alternative monomer belongs to a class of furan-derived lactones as candidates for ring-opening polymerization (ROP), which have been shown to produce high molecular weight polyesters because they follow the chain-growth mechanism. Two synthetic routes have been explored to produce such lactone monomers, and their polymerization behavior has been subsequently examined. The second such alternative is centered on a multifunctional furan acrylate monomer, methacrylate furan aldehyde (MFA). The studies tested a hypothesis that auto-tandem or cascading reaction involving the aldehyde functionality in MFA would undergo a benzoin condensation, then the consequent diacrylate would have the appropriate functionality for NHC catalyzed tail-to-tail coupling resulting in a proton transfer polymerization (HTP). It was found that the benzoin condensation was successful but an oxidation occurred at the α-hydroxy of the furoin diacrylate resulting in a highly electrophilic diketone furil diacrylate. Exploration of the coupling mechanism suggests that the enolate acts as a base catalyzing the oxidation. Through careful analysis of the adducts formed when the NHC was reacted with the furil diacrylate showed that the NHC had strong affinity for the diketone moiety thus blocking the HTP pathway. Overall, this work added significantly to our understanding of furans as monomers, NHC catalysis in furan monomer synthesis as well as polymerizations, and enhanced our ability to control thermal and mechanical properties of furan containing polymers.Item Open Access Effects of the addition of boron – nitride nanoplatelets to hydroxyapatite: processing, testing, and characterization(Colorado State University. Libraries, 2017) Aguirre, Trevor G., author; Holland, Troy B., advisor; Radford, Donald W., committee member; Neilson, James R., committee memberBioceramics range in biocompatibility from inert oxides that do not react with the body to the other extreme of materials that completely absorbed by the human body, but are prone to failure by fracture. Limited fracture toughness (KIC) and flexural strength (σFS) are major factors limiting wider scale application as structural implant materials. KIC and σFS of ceramics can be improved through grain size refinement and through the addition of various reinforcement materials. The bioceramic hydroxyapatite (HA), the primary inorganic component of bone, has excellent osteoconductivity which offers a suitable surface for new bone growth and integration but suffers from low KIC. To improve the KIC of HA we used boron nitride nanoplatelets (BNNPs), a strong and biocompatible material, making them excellent candidate for use in the human body. However, these materials have been shown to cause embrittlement of the material they are incorporated in; thus, it becomes important to understand the effect of BNNPs through analysis of the failure statistics of tested samples. Using spark plasma sintering to create these materials HA – BNNP composites with 0.5, 1.0 and 2.0 wt% BNNPs were fabricated. Sample grain sizes were measured to evaluate the effect the BNNPs had on the microstructure and the flexural strength, fracture toughness, and hardness were tested to observe the effect BNNP had on the mechanical properties of HA and as well as the failure statistics. To analyze the failure statistics of the HA BNNP composites the Weibull Distribution was used because studies have shown that the Normal Distribution does not accurately report the failure statistics of brittle materials. This work summarizes the effect of the addition of BNNPs to spark plasma sintered HA. The results of this study show that BNNPs are capable of increasing flexural strength and fracture toughness through grain size refinement but BNNPs lead to a measurable decrease in the reliability of the material, which is indicative of the predictability of measured material property value and yields information about the flaw distributions in these materials.Item Open Access Investigation of resin infusion consumable effect on fusion bond strength in the manufacture of a thermoplastic vertical axis wind turbine prototype(Colorado State University. Libraries, 2020) Bair, Jamison, author; Bradley, Thomas H., advisor; Radford, Donald W., committee member; Heyliger, Paul R., committee memberTo further research the economic viability, manufacturability, and wider adoption of Vertical Axis Wind Turbines (VAWT), a project team led by Steelhead Composites (SHC), with assistance from Colorado State University (CSU), National Renewable Energy Laboratory (NREL), and Arkema Inc. designed and fabricated VAWT rotor assembly with thermoplastic composite blades using novel fabrication techniques. Thermoplastics present many advantages over traditional thermosets including recyclability as well as the ability to be thermally welded and reformed without machining. Thermal welding, or fusion bonding can eliminate the need for adhesive bonding, a requirement in the manufacture of thermoset and thermoplastic turbine blades, as currently being produced. Colorado State University was tasked with using Elium®, a novel liquid poly methyl-methacrylate (PMMA) thermoplastic manufactured by Arkema to conduct the manufacture of protype vertical axis wind turbine blades. Elium® is a reactive, in-situ polymerizing thermoplastic that is processed using liquid processing techniques and it has mechanical properties comparable to counterpart thermosetting resins. The CSU research team developed a resin infusion molding process with closed two-part molds to create thin, hollow fiber reinforced airfoils. When high quality airfoils were successfully manufactured the team investigated the feasibility of fusion bonding end fittings into the hollow airfoils to reduce part count and mass. It was hypothesized that the consumables that produced a rough, matrix rich texture at the bond interface would lead to higher strength bonded joints. The fusion bonding focus investigated three different infusion consumables: Compoflex® RF3 a combination release film and flow media, G-FLOW™, a structural glass fiber flow media, and Release Ply Super A, a heavy weight nylon release film. The products produced varying surface textures that were measured using a surface profilometer to compare and quantify the roughness and form of the surface, to examine how the induced surface textures impacted the quality of fusion bonded joints. This hypothesis was tested via manufacture of double lap shear strength coupons which were tested via ASTM 3528. Processing parameters of the bulk heating fusion bonding process were varied included temperature, consolidation pressure and time, and cooling method. Strength testing results in addition to failure mode analysis and digital microscopy imaging were used to determine which consumables provided a higher bond strength in both glass fiber and carbon fiber Elium® thermoplastic reinforced specimens. The results of the double lap shear tests showed that with the right combination of surface texture and processing variables, lap shear strengths of over 16 MPa (2300 psi) were achieved with glass fiber reinforcements. Results indicated that more consistent strength values were obtained from infusion consumables that had smaller surface asperities, and that larger asperities often led to the inclusion of air bubbles creating voids thus reducing the strength of the bonded joints. Subsequent testing using carbon fiber as the reinforcement provided satisfactory values for lap shear strength and the team proceeded develop a process to fusion join to end attachment plates used to attach blades to the turbine hub. After successfully fusion bonding the tower to blade attachment plates into 129" long hollow airfoil sections, post-mold reforming was used to thermoform the blades into the desired geometry to complete a three-blade vertical axis wind turbine blade prototype.Item Open Access On the integration of materials characterization into the product development lifecycle(Colorado State University. Libraries, 2024) Dare, Matthew S., author; Simske, Steve, advisor; Yourdkhani, Mostafa, committee member; Herber, Daniel, committee member; Radford, Donald W., committee memberThe document is broken down into four sections whereby a more complete integration of materials characterization into the product development lifecycle, when compared to traditional approaches, is researched and considered. The driving purpose behind this research is to demonstrate that an application of systems engineering principles to the characterization sciences mechanism within materials engineering and development will produce a more efficient and comprehensive understanding of complex material systems. This will allow for the mitigation of risk, enhancement of relevant data, and planning of characterization procedures proactively. The first section proposes a methodology for Characterization Systems Engineering (CSE) as an aid in the development life cycle of complex, material systems by combining activities traditionally associated with materials characterization, quality engineering, and systems engineering into an effective hybrid approach. The proposed benefits of CSE include shortened product development phases, faster and more complete problem solving throughout the full system life cycle, and a more adequate mechanism for integrating and accommodating novel materials into already complex systems. CSE also provides a platform for the organization and prioritization of comprehensive testing and targeted test planning strategies. Opportunities to further develop and apply the methodology are discussed. The second section focuses on the need for and design of a characterizability system attribute to assist in the development of systems that involve material components. While materials characterization efforts are typically treated as an afterthought during project planning, the argument is made here that leveraging the data generated via complete characterization efforts can enhance manufacturability, seed research efforts and intellectual property for next-generation projects, and generate more realistic and representative models. A characterizability metric is evaluated against a test scenario, within the domain of electromagnetic interference shielding, to demonstrate the utility and distinction of this system attribute. Follow-on research steps to improve the depth of the attribute application are proposed. In the third section, a test and evaluation planning protocol is developed with the specific intention of increasing the effectiveness of materials characterization within the system development lifecycle. Materials characterization is frequently not accounted for in the test planning phases of system developments, and a more proactive approach to streamlined verification and validation activities can be applied. By applying test engineering methods to materials characterization, systems engineers can produce more complete datasets and more adequately execute testing cycles. A process workflow is introduced to manage the complexity inherent to material systems development and their associated characterization sciences objectives. An example using queuing theory is used to demonstrate the potential efficacy of the technique. Topics for further test and evaluation planning for materials engineering applications are discussed. In the fourth section, a workflow is proposed to more appropriately address the risk generated by materials characterization activities within the development of complex material systems when compared to conventional engineering approaches. Quality engineering, risk mitigation efforts, and emergency response protocols are discussed with the intention of reshaping post-development phase activities to address in-service material failures. While root cause investigations are a critical component to stewardship of the full system lifecycle during a product's development, deployment and operation, a more tailored and proactive response to system defects and failures is required to meet the increasingly stringent technical performance requirements associated with modern, material-intensive systems. The analysis includes a Bayesian approach to risk assessment of materials characterization efforts through which uncertainty regarding scheduling and cost can be quantified.Item Open Access Performance-based seismic retrofit (PBSR) methodology for multi-story buildings with full-scale experimental validation(Colorado State University. Libraries, 2015) Bahmani, Pouria, author; van de Lindt, John W., advisor; Heyliger, Paul R., committee member; Mahmoud, Hussam N., committee member; Radford, Donald W., committee memberRecent earthquakes such as Loma Prieta (1989) and Northridge (1994) in California have highlighted the poor performance of one class of existing buildings. Many older buildings were designed prior to the implementation of modern seismic design codes. Although building codes have clearly evolved, the problem is still unresolved for older buildings that are code-deficient such as soft-story wood-frame buildings. Many retrofit procedures have been proposed by the research and structural engineering communities including force-based and performance-based retrofit methodologies. A performance-based seismic retrofit (PBSR) methodology is developed and validated in this dissertation and is a method that seeks to meet or exceed minimum performance criteria specified by building stakeholders when the building is subjected to a predefined seismic intensity level. Unlike traditional force-based design methods, the PBSR method enables engineers to design and retrofit buildings based on the performance level expected by the stakeholders; and eventually, results in a more comprehensive method of retrofitting multi-story buildings. The objective of this study was twofold. The first objective was to develop a new displacement-based design (DBD) method with the ability to account for torsion (DBDT), thereby, generalizing the displacement-based design to be applied to linear and non-linear structures with vertical and torsional (horizontal) irregularities without the need for time-history analysis. This first objective involves the decoupling of translational and torsional mode shapes of the structure, standardizing the global stiffness and mass matrices, and finally combining the decoupled translational and torsional mode shapes to meet the designated performance criteria. The second objective was to develop a new performance-based seismic retrofit (PBSR) methodology for retrofitting existing multi-story buildings with torsional (horizontal) and vertical irregularities. The PBSR method was developed using the proposed DBDT method and was validated numerically to retrofit a three-story soft-story building with excessive torsion at all stories. The PBSR method was then modified to eliminate the torsion in the building and satisfy the designated performance criteria. This enables the design to use only the dominant translational mode shape (i.e., first mode shape) for the retrofit. This also eliminates the need for modal analysis and the decoupling of translational and torsional mode shapes makes it more straightforward for practice. The new simplified PBSR method for retrofitting multi-story buildings was then applied to a four-story soft-story wood-frame building with torsional irregularities at all stories and assessed numerically using non-linear time-history (NLTH) analysis. The method developed in this dissertation was validated experimentally by conducting a series of full-scale tests on a four-story 370 m² (4,000 ft²) soft-story wood-frame building at the outdoor uni-axial shake table at the University of California - San Diego's Network for Earthquake Engineering Simulation (NEES) laboratory. The test provided the first-of-its-kind (landmark) dataset for use by researchers and practitioners for retrofitting soft-story wood-frame buildings. The experimental test results showed that the retrofitted building met the designated performance criteria and essentially validated the PBSR method developed in this dissertation. It should be noted that although the PBSR method was only validated experimentally for the asymmetric soft-story wood-frame building, the method can be used for any type of structure provided the necessary details of design and material properties are addressed. Finally, in order to investigate the collapse mechanism of soft-story wood-frame buildings the un-retrofitted building was subjected to series of ground motion with increasing intensities until it collapsed. These series of tests are the first full-scale collapse tests of a full-size building.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.