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Browsing by Author "Radford, Donald, advisor"

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    Additive manufacture of dissolvable tooling for autoclave processing of fiber reinforced polymer composites
    (Colorado State University. Libraries, 2022) Morris, Isaac, author; Radford, Donald, advisor; Yourdkhani, Mostafa, committee member; Heyliger, Paul, committee member
    Autoclave processing of advanced fiber reinforced polymer composites (AFRPC) uses applied heat and pressure to yield high quality composite components. Geometrically accurate and thermally stable molds or tools are used to maintain the part form until the part cures and rigidizes. For high-volume production runs, molds may be made from materials such as metals, ceramics, or AFRPCs. However, tooling made from these materials can be costly to manufacture and are not suitable for low volume production runs. This is especially true for complex geometries in trapped tooling situations where the cured composite shape prevents tool separation. In this situation, composite manufacturers rely on sacrificial washout tooling materials that are machined or cast to shape to create the tool. However, these sacrificial materials still come with significant challenges. For example, the surfaces of these tools are often porous and require sealing, and their washout can result in corrosive waste that makes disposal challenging. Additionally, these tools are brittle and monolithic in nature, making them fragile to handle and slow to heat up during cure. An alternative may be to use high temperature, dissolvable thermoplastic materials in melt extrusion additive manufacturing to create complex washout tooling. However, there is a lack of information regarding the types of soluble materials and the structural configurations that make this type of tooling successful in autoclave use. To begin to address this, samples made from several materials, and one insoluble model material, were processed in stepwise fashion at increasing autoclave processing temperatures to evaluate the impacts of material and structure on autoclave robustness. Then, mid-sized composite specimens were produced on 3D-printed tooling that evaluated the interaction between the composite and the tool, including surface quality and deformation. Finally, a trapped tooling geometry was used to manufacture several composites at processing conditions of 157°C at 414kPa, well above the use temperature of the tested materials. These trials focused on reducing deformation by adjusting the tool wall thickness and vacuum bagging configuration. It was shown that 3D-printed dissolvable tooling can be used as an alternative to traditional washout tooling for autoclave processing. The materials Stratasys ST-130 and Infinite Material Solutions AquaSys 180 were used to manufacture tools that were processed at autoclave conditions of 121°C at 345kPa with minimal deformation. Surface quality was also found to be acceptable without machining or sealing, eliminating this step from the production of traditional washout tools. Finally, a modified tool design and vacuum bagging technique were demonstrated that significantly reduced the deformation of tooling at processing temperatures that significantly exceed the use temperature of the material.
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    Direct digital manufacturing of uniform thickness continuous fiber grid stiffened composites through tow spreading via roller based deposition
    (Colorado State University. Libraries, 2024) Ratkai, Harry, author; Radford, Donald, advisor; Yourdkhani, Mostafa, committee member; Heyliger, Paul, committee member
    Grid stiffened structures are an effective method for lightweighting designs. While continuous fiber composites are attractive materials for creating grid stiffened structures, there are two major impediments to the wider acceptance of such structures: the high capital costs for manufacturing and the material buildup at the crossover points. The high capital costs not only come from the complex tooling but also from the need to cure the parts after deposition. The material buildup at the crossover points is not only geometrically undesirable but can reduce the mechanical performance of the part. Many options to overcome this additional thickness have been implemented, but the majority cut the continuous fiber at the crossover, further reducing the performance. Previous work at Colorado State University has demonstrated that crossovers can be manufactured using a nozzle-based gantry printer and continuous glass fiber/PET commingled tow with a minimal thickness buildup at the crossover, all with radically reduced tooling, without compromising the structural performance. Unfortunately, the direct digital manufacturing system used did not utilize a cut and refeed system for the commingled tow; thus requiring the part to be made using continuous pathing or for a person to manually stop, cut and restart the tow at the end/beginning of each discrete path. These shortfalls of the nozzle-based printer make this technology, in its current form, impractical for adoption by industry. This work details the development of a robotic end effector for a new manufacturing method utilizing a heated roller for deposition and a programmable cut and refeed system. Initially, a comparison of the two methods of deposition, nozzle and roller, was done; both systems made crossover samples where part thickness and void and fiber volume fractions were measured. Next, an optimization of process parameters was performed on the beam and crossover sections, separately, for the roller-based end effector. Both the beams and crossovers were evaluated using thickness measurements, void and fiber volume fraction measurements and microscope imaging. Finally, a molding shoe was attached to the end effector to determine the effectiveness of molding the beam side walls, in-situ. It was demonstrated that the roller-based system can manufacture grid stiffened parts with less thickness deviations and fewer voids then the nozzle-based system. Additionally, optimized processing parameters were found for beams at three different deposition speeds, 450mm/min, 600mm/min and 750mm/min. Under the best conditions. The system is capable of direct digital manufacture of continuous fiber reinforced composite grids with under 2% void content. By slowing the deposition speed and increasing the consolidation force at the crossover points, the system is able to spread and thin the tow, thus, minimizing the thickness buildup at the crossover points. Using the understanding developed in determining optimized parameter two additional demonstrations of the capabilities of the system were completed: a preliminary example of full molding of the grid cross-section and the manufacture of curvilinear grids via in-plane steering. Combined, the outcomes demonstrate that a roller-based system with cut and refeed can produce grid stiffened structures with discrete fiber paths, that have crossovers of uniform thickness, at higher deposition rates than previous nozzle-based technology.
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    Extending the performance of net shape molded fiber reinforced polymer composite valves for use in internal combustion engines
    (Colorado State University. Libraries, 2007) Buckley, Richard Theodore, author; Stanglmaier, Rudolf, advisor; Radford, Donald, advisor
    Fiber Reinforced Composite (FRC) materials offer the possibility of reduced mass and increased structural performance over conventional metals. When used in reciprocating components of internal combustion engines, this may enable increased power and mechanical efficiency. Previously published work on FRC engine valves has both shown structural and thermal limitations.
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    Integrated optimization of composite structures
    (Colorado State University. Libraries, 2022) Lang, Daniel, author; Radford, Donald, advisor; Herber, Daniel, committee member; Chong, Edwin, committee member; Heyliger, Paul, committee member
    Many industries are exploring the application of composite materials to structural designs to reduce weight. A common issue that is encountered by these industries, however, is difficulty in developing structural geometries best suited for the materials. Research efforts have begun to develop optimization methodology to help develop structural shapes but have thus far only partially addressed optimization of the geometry. This dissertation provides a literature review of past efforts to develop optimization methodologies. Through that review it is identified that the subprocesses required to fully optimize a composite structure are mold shape optimization, ply draping analysis, kinematic partitioning, connection and joint definition, ply topology optimization and manufacturing simulations. To date, however, these subprocesses have primarily been applied individually and have not been integrated to develop fully optimized designs. In this research, a methodology is proposed to integrate established composite design and subprocesses to develop optimized composite structures. The proposed methodology sequentially and iteratively improves the design through mold shape optimization, ply draping analysis, kinematic partitioning, connection and joint definition, ply topology optimization and manufacturing simulations. Throughout the proposed methodology, checks are also integrated to ensure that the developed design meets design objectives and constraints. To test the methodology a case study is conducted to develop composite rail vehicle structures. As part of this case study, it is hypothesized that a composite structure designed through a fully integrated methodology will demonstrate reduced costs, mass and improved manufacturability compared to a structure where functions have only been partially integrated. When the proposed fully integrated methodology is applied to create a case study design, the hypothesis is validated. The design generated by the fully integrated optimization methodology has a 37% lower mass and a 56% lower cost to manufacture than a design that is developed through a partially integrated methodology. The case study also demonstrates that structures developed through the proposed methodology have improved manufacturability.
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    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 member
    Geopolymers 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.
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    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 member
    Continuous 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.