Vacuum-Assisted Resin Transfer Molding (VARTM) processes are becoming promising technologies in the manufacturing of primary composite structures in the aircraft industry as well as infrastructure. A great deal of work still needs to be done on efforts to reduce the costly trial-and-error methods of VARTM processing that are currently in practice today. A computer simulation model of the VARTM process would provide a cost-effective tool in the manufacturing of composites utilizing this technique. Therefore, the objective of this research was to modify an existing three-dimensional, Resin Film Infusion (RFI)/Resin Transfer Molding (RTM) model to include VARTM simulation capabilities and to verify this model with the fabrication of aircraft structural composites. An additional objective was to use the VARTM model as a process analysis tool, where this tool would enable the user to configure the best process for manufacturing quality composites. Experimental verification of the model was performed by processing several flat composite panels. The parameters verified included flow front patterns and infiltration times. The flow front patterns were determined to be qualitatively accurate, while the simulated infiltration times over predicted experimental times by 8 to 10%. Capillary and gravitational forces were incorporated into the existing RFI/RTM model in order to simulate VARTM processing physics more accurately. The theoretical capillary pressure showed the capability to reduce the simulated infiltration times by as great as 6%. The gravity, on the other hand, was found to be negligible for all cases. Finally, the VARTM model was used as a process analysis tool. This enabled the user to determine such important process constraints as the location and type of injection ports and the permeability and location of the high-permeable media. A process for a three-stiffener composite panel was proposed. This configuration evolved from the variation of the process constraints in the modeling of several different composite panels. The configuration was proposed by considering such factors as: infiltration time, the number of vacuum ports, and possible areas of void entrapment. / Ph. D.

Long fiber reinforced thermoplastic composites are used for creating lightweight, but mechanically sound, automotive components. Injection molding is a manufacturing technique commonly used for traditional thermoplastics due to its efficiency and ability to create complex geometries. Injection molding feedstock is often in the form of pellets. Therefore, fiber composites must be chopped for use in this manufacturing method. The fibers are cut to a length of 13 mm and then fiber attrition occurs during processing. The combination of chopping the fibers into pellets and fiber breakage creates a distribution of mostly short fiber lengths, with some longer fibers remaining. Discontinuous fiber reinforcements are classified as long for aspect ratios greater than 100. For glass fibers, that distinction occurs at a length of 1 mm, and for carbon fibers 0.5 mm. Traditional composite materials and manufacturing processes utilize continuous fibers with a controlled orientation and length. The use of chopped discontinuous fibers requires a method to predict the orientation of the fibers in the final molded piece because mechanical properties are dependent on fiber length and orientation. The properties and behavior of the flow of a fiber reinforced polymer composite during molding are directly related to the mechanical properties of the completed part. Flow affects the orientation of the fibers within the polymer matrix and at locations within the mold cavity. The ability to predict, and ultimately control, flow properties allows for the efficient design of safe parts for industrial uses, such as vehicle parts in the automotive industry. The goal of this work is to test material characterization techniques developed for measuring and predicting the orientation of fiber reinforced injection molded thermoplastics using commercial grade long carbon fiber (LCF) reinforced nylon 6,6 (PA 6,6). Forty weight percent LCF/PA 6,6 with a weight averaged fiber length of 1.242 mm was injection molded into center gated disks and the orientation was measured experimentally. A Linux based Numlab flow simulation process that utilizes the finite element method to model the flow and orientation of fiber reinforced materials was tested and modified to accurately predict the orientation for this composite and geometry. Fiber orientation models used for prediction require the use of empirical parameters. A method of using non-lubricated squeeze flow as an efficient way to determine the strain reduction factor, , and Brownian motion like factor, CI, parameters for short glass fiber polypropylene orientation predictions using the strain reduction factor (SRF) model was extended to use with the LCF/PA 6,6 composite. The 40 weight percent LCF/PA 6,6 material was compression molded and underwent non-lubricated squeeze flow testing. The flow was simulated using finite element analysis to predict the fiber orientation using the SRF model. The empirical parameters were fit by comparing the simulated orientation to experimentally measured orientation. This is a successful method for predicting orientation parameters that is significantly more efficient than optimizing the parameters based on fitting orientation generated in injection molded pieces. The determined orientation parameters were then used to reasonably predict the fiber orientation for the injection molded parts. The authors proved that the experimental and simulation techniques developed for the glass fiber reinforced polypropylene material are valid for use with a different, more complex material. / Doctor of Philosophy / Fibers reinforce thermoplastic polymers to create lightweight, but mechanically sound, automotive parts. Thermoplastics flow when heated and harden when cooled. This work compares two of the commonly used thermoplastics, polypropylene (plastic grocery bags, food storage containers) with a glass fiber reinforcement and a form of nylon called PA 6,6 with a carbon fiber reinforcement. Injection molding is a manufacturing technique commonly used for un-reinforced thermoplastics due to its efficiency and ability to create complicated shapes. Injection molding feedstock is often in the form of pellets. Therefore, fiber composites must be chopped for use in this manufacturing method. The fibers are cut to a length of 13 mm and then fiber breakage occurs in the injection molder. The combination of chopping the fibers into pellets and fiber breakage creates a range of lengths. This distribution consists of mostly short fiber lengths, with some longer fibers remaining. Discontinuous fiber reinforcements are classified as long for aspect ratios (the ratio of length over diameter) greater than 100. For glass fibers, that distinction occurs at a length of 1 mm, and for carbon fibers 0.5 mm. Traditional composite materials and manufacturing processes utilize continuous fibers with a controlled orientation and length, such as the weave pattern one might see in a carbon fiber hood. The use of chopped fibers requires a method to predict the orientation of the fibers in the final molded piece because mechanical properties are dependent on fiber length and orientation. The way that the plastic flows during molding is directly related to the mechanical properties of the completed part because flow affects the way that the fibers arrange. The ability to predict, and ultimately control, flow properties allows for the efficient design of safe parts for industrial uses, such as vehicle parts in the automotive industry. The goal of this work is to test the techniques developed for measuring and predicting the orientation of fiber reinforced injection molded thermoplastics using commercial grade long carbon fiber (LCF) reinforced nylon 6,6 (PA 6,6). LCF/PA 6,6 with an average fiber length of 1.242 mm was injection molded into a disk and the orientation was measured experimentally. A computer flow simulation process that utilizes the finite element method to model the flow and orientation of fiber reinforced materials was tested and modified to accurately predict the orientation for this composite and geometry. Fiber orientation models used for prediction require the use of parameters. There is no universal method for determining these parameters. A method of using non-lubricated squeeze flow as an efficient way to determine the parameters for short glass fiber polypropylene orientation predictions was extended to use with the LCF/PA 6,6 composite. The LCF/PA 6,6 material was compression molded and underwent non-lubricated squeeze flow testing. The flow was modeled to predict the fiber orientation. The empirical parameters were fit by comparing the simulated orientation to experimentally measured orientation. This is a successful method for predicting orientation parameters. The determined orientation parameters were then used to reasonably predict the fiber orientation for the injection molded parts. The authors proved that the experimental and simulation techniques developed for the glass fiber reinforced polypropylene material are valid for use with a different, more complex material.

This work is concerned with the processing of pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The processing methods used are injection molding, sheet extrusion, and extrusion blow molding. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur during processing. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of in situ composite strand properties on the properties of the injection molded composite, the melt temperature used in injection molding, TLCP concentration, and the melt temperature of the TLCP. It was found in this work that microcomposites can be processed by means of injection molding, sheet extrusion, and extrusion blow molding. It was necessary to process the materials at low temperatures to maintain the TLCP fibrils. However, HX6000, the higher melting TLCP allowed higher processing temperatures than Vectra A. When the TLCP fibrils were maintained, the properties of the TLCP reinforced composites did show reduced anisotropy as compared to an in situ composite. The tensile strength of the composites produced by all three methods was about equal. The modulus of the injection molded composites was slightly higher than that of the composite sheets, but the composite sheets showed a lower degree of anisotropy. In all three processing methods the modulus of the TLCP reinforced composite was a function of the modulus of the in situ composite strand used to produce the microcomposite. Therefore, it is recommended that to improve the properties of the microcomposites the properties of the in situ composite strands should be improved. Furthermore, the mechanical properties of the composites increased with increasing TLCP composition. To provide a basis of comparison the properties of the extruded sheets and the injection molded composites were compared to both the predictions of composite theory and the properties of glass reinforced composites. It was found that the modulus of the 10 wt% composites approached the predictions of composite theory, but at higher TLCP loadings the modulus showed negative deviations from the predictions of composite theory. This is believed to be the result of a reduction of fiber aspect ratio due to poor fiber distribution and fiber breakup. The modulus of the TLCP reinforced composites was about the same as the modulus of the glass reinforced composites produced by both sheet extrusion and injection molding. The tensile strengths were slightly lower than that of the glass reinforced composites. It is expected that as the modulus and strength of the reinforcing TLCP fibrils are improved the properties of the TLCP reinforced composites should exceed those of glass reinforced composites. It was concluded that the processing of microcomposites is a viable means of producing composites based on TLCPs and thermoplastics with good mechanical properties and low degrees of mechanical anisotropy. / Ph. D.

Methods of processing polypropylene (PP)/ liquid crystalline polymer blends to obtain high mechanical properties from injection molded samples were investigated in this dissertation. Three liquid crystalline polymers (LCPs), two liquid crystalline (LC) copolyesters and one LC poly(ester-amide), were used. The PP/LCP blends were compatibilized with a maleic anhydride grafted polypropylene (MAP) to enhance the mechanical properties. The effect of increasing MAP content on the mechanical properties, morphology, and interfacial tension of injection molded tensile bars and plaques made from blends with 30 wt% LCP was investigated. It was determined that MAP enhances both the tensile strength and modulus, but the tensile strength is increased to a greater degree than the tensile modulus. For the LC copolyesters, the tensile strength appeared to reach a maximum while for the LC poly(ester-amide) the tensile strength increased without limit in the range of MAP contents studied. Simultaneously, a finer dispersion was created as the MAP content was increased. Calculation of the interfacial tension from contact angle measurements indicated that the interfacial tension decreased as MAP was added to the PP matrix. Analysis of the MAP concentration after blending indicated that MAP did not react with the LCP, but enhanced tensile properties resulted from physical interaction such as hydrogen bonding. This mechanism is consistent with the greater property improvements found in the LC poly(ester-amide) blends where the amide group is expected to undergo stronger hydrogen bonding than the ester group. Analysis of the injection molding of these blends found that heat transfer and solidification significantly affected the flexural modulus of these blends. Injection molding conditions such as fill time, mold thickness, mold temperature and melt temperature were investigated in three molds of different thicknesses. Different processing relationships were found between the LC copolyesters and the LC poly(ester-amide). For the former LCP blends, the highest moduli were obtained from the thinnest mold in a manner parallel to that of the moduli of neat LCPs. For the latter LCP blends, the highest moduli were obtained in the intermediate thickness mold. The differences between the copolyester and LC poly(ester-amide)s processing / property relationships were related to the melt rheology of the LCPs. For the LC copolyesters, maximum mechanical properties were obtained when the melt temperature was selected so that the storage and loss moduli of the LCP were nearly equal. This equality of storage and loss moduli could not be achieved with the LC poly(ester-amide). In addition, upon cooling, the storage and loss moduli of the LC poly(ester-amide) indicated that rapid solidification occurred while a much lower rate of solidification was indicated for the LC copolyesters. In addition the mechanical properties were sensitive to the rate of cooling as indicated by the Graetz number. It was speculated that attainment of the highest mechanical properties was related to the LCP being deformed during the filling stage followed by rapid solidification of the LCP morphology upon cessation of flow. / Ph. D.

Great improvements are continuously being made in the solid free form fabrication (SFF) industry in terms of processes and materials. Fully functional parts are being created directly with little, if any, finishing. Parts are being directly fabricated with engineering materials such as ceramics and metals. This thesis aims to facilitate a substantial advance in rapid prototyping capabilities, namely that of fabricating parts with continuously heterogeneous material compositions. Because SFF is an additive building process, building parts layer-by-layer or even point-by-point, adjusting material composition throughout the entire part, in all three dimensions, is feasible. The use of fine powders as its build material provides the potential for the Selective Laser Sintering (SLS), ThreeDimensional Printing (3DP), and Freeform Powder Molding (FPM) processes to be altered to create continuously heterogeneous material composition. The current roller distribution system needs to be replaced with a new means of delivering the powder that facilitates selective heterogeneous material compositions. This thesis explores a dense phase pneumatic conveying system that has the potential to deliver the powder in a controlled manner and allow for adjustment of material composition throughout the layer. / Master of Science

M.S.

The goal of this work is to develop and characterize a manufacturing process that is able to create metal matrix composites with complex cellular geometries. The novel manufacturing method uses two distinct additive manufacturing processes: i) fabrication of patternless molds for cellular metal castings and ii) printing an advanced cellular ceramic for embedding in a metal matrix. However, while the use of AM greatly improves the freedom in the design of MMCs, it is important to identify the constraints imposed by the process and its process relationships. First, the author investigates potential differences in material properties (microstructure, porosity, mechanical strength) of A356 — T6 castings resulting from two different commercially available Binder Jetting media and traditional 'no-bake' silica sand. It was determined that they yielded statistically equivalent results in four of the seven tests performed: dendrite arm spacing, porosity, surface roughness, and tensile strength. They differed in sand tensile strength, hardness, and density. Additionally, two critical sources of process constraints on part geometry are examined: (i) depowdering unbound material from intricate casting channels and (ii) metal flow and solidification distances through complex mold geometries. A Taguchi Design of Experiments is used to determine the relationships of important independent variables of each constraint. For depowdering, a minimum cleaning diameter of 3 mm was determined along with an equation relating cleaning distance as a function of channel diameter. Furthermore, for metal flow, choke diameter was found to be significantly significant variable. Finally, the author presents methods to process complex ceramic structure from precursor powders via Binder Jetting AM technology to incorporate into a bonded sand mold and the subsequently casted metal matrix. Through sintering experiments, a sintering temperature of 1375 °C was established for the ceramic insert (78% cordierite). Upon printing and sintering the ceramic, three point bend tests showed the MMCs had less strength than the matrix material likely due to the relatively high porosity developed in the body. Additionally, it was found that the ceramic metal interface had minimal mechanical interlocking and chemical bonding limiting the strength of the final MMCs. / Ph. D.

The InsulPatch is a novel integrated patch-pump device used to deliver drugs, especially macromolecular drugs that are difficult to deliver through an oral pathway and that require transdermal delivery. The patch-pump is a promising replacement for conventional syringes and battery-powered pumps because it is slim, powerless, painless, and relatively inexpensive. The majority of this thesis focuses on the fabrication and testing of microfluidic devices for the delivery of insulin, which is a model drug that is widely used and needs to be delivered transdermally. In this thesis, we demonstrate the fabrication of the patch-pump, which includes an insect-mimetic microfluidic pump fabricated using photolithography and replica molding, and a microneedle array fabricated using 3D printing. The microfluidic pump is used to drive the fluid flow powered by pressurized air or the user’s pulse, and the microneedle array is used to inject the fluid through the skin painlessly. Using pressurized air-driven flow testing, we have tested the flow rate across microfluidic pumps of various flow channel widths over a range of physiologically relevant actuation frequencies and pressures. We have found that for the specific channel design we have been using, the flow rate generally positively correlates with the actuation pressure. For devices with wider flow channels, the flow rate generally negatively correlates with the actuation frequency, whereas the flow rate increases and then decreases with increasing actuation frequency for devices with narrower flow channels. This property of these devices is beneficial in insulin delivery because the demand for insulin is generally reduced in vigorous exercise (with elevated heart rate/actuation frequency) and increased in hypertension patients (with elevated blood/actuation pressure). A major future direction of the study is to test a wide range of device designs in a sample of human subjects by attaching the device onto the wrist and measuring the pulse-driven flow across the device. We can further change the channel design parameters of the device so that it will be ideal for insulin delivery. Using the ex vivo flow testing and human subject data, we can further tailor the device design to specific patients using a genetic algorithm-guided optimization based on the heart rate and blood pressure of the patient and the desired flow rate. We will also perform computational modeling using COMSOL Multiphysics to predict the flow across devices of different designs as well as to understand the physics behind the pulse-driven flow. Finally, a 3D-printed insulin reservoir will be incorporated into our patch-pump system for the storage of U-500 insulin. / M.S. / The InsulPatch is a slim, powerless device (“patch-pump”) that can be used to deliver drugs through the skin, especially designed for drugs that are difficult to deliver orally. The patch technology is a promising replacement for conventional injection using syringes and bulky battery-powered pumps. At this stage, the primary drug that our device aims to deliver is insulin, which generally needs to be delivered through the skin. In this thesis, we demonstrate how our patch-pump is made and how its performance is tested. The patch-pump has two parts: the microfluidic pump and the microneedle array. The microfluidic pump is fabricated using a technique called photolithography, in which a photosensitive polymer is selectively cured by UV light, and replica molding, in which the precursor of another polymer is poured on a mold and cured. The microneedle array is made using 3D printing and designed in such a way so that it can be readily connected to the microfluidic pump. The microfluidic pump is used to drive the fluid flow powered by the user’s pulse, and the microneedle array is used to inject the fluid through the skin painlessly. Through testing the flow across the microfluidic pump prototypes using pressurized air, we characterized the correlation between the flow rate of fluid across the device and parameters including the actuation pressure and frequency of the pressurized air as well as the width of the flow channel. Future directions of the study include testing the devices in human subjects to characterize pulse-driven flow across the devices, computational modeling of the devices, and further changes of the device design to optimize the performance of the device. We will also optimize the device design computationally to tailor the device design to specific diabetic patients. Finally, we will incorporate a 3D-printed insulin reservoir into our system for the storage of insulin solution. / Withhold all access to the ETD for 1 year / patent / I hereby certify that, if appropriate, I have obtained and submitted with my ETD a written permission statement from the ower(s) of each third part copyrighted matter to be included in my thesis or dissertation, allowing distribution as specified above. I certify that the version I submitted is the same as that approved by my advisory committee.

Vacuum assisted resin transfer molding (VARTM) is a low cost resin infusion process being developed for the manufacture of composite structures. VARTM is being evaluated for the manufacture of primary aircraft structures, including foam sandwich composite materials. One of the benefits of VARTM is the ability to resin infiltrate large or complex shaped components. However, trial and error process development of these types of composite structures can prove costly and ineffective. Therefore, process modeling of the associated flow details and infiltration times can aide in manufacturing design and optimization. The purpose of this research was to develop a process using VARTM to resin infiltrate stitched and unstitched dry carbon fiber preforms with polymethacrylimide foam cores to produce composite sandwich structures. The infiltration process was then used to experimentally verify a three-dimensional finite element model for VARTM injection of stitched sandwich structures. Using the processes developed for the resin infiltration of stitched foam core preforms, visualization experiments were performed to verify the finite element model. The flow front progression as a function of time and the total infiltration time were recorded and compared with model predictions. Four preform configurations were examined in which foam thickness and stitch row spacing were varied. For the preform with 12.7 mm thick foam core and 12.7 mm stitch row spacing, model prediction and experimental data agreed within 5%. The 12.7 mm thick foam core preform with 6.35 mm row spacing experimental and model predicted data agreed within 8%. However, for the 12.7 mm thick foam core preform with 25.4 mm row spacing, the model overpredicted infiltration times by more 20%. The final case was the 25.4 mm thick foam core preform with 12.7 mm row spacing. In this case, the model overpredicted infiltration times by more than 50%. This indicates that the model did not accurately describe flow through the needle perforations in the foam core and could be addressed by changing the mesh elements connecting the two face sheets. / Master of Science

Bipolar plate material and fabrication costs make up a significant fraction of the total cost in a polymer electrolyte membrane fuel cell stack. In an attempt to reduce these costs, a novel manufacturing method was developed for use with composite materials. Conductive fillers were mixed with a polypropylene binder and molded into single cell monopolar plates. A fuel cell test stand, capable of testing six cells simultaneously, was used for long-term corrosion testing. In-situ tests took place in 5 cm2 active area fuel cells with cathode humidification. Using data from test cells containing graphite monopolar plates as a baseline, two composite formulations, were able to produce power at 66-79% of the baseline power. Power output from one cell remained in this range for over 200 hours, while the other sample experienced surface oxidation and eventually failed. With improvements in part conductivity coming from conductive polymers, this manufacturing technique holds the promise of producing monopolar and bipolar plates that could eventually be scaled up for use in fuel cell stacks. / Master of Science