Mechanical Engineering & Applied Mechanics

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Research from the Department of Mechanical Engineering & Applied Mechanics. The department website may be found at https://www.ndsu.edu/me/

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A Single-Cylinder Internal Combustion Engine Test Unit for the Engineering Laboratory
(North Dakota State University, 1962) Strege, Loren Douglas
The study of the reciprocating internal combustion engine is of prime importance to the student engineer. In our present civilization, the number of units and the total rated power of internal combustion engines in use is far greater than that of all other prime movers combined. Many basic engineering problems are present in the study of the operation of internal combustion engines. A number of mechanical and electrical devices have been developed to aid the engineer in his studies of engine performance. The purpose of this project is to provide the Mechanical Engineering Department of the North Dakota State University with an addition to its laboratory facilities which will enable the student to do additional experimental work in the internal combustion engines field.
Impact. of Environmental Conditions on Fiberglass-reinforced Polyurethane Foam Composites
(North Dakota State University, 2010) Fisk, Aron Mark
Incorporating reinforcement within a polymer (i.e. composite) can obtain substantial performance increases. However, composites may he susceptible to conditions that could have a significant impact on their performance. The objective of this study was to characterize SpaceAge Synthetics (SAS) fiberglass-reinforced rigid, closed-cell polyurethane foam (PU) after subjected to various environmental conditions. SAS composites were characterized as a function of material composition after conditioned to extreme temperatures, moisture, ultraviolet irradiation (UV), or a combination thereof. The experimental process involved accelerated conditioning to further induce property changes and assure long-term integrity. Empirical expressions for SAS composites were generated to represent performance changes for different environmental conditions. Increasing temperature 93 °C from ambient showed an 18% decrease in strength and 24% decrease in stiffness for a 450 kg/m3 foam density reinforced with 7.6% fiber volume fraction. This performance loss resulted from the ductility of the polymer increasing with temperature. Decreasing temperature 68 °C from ambient showed a 56% increase in strength and 26% increase in stiffness. When SAS composites were subjected to moisture at room temperature, no statistical difference was observed after being exposed to l 00% RH for 72 h duration. These mechanical performance analyses included varying material parameters such as: foam density, fiber content, void content, and thickness. The addition of heat to the l 00% RH moisture drastically reduced mechanical performance up to 33% in strength and 22% in stiffness. Ultraviolet irradiation caused chemical changes within the SAS composites, which was first noted by the pronounced color shift within the yellowness index (YI). Additional reinforcement near the surface created a 269% lower shift in YI. It was observed that initially cross-linking occurred while at the same time chain scission was occurring at a larger rate. Fourier Transform Infrared Spectroscopy proved that UV penetrated 0.25 mm within the surface, showing the effects occur mainly on the surface. Finally, SAS composites exhibited a 31 % increase in strength and a 12% increase in stiffness with a post cure process. Post curing for 4 h at 100 °C raised the glass transition temperature from 119 °C to 128 °C. The performance increase was attributed from the post cure process inducing additional cross-linking within polymer chains.
Computational Simulation of Droplets Wetting on Micro and Nano Filaments
(North Dakota State University, 2010) Bedarkar, Amol Anil
In this thesis, wetting properties of liquid droplets on micro and nano filaments were explored. First, droplet-on-filament systems were considered, made of liquid droplets and wetting between parallel filaments of identical geometries and surface wetting properties. Criteria for morphology transition between barrel-shaped droplet and droplet-bridge morphology was determined in terms of critical droplet volume at varying filament spacing, droplet volume, and contact angle. A family of wetting characteristic curves was obtained as a universal law of morphology transition in such systems. Additionally, wetting lengths of the above droplet-on-filament systems were demonstrated at varying geometries and surface properties. Secondly, a surface finite element method was employed to simulate the capillary torque generated in a droplet bridge formed between two misaligned filaments at varying filament spacing, contact angle, droplet volume, and filament orientation angle. Consequently, a novel, hydroelastic model was developed to examine the capillary effect in the mechanical response of ultrathin, soft filaments wetted with droplets and subjected to axial stretching. The filament was modeled as a hyperelastic, MooneyRivlin solid, and an explicit stress-stretch relationship was determined. The results obtained in this research broaden the theoretical understanding of droplet wetting and spreading on filaments and are applicable for design and analysis of filament-based microfluidic devices, biological cell manipulators, drug delivers, fiber wetting property differentiators, etc.
Implementation Of Particle Model Control Approach To A Fixed Axle UGV
(North Dakota State University, 2010) Gupta, Nikhil
Robotic vehicles are normally modeled as rigid bodies under general motion, combining translation and rotation motions. While such modeling results in motion controllers that are easy to implement, these controllers are also limited in the number of degrees of freedom (DOF) that can be controlled. The robotic vehicle with limited DOF operates well in structured terrain conditions with sufficient stability and friction. When the vehicle is operated in unstructured terrains, such as those that are sandy, snowy, or steep terrains, which might be slippery, such an approach fails to operate well. Since additional applications of robotic vehicles are in unstructured terrains, it is important to find alternative control models that will increase the number of controllable DOF and add more robustness and flexibility to the vehicle's performance. This thesis proposes the modeling of a vehicle as a system of particles centered at the wheels, with each particle controlled independent of one another in order to achieve the desired vehicle motion. In this work, the Particle Model Control approach was tested on the robotic platform BIBOT-1. The work illustrated the major vehicle kinematics under different steering modes and how the controls for the robotic motion can be formulated on the basis of Particle Modeling. A control system, based on Particle Modeling using decentralized control architecture, was designed and tested on BIBOT-1. The preliminary test results obtained from the trial runs were then analyzed on the basis of root mean square (R.M.S.) error performance factors. Some future work was also suggested in order to gather more results and validate the modeling approach.
A Molecular Dynamics Study of Mechanical Properties of Carbon Nanotube Polymer Composites and Graphene Nanoplatelet Polymer Composites
(North Dakota State University, 2010) Yerramaddu, Suchitra Reddy
Carbon nanotubes have been the main focus in science and engineering fields lately for their extraordinary properties. But carbon nanotube fabrication process is very expensive, particularly for reinforcements and structural composite applications. Instead of working towards developing lower cost nanotubes, an alternate solution to resolve the problem is to formulate a cost effective reinforcement referred to as graphene nanoplatelets. These nanoplatelets have excellent mechanical as well as electronic properties opening up for several applications in various fields. Their structure with carboncarbon bonds make them stronger and stiffer. Single nanotubes can be used as reinforcements in one direction, while the graphite nanoplatelets are effective in two directions yielding a higher degree of stiffness and strength in a matrix In this thesis, a molecular dynamic computer simulation technique was used to explore the atomic scale and dynamics of graphene nanoplatelets and carbon nanotubes embedded in polyethylene matrix. The mechanical properties of the carbon nanotubes and nanoplatelets polymer composite models were studied individually along with a comparison between composite models. The overall system was modeled using material studio software with the implementation of periodic boundary conditions to determine the properties. The stress strain curves revealed that the length and the volume fraction of the nanotube/nanoplatelets had a significant effect on the mechanical properties of the composite. The stiffness of the composite with long reinforcement length increased relative to the polymer in the longitudinal direction and shows an anisotropic behavior. Significant enhancement was observed in the Young's modulus with the increase in the volume fraction of the nanotubes/nanoplatelets because of the well known effect of the increase in the load transfer between the polymer and the reinforcements. Also increasing the volume fraction of the short nanotubes/nanoplatelets provided very little improvement in stiffness compared to the longer length nanotubes/nanoplatelets. Results also showed that the graphene nanoplatelet reinforced composite properties were very comparable to the nanotubes reinforced composites even under weak vander Waal interactions.
Foaming Kinetics of Closed Cell Rigid Polyurethane Foam
(North Dakota State University, 2010) Meyer, Kimberly Nicol
Rigid polyurethane foams have shown promise in several applications as a means to reduce weight without compromising structural properties. Information about the chemical formula of the liquid components, the reaction to produce foaming, and the curing kinetics of rigid polyurethane foam are discussed. The chemical formulas of the liquid components are described, and the reaction required to produce foaming and cure of the polyurethane is stated. The foaming kinetics of the polyurethane were determined based on experimental work as well as theoretical modeling. It was determined that there was a relationship between the initial load the frame was placed under and the amount of pressure measured during the foaming process. The theoretical modeling was conducted for an equilibrium scheme as well as viscosity and diffusion controlled stages. Each of the models predicted the bubble growth to be much quicker than was seen in experimental work, but captured dimensional properties in the foam. The curing kinetics of the liquids and thermal profile of the foaming reaction were measured and a plan for incorporation into future modeling is discussed.
Parametric Investigation of a Dielectric Barrier Dishcarge Plasma Actuator
(North Dakota State University, 2010) Bejawada, Narender Goud
The dielectric barrier discharge (DBD) plasma actuator is considered an effective flow control device in various aerospace applications such as drag control, lift control, and stall control. The DBD plasma actuator has many potential benefits in active flow control applications, such as an absence of moving parts and low power draw. Numerous studies have been done to estimate the effect of plasma flow on specific aerospace applications. These studies have revealed that the performance of the plasma actuator depends on a number of parameters, such as operating voltage and currents, materials, and the surrounding air velocity, to name a few. Unique combinations of these parameters are required for optimal performance of the actuator; therefore, robust parametric studies have been undertaken to fully predict the plasma-based flow fields. The present study focuses on evaluating the influence of electrical, geometrical and material parameters on the single DBD plasma actuator flow. The electrical parameters include voltage and frequency, whereas electrode gap orientations and dielectric materials are considered geometrical and materials parameters, respectively. The parametric study was done by estimating the plasma-induced velocity in quiescent media with the Particle Image Velocimetry (PIV) system for various actuator settings and operating conditions. The effects of the above parameters and characteristic behavior on the single DBD plasma actuator are discussed and compared. The obtained maximum velocities for different settings and operating conditions are used as a basis for comparison. Results showed that the operating voltage was the maJor parameter influencing the actuator performance, and the electrode gap orientations (±1 mm) had negligible effect. IV
Experimental Characterization of a Novel Integrated Flow Control Method
(North Dakota State University, 2010) Baqui, Muhammad Niamul
Flow control methods can be used in many areas of aerodynamics such as separation control, wind turbines, landing gears and micro satellites. Flow separation in the boundary layer is one of the fundamental problems of aerodynamics. Separated flow in the airfoil boundary layer causes the aircraft to stall. Blowing and Dielectric Barrier Discharge (DBD) Plasma Actuator based techniques have proven successful in limited applications of separation control. However, Blowing techniques require high pressure source and Plasma Actuators are only successful in low speed application. The current research incorporated experimental techniques in characterizing a novel integrated flow control method by combining blowing flow control with Dielectric Barrier Discharge (DBD) Plasma Actuator based flow control. Integrated control would be applicable in wider flow domain than individual plasma or blowing. Initially, characterization experiments were performed as a proof of concept for the integrated control and then, the integrated control was applied in airfoil separation control. Characterization experiments were performed with a vertically fired cylindrical jet having plasma actuator around the jet periphery. The cylindrical jet was used to simulate blowing. The results obtained from characterization experiments indicated 63% reduction in blowing ratio due to plasma addition. The integrated control was placed on NACA 0025 airfoil with blow opening at 25% x/C and plasma actuator at 25.5% x/C location. Windtunnel tests were performed at freestream velocities of 3 mis and 4.5 mis with airfoil angle set at 10 degree. Results indicate 110% increase in airfoil near wall velocity for 3mls when integrated control was applied. Separation was experienced in the region when other flow control methods were used.
Performance Prediction Model for a Hybrid PVT System
(North Dakota State University, 2010) Hasan, Md. Arif
Photovoltaic cells convert, depending on the cell type, 6-18% of the incoming solar radiation into electricity with a higher percentage converted into heat. The heat in turn affects the cell temperature which has direct impact on its efficiency. In literature, both water and air have been used for PV cooling through a thermal unit attached to the back of the module yielding a photovoltaic-thermal (PVT) system. But the use of water requires more extensive modifications to prevent leakage and corrosion. Hence, an air channel operating on forced convection that would substantially improve the heat transfer aspects was chosen. This study investigates the performance of a low-cost heat-extraction improvement in the channel of a PVT air system that achieves higher thermal output and PV cooling while keeping the electrical efficiency at acceptable level. This study presents the use of a "helical insert" along the air channel as heat transfer augmentation that improves the PVT system's overall performance. Based on energy balance of each component of PVT system, an analytical expression for the temperature of the PV module, back wall and the outlet air has been derived. The developed model was first validated with the experimental data obtained by researchers. By confirming a good agreement with the experimental data, simulations were carried out to optimize various operating parameters, like the channel hydraulics, air mass flow rate, twist angle of helical insert and number of inserts. Then the steady-state thermal efficiency of the modified system equipped with helical insert is compared with those of typical PVT air systems. The modification results in a substantial increase m the overall thermal and electrical efficiencies to about 66.5% and 13.5%, respectively. Hence, these techniques would positively impact the applications of PV systems, more specifically Building Integrated Photovoltaics (BIPV).
Potential for Industrial Vehicle Electrical Applications
(North Dakota State University, 2011) Hill, Aaron Glen;
Synthetic metals are a branch of material science that deals with conducting organic molecules. The quantum mechanics of these materials show that doping can fundamentally change the conduction method and significantly increase their conductivity. Addition of conductive fillers to these synthetic metals can create a composite with even higher conductivities, with the most promising being carbon nanotubes. Ultimately, most of the research into synthetic metals is utilized for the creation of new technologies, but replacing metal in existing systems has many benefits, such as lighter weight and improved corrosion resistance. Industrial vehicle electrical systems are one such system that could benefit from synthetic metals via simplified manufacturing, assembly, and increased robustness. This paper explores the conduction methods in synthetic metals and carbon nanotubes, looks at past research on synthetic metals and conductive composites, and postulates what future research would be required to, make synthetic metals commercially viable in existing industrial vehicle applications.
Numerical Simulation of a Direct Expansion Geothermal Heat Pump Using Carbon Dioxide in a Transcritical Cycle
(North Dakota State University, 2011) Austin, Brian Thomas
Many of the synthetic refrigerants used in heat pump and air conditioning systems are potent greenhouse gases. In light of the increasing concern regarding climate change, there has been an increased interest in natural refrigerants such as carbon dioxide which have a comparatively negligible impact on climate change. Direct expansion geothermal heat pumps require a very large volume of refrigerant, making the use of a natural refrigerant particularly beneficial from an environmental perspective. In this study a numerical model has been developed to analyze the steady state performance of a direct expansion geothermal heat pump water heater using carbon dioxide in a transcritical cycle. The system incorporates a compressor, a counter-flow gas cooler, an expansion device and a ground heat exchanger which is the system evaporator. The model was developed by means of thermodynamic, heat transfer and fluid flow analysis of each component of the system. A comparison between predicted component performance and experimental results available in the literature indicated that the simulation can provide a reasonably accurate representation of an actual system. Given this verification, the simulation was used to gain an understanding of the direct expansion CO2 geothermal heat pump's performance under varying design and operating parameters. The salient parameters which were studied include: compressor speed, ground coil length, number of ground circuits and gas cooler length. The effect of monthly soil temperature variation was also investigated. The parametric study revealed several factors which are important for system optimization. First, at any given soil temperature an optimum mean evaporation temperature exists; even a small deviation from this optimum can have a significant impact on coefficient of performance. Another important factor is the number of evaporator circuits. Finally, the gas cooler and evaporator capacities were shown to have a large impact on performance; heat exchanger capacities should be matched for optimum performance. Utilizing the findings of the study, an optimized system was simulated and compared to the baseline. The optimized system achieved a coefficient of performance of 2.58, representing an 18% improvement over the baseline system. Heating capacity increased 17% to 12.3 kW. The study suggests that with further research and optimization, carbon dioxide can perform well in a direct expansion geothermal heat pump and is a suitable replacement for more environmentally degrading refrigerants.
Performance Analysis of an Advanced Emission Reduction Technology Engine During Diesel-Hydrogen Dual Fuel Operation
(North Dakota State University, 2011) Bottelberghe, Bottelberghe
The primary objective of this study was to determine the capability of a CAT engine controlled by an advanced combustion emission reduction technology (ACERT) electronic control module to operate in a dual fuel mode. A CAT 6.6-liter ACERT test engine was outfitted to operate on a hydrogen-diesel fuel mixture. A continuous stream of hydrogen was infused into the intake air charge after the turbocharger. At 50% of rated load, the addition of hydrogen, at three different speeds (1300, 1800, and 2100 RPM), was examined. The hydrogen addition varied from 0-60% of input energy. The maximum amount of hydrogen added before knock occurred, for 1300, 1800, and 2100 RPM, was 54%, 46%, and 55%, respectively. At 1300 RPM, the addition of hydrogen resulted in a decrease in specific energy consumption (SEC) for all levels of hydrogen. For 1800 and 2100 RPM, the SEC improved only when hydrogen was added beyond 46% and 55%, respectively. Emissions testing, while using hydrogen, showed a consistent decrease in carbon dioxide (CO2) emissions and an increase in nitrogen oxides (NOx) emissions for all test speeds. The carbon monoxide (CO) emissions showed improvement at levels of hydrogen exceeding 40% for all test speeds. The hydrocarbon (HC) emission did not vary during the addition of hydrogen.
Numerical Methods for Fractional Optimal Control and Parametric Problems
(North Dakota State University, 2011) Hasan, Md. Mehedi
Fractional derivatives (FDs) or derivatives of arbitrary order have attracted considerable interest in the past few decades, and almost every field of science and engineering has applications of fractional derivatives. Since fractional derivatives have such property as being non-local, it can be extremely challenging to find analytical solutions for fractional optimization problems, and in many cases, analytical solutions may not exist. Therefore, it is of great importance to develop approximate or numerical solutions for such problems. The primary focus of this thesis is to develop numerical schemes to solve optimization problems in fractional orders. Numerical methods for integer order problems of Variational Calculus, using the Euler-Lagrange equation, have already been well established. A Fractional Variational Calculus Problem (FVCP) is a problem in which either the objective functional or the constraints or both contain at least one fractional derivative term. There is a critical need to develop numerical algorithms for solving FVCPs. The main contributions of this thesis is to develop formulations and solution methods for various fractional order optimization problems, including fractional optimal control problems, linear functional minimization problems and isoperimetric problems in fractional orders. The FDs are defined in terms of the Riemann-Liouville or Caputo definitions. Numerical schemes have been developed to obtain the numerical results for various problems. For each scheme, the rate of convergence and the convergence errors are analyzed to ensure that the algorithm yields stable results. Various fractional orders of derivatives are considered and as the order approaches the integer value of I, the numerical solution recovers the analytical result of the corresponding integer order problem.
Stress-Function Variational Method and Its Applications in the Strength Analysis of Bonded Joints and Hard Coatings
(North Dakota State University, 2011) Jenson, Robert Allen
High concentrations of interfacial stress near the adherend ends are primarily responsible for the debonding failure of bonded joints, such as those structured extensively in civil and structural engineering; aeronautical, ground, and marine vehicles; and flexible electronics and microelectronic packaging. Accurate determination of these interfacial stresses is crucial to improved structural design and optimization as well as health monitoring of the structures in which such joints are found. A variety of joint models have been available in the literature for joint strength analysis and structural design. Yet, a few deficiencies still exist in most of these models in accurate prediction of joint stresses, including the violation of the generalized Hooke's law of the adhesive layers and failure to satisfy the physical traction conditions at the free edges of joint adherends. In this thesis, a generalized stress-function variational method is developed for the determination of the interfacial shear and normal stresses in general bonded bimaterial joints subjected to mechanical and thermomechanical loads. Specifically, three types of joints are considered in this study, including single-sided bonded joints, single-sided strap joints, and single-lap joints. During the formulation, two unknown interfacial stress functions are directly introduced to satisfy the traction boundary conditions of the joints; the Euler-Bernoulli elementary beam theory and 2D elasticity are used to determine the stress components of the adherends in terms of the interfacial stress functions. By utilizing the theorem of minimum complementary strain energy, the governing equations of the bimaterial joint are obtained as a system of two coupled 4th-order ordinary differential equations (ODEs) of the introduced stress functions. These ODEs are formatted into a generalized eigenvalue problem, and are further solved numerically by designing robust and efficient computational codes using MATLAB™. The results of the analysis are validated by comparison with elementary mechanics of materials as well as detailed finite element analysis (FEA) using ANSYS™; the current models can accurately satisfy the shear stress-free boundary conditions at the adherend edges. In addition, the proposed method is further applied to the analysis of progressive cracking in hard coatings. In this analysis, a cracked hard coating layer bonded onto a substrate is modeled as a single-sided bonded joint, and the expressions of strain energy derived in this study are incorporated into energy-based cracking criteria of the system. Using the above variational method, the critical loads (i.e., applied axial stress, shear force, bending moment, or temperature change) for initial cracking can be determined. Thus, the present method is also capable of modeling progressive cracking in hard coating systems.
Aerosol-Based Ultrafine Material Deposition for Microelectronics
(North Dakota State University, 2012) Hoey, Justin Michael
Aerosol-based direct-write refers to the additive process of printing CAD/CAM features from an apparatus which creates a liquid or solid aerosol beam. Direct-write technologies are poised to become useful tools in the microelectronics industry for rapid prototyping of components such as interconnects, sensors and thin film transistors (TFTs), with new applications for aerosol direct-write being rapidly conceived. This research aims to review direct-write technologies, with an emphasis on aerosol based systems. The different currently available state-of-the-art systems such as Aerosol Jet™ CAB-DW™, MCS and aerodynamic lenses are described. A review and analysis of the physics behind the fluid-particle interactions including Stokes and Saffman force, experimental observations and how a full understanding of theory and experiments can lead to new technology such as nozzle designs are presented. Finally, the applications of aerosol direct-write for microelectronics are discussed in detail including the printing of RFID antennas, contacts and active material for TFTs, the top metallization layer for solar cells, and interconnects for circuitry.
A Survey for Industrial Uses of Distiller's Dried Grains with Solubles (DDGS)
(North Dakota State University, 2012) Haugsdal, Joshua Louis
The increase in demand for corn ethanol has caused an increase in distiller’s dried grains with solubles (DDGS), which is a byproduct of ethanol production. DDGS is a cheap byproduct and is primarily used for livestock feed filler. DDGS contains oils and proteins from corn and in this research we showed that corn oil and proteins could be extracted with ethanol. Zein protein is the main protein in DDGS and has been shown to have good adhesive properties. This protein was used as a binder in biocomposites with the DDGS after extractions and soy protein isolate (SPI). Mechanical properties and water resistance of the composites were studied. A wood adhesive was also prepared using the zein and cellulose nano-fibrils (CNF) as the adhesive reinforcement. Rheological tests were performed to study the flow property of the adhesive. This research demonstrated the potential of DDGS to be used as a raw material for multiple value-added industrial uses.
The Physico-Chemical Investigation of Interfacial Properties in Natural Fiber/Vinyl Ester Biocomposites
(North Dakota State University, 2012) Huo, Shanshan
Bast fibers are one of most widely used types of cellulosic natural fibers. Flax fibers, a specific type of bast fiber, have historically been used as reinforcements in composites because they offer competitive advantages, including environmental and economic benefits, over mineral-based reinforcing materials. However, the poor interfacial properties due to the hydrophilicity of flax fibers and the hydrophobicity of most polymer matrices reduce the mechanical performance of flax thermoset composites. On the other hand, the structure of flax fiber is more complex than synthetic fibers, which causes most of traditional mechanical tests from the transverse direction to evaluate the interfacial properties of flax composites are not valid. In this study, the physical and chemical properties of flax fibers, vinyl ester resin and their composites are investigated. A comprehensive understanding of flax fiber, vinyl ester systems and their composites has been established. Surface modifications to the flax fiber and chemical manipulations on vinyl ester systems have been studied to improve the interfacial properties of flax/vinyl ester biocomposites. A new chemical manipulation method for vinyl ester system has been invented. The specific interlaminar shear strength of alkaline treated flax/VE with 1.5% AR shows approximately 149% increase than untreated flax/VE composites. NaOH/Ethanol treated flax/VE with AR shows 33% higher in specific flexural modulus and 73% better in specific flexural strength than untreated flax/VE composites. In addition, AR modified alkaline treated flax composites performs approximately 75% better in specific tensile modulus and 201% higher in specific tensile strength than untreated flax/VE composites. Flax/VE composite with high elastic modulus, which is higher than their theoretically predicted elastic modulus, was achieved. The effects of thermal properties of flax fibers and vinyl ester resin systems on the interfacial properties of their biocomposites were also studied. The theory of modifying the thermal properties of flax and vinyl ester to improve the interfacial adhesion has been proved by the study of the thermal residual stresses in their composites by XRD techniques.
Experimental Characterization of Aerosol Flows Through Micro-Capillaries
(North Dakota State University, 2012) Robinson, Michael Jake
Understanding the forces which dictate fluid particle interaction is of high interest in the field of aerosol jet Direct Write (DW). Several methods utilizing shadowgraphy and Mie scattering were used to visualize particle flow exiting micro-capillaries. Experiments were designed such that results would offer insight into the effects of Stokes and Saffman force on particle trajectories. Comparison to these results allowed for the development of a theoretical model which was validated and used to optimize nozzle geometries for particle focusing. Optimized nozzle geometries resulted in the conclusion that under certain conditions Saffman force is applicable given an appropriate correction factor. Experimental results showed the successful collimation of aerosol particles into beams with widths as small as the particles diameter. Additionally, a Small Particle Sizing Algorithm (SPSA) utilizing standard shadowgraphy techniques was developed allowing for the simultaneous sizing and positioning of particles ranging from 3-10 µm in diameter.
High-Performance Simulations for Atmospheric Pressure Plasma Reactor
(North Dakota State University, 2012) Chugunov, Svyatoslav
Plasma-assisted processing and deposition of materials is an important component of modern industrial applications, with plasma reactors sharing 30% to 40% of manufacturing steps in microelectronics production [1]. Development of new flexible electronics increases demands for efficient high-throughput deposition methods and roll-to-roll processing of materials. The current work represents an attempt of practical design and numerical modeling of a plasma enhanced chemical vapor deposition system. The system utilizes plasma at standard pressure and temperature to activate a chemical precursor for protective coatings. A specially designed linear plasma head, that consists of two parallel plates with electrodes placed in the parallel arrangement, is used to resolve clogging issues of currently available commercial plasma heads, as well as to increase the flow-rate of the processed chemicals and to enhance the uniformity of the deposition. A test system is build and discussed in this work. In order to improve operating conditions of the setup and quality of the deposited material, we perform numerical modeling of the plasma system. The theoretical and numerical models presented in this work comprehensively describe plasma generation, recombination, and advection in a channel of arbitrary geometry. Number density of plasma species, their energy content, electric field, and rate parameters are accurately calculated and analyzed in this work. Some interesting engineering outcomes are discussed with a connection to the proposed setup. The numerical model is implemented with the help of high-performance parallel technique and evaluated at a cluster for parallel calculations. A typical performance increase, calculation speed-up, parallel fraction of the code and overall efficiency of the parallel implementation are discussed in details.
Fabrication and Mechanical Characterization of Novel Hybrid Carbon-Fiber/Epoxy Composites Reinforced with Toughening/Self-Repairing Nanofibers at Interfaces
(North Dakota State University, 2012) Rahman, Md. Arifur
This research was aimed at fabrication and characterization of novel hybrid carbon-fiber/epoxy composites reinforced with toughening/self-repairing nanofibers at interfaces. For interfacial toughening, continuous electrospun polyacronitrile (PAN) and carbon nanofibers (CNFs) were incorporated between carbon fabrics to form the ultrathin toughening interlayers after resin infusion and curing. Mode I interlaminar fracture tests showed that PAN nanofibers can noticeably enhance the fracture toughness of Epon 862 based composites, while the toughening results were scattered for SC-15 resin based system. Furthermore, core-shell dicyclopentadiene (DCPD)/PAN nanofibers mats were fabricated by coelectrospinning, which were inserted between carbon fabrics and formed the ultrathin self-repairing interlayers after resin infusion and curing. Three-point bending tests showed up to 100% recovery of the flexural stiffness of pre-damaged composite specimens by the core-shell nanofibers. The research demonstrated novel high-strength, self-healing lightweight structural composites for broad applications.

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