Mechanical Engineering & Applied Mechanics Masters Theses

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Additive Manufacturing of Short-Fiber Composites via Stereolithography
(North Dakota State University, 2018) Simpson, Patrick Glenn
The effectiveness of using a dual curing system, consisting of a photo and thermal initiator, for the additive manufacturing of carbon fiber short-fiber composites via stereolithography was investigated. The necessary processing parameters were developed that resulted in successful printing and curing of composites at a 5% fiber volume. The effects of layer height and print orientation of the short-fiber composites were evaluated for their effect on the material properties. There was no increase in the flexural modulus or fracture toughness, and a decrease the tensile and flexural strength of the short-fiber composites produced. This was found to be due to weak fiber/matrix interfacial properties, a wide fiber length distribution, and issues with fiber volume consistency. An increase in the tensile modulus was seen and that it could be manipulated with adjustments to layer height and part orientation.
Advanced Measurements and Analyses of Flow Past Three-Cylinder Rotating System
(North Dakota State University, 2020) Ullah, Al Habib
Interaction of flow structures from a three-cylinder system is complex and important for fundamental and engineering applications. In this study, experiments using hotwire, 2D PIV, and Tomography are to be conducted to characterize the fluid flow at various Re number and rotation speeds. The Reynolds number considered based on the diameter of the single-cylinder ranges from 37 to 1700. The peaks in the frequency spectrum obtained from the hotwire study show a unique relation of Strouhal number as a function of static incident angle, RPM, and Reynolds number. From the 2D PIV and 3D tomography experiment, vorticity and velocity results characterize the interaction of wake flow from individual cylinders and as a function of the rotational speeds. Besides, the Standard deviation map shows the turbulence intensity variation at the various static and rotating conditions. The obtained results at static conditions are found to be consistent with the previous computational study.
Assessment of Native Aortic Stenosis Hemodynamics and Clinical Evaluation Methods Using Steady State Computational Fluid Dynamics and Computed Tomography-Derived Geometry
(North Dakota State University, 2012) Traeger, Brad James
Aortic stenosis is the most common valvular heart disease with a prevalence of 2% among individuals over 65 years and 4% over 80, in developed countries. Accurate valve assessment for intervention timing is critical. Using only routinely obtained clinical data, this research aims to present accurate recreations of in vivo transvalvular hemodynamics using computational fluid dynamics (CFD) and validate Gorlin formula and echocardiography (echo)/continuity techniques. The in vivo valve was compared to simplified and idealized geometries. Instantaneous anatomic orifice area (AOA_max) was underestimated by about 40% by Gorlin's formula and (dP_mean). Time-averaged orifice area (EOA_mean), by an echo/continuity, was about 40% smaller than the AOA_max. The Gorlin formula better assesses AOA_max using (dP_{mean eff}). dP_{mean eff} is required for Gorlin formula approximation of AOA_max and echo/continuity overestimates EOA_mean with increasing error for lower flow rates. Correlations between EOA and AOA should only be made as instantaneous or only time-averaged comparisons.
Atomic Force Microscopy-Based Nanomechanical Characterization of Kenaf Microfiber and Cellulose Nanofibril
(North Dakota State University, 2021) Parvej, M Subbir
Kenaf fiber is increasingly getting the attention of the industries due to its excellent mechanical properties, feasibility, growth rate, and ease of cultivation. On the other hand, cellulose nanofibril is one of the important building blocks of all the bast fibers which significantly contributes to their mechanical properties. However, most of the studies in the literature have estimated the value of axial elastic modulus for fiber-bundles which has some unavoidable issues resulting in incorrect modulus. Moreover, the transverse elastic modulus is another important parameter that also needs to be studied. Hence, to compensate for the gap in the literature, a single unit of both kenaf microfiber and cellulose nanofibril have been subjected to nanomechanical characterization to analyze their surface morphology and determine their elastic modulus in the axial and transverse direction. The experiments also pave to a protocol to characterize micro and nanofibrils nanomechanically and determine their elastic moduli.
Best Practices in Computational Fluid Dynamics Modeling of Cerebral Aneurysms using ANSYS CFX
(North Dakota State University, 2015) Nordahl, Emily Rose
Today many researchers are looking toward computational fluid dynamics (CFD) as a tool that can help doctors understand and predict the severity of aneurysms, but there has yet to be any conclusive proof of the accuracy or the ease of implementation of this CFD analysis. To help solve this issue, CFD simulations were conducted to compare these setup practices in order to find the most accurate and computationally efficient setup. These simulation comparisons were applied over two CFD group challenges from the CFD community whose goal was not only to assess modeling accuracy, but the analysis of clinical use and the hemodynamics of rupture as well. Methodology compared included mesh style and refinement, timestep comparison, steady and unsteady flow comparison as well as flow rate amplitude comparison, inlet flow profile conditions, and outlet boundary conditions. The “Best Practice” setup gave good overall results compared with challenge participant and in-vitro data.
Bioprinting of Pancreatic Cancer Cells for Improved Drug Testing
(North Dakota State University, 2019) Rehovsky, Chad Austin
Currently, many drugs are preclinically tested on two-dimensional cell cultures. However, this method does not adequately replicate the cellular interactions or diffusion gradient that occur in three-dimensional tissues, leading to poor indicators of how a drug may affect human tissues. The objective of this project was to use bioprinted pancreatic cancer cell cultures as a platform for three-dimensional drug testing. Various bioink formulations of cellulose, gelatin, and alginate were evaluated to determine which provided the best printability and cell viability. A cellulose nanocrystal and alginate hydrogel showed superior printability due to its shear thinning properties. Additionally, initial cell viability was nearly 80%, and it remained above 60% over four days. Use of a custom spinning bioreactor at 50 rpm resulted in no improvements to cell viability. Overall, the system shows potential as a drug testing platform to evaluate the effectiveness of various drug formulations on three-dimensional pancreatic cancer cell cultures.
Characterization of a Lab-Scale Polymethylmethacrylate and Gaseous Oxygen Hybrid Rocket
(North Dakota State University, 2022) Dixon, Porter
Hybrid rockets are a type of chemical rocket propulsion where the reactants are in different phases. Historically, hybrid rockets have been underutilized in the aerospace industry. However, due to their simple nature, they are easy to construct and test. Research on hybrid rocket propulsion was conducted using optically clear polymethylmethacrylate and gaseous oxygen with a nozzle designed to achieve Mach 2. Characterization was performed using combustion simulations available from NASA and measurements with pressure transducers, thermocouples, a load cell, and high-speed cameras. The test stand and hybrid rocket itself were designed by previous senior design groups. From the results, performance parameters such as the characteristic velocity, thrust coefficient, and specific impulse were calculated for various test times and oxidizer mass flow rates. Testing has shown that the rocket can be run safely and successfully numerous times.
Characterization of Mechanical Properties in Hybridized Flax and Carbon Fiber Composites
(North Dakota State University, 2013) Flynn, Jeff
Natural fiber composites have been found to exhibit suitable mechanical properties for general applications. However, when high strength applications are required, natural fibers are typically not considered as a practical fiber. One method for increasing the field of application for natural fibers is by increasing their mechanical properties through hybridizing them with synthetic fibers. The effects of hybridizing flax fibers with carbon fibers were investigated in this research to determine the trends in mechanical properties resulting from varied carbon and flax fiber volumes. The research found an increase in mechanical properties when compared to 6061 aluminum at matching composite stiffness values. The following mechanical property gains were obtained: 2% tensile chord modulus, 252% tensile strength, 114% damping ratio, and a 49% weight savings. Experimental tensile values were also compared to tradition modulus prediction models such as rule of mixtures and Halpin-Tsai, and were found to be in good agreement.
Characterization of Regenerated Silk Material for Biomimetic Spinning and Film Casting
(North Dakota State University, 2018) Hoffmann, Bradley Thomas
Natural silks produced by spiders and silkworms exhibit tailorable mechanical performance yet to be achieved synthetically. This phenomenon is derived from a biological system that has been evolutionarily optimized. In efforts to harness this elusive promise of tailorable bio-material fabrication, a study was conducted to investigate: 1) silk solution processing, 2) silk spinning via a biomimetic spinning system, [and] 3) dispersions of carbon nanotubes into regenerated silk by spinning and casting. A formic acid calcium chloride solvent system was chosen by rheological characterization for further processing. Fibers were spun through the biomimetic system using hydrodynamic fluid focusing (HF) yielding predictable diameters, with improved mechanical performance correlated to smaller diameter fibers resulted from HF. Alternatively, carbon nanotubes functionalized with carboxylic-acid (CNTC) and non-functionalized (CNTNF) were integrated into spinning and casting processes. Decreases in performance was observed in CNTNF constructs, however an increase was present in CNTC suggesting structural integration of silk proteins.
Characterizing the Operation of a Dual-Fuel Diesel-Hydrogen Engine near the Knock Limit
(North Dakota State University, 2014) Kersting, Lee
A CAT C6.6 turbocharged diesel engine was operated in dual-fuel diesel-hydrogen mode. Hydrogen was inducted into the intake and replaced a portion of the diesel fuel. Hydrogen was added across multiple engine speeds and loads until reaching the knock limit, identified by a threshold on the rate of in-cylinder pressure rise. In-cylinder pressure and emissions data were recorded and compared to diesel-only operation. Up to 74% H2 substitution for diesel fuel was achieved. Hydrogen addition increased thermal efficiency up to 32.4%, increased peak in-cylinder pressure up to 40.0%, increased the maximum rate of pressure rise up to 281%, advanced injection timing up to 13.6°, increased NOx emissions up to 224%, and reduced CO2 emissions up to 47.6%. CO and HC emissions were not significantly affected during dual-fuel operation. At 25% load an operating condition was observed with low NOx and nearly 0 CO2 emissions, which however exhibited unstable combustion.
Computational Investigation of Low-Pressure Turbine Aerodynamics
(North Dakota State University, 2015) Flage, Alexander Paul
The design of today’s gas turbine engines is heavily reliant on accurate computational fluid flow models. Creating prototype designs is far more expensive than modeling the design on a computer; however, current turbulence and transitional flow models are not always accurate. Several turbulence and transition models were validated at North Dakota State University by analyzing the flow through a low pressure turbine of a gas turbine engine. Experimental data for these low pressure turbines was provided by the University of North Dakota. Two separate airfoil geometries are analyzed in this study. The first geometry is a first stage flow vane, and the second geometry is an incidence angle tolerant turbine blade. Pressure and heat transfer data were compared between computations and experiments on the turbine blade surfaces. Simulations were conducted with varying Reynolds numbers, Mach numbers, and free stream turbulence intensities and were then compared with experiments.
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.
Computational Simulations of Compressible Transitional Flows in a Turbine Vane Cascade
(North Dakota State University, 2019) Perrault, Alan James
In order to improve the efficiency and reduce the emissions of aircraft engines, new combustor designs have been developed to reduce outlet temperatures and increase mixing. At high altitudes, the low pressure and low Reynolds number flow would normally produce a laminar boundary layer on the turbine vanes. The increased turbulence generated by these newer combustors can cause transitional flow on the vane surfaces, which leads to increased heat transfer. Accurate computational simulations can reduce development costs by allowing rapid iteration of designs. Aerodynamic and heat transfer characteristics of the first stage stator vane from a high-altitude UAV has been computationally analyzed using ANSYS CFX. The computational results are compared with compressible flow experiments which were previously conducted at the University of North Dakota. The aerodynamic results show excellent agreement across the vane surface; however, some discrepancies are present in the transition region for the heat transfer results.
Computational Simulations of Flow Past a Rotating Arrangement of Three Cylinders Using Hybrid Turbulence Models
(North Dakota State University, 2020) Thomas, Nick Leonard
Over the past 25 years, advances in the field of turbulence modeling have been made in an effort to resolve more scales, preserving unsteadiness within a flow. In this research two hybrid models, Scale-Adaptive Simulation (SAS) and Stress-Blended Eddy Simulation (SBES) are implemented in solving the highly unsteady flow over a rotating arrangement of three cylinders. Results are compared to those from wind tunnel experiments carried out at North Dakota State University. Both models show close agreement with first and second order turbulence quantities, and SBES shows much greater flow structure detail due to its ability to resolve smaller scales. The Strouhal number for the flow is found to be a function of the rotational speed of the arrangement with von Karman-like structures resulting from each cylinder's wake over a full rotation. SAS shows a constant computational cost as Re increases while the SBES's computational cost increases relatively linearly.
Design and Control of a Micro/Nano Load Stage for In-Situ AFM Observation and Nanoscale Structural and Mechanical Characterization of MWCNT-Epoxy Composites
(North Dakota State University, 2017) Leininger, Wyatt C.
Nanomaterial composites hold improvement potential for many materials. Improvements arise through known material behaviors and unique nanoscale effects to improve performance in areas including elastic modulus and damping as well as various processes, and products. Review of research spurred development of a load-stage. The load stage could be used independently, or in conjunction with an AFM to investigate bulk and nanoscale material mechanics. The effect of MWCNT content on structural damping, elastic modulus, toughness, loss modulus, and glass transition temperature was investigated using the load stage, AMF, and DMA. Initial investigation showed elastic modulus increased 23% with 1wt.% MWCNT versus pure epoxy and in-situ imaging observed micro/nanoscale deformation. Dynamic capabilities of the load stage were investigated as a method to achieve higher stress than available through DMA. The system showed energy dissipation across all reinforce levels, with ~480% peak for the 1wt.% MWCNT material vs. the neat epoxy at 1Hz.
Development and Characterization of Reactive Extrusion Additive Manufacturing System and Polymer
(North Dakota State University, 2021) Patton, Dallas
Additive manufacturing with polymers can rapidly produce complex geometry and prototypes but does not usually utilize thermoset polymers aside from photocurable polymers. In this study two-part reactive thermoset resin systems were used to additively manufacture parts utilizing a commercial resin and a custom resin system. Two displacement syringe drivers were used to feed each part of the reactive resin into a mix chamber that utilized a helical static mix rod and was extruded through a 3D printed nozzle. After print parameters were fine-tuned, the resulting reactive resin specimens featured high strength, quick curing, and fast deposition rate. Optimization of the resin system is required to allow for support structures to be created as well as for overhangs and other additive manufacturing advantages to be realized. Continued study on reactive extrusion methods can lead to the utilization of continuous fiber to allow for the creation of complex geometry high performance composites.
Development of an Advanced Composite Material Consisting of Iron Matrix Reinforced with Ultra High Temperature Ceramic Particulate (TiB2) with Optimum Properties
(North Dakota State University, 2016) Jahani, Babak
This study was intended to investigate the mechanical properties and microstructure of iron based composite reinforced by ultra high temperature ceramics fabricated by powder metallurgy technique. The fabrication parameters were optimized and composite samples with different volume fraction of TiB2 were fabricated and were subjected to different mechanical tests. The results indicated improving in mechanical properties of Fe-TiB2 composites by increasing the volume fraction of TiB2 up to 20 vol%. More TiB2 particles didn’t improve the mechanical properties of composite, instead adversely affected it due to increasing the chance of agglomeration and porosity in entire microstructure. Another finding showed the twofold characteristic of TiB2 on mechanical properties of composite via increasing the hardness and decreasing the bulk density of composite. Finite Element Analysis (FEA) have also been performed on microstructural based developed models to simulate failure of composites. Numerical simulation results could verify the experimental results.
Development of Biobased Composites of Structural Quality
(North Dakota State University, 2015) Taylor, Christopher Alan
Highly biobased composites with properties and costs rivaling those consisting of synthetic constituents are a goal of much current research. The obvious material choices, vegetable oil based resins and natural fibers, present the challenges of poor resin properties and weak fiber/matrix bonding, respectively. Conventional methods of overcoming poor resin quality involve the incorporation of additives, which dilutes the resulting composite’s bio-content and increases cost. To overcome these limitations while maintaining high bio-content and low cost, epoxidized sucrose soyate is combined with surface-treated flax fiber to produce biocomposites. These composites are fabricated using methods emphasizing scalability and efficiency, for cost effectiveness of the final product. This approach resulted in the successful production of biocomposites having properties that meet or exceed those of conventional pultruded members. These properties, such as tensile and flexural strengths of 223 and 253 MPa, respectively, were achieved by composites having around 85% bio-content.
Development of Biobased Sandwich Structures for Mass Transit Application
(North Dakota State University, 2012) Munusamy, Sethu Raaj
Efforts to increase the biobased content in sandwich composites are being investigated to reduce the dependence on synthetically produced or mined, energy-intensive materials for numerous composite applications. Vegetable oil-based polyurethane foams are gaining recognition as good substitutes for synthetic counter parts while utilizing bast fiber to replace fiberglass is also gaining credence. In this study, soy oil-based polyurethane foam was evaluated as a core in a sandwich construction with facesheets of hybridized kenaf and E-glass fibers in a vinyl ester resin matrix to replace traditionally used plywood sheeting on steel frame for mass transit bus flooring systems. As a first step towards implementation, the static performance of the biobased foam was compared to 100% synthetic foam. Secondly, biobased sandwich structures were processed and their static performance was compared to plywood. The biobased sandwich composites designed and processed were shown to hold promise towards replacing plywood for bus flooring applications by displaying an increase of 130% for flexural strength and 135% for flexural modulus plus better indentation values.
Dried Distillers Grains With Solubles as a Multifunctional Filler in Wood Particleboards
(North Dakota State University, 2015) Sundquist, David John
Dried Distillers Grains with Solubles (DDGS) has been investigated for its use as a functional filler in wood particleboards bonded with Melamine Urea Formaldehyde. Both the concentration of the DDGS filler – 5, 10, and 15 wt. % – and the particle size of the filler – 125, 300, and 500 μm – has been considered. It was presumed that the additional protein and fats in the lignocellulosic DDGS would increase strength and water resistance of the particleboards. Chemical analysis, thermogravimetric analysis, and differential scanning calorimetry were used to analyze the DDGS filler. A variety of mechanical tests were performed including: flexural, internal bond, hardness, screw withdrawal, linear expansion, and water absorption. The results show that DDGS bonded to the MUF resin. At concentrations of 5 wt. % DDGS with particles of 500 μm produced superior properties compared to the control panel were achieved while the other blends remained equivalent to the control.

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