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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Additive manufacture of advanced composites using reactive resins and continuous carbon fiber
(North Dakota State University, 2024) Aryal, Bibek
To overcome the significant limitations such as slow processing times, substantial energy needs of conventional additive manufacturing technology, reactive extrusion additive manufacturing (REAM) process was developed. As printed objects with neat reactive resin exhibited insufficient mechanical performance for advanced application, continuous fiber reinforcement is an effective route to improve mechanical performances. Continuous carbon fiber reinforced 3D printing was performed using a commercially available reactive resin system and an experimentally synthesized one at NDSU. The mechanical properties of the printed carbon fiber reinforced samples were compared with the neat resin samples. The tensile strength of printed sample using Pentaerythritol-xylendiamine resin system increased by 217% with 2.88% carbon fiber content. Similarly tensile strength of Epon-Epikure sample increased by 151% with the fiber-volume fraction of 4.4%. Therefore, reinforcement with continuous carbon fiber has potential to overcome the barrier of low mechanical strength exhibited by neat reactive resin system.
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.
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.
Application of Cellulose Nanocrystals and Zinc Oxide as a Green Fire-Retardant System in High Density Polyethylene
(North Dakota State University, 2019) Vahidi, Ghazal
Polymeric materials are widely used in diverse applications. However, a major weakness in the majority of the thermoplastic polymers is their lack of ability to resist fire. Most of the chemicals and additives currently used to improve fire retardancy have deleterious effects on the environment. This research focuses on developing an environmentally safe and effective fire-retardant system for high density polyethylene (HDPE), using cellulose nanocrystals (CNCs) and zinc oxide (ZnO). The effect of CNCs coated with nano ZnO has been investigated for improving the fire resistance properties of the HDPE. Improved dispersion of CNCs into HDPE matrix was achieved by employing maleic anhydride as a coupling agent. It was found that addition of CNCs-ZnO can introduce a reasonable level of flame retardancy in HDPE matrix in addition to improving the maximum tensile strength and elongation at break.
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.
Brain Tissue Mechanical Characterization and Determination of Brain Response under Confined Blasts Explosions
(North Dakota State University, 2015) Rezaei, Asghar
Mechanical experimental tests including stress relaxation, simple monotonic ramps, and impact loads were performed on porcine brain tissues to investigate the response of the brain under different loading scenarios. Linear viscoelastic models were employed to determine the applicability and limitations of the linear mechanical models in tension. In addition the lowest and highest stress values, which can be possibly applied to the tissue due to change in the strain rates, were investigated using stress relaxation experiments to implicitly address the two levels of strain rates. Porcine brainstem samples were tested in six stress relaxation experimental settings at strain amplitudes ranging from 5% to 30% in compression. The lowest stress was directly measured from long-term responses of stress relaxation experiments when the stress values remained constant. The highest stress level was determined by using the quasi-linear viscoelasticity theory and estimating the instantaneous stress of the samples at six strain amplitudes. It was hypothesized that there is a correlation between the two pure elastic behaviors. The hypothesis was true as a strong linear correlation was found between the two elastic responses. The results showed that the instantaneous stress values were 11 times greater than the long-term stress values, practically similar across all strain amplitudes. In the second part of the thesis, a number of computational studies were conducted using a validated human head model. The head model included major components of human head and underwent different blast scenarios in open and confined spaces. The study investigated the effect of reflections from the walls. The results show that when the head was in the vicinity of the wall, the biomechanical parameters were dramatically increased, especially in the corners. Comparing brain biomechanical parameters in confined, semi-confined, and open spaces under blast loads, the brain sustained greater stress and strain values, with larger duration of the loads, in confined spaces. Also, a primary blast injury (PBI) with a tertiary blast injury (TeBI) in a confined space was compared. The results indicated that the PBI due to the incident shock wave was much more injurious than TeBI due to blunt impact.
Breast Cancer Screening in Native American Women at an Urban Minnesota Community Clinic
(North Dakota State University, 2015) Vaishnav, Molly Cassandra
The Native American Community Clinic (NACC) in Minneapolis, MN, expressed a need for a breast cancer screening patient education brochure and a policy regarding breast cancer screening, due to the absence of these in their clinic. Native American women have some of the lowest breast cancer screening rates along with the poorest five-year survival rate for breast cancer. Early screening and detection of breast cancer is thought to be the key to survival. The reason for these low breast cancer screening rates among Native American female patients is multifactorial, but lack of knowledge and provider recommendation are two known barriers. The purpose of this practice improvement project was to develop a culturally appropriate breast cancer screening patient education brochure with a policy that outlines use. The healthcare providers, medical director, and the patient advisory group at the NACC evaluated the brochure, and the medical director evaluated the policy. The Plan, Do, Study, Act method was utilized to facilitate the process and address the clinic goals. The project first reviewed current guidelines and literature for breast cancer screening. After one set of guidelines was selected, the brochure was created. The healthcare providers, medical director, and patient advisory group members were then given a qualitative survey. The responses to the survey gave suggestions for revisions, which were made to the brochure. Revisions included things such as using different guidelines, including more information on mammography, and including photographs of Native American women. The policy was then created. The policy included which guidelines to use when offering screening, whom to offer screening to, and guidance on how to properly document breast cancer screening and education after each visit. The medical director was then given a qualitative survey, which inquired about necessary revisions. The medical director suggested only one minor revision (change in wording). Following a total of four meetings and multiple revisions, the educational brochure and policy were approved by the NACC medical director. Future research should focus on expanding culturally appropriate patient education materials in clinical settings, such as the NACC.
Cavitation Inception and Contaminant Effects
(North Dakota State University, 2014) Jordahl, Jennifer Marie
Within a liquid, it is possible to lower the pressure to a point in which the nuclei gas bubbles will cause cavitation inception. During this drop in pressure, at constant temperature, the bubble tension will increase to the inception pressure. The difference between vapor pressure and the pressure where inception occurs is the tensile strength of the liquid. Frankel introduced the calculation of the potential tensile strength of a liquid. Studies show a drastic difference in the calculated potential tensile strength of a liquid and the tensile strength obtained through experimentation. Environmental effects or contaminants affect cavitation inception. Studying the mechanics of a bubble will help one to predict if inception, and later cavitation, may occur and to what extent.
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.
Characterization, Long-Term Behavior Evaluation and Thermo-Mechanical Properties of Untreated and Treated Flax Fiber-Reinforced Composites
(North Dakota State University, 2017) Amiri, Ali
In recent years there has been a resurgence of interest in the usage of natural fiber reinforced composites in more advanced structural applications. Consequently, the need for improving their mechanical properties as well as service life and long-term behavior modeling and predictions has arisen. In a step towards further development of these materials, in this study, two newly developed biobased resins, derived from soybean oil, methacrylated epoxidized sucrose soyate and double methacrylated epoxidized sucrose soyate are combined with untreated and alkaline treated flax fiber to produce novel biocomposites. Vinyl ester reinforced with flax fiber is used as control in addition to comparing properties of biobased composites against commercial pultruded composites. Effects of alkaline treatment of flax fiber as well as addition of 1% acrylic resin to vinyl ester and the two mentioned biobased resins on mechanical properties are studied. Properties are evaluated in short-term and also, after being exposed to accelerated weathering (i.e. UV and moisture). Moreover, long-term creep of these novel biobased composites and effect of fiber and matrix treatment on viscoelastic behavior is investigated using Time-temperature superposition (TTS) principle. Based on the results of this study, the TTS provides an accelerated method for evaluation of mechanical properties of biobased composites, and satisfactory master curves are achieved by use of this principle. Also, fiber and matrix treatments were effective in increasing mechanical properties of biobased composites in short-term, and treatments delayed the creep response and slowed the process of creep in composites under study in the steady state region. Overall, results of this study reveal the successful production of biocomposites having properties that meet or exceed those of conventional pultruded members while maintaining high biocontent. Composites using treated flax fiber and newly developed resins showed less degradation in properties after accelerated weather exposure. Procedures and methods developed throughout this study, as well as results presented are essential to further development of these novel materials and utilizing them in more advanced structural applications. Results presented in this dissertation have been published as 5 peer reviewed journal articles, 2 book chapters and have been presented in 6 national and international conferences.
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 Biomechanics of Blast-Induced Traumatic Brain Injury: Role of Loading Directionality, Head Protection, and Blast Flow Mechanics
(North Dakota State University, 2015) Sarvghad-Moghaddam, Hesam
In this dissertation, blast-induced traumatic brain injury (bTBI) is studied with respect to the blast wave directionality, mitigation capability of helmet/faceshield, and blast flow mechanics using finite element (FE) and computational fluid dynamics (CFD) schemes. For the FE study, simulations are performed on a detailed FE head model using LS-DYNA, and CFD simulations are carried out using the ANSYS-CFX to examine the underwash development by analyzing the behavior of blast flow from different directions. The following tasks are conducted. First, the effects of the loading direction on the mechanical response of the head and brain is investigated through impact and blast induced loading on the head. Due to the differences in the shape, function, and tolerance of brain components, the response of the head/brain varies with the direction of the impact and blast waves. In identical situations, the head shows to have lower tolerance to side loading. Second, the inclusion of the faceshield as a potential head protective tool against blast threats is evaluated with respect to blast direction. The helmet-faceshield and helmeted assemblies are shown to be most efficient when the head is exposed to blast from the front and top sides, respectively. Faceshield is observed to be effective only in front blast as it might impose either adverse or no effects in other directions. The shockwaves are seen to form a high pressure region in head-helmet-faceshield gap (underwash effect) which induces elevated pressures on the skull. Third, the underwash effect’s mechanism is investigated through CFD simulations of supersonic shockwave flow around the helmeted head assemblies. CFD results reveals that the backpressure is produced due to the creation of a backflow in the exterior flow on the outgoing interior flow. The bottom and side shockwave directions predict the highest underwash overpressures, respectively. Finally, the ICP and shear stress of the brain is evaluated in case of underwash incidence. FEA results show that underwash overpressure greatly changes with the blast direction. It is concluded that underwash clearly altered the tissue response of the brain as it increases ICP levels at the countercoup site and imparts elevated skull flexure.
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.

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