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Experimental Studies Of Fatigue Performance Of Inconel 718 And Fiberglass Reinforced Vinylester, Sean Gribbin

Master's Theses and Capstones

Fatigue performance of structural materials depend on their microstructure and manufacturing processes. In this thesis, two different materials are investigated: additively manufactured Inconel 718 and a fiberglass reinforced vinylester composite.

The microstructural features of a direct metal laser sintered Inconel 718 are compared to a traditionally manufactured wrought Inconel 718. The effects of 3D printing direction and heat treatment are studied. Low cycle fatigue specimens manufactured by Turbocam International are tested at strain amplitudes from 0.6% to 1.4% engineering strain. These data are correlated to the microstructural features seen in the electron backscatter diffraction. High cycle fatigue specimens are tested …

Experiments And Analysis Of Aluminum Tube Hydroforming, Adam Ryan Kaplan

Master's Theses and Capstones

This is a thesis on the development of an experimental table-top sized tube hydroforming machine at the University of New Hampshire. This thesis documents the design of the machine and the exploration of the forming envelope of the device via finite element modeling of the forming process. Several experiments on Al-6061-T4 tubes were used to evaluate the plastic behavior and strain limits of the tube in the axial and circumferential (hoop) directions. Two of these material tests, the uniaxial tension test and the ring hoop tension tests, were simulated with finite element models to refine the Al-6061-T4 plasticity curve, including …

Design, Mechanical Modeling And 3d Printing Of Koch Fractal Contact And Interlocking, Mona Monsef Khoshhesab

Master's Theses and Capstones

Topological interlocking is an effective joining approach in both natural and engineering systems. Especially, hierarchical/fractal interlocking were found in many biological systems and can significantly enhance the system mechanical properties. Inspired by the hierarchical/fractal topology in nature, mechanical models for Koch fractal interlocking were developed as an example system to better understand the mechanics of fractal interlocking. In this investigation, Koch fractal interlocking with and without adhesive layers were designed for different number of iterations N. Theoretical contact mechanics model was used to capture the deformation mechanisms of the fractal interlocking with no adhesive layers under relatively small deformation. Then …

Chatter Simulation And Detection In Cnc Milling, Jonathan Steven Shepard

Master's Theses and Capstones

A key feature to maintaining a safe and efficient machining operation is the avoidance of unstable vibrations of the cutting tool, commonly called chatter. This thesis explores chatter simulation and a new chatter detection algorithm developed for use in a CNC milling machine. This algorithm, based on a once per revolution sampling method, samples forces experienced during the milling process, and calculates the variance of the differences between consecutive samples. As a selected level of variance, chatter is assumed. An existing milling simulation program is modified to produce a stability lobe diagram for a given CNC machine, workpiece material, and …

Coordination Of Leader-Follower Multi-Agent System With Time-Varying Objective Function, Zalan Mark Fabian

Master's Theses and Capstones

This thesis aims to introduce a new framework for the distributed control of multi-agent systems with adjustable swarm control objectives. Our goal is twofold: 1) to provide an overview to how time-varying objectives in the control of autonomous systems may be applied to the distributed control of multi-agent systems with variable autonomy level, and 2) to introduce a framework to incorporate the proposed concept to fundamental swarm behaviors such as aggregation and leader tracking. Leader-follower multi-agent systems are considered in this study, and a general form of time-dependent artificial potential function is proposed to describe the varying objectives of the …

Analytical, Experimental And Numerical Study On The Mechanical Behavior Of 3d Printed Auxetic Chiral Structures, Yunyao Jiang

Master's Theses and Capstones

A unique deformation mechanism of auxetic chiral structure was investigated via integrated analytical, experimental and numerical approaches. This unique deformation mechanism is the auxetic effect due to internal rotation. In this thesis, first, a rigid-rod-rotational-spring model was developed to capture the quantitative relation between the Poisson’s ratio and internal rotation of the cells in the auxetic chiral structure. It was concluded that the auxetic effects will be amplified with elevated internal rotation. Then, based on this concept, two new auxetic chiral structures were designed: (1) auxetic chiral structure with soft hinges at the corners, and (2) auxetic chiral structure with …

Extraterrestrial Resource Prospecting Using Particle Swarm Optimization And Conflict Based Search, Michael Andrew Johnson

Master's Theses and Capstones

Extraterrestrial prospecting missions will be an important first step in preparation of the harvesting and extraction of natural resources in space. Additionally, knowledge from a prospecting mission will allow the subsequent harvesting or mining mission to efficiently extract resources. Due to the risk and cost of manned space-flight, these prospecting missions will be robotic in nature, and will enable investors to weigh risk and return of a harvesting mission.

The research presented here explores a hypothetical automated prospecting mission on the Martian surface using landscapes simulated from the Mars Global Surveyor satellite. In this mission, a swarm of autonomous exploration …

Ductility Of 304 Stainless Steel Under Pulsed Uniaxial Loading, Graham Webb Cullen

Master's Theses and Capstones

The enhanced ductility that 304 stainless steel is exhibited under pulsed loading (Zhang, 2009) is investigated here using a combination of experiments and analysis. The simplest loading case, i.e., uniaxial tension, was selected to avoid the complicating effects of multiaxial stress states and/or contact and friction with a rigid die. Three types of tensile tests were performed: monotonic, pulsed and hold. For a range of strain rates, the pulsed and the hold tests exhibited different elongation-to-fracture from the monotonic tests. Digital image correlation and infrared thermography were employed to further probe this behavior. It was discovered that since the pulsed …

Experimental Apparatus For Continuous-Bending-Under-Tension And Experiments On A6022-T4, Timothy John Roemer

Master's Theses and Capstones

An experimental technique called Continuous-Bending-under-Tension (CBT) can produce elongations over two times that of a standard tensile test by preventing the necking instability from occurring. This is achieved by superposing plastic bending on tension along the gauge length of the material using three rollers. The specimen is kept under tension as the rollers apply three-point bending while cyclically traversing the gauge length. This subjects the specimen to plastic deformation only in the region that is visited by the rollers. Details on the design of various subsystems of this unique CBT machine are presented. The results for a variety of CBT …

Design And Evaluation Of A Force Platform-Type Instrument To Measure Rate Change In Mass And Centroid Of An Ablating Body, Travis Paul Trottier

Master's Theses and Capstones

This study pertains to the design and evaluation of a force-platform type instrument comprised of three strain gauge load cells, intended to measure the rate of change in mass and centroid position of an object undergoing rapid ablation by heated flow of air. The strain gauges are affixed to a steel frame, oriented in a triangle beneath a 25 X 20 cm rectangular platform, into which is machined a 9 X 9 regular grid for the purpose of static calibration. An algorithm derived from first principles is used to convert the distribution of the applied load among the strain gauges …

Modified Hybrid Modeling Technique For Flexible Spin-Stabilized Spacecraft Applied To Nasa's Magnetospheric Multiscale (Mms) Mission Tablesat Generation Ic (Tablesat Ic), Chris Hashem

Master's Theses and Capstones

This continued research uses a hybrid dynamic algorithm to mathematically model the attitude dynamics of a flexible spacecraft. While a full finite element model would be the most accurate model, it also would be a huge computational burden on MMS. This method is meant to be an accurate approximation while still being computationally reasonable for on-board, real-time calculations. The algorithm uses Euler’s Moment Equations to propagate the dynamics of the spacecraft hub while finite element analysis is used to calculate the flexible boom displacements and update the systems mass moment of inertia tensor. This algorithm is iterative and the FEM …

Development Of A Biaxial Loading Frame For Thin Sheet Cruciform Specimens, Joseph Frederick Wilson

Master's Theses and Capstones

Characterization of the evolving yield loci and forming limit diagrams for sheet materials under biaxial loading is necessary for the development of accurate sheet metal forming process simulations. Biaxial tension testing has been shown to have significant advantages over the current computational and experimental methods for such material characterization; however, the few commercially available loading frames are far too large and expensive to be practical for most metal forming research laboratories. To address this problem, the University of New Hampshire’s Mechanics, Materials, and Manufacturing Lab is working to design a practical servohydraulic biaxial loading frame for such metal forming laboratories. …

Experimental Investigation Of Plastic Anisotropy Of Commercially-Pure Titanium, Madhav Baral

Master's Theses and Capstones

The plastic anisotropy of Commercially-Pure Titanium (CP-Ti, or Grade 2 Ti) is probed with an extensive set of experiments, performed on a hot-rolled CP-Ti plate of 12.7 mm thickness. The experiments reported here are: 1) uniaxial tension at 15o angles to the rolling direction (RD) of the plate, 2) uniaxial tension in the thickness, or normal direction (ND) of the plate, 3) uniaxial compression at 15o angles to the RD, as well as in ND, 4) plane-strain tension at 15o angles to the RD, 5) plane-strain compression at 15o angles to the RD. A total of 30 experiments (and two …

High-Frequency Broadband Seafloor Backscatter In A Sandy Estuarine Environment, Eric James Bajor

Master's Theses and Capstones

Seafloor backscatter collected with high-frequency (> 100 kHz) hydrographic echosounders has become an important aspect of seafloor characterization for benthic ecologists and other scientists. The mechanisms that control acoustic scattering at these high frequencies are not completely understood, although surficial roughness and the presence of discrete particles (e.g., shell hash) are likely contributors. To further our understanding of the impact these mechanisms have on seafloor scattering, broadband (100-250 kHz) acoustic measurements were taken at a grazing angle of 45° in a shallow-water, sandy environment with a known presence of shell hash. Stereo imagery was collected simultaneously to quantify the surficial …

Dynamics Of A Tension Force-Driven Wave Energy Converter, Jason Ebner

Master's Theses and Capstones

Two prototype wave energy buoys were designed, modeled, constructed and field tested at the University of New Hampshire's Center of Ocean Renewable Energy offshore site utilizing Oscilla Power Inc.'s power take-off (PTO) units. Oscillating wave forces are used to power the PTOs. Due to design limitations in a taut-moored buoy system having inline PTOs, a suspended heave plate system was proposed. Tension oscillations in the vertical stay from the slack-moored buoy to the heave plate were used to drive the PTOs. To verify the heave plate concept met the oscillating tension amplitudes required, dynamic tests were performed using Froude scaled …

Streamline Geometry Analysis Of Turbulent Fluid Flows, Michael Dunstan

Master's Theses and Capstones

Energy in turbulent flows is transported down coherent vortical structures of different shapes and sizes. Experiments have shown that the vortical structures contain field lines that are curved in nature. Several procedures have been investigated to determine the size and location of the coherent vortical motions, as of yet there has not been a widely accepted method that exactly depicts these structures. Among the current methods of determining the coherent features of the flow, structures determined by the second largest eigenvalue of the symmetric part of the gradient of the Navier-Stokes equation has received recent attention. Another method proposed is …

Investigation On Epoxy Resin Yielding Under Pure Hydrostatic Stresses And A Novel Method To Reduce Microcracking, Hesam Jafari

Master's Theses and Capstones

Microcracking and failure in the resin pockets of 3D woven composites is caused by coefficient of thermal expansion mismatch between composite components during cooling from the curing temperature. The failure of the matrix is known to be dependent on triaxial stress state. This study presents first measurements of the effect of pure hydrostatic stress on the failure of epoxy resin as a function of temperature. We found that failure triaxial stress for epoxy resin is not strongly temperature dependent. Strategies to reduce or eliminate microcrackings by means of modifications of the curing schedule are also presented. We show that it …

Biaxial Stress Testing Of Ss-304l Microtubes By Axial Load And Internal Pressure, Peter William Ripley

Master's Theses and Capstones

The mechanical behavior and material properties of a Stainless Steel SS-304L microtube, with an OD of 2.40 mm and wall thickness of 160 µm, was investigated through uniaxial, isothermal, biaxial, and metallographic testing. The grain structure, microhardness, and tube eccentricity were investigated using optical microscopy. The rate- and temperature-dependence of the material was characterized by isothermal uniaxial tension experiments. A biaxial experimental setup, consisting of a 2 kN electromechanical tensile stage and a 1.4 kbar hydraulic pump, was created to internally pressurize and axially load the microtube in biaxial stress states. Fourteen radial nominal stress path tests were conducted to …

Development Of The Nasa Celestial Navigation Method For Dynamic Extraterrestrial Surface Navigation, Jared Carl Perkins

Master's Theses and Capstones

The Celestial Navigation (CelNav) method was developed in conjunction with NASA Goddard Space Flight Center, to provide accurate location data for extraterrestrial surface navigation without the use of a global positioning system (GPS) or a ground/relay station. CelNav is a minimal sensor/power solution originally developed for static Lunar surface navigation. However, dynamic navigation via CelNav requires high-accuracy state estimates, due to the absence of key sensors such as a gyroscope, GPS, and a magnetometer. In this thesis, robust nonlinear state estimation techniques (the Sliding Mode Observer, the Extended Kalman Filter, and the H-Infinity Filter) are used with CelNav to accurately …