Browsing by Author "Dr. Jeffrey Eischen, Committee Member"
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- Characterization of Epoxy-hybrid nano-particle Resins for ambient cure VARTM Processes(2008-05-10) Caldwell, Mary Kathryn; Dr. Eric Klang, Committee Member; Dr. Kara Peters, Committee Chair; Dr. Jeffrey Eischen, Committee MemberThis thesis presents the mechanical characterization of fire resistant epoxy-hybrid resin systems suitable for ambient cure VARTM processes. Several new epoxy-hybrid nano-particle resins were developed and tested for use in large scale composite structures. Based on the viscosity, Tg, and cure time requirements twelve of these resins systems were pre-selected for mechanical testing. Neat resin castings were tested in tension to determine the elastic modulus, tensile strength and maximum elongation. From these results, six of the resin systems were further cast in unidirectional glass fiber laminates. Transverse tension and short beam shear testing was performed on all laminates to determine the mechanical properties of the glass/epoxy systems. Two of the epoxy-hybrid resin systems showed promising behaviors, having a higher transverse modulus and ultimate strength than the original benchmark vinyl-ester resin. Additionally, fiber Bragg grating sensors were embedded in one benchmark vinyl-ester laminate and one epoxy-hybrid laminate during the cure cycle. Taking advantage of both the extrinsic and intrinsic properties of these sensors, residual strains, temperature changes, and degree of cure of the resin were monitored. In addition to having a higher modulus of elasticity and ultimate strength, these new epoxy-hybrid nano-particle resin laminates showed minimal temperature increases during cure and smaller residual strains than the comparable vinyl-ester resin laminates.
- Database for Real-Time Loading Path Prediction for Tube Hydroforming(2009-11-02) Deshmukh, Karan; Dr. Gracious Ngaile, Committee Chair; Dr. Jeffrey Eischen, Committee Member; Dr. Kara Peters, Committee Member
- Design of Reflective Optical Systems(2007-01-22) Wanna, Nadim George; Dr. Thomas Dow, Committee Chair; Dr. Ron Scattergood, Committee Member; Dr. Jeffrey Eischen, Committee MemberThe primary objective of this research is to develop optical and opto-mechanical design procedures for reflective optical systems. Challenges in fabrication and testing have limited the choice of surfaces used in the design of reflective optical systems to rotationally symmetric surfaces. Freeform surfaces or non-rotationally symmetric surfaces are necessary to meet challenging performance and packaging requirements. To gain familiarity with optical and opto-mechanical design techniques, two systems were considered: a two mirror Ritchey-Chrétien telescope and a Three Mirror Anastigmat. The two mirror Ritchey-Chrétien optical system using rotationally symmetric hyperbolic surfaces is designed. The opto-mechanical design incorporates the use of radial and axial fiducial surfaces to locate the two mirrors onto a tube relating the optical surfaces to each other and to the detector through a spacer plate. Optical performance improvement over the two mirror telescope is achieved with the addition of a third mirror. The Three Mirror Anastigmat (TMA) optical design uses off-axis conic sections of a rotationally symmetric system. Further improvement to the optical performance is achieved with a freeform TMA optical system and optical surface fabrication feedback to the designer. Opto-mechanical design of the TMA incorporates the use of a telescope frame to constrain each mirror in six degrees of freedom and relate the optical surfaces to each other and to the detector. The mirrors are held in place through independent mounting clamps to sustain high gravitational acceleration with minimum optical surface distortion. The two mirror telescope optical performance is limited by optical aberrations especially at high field angles. Locating the mirrors on a tube over-constrains the components and distorts the optical surfaces. Multiple assembly configurations or non-repeatability is due to symmetry of mounting screws. Impressive optical performance, 58 times wavefront error improvement over the two mirror system, is achieved with an unobstructed TMA optical system using freeform surfaces. A snap-together repeatable assembly without adjustments is designed using conventional fiducial techniques and independent mounting clamps minimizing optical surface distortion.
- Development of Closed Cell Metallic Foam Using Casting Techniques(2004-11-29) O'Neill, Adrian Thomas; Dr. Afsaneh Rabiei, Committee Chair; Dr. Jeffrey Eischen, Committee Member; Dr. William Roberts, Committee MemberThe research sited in this paper involves the development of a new metal foam composite material using casting techniques. This work included the design of the material and the development of a process to produce the metal foam. The materials used to produce the foam consisted of low carbon steel hollow spheres and an aluminum alloy. The foam is comprised of steel hollow spheres packed into a random dense arrangement, with the interstitial space between spheres infiltrated with a casting aluminum alloy. Using prefabricated hollow spheres assures a uniform pore size and cell wall thickness. Casting a metal into the interstitial space provides a solid media to add structural support to the foam. The goal of this research has been to develop metal foam that demonstrates improvements in product uniformity and mechanical properties over the currently available foams. To accomplish this goal, the study included the identification of the various technologies used to manufacture metal foams, the assessment of the improvements needed to augment the quality of foamed metals, and the design of a new product and processing technique that substantiates these goals. The experimental equipment was designed and procured, while the raw materials were obtained. Then the hollow sphere foam samples were successfully produced. Using these samples a series of characterization studies was done to qualify and quantify the results. These findings were then compared to presently published data to gauge the relative success of the work. The hollow sphere metal foam developed in this study displayed significant improvements in the measures of compressive strength and energy absorption capacity, all the while maintaining the characteristic properties of cellular metals. The improvements were measured against the next best existing technology. The newly developed foam averaged 67 MPa over a region of 10 – 50% strain, with densification beginning at approximately 50% strain. The value for energy absorption is 30 MJ/m3 at 50% strain. This foam also has a strength to density ratio on level with the best reported results to date. The combination of these properties gives opportunity for use in previously unidentified applications, such as an energy absorption media for buildings subject to seismic motion. This foam can also be designed in such applications as automobile crumple zones, as structural members in air and space craft, and in biomedical prosthesis. Several areas for improvement have been identified for this technology. The bonding strength between sphere and matrix needs improvement, and different material choices and processing changes have been identified in this research to achieve these improvements. The packing density of the spheres can be improved, and a new method of vibrating the sphere arrangement prior to molding may increase the packing density. The porosity of the aluminum matrix can be reduced, and the design of the casting mold and processing conditions can be modified to reduce undesirable porosity. Additional testing methods have been identified to further characterize the foam and reveal insights for further improvement. The iterative process of sampling, characterization, and analysis will continue to improve this product to satisfy the objectives of this research program.
- Finite Element Modeling of the Left Atrium to Facilitate the Design of an Endoscopic Atrial Retractor(2006-04-17) Jernigan, Shaphan Rees; Dr. Denis Cormier, Committee Member; Dr. Jeffrey Eischen, Committee Member; Dr. Gregory Buckner, Committee ChairWith the worldwide prevalence of cardiovascular diseases (CVDs), much attention has been focused on simulating the characteristics of the human heart to better understand and treat cardiac disorders. The purpose of this study is to build a finite element model of the left atrium that incorporates detailed anatomical features and realistic material characteristics to investigate the interaction of heart tissue and surgical instruments. This model is used to facilitate the design of an endoscopically deployable atrial retractor for use in minimally invasive, robotically assisted (MIRA) mitral valve repair. The left atrial geometry is imported directly from MRI data of an explanted porcine heart, and material properties are derived from experimental testing of cardiac tissues. Model accuracy is verified by comparing simulated cardiac wall deflections to those measured by MRI. Finite element analysis is shown to be an effective tool for analyzing instrument/tissue interactions and for designing surgical instruments.
- An Integrated Approach to Lubricant Development in Cold Forging(2008-05-04) Karkhanis, Nikhil Sudhakar; Dr. Jay Tu, Committee Member; Dr. Jeffrey Eischen, Committee Member; Dr. Gracious Ngaile, Committee ChairLubrication plays a very important role in the metal forming industry. Almost every metal forming process requires some form of lubrication or the other in order to obtain the desired component. Presently, various kinds of lubricants are being used in industry for different processes based on the lubricant properties and the process requirements. One of the primary objectives of this study is to establish a lubricant development methodology which is based on a thorough understanding of the lubrication mechanisms involved and the metal forming process itself. Evaluating the performance of a lubricant is an essential part of the development process. Various standard tribological tests employed in industry were used in this study. This involved both experimental and finite element analysis of the tests. Certain critical tribological parameters were identified for evaluating the performance of the lubricants and these were recorded for further analysis. Another important objective of this study is to develop a simulation databank which would contain the finite element simulations for the major forging components used in industry. The creation of this databank is an essential part of the proposed integrated approach to lubricant development. This databank will enable lubricant developers to optimize their product for particular forging applications. A case study was undertaken to prove the usefulness of the integrated approach. The new technique was applied to the development of a new polymer based environment friendly lubricant. The target process for this lubricant was tube drawing and hence it was necessary to get a lubricant with optimum properties for this process. The required performance parameters were identified through the critical tribo-mechanical parameters. Accordingly, the appropriate tribological tests were selected for lubricant evaluation. Initially, a set of eleven lubricant formulations were taken for testing, each with a slightly different chemical formulation. In order to narrow down the suitable lubricant formulation, a low severity friction test such as the ring test was performed. Once the better performing formulations were identified, a more severe friction test was employed to narrow down on the best possible lubricant formulation. During the entire process, the lubricant developer modified the chemical formulations slightly based on the test results. The result of this was improved performance in the lubricants.
- Investigation of Tube Hydroforming Process Envelope for Macro/Meso Scalability(2008-06-11) Gibson, M. Christopher; Dr. Kara Peters, Committee Member; Dr. Jeffrey Eischen, Committee Member; Dr. Gracious Ngaile, Committee Chair
- Live Axis Turning(2005-12-06) Buescher, Nathan P; Dr. Jeffrey Eischen, Committee Member; Dr. Ronald Scattergood, Committee Member; Dr. Thomas Dow, Committee ChairThe goal of this research is to develop a new method to create Non-Rotationally Symmetric (NRS) optical surfaces that overcomes the limitations of the current techniques and is fast, accurate and inexpensive. The term Live-Axis turning (LAT) has been coined to describe a lightweight, linear-motor driven, air bearing slide that can be used to fabricate NRS surfaces. The system described was developed at the Precision Engineering Center (PEC) in an effort to create a long-range fast tool servo to fabricate future NASA optics. The slide designed for the system is a triangular cross-section, lightweight (0.6 kg) honeycomb aluminum slide driven by a linear motor (64 N maximum force) resulting in an acceleration capability of 10 g. Additionally, a damper was added to the system to investigate the effects of physical damping on surface quality. The LAT axis was mounted on a Nanoform 600 diamond turning machine and both flat surfaces and tilted flat surfaces were machined to assess the performance of the system, which has a rise time of less than 2 msec. The 12.5 mm diameter flat surfaces had surface finishes of 16 nm without damping and 14 nm with damping, with both having a figure error of less than ½ wave. 25 mm diameter tilted flat surfaces, using a maximum stroke of +/- 1 mm at 5 Hz, had a surface finish of 24 nm without damping and 20 nm with damping. The figure error for the damped and undamped parts was +/- 25 microns.
- Microstructural Modeling and Design Optimization of Adaptive Thin-Film Nanocomposite Coatings For Durability and Wear(2009-02-17) Pearson, James Deon; Dr. Mohammed Zikry, Committee Chair; Dr. Kara Peters, Committee Member; Dr. Yong Zhu, Committee Member; Dr. Jeffrey Eischen, Committee MemberAdaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized microstructurally-based finite-element techniques. A new microstructural computational technique for efficiently creating models of nanocomposite coatings with control over composition, grain size, spacing and morphologies has been developed to account for length scales that range from nanometers to millimeters for efficient computations. The continuum mechanics model at the nanometer scale was verified with molecular dynamic models for nanocrystalline diamond. Using this new method, the interrelated effects of microstructural characteristics such as grain shapes and sizes, matrix thicknesses, local material behavior due to interfacial stresses and strains, varying amorphous and crystalline compositions, and transfer film adhesion and thickness on coating behavior have been investigated. A mechanistic model to account for experimentally observed transfer film adhesion modes and changes in thickness was also developed. One of the major objectives of this work is to determine optimal crystalline and amorphous compositions and behavior related to wear and durability over a wide range of thermo-mechanical conditions. The computational predictions, consistent with experimental observations, indicate specific interfacial regions between DLC and ductile metal inclusions are critical regions of stress and strain accumulation that can be precursors to material failure and wear. The predicted results underscore a competition between the effects of superior tribological properties associated with MoS2 and maintaining manageable stress levels that would not exceed the coating strength. Varying the composition results in tradeoffs between lubrication, toughness, and strength, and the effects of critical stresses and strains can be controlled for desired behavior. The analysis also indicates that coating strength increases at a higher rate than the internal coating stresses with decreasing grain size. For transfer films, the present study underscores the beneficial material effects of increasing transfer film thickness and reducing transfer film extrusion due to increased thickness.
- Photonic Bandgap Fibers For Transverse Strain Sensing(2009-02-22) Van Vickle, Patrick Stephen; Dr. Kara Peters, Committee Chair; Dr. Tasnim Hassan, Committee Member; Dr. Larry Silverberg, Committee Member; Dr. Jeffrey Eischen, Committee MemberThis research examines the change in bandgap characteristics of Photonic Bandgap (PBG) fibers under transverse loading for applications such as fabrication and service life monitoring of composite structures. Photonic Bandgap (PBG) fibers rely on Bragg reflection conditions in the plane of optical fiber crosssection and therefore offer great potential as transverse strain sensors which are insensitive to axial loading and temperature variations. A numerical study of the effect on the bandgap in PBG fibers under transverse loads is thus performed in this dissertation. First the fundamental equations for lightwave propagation in classical stepindex fibers, microstrucured holeyfibers and PBG fibers are reviewed. The behavior of each for sensing purposes is also discussed. The structural deformation and electromagnetics modeling of a PBG fiber is then performed using the Finite Element Method (FEM) because this method offers the ability to examine arbitrary fiber configurations, specifically through deformation where the fiber is no longer circularly symmetric. The FEM models were run for both uniaxial crush loads and uniform pressure loads for both silica and a doped PMMA material targeting strains up to approximately 6% at the boundary of the fiber. The results showed that degradation of the bandgap occurs with loading and that axis specific loading information may be obtained in fibers whose material normal and shear Pockel’s constants differ by approximately 50% or more, although the exact difference required is not known. In the case of the PMMA uniform pressure load it was determined that the combination of loading and fiber characteristics may cause the bandgap to switch modes which may interfere with actual sensor implementation and should be avoided. The cross-section of the fiber studied was not rotationally symmetric which resulted in nonsymmetric optical output from the uniform pressure case. While fibers of this construction are likely to not be rotationally symmetric by design, the actual manufacture of the fibers results in a cross section that more closely approximates this condition.
- A Systematic Study on the Mechanical and Thermal Properties of Open Cell Metal Foams for Aerospace Applications(2004-12-01) Azzi, Wassim Elias; Dr. Jeffrey Eischen, Committee Member; Dr. William Robertrs, Committee Member; Dr. Afsaneh Rabiei, Committee ChairJet engine operating temperatures have been on the rise since the inception of the jet engine. High Operating temperatures mean increased efficiency, more power, and lesser emissions. However, operating temperatures of jet engines are limited by the operating temperatures of the turbine material. This temperature must not be exceeded or else it will damage the turbine components. To solve this problem, complex cooling schemes have been adopted. They employ the use of outside air to dilute the high combustion temperatures to make them suitable for turbine section exposure. This leads to a non-uniform temperature profile leaving the combustion area and therefore decreasing the overall engine performance by introducing thermal cycling and inconsistencies in operational temperatures. This research suggests placing an ultra-high temperature open cell metal foam ring in front of the combustion area and directly before the turbine section. Open cell foam with their 3-dimensional geometry help mix the hot and cool gasses entering the turbine area creating a more uniform temperature profile. This increases efficiency by raising the operational temperature of the jet engine. It also contributes to an increased lifetime since the mixing function of the metallic foam will reduce thermal cycling fatigue on turbine vanes and blades. This research presents a full investigation on the feasibility of this idea; it studies the potential of producing ultra-high temperature metallic foam from a list of currently available as well recently engineered materials. This work also investigates the pressure drop and heat transfer associated with the foam for a full assessment of the design. Infrared imaging for heat transfer measurements done on Al foam of 5 and 10 PPI (pores per inch) samples showed the mixing role of the metal foam as a function of thickness; it showed improvement of the temperature profile resulting from the averaging the hot and the cool gasses. Pressure drop testing provided data on pressure drop in Al foams in the compressibility region of air. Up to this point, similar data was not available. Pressure drop testing revealed that with careful design of pore size, ligament thickness and foam thickness, taking into consideration heat transfer capabilities of the foam, a feasible design of an ultra-high temperature open cell foam ring can be achieved with minimal pressure drop and increased heat transfer capabilities.