Mode I interlaminar fracture of 3k 8-Harness-Satin Carbon cloth, with identical fill and weft yarns, pre-impregnated with Newport 307 resin was investigated through the DCB test (ASTM D5528). Crack propagations along both the fill and weft yarns were considered for both post-bonded (co-bonded) and co-cured laminates. A patent-pending delamination insertion method was compared to the standard Teflon film option to assess its applicability to mode I fracture testing. The Modified Beam Theory, Compliance Calibration method, and Modified Compliance Calibration method were used for comparative purposes for these investigations and to evaluate the validity of the proposed Equivalent Stiffness (EQS) method. Crack propagation, in all specimens, proceeded in a run-arrest manner for both delamination directions. Energy dissipation in the form of transverse yarn debonding, matrix deformation, and out of plane crack growth was witnessed for specimens with delaminations along weft yarns. A complete comparison between post-bonded and co-cured laminates was not achieved. The patent pending delamination insertion method was found to cause fewer instances of non-linear crack initiation behavior than the Teflon insert and, when non-linear behavior did occur, it was less prevalent. The EQS method was found to achieve fracture toughness values within 5% of the other three data reduction methods for 63% of the propagation values and achieved conservative values for over 33% of the propagations. Suggestions for future studies aimed at completing the comparisons above are provided in Chapter 5.

The launch environment experiences many vibration, shock, and acoustic loads. A great concern is the high random vibration levels that can damage components and spacecraft structures, which can cause a mission failure. An effective method of reducing high frequency energy is using isolators. Overall, the need for vibration isolation has been increasing because there has been an increase in the use of mechanisms in which vibrations are prevalent. In addition, there has not been extensive research on the effects of isolators that are outgassed and cured. Therefore, it is important to investigate and understand the vibrational effects on isolators. It is convenient to outgas and cure isolators for the benefit of some components because that eliminates contamination, but outgassing and bake-out could potentially affect the frequency response of the isolator system in a negative way. It is valuable to investigate how much outgassing and bake-out might affect the performance, if any, of the vibration isolator in order to benefit companies who may need that kind of information. The vibration isolators used for the purpose of this research were twenty E22-02-40 isolators provided by Barry Controls, a Hutchinson Group Company. The E22-02-40 isolators were outgassed and cured (heated at high temperatures) in order to be turned from grade C into grade A level for outgassing. Then the vibrational performance of those isolators were tested and compared to the isolators that were not outgassed and not cured. Vibration tests were run in the flat frequency spectrum and high frequency spectrum. The maximum percent difference occurred in the grade A level isolators, in which the first frequency mode increased by 33.3 % in the z direction from the grade C isolators. A numerical finite element analysis was performed on Abaqus/CAE in order to verify the experimental results. In addition, a swelling test was conducted on the isolators to test their physical characteristics change after they were outgassed and cured.

A study was conducted to investigate simple, cost-effective manufacturing techniques to delay skin-core delamination, micro-buckling and bearing stress failures resulting from fastener-hole interactions. Composite sandwich panels, with and without damage arrestment devices (DADs), were subjected to monotonic compression at a rate of 5mm per second, and compression-compression fatigue at 50% yield at an amplitude of 65%, under temperatures of 75, 100, 125, 150, 175, and 200 °F. The sandwiches tested were composed of two-layer cross-weave carbon fiber facesheets, a polyurethane foam core, and an epoxy film adhesive to join the two materials. The most successful method to delay the aforementioned failures involved milling rectangular slots in the foam core perpendicular to the holes and adding three additional layers of carbon fiber cross-weave. For the monotonic cases, the ultimate load increases were 97, 87, 100, 131, 96, and 119% for each of the respective temperatures listed above with a negligible weight increase. For the fatigue cases, the number of cycles for each test case was nearly identical. This still represents a large improvement because the yield used in the loading condition for the specimens with DADs was 97% greater than the specimens without DADs. The experimental results were compared with a finite element model (FEM) built in Abaqus/CAE. The numeric and experimental results showed a strong correlation. All test specimens were manufactured and tested in the California Polytechnic State University Aerospace/Composites Laboratory.

While composite structures exhibit exceptional strength and weight saving possibilities for engineering applications, sometimes their overall cost and/or material performance can limit their usage when compared to conventional structural materials. Meanwhile ‘biocomposites’, composite structures consisting of natural fibers (i.e. bamboo fibers), display higher cost efficiency and unique structural benefits such as ‘sustainability’. This analysis will determine if the integration of these two different types of composites are beneficial to the overall structure. Specifically, the structure will consist of a one internal bamboo veneer biocomposite ply; and two external carbon fiber weave composite plies surrounding the bamboo biocomposite. To acquire results of this study, the hypothesized composite structure will consist of varied trapezoidal corrugated specimens and tested in uniaxial compression loading. Thereafter, this test data will be used to ultimately design, manufacture, and test a structural biocomposite/composite box, intended to carry extremely high compressive loads; relative to its own weight. A finite element analysis of this test will be used to validate experimental data. After running the experiment, the carbon fiber with bamboo test sample results were compared to that of only carbon fiber test sample. The carbon fiber samples resulted in a maximum compressive load difference of only 23% higher loads when compared to the carbon fiber with bamboo, on average. These findings are discussed throughout.

Carbon emissions are known to cause decay of the Ozone layer in addition to creating pollutant, poisonous air. This has become a growing concern among scientists and engineers across the globe; if this issue is not addressed, it is likely that the Earth will suffer catastrophic consequences. One of the main culprits of these harmful carbon emissions is fuel combustion. Between vehicles, power plants, airplanes, and ships, the world consumes an extraordinary amount of oil and fuel which all contributes to the emissions problem. Therefore, it is crucial to develop alternative energy sources that minimize the impact on the environment. One such technology that is currently being researched, is the Solid Oxide Fuel Cell (SOFC). This is a relatively simple device that converts chemical energy into electrical energy with no harmful emissions. For these devices to work properly, they require an electrolyte material that has high ionic conductivity with good phase stability at a variety of temperatures. The research presented in this study will concentrate intensively on just one of the many candidates for SOFC electrolytes. 1 mol% CeO2 – 10 mol% Sc2O3 – 89 mol% ZrO2 manufactured by Treibacher Industries was analyzed to better understand its sintering properties, phase stability, and molecular structure. Sintering was performed at temperatures ranging from 900oC to 1600oC and the shrinkage, density and porosity were examined for each temperature. Raman Spectroscopy and X-Ray Powder Diffraction were also conducted for comparison with other known compositions to see if the powder undergoes any phase transitions or instability.

No description available.

<p>This thesis is concerned with a theoretical and experimental investigation of a duckbill valve (DBV). Duckbill valves are non-return valves made of a composite material, which deforms to open the valve as the upstream pressure increases. The head-discharge behavior is a fluid-structure interaction (FSI) problem since the discharge depends on the valve opening that in turn depends on the pressure distribution along the valve produced by the discharge. To design a duckbill valve, a theoretical model is required, which will predict the head-discharge characteristics as a function of the fluid flow through the valve and the valve material and geometry.</p> <p>The particular valves of concern in this study, which can be very large, are made from laminated, fiber-reinforced rubber. Thus, the structural problem has strong material as well as geometric nonlinearities due to large deflections. Clearly, a fully coupled FSI analysis using three-dimensional viscous flow would be very challenging and therefore, a simplified approach was sought that treats the essential aspects of the problem in a tractable way. For this purpose, the DBV was modeled using thick shell finite elements, which included the laminates of hyperelastic rubber and orthotropic fabric reinforcement. The finite element method (FEM) was simplified by assuming that the arch side edges of the valve were clamped. The unsteady 1D flow equation was used to model the ideal fluid dynamics that enabled a full FSI analysis. Moreover, verification for the ideal flow was carried out using a transient, Reynolds-averaged Navier-Stokes finite volume solver for the viscous flow corresponding to the deformed valve predicted by the simplified FSI model.</p> <p>In order to validate the predictions of the FSI simulations, an experimental study was performed at several mass flow rates. Pressure drops along the water tunnel, valve inlet and outlet velocity profiles were measured, as well as valve opening deformations as functions of upstream pressures.</p> <p>Additionally, the valve deformations under various back pressures were analyzed when the downstream pressure exceeded the upstream pressure using the layered shell model without coupling and with simplified boundary constraints to avoid solving the contact problem for the inward-deformed duckbill valve. Flow-induced vibration (FIV) of the valve at small openings was also examined to improve our understanding of the valve stability behaviour. Some interesting valve oscillation phenomena were observed.</p> <p>Conclusions are drawn regarding the FSI model on the predictions and comparisons with the experimental results. The transient 1D flow equation has been demonstrated to adequately model the fluid dynamics of a duckbill valve, largely due to the fact that viscous effects are negligible except when the valve is operating at very small openings. Fiber reinforcement of the layered composite rubber was found to play an important role in controlling duckbill valve material stretch, especially at large openings. The model predicts oscillations at small openings but more research is required to better understand this behaviour.</p> / Doctor of Philosophy (PhD)

The primary objective of this research is to formulate a methodology of assessing the maximum impact loading condition that will incur onto an aircraft’s landing gear system via Finite Element Analysis (FEA) and appropriately determining its corresponding structural and impact responses to minimize potential design failures during hard landing (abnormal impact) and shock absorption testing. Both static and dynamic loading condition were closely analyzed, compared, and derived through the Federal Aviation Administration’s (FAA) airworthiness regulations and empirical testing data. In this research, a nonlinear transient dynamic analysis is developed and established via NASTRAN advanced nonlinear finite element model (FEM) to simulate the worst-case loading condition. Under the appropriate loading analysis, the eye-bar and contact patch region theory were then utilized to simulate the tire and nose wheel interface more accurately. The open geometry of the nose landing gear was also optimized to minimize the effect of stress concentration. The result of this research is conformed to the FAA’s regulations and bound to have an impact on the design and development of small and large aircraft’s landing gear for both near and distant future.

Since their discoveries, carbon nanotubes have been widely studied, but mostly in the forms of 1D individual carbon nanotube (CNT). From practical application point of view, it is highly desirable to produce carbon nanotubes in large scales. This has resulted in a new class of carbon nanotube material, called the vertically aligned carbon nanotube arrays (VA-CNTs). To date, our ability to design and model this complex material is still limited. The classical molecular mechanics methods used to model individual CNTs are not applicable to the modeling of VA-CNT structures due to the significant computational efforts required. This research is to develop efficient structural mechanics approaches to design, model and characterize the mechanical responses of the VA-CNTs. The structural beam and shell mechanics are generally applicable to the well aligned VA-CNTs prepared by template synthesis while the structural solid elements are more applicable to much complex, super-long VA-CNTs from template-free synthesis. VA-CNTs are also highly “tunable” from the structure standpoint. The architectures and geometric parameters of the VA-CNTs have been thoroughly examined, including tube configuration, tube diameter, tube height, nanotube array density, tube distribution pattern, among many other factors. Overall, the structural mechanics approaches are simple and robust methods for design and characterization of these novel carbon nanomaterials