Elevators are a necessary component of the modern urban and suburban life. The guide rails the car and counterweight move on are the most sensitive parts when it comes to de-habilitating damage that can be caused by an earthquake. Conventional sensors are becoming obsolete in sensing for today's multistory buildings because they don't monitor the structural health of the guide rails. This sensing task falls into the fiber sensing niche market because of a fiber sensor's ability to be multiplexed. Previous work by Taplin and Jackson showed demodulation of the interference spectrum of two Fabry-Perot cavities using Fourier analysis. The goal of this research is to use Fourier analysis to demodulate the spectrum of four multiplexed extrinsic Fabry-Perot fiber interferometers for strain measurements. Comparisons of fiber, foil, and theoretical strains are made. Also, experiments showing the system's air-gap stability and crosstalk are provided. / Master of Science

Due to the cost and difficulty of conducting direct tensile and compression creep testing on engineering ceramics, four-point bending creep test methods are often used as an alternative. Stress distribution in the bending specimen is nonlinear, so a proper interpretation method is needed to get creep properties from data produced by four-point bending creep tests. The method of Hollenberg et al. and the method of Chuang are among the methods to predict the creep parameters from bending creep test data. However, bending creep test methods are often doubted for quantitative creep analysis with reasons like uncertainties from contact point shift or frictional effects in four-point bending creep tests. Finite element simulations of the four-point bending creep tests were performed to evaluate the limitations and abilities of four-point bending creep tests and the methods to predict creep parameters from bend test data. Material model for asymmetric creep behavior (different creep rate in tension and in compression) of ceramics material were developed by modifying the existing symmetric creep model and implemented in the inhouse non-linear finite element code. Explicit finite element method (dynamic relaxation) was successfully used to consider both, the frictional effects between loading rollers and specimen, and asymmetric creep properties of ceramics material. The developed asymmetric creep material model was verified by the simulation of C-ring compression creep test and comparison with published experimental data. It was found that when friction between loading rollers and specimen was not applied in the simulations, both Hollenberg’s and Chuang’s methods well predicted creep parameters from bend creep simulation data. But, when friction was high as in normal bend creep tests, the pre-exponent (A) was highly underestimated. Prediction of stress exponent (n) was not affected much by friction. Bend test set-up with rolling-pins in ASTM C 1211 was recommended to reduce the frictional effects in bend creep tests and a proof simulation was performed. The simulation showed that the test set-up in ASTM C 1211 effectively removed the frictional effect of the frequently used creep test set-up and the effect of bending moment increase due to the rolling of loading pin was minor. / Thesis / Master of Applied Science (MASc)

Chloride ion induced corrosion of reinforcing steel in concrete bridge decks has become a major problem in the United States. Latex modified concrete (LMC), low slump dense concrete (LSDC) and hot-mix asphalt membranes (HMAM) overlays are currently some of the most used rehabilitation methods. Epoxy coated reinforcing steel (ECR) was developed and promoted as a long term corrosion protection method by the Federal Highway Administration (FHWA). However, recent evidence has suggested that ECR will not provide adequate long term corrosion protection. The Reynolds Metals Company has developed an aluminum bridge deck system as a proposed alternative to conventional reinforced steel bridge deck systems. The deck consists of a polymer concrete overlay and an aluminum substrate. The purpose of this investigation is to evaluate the bond durability between the overlay and the aluminum substrate after conditioning specimens in various temperature and humidity conditions. The average critical strain energy release rate, Gcr, for each specimen was measured using a modified mixed mode flexure (MMF) test. In this investigation the strain energy release rate is a measure of the fracture toughness of the interface between the polymer concrete overlay and the aluminum substrate. The different environmental conditionings all had a significant effect on the bond durability. Specimens conditioned at 30 degrees C [86 degrees F], 45 degrees C [113 degrees F] and 60 degrees C [140 degrees F] at 98 % relative humidity all showed a decrease in interfacial bond strength after conditioning. A decrease in the interfacial bond strength was also observed for the specimens conditioned in freezing and thawing cycles as well as specimens conditioned in a salt water soak. Of the exposure conditions used in this investigation, the only one that showed an increase in the bond strength was drying the specimens continuously in an oven at 60 degrees C [140 degrees F]. / Master of Science

The objective of this study is to evaluate the bond durability of an epoxy-based polymer concrete wearing surface bonded to aluminum bridge decks. In the bridge design, an aluminum alloy bridge deck is used with a polymer concrete wearing surface. A modified mixed mode flexure fracture test was developed to assess the bond durability of specimens aged in the following environmental conditionings: 30°C [86°F], 98% RH; 45°C [113°F], 98% RH; 60°C [140°F], 98% RH; freezing and thawing; salt (NaCl) water soak; and 60°C [140°F], dry. The exposure times varied from none to twelve months. The critical strain energy release rate (Gc) of the bond was determined using a compliance technique. In spite of considerable scatter in the data, the results suggested that the interfacial bond toughness had been degraded by exposure conditions. The aging appeared to affect the polymer concrete overlay (silica aggregates/epoxy bond) as well. Fracture analysis and finite element modeling were completed for linear elastic behavior. Analytical and numerical solutions were in reasonably good agreement. Characterization of the bridge components and failure specimens were accomplished using analytical measurements including thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Techniques employed in the surface analysis included x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). / Master of Science

Proton exchange membrane fuel cells typically consist of stacks of membrane electrode assemblies sandwiched between bipolar plates, effectively combining the individual cells in series to achieve the desired voltage levels. Elastomeric gaskets are commonly used between each cell to insure that the reactant gases are isolated; any failure of a fuel cell gasket can cause the reactants to mix, which may lead to failure of the fuel cell. An investigation of the durability of these fuel cell seals was performed by using accelerated characterization methods. A hydrocarbon sealant was tested in five different environments to simulate fuel cell conditions. Viscoelastic properties of these seals were analyzed using momentary and relaxation compressive stress tests. Material properties such as secant modulus at 100% strain, tensile strength, and strain at failure were determined using dog-bone samples aged at several different imposed strains and aging times in environments of interest. Tearing energy was evaluated using trouser test samples tested under different rates and temperatures after various environmental aging conditions. Additionally, tearing tests were conducted on samples tested in liquid environment. A viscoelastic and mechanical property characterization of these elastomeric seals under accelerated aging conditions could help understand the behavior and predict durability in the presence of mechanical and environmental loading. Additionally, the effects of confinement have been evaluated for a bonded joint with varying thickness along the bonded direction. The Dreaming project is a glass art project in Fredrick, MD which incorporates such a varying thickness joint where thermal expansion of the adhesive has caused the glass adherend to break and debonding of the sealant. To examine this joint design, finite element analysis has been used to determine the effects of thermal expansion on such a complex geometry. Nine different test geometries have been evaluated to determine the effect of confinement coupled with thermal expansion on joint design with an elastomeric adhesive. Once evaluated, design changes were performed to try to reduce the loading while maintaining the general joint design. Results of this analysis can be used to determine the effects of confinement on a complex elastomeric joint. / Master of Science

Force and moment balances have proved to be essential in the measurement and calculation of aerodynamic properties during wind tunnel testing. With the recent advancements of technology, new fiber optic sensors have been designed to replace the conventional foil strain gage sensors commonly found on balances, thereby offering several distinct advantages. The use of fiber optic sensors on a balance brings with it some potential advantages over conventional strain gage balances including increased resolution and accuracy, insensitivity to electromagnetic interference, and the capability of use at high temperatures. By using the fiber optic sensors, some of the limitations of the conventional balance can be overcome, leading to a better overall balance design. This thesis considers an initial trial application of new fiber optic sensors on a conventional, six-component sting balance while retaining the original foil strain gage sensors for comparison. Tests were conducted with a blunt, 10º half-angle cone model in the Virginia Tech 9x9 inch Supersonic Wind Tunnel at Mach 2.4 with a total pressure of 48 psia and ambient total temperature of 25.3ºC. Results showed a close comparison between the foil strain gages and the fiber optic sensor measurements, which were set up to measure the normal force and pitching moment on the blunt cone model. A Finite Element Model (FEM) of the sting balance was produced in order to determine the best locations for the fiber optic sensors on the sting balance. Computational Fluid Dynamics (CFD) was also used in order to predict and compare the results acquired from all of the sensors. / Master of Science

Vast improvements in robotics and wireless communication have made teleoperated robots significantly more prevalent in industry, defense, and research. To help bridge the gap for these robots in the workplace, there has been a tremendous increase in research toward the development of biomimetic robotic hands that can simulate human operators. However, current methods of control are limited in scope and do not adequately represent human muscle memory and skills. The vision of this thesis is to provide a pathway for overcoming these limitations and open an opportunity for development and implementation of a cost effective methodology towards controlling a robotic hand. The first chapter describes the experiments conducted using Flexpoint bend sensors in conjunction with a simple voltage divider to generate a cost-effective data glove that is significantly less expensive than the commercially available alternatives. The data glove was able to provide sensitivity of less than 0.1 degrees. The second chapter describes the molding process for embedding pressure sensors in silicone skin and data acquisition from them to control the robotic hand. The third chapter describes a method for parsing and observing the information from the data glove and translating the relevant control variables to the robotic hand. The fourth chapter focuses on the feasibility of the brain computer interfaces (BCI) and successfully demonstrates the implementation of a simple brain computer interface in controlling a robotic hand. / Master of Science

Free-Fall Penetrometer (FFP) testing is an easy and rapid test procedure for seabed sediment characterization favorable to conventional geotechnical testing mainly due to its cost-effectiveness. Yet, FFP testing results are interpreted using empirical correlations, but difficulties arise to understand soil behavior under the high-strain rate (HSR) loading effects during rapid FFP penetration. The numerical simulation of FFP-soil interaction is also challenging. This study aims to numerically analyze FFP testing of saturated loose sands using the particle-based Material Point Method (MPM). The numerical analysis was conducted by simulating calibration chamber FFP tests on saturated loose quartz sand. The numerical results using quasi-static properties resulted in a reaction of the sand softer than the actual calibration chamber test. This implied the necessity of considering HSR effects. After performing parametric analyses, it was concluded that dilation plays an important role in the response of sand-water mixtures. Comparison of dry and saturated simulations showed that FFP penetration increases when the soil is dry and tends to develop a general bearing capacity failure mechanism. This is because the pore water increases the stiffness of the system and due to the increased strength that develops in saturated dilative sands when negative pore pressures develop. Local bearing failure mechanism is observed in all saturated simulations. Finally, numerical CPT (quasi-static) and FFP tests were used to examine the strain rate coefficient used in practice (K); and a consistent range between 1 to 1.5 was obtained. / Master of Science / Accurate characterization of seabed sediments is crucial to understand sediment mobilization processes and to solve nearshore engineering problems such as scouring around offshore structures. Its portability, low testing effort, and repeatability make FreeFall Penetrometer (FFP) testing a highly cost-effective sediment characterization test. Nevertheless, due to the complex penetration mechanism of FFPs in soils (e.g., high-strain rate effects due to rapid FFP loading), converting FFP output into practical information is complicated, and it heavily relies on empirical correlations. This thesis presents a numerical analysis of FFP testing on saturated sand using the Material Point Method. First, the simulation results were compared with laboratory tests. Later, a parametric study was performed to understand the effect of different material parameters on the FFP response and to highlight in a simplified manner the effects of rapid loading on the sand behavior. Additional simulations in dry sand (without water) revealed that dry conditions provide larger FFP penetrations than saturated ones for the same material parameters. Lastly, the strain rate coefficient, which is a parameter required in one of the most common empirical methods for converting FFP output into geotechnical parameters, was back-calculated. The results were consistent with values used in practice for similar conditions.

This thesis presents a novel method for the correlation of FEM results to experimental test results known as the "Load updating method." Specifically, the load updating method uses the math model from the FEM and the strains measured from experimental or flight test data as inputs and then predicts the loads in the FEM which would result in strains that would correlate best to the measured strains in the least squared sense. In this research, the load updating method is applied to the analysis of a complex frame structure whose validation is challenging due to the complex nature of its structural behavior, load distributions, and error derived from residual strains. A FEM created for this structure is used to generate strain data for thirty-two different load cases. These same thirty-two load cases are replicated in an experimental setup consisting of the frame, supporting structure, and thirty actuators which are used to load the frame according to the specifications for each of the thirty-two load conditions. A force-strain matrix is created from the math model in NASTRAN using unit loads which are separately applied to each load point in order to extract strain results for each of the locations of the seventy-four strain gages. The strain data from the structural test and the force-strain matrix is then input into a Matlab code which is created to perform the load updating method. This algorithm delivers a set of coefficients which in turn gives the updated loads. These loads are applied to the FEM and the strain values extracted for correlation to the strains from test data. It is found that the load updating method applied to this structure produces strains which correlate well to the experimental strain data. Although the loads found using the load updating method do not perfectly match those which are applied during the test, this error is primarily attributed to residual strains within the structure. In summary, the load updating method provides a way to predict loads which, when applied to the FEM, would result in strains that correlate best to the experimental strains. Ultimately, this method could prove especially useful for predicting loads in experimental and flight test structures and could aid greatly in the Federal Aviation Administration (FAA) certification process. / Master of Science / The research presented in this thesis provides a new way for correlating data obtained during structural testing with results obtained from computer analysis known as the finite element method (FEM). During the process of certifying an aircraft structure with the FAA, it is important to be able to demonstrate that the results obtained for a given structure with a computer model matches the results produced by a real world experiment within a reasonable tolerance. Traditionally, differences between these two results have been accounted for by adjusting the model within the computer until its results match those from the test. However, in this research the loads which are applied on the computer model are changed instead until loads are found which produce results in the computer models that match those from testing. This method, known as the load updating method, therefore provides a way to predict loads on a structure where the loads are unknown such as a flight test article. Here, the ability of the load updating method to predict loads on a complex three dimensional frame structure is explored and the accuracy of the results studied by comparing the results to those from a structural test whose loads are known. It was found that the load updating method does indeed predict unknown loads to a reasonable accuracy and could aid future design efforts immensely.

Thermomechanically bonded spunbond nonwoven fabrics contain discrete bonds that are formed by melted and fused fibers. Through equi-biaxial tensile testing and simultaneous image capture, the mechanical response of individual bonds was studied through loading in the preferential fiber direction, the machine direction, and in the direction that is perpendicular, the cross direction, of the fabric web. Independent biaxial force and displacement data were collected and analyzed, and the maximum force and stiffness of the bonds in the machine and cross directions were found to be statistically different. After scaling the maximum force and stiffness by a relative basis weight parameter, a fiber orientation parameter, and the width of the bond itself, the peak force and stiffness in the machine and cross directions were found to no longer be statistically different. This indicates that basis weight, fiber orientation, and bond size dictate the biaxial mechanical behavior of the bonds. Furthermore, significant fiber debonding was observed in all the bonds tested, effectively suggesting bond disintegration into the individual component fibers during testing. Digital image correlation, using the captured images, was utilized to calculate local and average Eulerian strains of the bond during the initial stages of the test. The strain experienced by the bonds in the machine direction was always positive and increasing as the biaxial load increased. The strain in the cross direction, however, experienced increasing and decreasing strain. Local strain maps revealed the highly inhomogeneous strain response of the bonds under biaxial loading. / Master of Science / For numerous industrial and consumer applications, such as the medical, automotive, packaging, and consumer goods, nonwoven fabrics are often thermomechanically bonded at discrete bond locations in patterns appropriate for the intended use. To produce the nonwoven, fibers are extruded onto a belt and the mat of fibers is passed through a calendar roll to form the thermomechanical bonds. As the fibers move on the belt, there is a preferential fiber direction parallel to the belt. Mechanical biaxial tensile tests were performed on nonwoven sheets in order to gain insight into the response parallel and perpendicular to the preferential fiber direction. Force and displacement data were collected and the maximum force and stiffness response parallel to the preferential fiber direction were found to be significantly higher than perpendicular to the preferential fiber direction. Strain measurements were also performed to examine the local strain of the bonds. Knowledge of the biaxial tensile behavior of bonds in nonwovens allows manufacturers to make informed decisions about the ultimate final application of the nonwoven.