In December of 1987 tests were conducted in the Virginia Tech Stability Wind Tunnel on a full-scale model of a fiber optic mortar projectile. The desired model configurations were sting-mounted on the Stability Tunnel STO-1 strain gauge balance. The sting was mounted on a streamlined vertical pylon which provided remote rotation in both pitch and yaw while maintaining the center of the balance along the tunnel centerline. The model inputs included the six-component force and moment data in body coordinates and the pressure data from the five pressure taps located within the model. The tunnel inputs were the static temperature, static pressure, and dynamic pressure. The angle of attack and yaw angle were input manually by the tunnel operator. The data analysis for the preliminary test program was intended to define the aerodynamic qualities of various components and configurations to aid in the redesign of the projectile. / Master of Science / incomplete_metadata

Losses induced in a single-mode fiber due to periodic spatial deformations along the fiber axis have been investigated spectrally. Deformation losses in several single-mode fibers were found to be strongly wavelength dependent. This wavelength dependence was characterized by narrow attenuation bands in the transmission spectra of periodically deformed fibers. The attenuation bands were shown to shift as the spatial deformation period was varied. The amplitude and location of the attenuation bands were recorded as the number and amplitude of spatial deformations on the fiber were varied. The backreflected spectra of deformed fibers were also studied. Applications of wavelength dependent losses in periodically perturbed single-mode fibers are proposed. In particular, a self-referenced, intensity-based, fiber sensor is suggested. A distributed sensor is proposed using several sets of deformations with different periods induced on the same fiber to measure the same physical measurand at multiple locations along the length of the fiber. Based on this scheme, a multiplexed fiber sensor is envisioned, capable of measuring different physical variables on the same fiber. Optical notch filters can be made by using the notch-like characteristic of each attenuation band. Methods to induce permanent, periodic, axial deformations on an optical fiber are discussed. Spectral investigation of two-mode fibers with photo-induced refractive index changes is suggested. The proposed investigations would eliminate the need for external deformers to perturb the fiber and yield an intrinsic fiber sensor for sensing different physical variables. / Master of Science

This thesis describes the implementation of a mechanical strain sensor which uses concentric core optical fiber waveguide as the sensing element. When this particular type of fiber is strained, a transfer of optical power occurs between propagating modes in the two concentric cylindrical cores of the fiber. This strain-induced redistribution of optical power may be detected at the output end of the fiber using either two separated optical detectors or a two dimensional detector array. The calibrated strain sensitivity of the sensor is reported and suggestions for continuing research are discussed. / M.S.

The effect of carrier concentration and dye type on carrier and dye uptake of Dacron type 54 yarn was determined. Disperse Red 60 and Disperse Yellow 54 dyes were used. 0-phenyl phenol was used with six different concentrations of this carrier (0, 1, 2, 3, 4 and 5 gm/l). Spun Dacron type 54 polyester yarn of 490 denier weighing ten grams was obtained. Dyeing was done using the Ahiba Texomat dyeing machine. The standard composite curves and equations were established for both dyes as well as the carrier. The dye in the yarn was extracted with dimethyl formamide as a solvent using the Fisher Shaking Water Bath. To measure the dye and carrier uptake of the polyester yarn, the extraction and dye bath solutions were analyzed spectrophotometrically. A two-way factorial Analysis of Variance (ANOVA) was used to test the hypotheses. The first null hypothesis indicating that there will be no difference in the uptake of disperse dye by polyester fiber due to initial carrier concentration was rejected. The second null hypothesis indicating that there will be no difference in the uptake of disperse dye by the polyester fiber due to dye type was also rejected. The third and fourth null hypotheses of no difference in the carrier uptake of polyester fiber due to initial carrier concentration and dye type respectively were likewise rejected. The results of this study indicated that both carrier concentration and dye type as well as their interaction have a significant effect on dye and carrier uptake of the polyester yarn. / Master of Science

High resolution Optical Time Domain Reflectometry (OTDR) measurements have recently allowed spatial resolutions of less than one millimeter. These capabilities indicate that OTDR techniques may be suitable for non-conventional applications such as the determination of fiber strain. This thesis presents an investigation of how high resolution OTDR techniques can be used in such applications. The concept of fiber segmentation via partially reflective optical splices for local strain measurements is discussed both from a theoretical and practical standpoint. Experimental results demonstrating the feasibility of such local strain measurements are also given. Another part of this investigation considers the practical details of the proposed strain measurement technique, addressing such topics as launching conditions, and environmental factors. Possible applications of the local strain measurement techniques, such as two- and three-dimensional stress analysis, and strain determination of fiber optic cables, are also presented. These applications also include the development of small, easy to manufacture elastomeric optical splices, which were shown to yield acceptable performance < 0.2 dB losses) for multimode fibers. / Master of Science

Optical fiber systems have been developed during the past twenty-five years with primary applications in long distance, high speed digital information communication. Optical fiber sensors have also been developed over the past fifteen years for the nondestructive inspection and evaluation of materials used in the aerospace, energy, transportation, and medical industries. Optical fibers may be used as the field-sensitive elements in sensors for the measurement of environmental parameters such as displacement, strain, temperature, vibration, chemical concentrations and electromagnetic fields. Their advantages for such measurements include 1) an inherent immunity to electromagnetic interference (EMD), 2) avoidance of ground loops, 3) the capability of responding to a wide variety of measurands, 4) excellent resolution, 5) the avoidance of sparks, especially important for applications within explosive environments, and 6) operation at temperatures of approximately 800°C for silica waveguides and above 1900°C for sapphire waveguides. Phase-modulated optical fiber sensors have been shown to possess the highest sensitivities to a given measurand. This dissertation describes several novel phase-modulated optical fiber sensors. The sensors described include a strain gage, a temperature sensor for applications up to and including 1700°C, a displacement sensor with sub-Angstrom resolution, and a vibration mode filter. For each sensing concept, a description and method of operation is given, followed by fabrication methods and experimental results. / Ph. D.

Changes in heat content are almost universally associated with chemical reactions. Thermometry as an analytical tool has been extensively researched and developed. Finding solutions to problems involving thermal isolation, specificity, sensitivity, and cross-sensitivity remain as active areas of interest. Fiberoptic interferometers, which use phase phenomena associated with propagating light, are extremely sensitive to heat. This research has focused on a special "birefringent" optical fiber. Two channels of information are generated in this single-fiber interferometer which correspond to the heat evolved from a catalytic reaction isolated on the fiber surface. Because of the unique transduction mechanism associated with the "birefringent" optical fiber, this device is sensitive to heat and remarkably insensitive to pressure. Details of the characterization and development of the birefringent optical fiber into a useful analytical probe are presented. / Ph. D.

The purpose of the dissertation research was to investigate the effect of cold ammonia gas plasma irradiation on the dyeability of poly(m-phenylene isophthalamide) fibers (Nomex Type 430) with acid dyes. Unmodified Nomex filament yarns were irradiated by ammonia radio frequency glow discharge plasma with constant input power (100 W) and plasma pressure (1 torr) inside the reactor; exposure times were 60, 120 and 180 seconds. The modification in dyeability of plasma irradiated yarns was studied by dyeing with three anthraquinone based acid dyes (C.I. Acid Green 25, C.I. Acid Blue 45, and C.I. Acid Blue 80) and measuring dyebath exhaustion and color strength (K/S) of dyed yarns. The improvement in dyeability of plasma irradiated Nomex filament yarn was investigated by studying the surface chemical composition, surface amine concentration, surface topology, and wettability. Surface chemical composition was analyzed by x-ray photoelectron spectroscopy (XPS). The surface amine concentration was evaluated by studying the plasma amination kinetics through ion-exchange reactions between the ionic dye Ponceau Red 3R and Nomex filament yarn. Surface topology of plasma irradiated filament yarns was studied with high resolution scanning electron microscopy (HR-SEM). The wettability of the irradiated Nomex filament yarns was analyzed in terms of grams of deionized water absorbed per gram of fiber after immersing the yarn specimens in de-ionized water for three time periods (15 s, 30 s, 60 s). The effect of irradiation on the filament yarns’ tensile properties was evaluated by measuring breaking tenacity, elongation at break, and toughness. Statistical analyses of data on various parameters included analysis of variance (ANOVA), orthogonal polynomial contrasts between means, and post-hoc Newman-Keuls tests between means. XPS spectra showed a higher concentration of both oxygen and nitrogen atoms at the Nomex filament surface after irradiation. Plasma amination kinetics indicated substantially more primary amino functional groups at the filament yarn surface after the plasma irradiation. SEM photomicrographs of plasma irradiated filament yarn indicated surface etching at low magnification (1,600 X) and surface cavitations at higher magnification (25,000 X). The wettability of irradiated Nomex filament yarns with de-ionized water was significantly higher compared to nonirradiated specimens. The dyeability of ammonia plasma irradiated Nomex filament yarns with acid dyes was improved as indicated by higher dyebath exhaustion and higher color strength. The dyebath exhaustion for the three dyes did not vary noticeably with respect to irradiation times (60 s, 120 s, 180 s). Ammonia plasma treatment adversely affected the tensile properties of Nomex filament yarn to a significant extent only after 180 s. Breaking elongation and toughness were more severely affected after 180 s plasma treatment than was the breaking tenacity. / Ph. D.

Changes in nylon 6.6 and polyester filament yarns were determined after heat treatment with dry heat at various temperatures under constant length conditions. An attempt was made to relate structural changes and changes in physical properties due to heat setting. Density, obtained by the density gradient column technique, was used to calculate the degree of crystallinity as a structural parameter. Filament tensile strength and elongation at break were measured on a constant-rate-of-extension machine, and then toughness of the sample was obtained from the load elongation curve. The amount of dye uptake was estimated spectrophotometrically. Degree of crystallinity increased significantly as temperature increased for both nylon 6.6 and polyester fibers. Tenacity decreased substantially for nylon 6.6 and increased marginally for polyester. Elongation and toughness at break decreased for both nylon 6.6 and polyester. Tenacity of nylon 6.6 decreased despite an increase in degree of crystallinity. This suggests degradation of the fibers. Therefore, degree of crystallinity appeared to be of little importance as a contributor to change in tensile strength for degraded nylon 6.6. Tenacity of polyester was well predicted by degree of crystallinity. As crystallinity increased, tenacity of polyester increased. Elongation and toughness of both nylon 6.6 and polyester decreased as degree of crystallinity increased, but the relationship to crystallinity for polyester was not significant. Dyeability of both nylon 6.6 and polyester was well predicted by degree of crystallinity. In both cases, the amount of dye uptake decreased as crystallinity increased. This research suggests that determinations for structural changes such as degradation and orientation might be utilized in addition to crystallinity to predict tenacity of nylon 6.6 and elongation and toughness of polyester. / Ph. D.

Space simulated thermally induced deformations and stresses in continuous fiber-reinforced composites were investigated with a micromechanics analysis. The investigation focused on two primary areas. First, available explicit expressions for predicting the effective coefficients of thermal expansion (CTE's) for a composite were compared with each other and with a finite element (FE) analysis, developed specifically for this study. Analytical comparisons were made for a wide range of fiber/matrix systems, and predicted values were compared with experimental data. All of the analyses predicted nearly identical values of the axial CTE, α₁, for a given material system, and all of the predictions were in good agreement with the experimental data. Results from the FE analysis, and those from the solution of a generalized plane strain boundary value problem, were in excellent agreement with each other and with the experimental data for the transverse CTE, α₂. Less rigorous formulations were in poor agreement with the experimental data. The second area of investigation focused on the determination of thermally induced stress fields in the individual constituents. Stresses predicted from the FE analysis were compared to those predicted from a closed-from solution to the composite cylinder (CC) model, for two carbon fiber/epoxy composites. A global-local formulation, combining laminated plate theory and FE analysis, was used to determine the stresses in multidirectional laminates. Thermally-induced damage initiation predictions were also made. The type of analysis (i.e. CC or FE) was shown to significantly affect the distributions and magnitudes of the predicted stresses. Thermally-induced matrix stresses increased in absolute value with increasing fiber volume fraction but were not a strong function of fiber properties. Multidirectional [0₂/±θ]s laminates had larger predicted thermally induced matrix stresses than unidirectional ([0]) laminates, and these stresses increased with increasing lamination angle θ. Thermally-induced matrix failure predictions, using a maximum stress failure criterion based on the normal interfacial stress component and the measured transverse lamina strength, were in excellent agreement with experimental data. / Ph. D.