The feasibility of utilizing TiB₂-reinforced near-gamma TiAl intermetallic matrix composites (IMCs) as a reinforcing entity within a commercially pure Ti matrix was investigated. IMCs are "ceramic-like" at ambient to moderate temperatures, and “metallic-like" in their deformation behavior above their brittle-to-ductile transition temperature, thus IMCs create opportunities to create unique in-situ composite microstructures otherwise unattainable using conventional ceramic reinforcements. CP titanium composites reinforced with 20 vol% of near-gamma TiAl IMC were produced by powder blending and densifying via high temperature extrusion deformation processing. The microstructures of the in-situ processed composites were characterized in terms of size, aspect ratio and average spacing of the IMC reinforcement. The microstructural features were correlated to observed mechanical behavior of the composites relative to the unreinforced matrix. The results indicate that the strengthening is derived from microstructural changes within the matrix due to the presence of the IMC particles, and solid solution strengthening due to the diffusion of Al from the reinforcing IMC phase into the Ti matrix. The increase in flow strength due to the former contribution correlates with the inverse square root of the IMC interparticle spacing. / Master of Science

Fiber optic interferometric sensors have been used to measure a number of physical measurands like strain and temperature. Among the different interferometric sensor configurations in use today, the Fabry-Perot interferometer has been shown to have a high sensitivity. The extrinsic Fabry-Perot sensor (EFPI) is a very good candidate for smart structure applications. In this thesis, a new configuration of the extrinsic Fabry-Perot interferometer is developed and demonstrated. This new configuration, based on four-beam interference, utilizes two EFPI sensor heads on a single directional coupler in a Split-cavity Cross-coupled Extrinsic Fiber Interferometer (SCEFI) arrangement. This sensor configuration eliminates the need for biasing the phase difference at the quadrature point. The spectrum analysis scheme, devised for signal demodulation of the SCEFI output allows a linear readout of the phase shift. Both dynamic and static phase shifts are considered. The spectrum analysis scheme developed in this thesis, also allows independent measurements of the phase shift in the two sensor heads. This leads to the multiplexing of two sensors, using a single source and a single coupler. The application of the SCEFI to two-sensor multiplexing is demonstrated experimentally in this thesis. Other significant applications of this new sensor configuration are also discussed. / Master of Science

Master of Science

Recently there has been an increased interest in the generation of ceranlic powders composed of nanosize particles with a narrow size-distribution and high purity. It has been shown that ceramics sintered from these ultrafine partic1es exhibit improved mechanical and electrical properties. The present research has attempted to control the growth of the ceramic particles in a relatively simple continuous flow process by placing charges on the forming particles and controlling their evolution with an electric field. Nanosize TiO₂ powder was produced using a multi-stream, co-annular reactor. The heat source was a cylindrical H₂/0₂ diffusion flame located around the outside of reaction zone. The effect on the powder size, shape, and size distribution due to particle charging, applied electric fields, and varying reactant concentrations were investigated. The temperature field within the reaction zone was uniform radially and ramped axially from 600 to 1100 K. The reactant stream passed through a 10 millicurie Po-21 0 alpha source within the burner with the intention of creating a bipolar ion concentration. In the presence of an electric field, this ionization can lead to either a unipolar-negative or unipolar-positive particle charging environment. The electric field across the reaction zone was varied in an attempt to control particle residence time. / Master of Science

This discussion develops an approach for using fractal geometry and diffusion limited aggregation to describe highway traffic flow. The formulation is platoon based and is most applicable for describing uninterrupted-flow facilities. The model explains empirical models in terms of fractal dimensions. The concepts of change in length of a platoon and a discrete spacing unit are described for the first time in this paper. Boundary values of various fractal dimensions are calculated for different HCM freeway LOS designations. A state of flow equation established in the model represents both microscopic and macroscopic aspects of a traffic stream. Using the same traffic flow model, recurring and nonrecurring types of congestion were quantified. A congestion evaluation index was developed to address the two types of congestion which can also be used as an performance-measure in monitoring a Congestion Management System (CMS). A few ideas were suggested for quantifying indirect benefits of CMS and furthering the present research trend. / Master of Science

A novel coupler measurement station and technique for manufacturing fused biconical tapered multi-port multimode couplers with improved uniformity among ports is presented. Improvement in the uniformity of the couplers is achieved by diffusion of the minimum taper region of the coupler. The phenomenon of dopant transport from the core to the cladding (or from the cladding to the core) at high temperatures is known as diffusion. Diffusion of a germanium-doped core results in the germanium dopants migrating from the core into the cladding thus increasing the effective diameter of the core which is accompanied by a decrease in the refractive index. The cores of individual fibers in the minimum taper region are a few micrometers apart. Diffusion thus results in a minimum taper region that has approximately uniform refractive index leading to better uniformity among ports. The experimental setup and results of diffusion tests on multimode fiber with different core/cladding ratios are presented. A coupler station that is capable of making bi- directional measurements of the coupler is demonstrated successfully. The coupler station also enables a user to dynamically monitor the ports of the coupler during manufacture, and can be adapted to manufacture star couplers ranging in size from two to sixteen fibers. / Master of Science

Microbends are axial distortions on the optical fiber that have a spatial wavelength small enough to effect coupling between guided and radiation or cladding modes. The magnitude of this wavelength-dependent coupling is a function of the nature and the number of microdefonnations. Since these periodic perturbations lead to an attenuation in signal level, they are avoided in fiber-based communication systems. However, controlled induction and signal processing of microbending losses has led to the fabrication of novel optical fiber~based sensors, devices, and components. A systematic study of microbending effects in singlemode optical fibers is presented in this thesis. The theoretical analysis is based on the coupling between the fundamental LP₀₁ mode to discrete cladding modes. An algorithm is developed to characterize optical attenuation as a function of the spatial period of the microbend defonnation. Optical attenuation peaks are described in terms of central wavelength, amplitude and spectral width. An excellent correlation is shown between the experimental results and the theoretical predictions, with nominal errors less than 2.5%. The algorithm developed may be used with any commercially available singlemode fiber, and any kind of microbend de former apparatus, provided the microbend defonnation function â ±(z) is known accurately. Based on the above analysis, a wavelength-tunable fiber polarizer is proposed and demonstrated. The polarizer is fabricated by inducing a periodic perturbation on a high birefringence singlemode optical fiber. The fiber thus exhibits polarization· selective attenuation characteristics. The operating wavelength is shown to be tunable by changing the spatial period of the defonnation. A polarization extinction ratio of 25 dB is obtained with an attenuation of 1.3 dB, at an operating wave length of 1177 nm. / Master of Science

It is believed that the noise produced in squeaking dashboards is caused by the drop in friction force during the transition from static to kinetic conditions between the mating plastic components of the dashboard. The frictional behavior of a polymer determines whether there is a drop in friction force during this transition. This study investigates the frictional behavior of polymers under dry sliding conditions. Various compositions of ABS plastic along with Polypropylene were tested in a flat-on-flat configuration. There appears to be no consistent evidence of surface roughness effects on the magnitude of the drop in friction force. The surface roughness did have an effect on the frictional behavior of the polymers as did the material composition. A new test apparatus was designed to study the transition from static to kinetic conditions more closely. A computer model was developed to simulate this transition. The computer model was used to illustrate the effect of the friction-velocity curve on the frictional behavior of a surface interaction. A few conclusions are made about which friction mechanisms are in control of the polymer-on-polymer tribological system. / Master of Science

An experimental program was conducted at NASA Langley Research Center, in Hampton Virginia, that included development and evaluation of an operational facility for wall drag measurement and evaluation of the total drag of various wall configurations. The drag of three possible supersonic combustor wall configurations was measured to determine if reduction in skin friction and/or wave drag could be achieved through the use of cavities, vented cavities, and/or mass addition. Data are presented herein as average drag force, wall static pressure distributions and focusing schlieren images. The experimental model consisted of a series of interchangeable aluminum plates attached to an air-bearing suspension system. The system was equipped with load cells that measured forces up to 10 pounds in the drag direction only. The plates were exposed to a Mach 2 air stream at a total pressure of 115 psia. This flow field contained a train of relatively weak, unsteady, reflecting shock waves that were produced by the Mach 2 nozzle and plenum chamber assembly. Mass addition was successfully employed to alter the plate drag in both the transpiration and cavity configurations. Three plate configurations were tested: a flat plate, a plate with air transpiration, and a cavity plate equipped for the introduction of bleed air into the cavity. The resulting data base consists of drag data at Mach 2 for a standard flat plate, and two wall configurations tested with bleed mass flow rates ranging from 0.00 to 0.06 lbm/sec. The experimental wall static pressure distributions and the focusing schlieren images are shown to compare favorably with the CAN-DO computer analysis results. / Master of Science

The accessibility of consumer products is an issue for many people with special needs. This study addresses the usability of non-single-lens reflex (NSLR) cameras for people with limited hand grip strength and finger dexterity, namely people with quadriplegia or people with arthritis. It proposes a three-phase methodology to eliminate or mitigate accessibility barriers on a consumer product. A usability test was conducted with a NSLR camera. Problems were recorded with the Critical Incident technique. Prioritization of the problems reported by the subjects show that the shutter release control and the camera grip are the two major accessibility barriers of the product. Four new camera models were developed: three with gripping aids (rubber pads, a thumbsleeve, or a handle) and one with a remote wired shutter release control. A fifth model was obtained by combining the remote shutter release control and the handle. A designed experiment was conducted with the five models and the standard camera. Performance measurements of framing tilt and camera shake were collected, as well as subjective opinions. Results indicate a recurrent difference between performances of quadriplegics and performances of other subjects. The remote shutter release control was shown to eliminate accessibility barriers. The handle also increased ease of grip and camera stability for disabled subjects. / Master of Science