An experimental analysis of specimens taken from a thick, filament-wound composite material pressure vessel (cylinder) was performed by testing tensile coupons with various semi-elliptical surface notches. The strength of specimens with small notches was found to be notch insensitive. The strength of specimens with larger notches depended on the size of the notch. The fracture toughness of the laminate was found by applying a general fracture-toughness parameter approach. Using this value, several approaches were employed to predict failure loads. The accuracy of the approaches depended on the size of the notches. In general, the linear-elastic fracture mechanics method overpredicted the failure strength of specimens with intermediate sized notches, but predicted failure strength accurately for specimens with large notches. A strength of materials approach accurately predicted notched strength only for specimens with small notches. Notched strength was more accurately predicted for all notch sizes using an empirical approach, with the notch area used to predict failure instead of the notch depth, which was used in the linear-elastic fracture mechanics and strength of materials approaches. / M.S.

The use of cellular foam as a core material in light-weight structural applications is of considerable interest. However, advances in this technology have been limited due to the lack of information concerning the macroscopic material behavior of cellular foams. Of particular interest in the design of composite structures is the shear modulus, G, of the core material, which must be established with a high degree of accuracy. Current ASTM test methods for shear modulus determination were researched and found inadequate for testing cellular foam materials. The difficulty in testing foam and the inaccuracies associated with the standard test methods established the need for the development of a test method for these materials. The test method (test fixture and test procedure) developed for cellular foam materials is presented. The design of the test fixture and the finite element analysis performed to determine fixture accuracy are discussed in detail. Additionally, the test procedure is presented, as well as the results for the 32 tests performed.

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

published_or_final_version / Dentistry / Master / Master of Dental Surgery

A new interferometric method which indirectly measures the total chromatic dispersion of a single mode fiber is demonstrated. The technique utilizes a short length of fiber, an unmodulated broadband source, simple low frequency electronics, and a standard interferometer. The concept of this measurement is based on the behavior of the uncorrelated individual bursts of light from the elemental emitters that constitute a thermal source. Their propagation through a dispersive media, e.g., silica fiber, which is placed in one arm of the interferometer, is delayed and broadened. They will interfere with their counterpart from the other arm, generating a train of time-varying fringes as one mirror of the interferometer is uniformly translated. The local frequency of the fringes at a given position of the moving mirror is a direct measure of the instantaneous wavelength, while the mirror position itself demarks the corresponding relative delay. A colinearly launched HeNe laser beam is used as a reference to calibrate the other source's fringe width and location of the mirror. In this experiment, an edge-emitting LED of λo = 830 nm and Δλ = 60 nm was used. The tested fibers had a length of 27.9 cm and 38.3 cm, which made the width of the crosscorrelation function approximately 100 times greater than the source's coherence length. The speed of the mechanically driven mirror set the frequency of the HeNe fringes to approximately 800 Hz with an r.m.s. fluctuation around the mean of 0.2%. The SNR of the HeNe fringes was four times larger than the LED's. Ten different runs for each fiber were executed. Data from the two sets of simultaneous measurements of delay versus wavelength were used to fit the best linear and quadratic polynomials with a minimum residual mean error square. The derivative of this function with respect to wavelength gave the dispersion relation. The accuracy of measured delay and wavelength were 0.1 ps and 6 nm, respectively. The dispersion value and its standard error for the best linear fit was approximately 117 ∓ 2 ps/km nm. The standard error for the quadratic fit was much larger due to the high noise level accompanying signal. A thorough investigation of the noise sources, accuracies, standard error of the polynomial's coefficient, and SNR analysis is conducted. This measurement is simple and has the potential of achieving substantially higher accuracy--especially for the longer wavelength region where dispersion is minute.

No description available.

No description available.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of science in Engineering. Johannesburg, 1992. / This project involves the comparison of different failure criteria with experimental results for fibre composite materials, and investigates the usefulness of acoustic emission in composite testing. Three sets of specimens were tested to failure in tension. The specimens had various ply orientations and were tested using acoustic emission to determine ply failures. Carbon and glass fibre reinforced epoxy pre-impregnated specimens were used. The testing machine was an ESH testing machine, and a physical Acoustics corporation computer and data acquisition unit were used to record data from a piezo-electric sensor. Suitable failure criteria should be chosen on the basis of ply orientation and material type (eg fibre stiffness), a combination of criteria being used if necessary. Acoustic emission was successfully used to detect ply failure in multi-layered laminates. / AC2017

A novel approach has been introduced in making flexible armor composites. Armor composites are usually made by reinforcing Kevlar fabric into the mixture of a polymer and nanoscale particles. The current procedure deviates from the traditional shear thickening fluid (STF) route and instead uses silane (amino-propyl-trimethoxy silane) as the base polymer. In addition, a cross-linking fixative such as Glutaraldehyde (Gluta) is added to the polymer to create bridges between distant pairs of amine groups present in Kevlar and silated nanoparticles. Water, silane, nanoparticles and Gluta are mixed using a homogenizer and an ultra-sonochemical technique. Subsequently, the admixture is impregnated with Kevlar - bypassing the heating and evaporating processes involved with STF. The resulting composites have shown remarkable improvement in spike resistance; at least one order higher than that of STF/Kevlar composites. The source of improvement has been traced to the formation of secondary amine C-N stretch due to the presence of Gluta. / by Vincent Lambert. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.