A method of fabrication of a novel cellular composite structure has been devised based on a convoluted sheet of resin-impregnated fabric. The flexural properties of this structure with and without facings have been assessed in four point bending. In flexure the load deflection trace is linear up to a point at which a critical load is reached and the structure fails by a gradual buckling mechanism. The second moment of area of the structure's cross-section has been approximated to that of a square packed array of composite cylinders of equivalent dimensions and this successfully predicts beam properties. The effects of span and tube element geometry on flexural properties were studied to establish a method of predicting the mechanical response of a cellular composite beam in flexure. A failure criterion for the buckling of individual composite cylinders was applied to the cellular composite structure enabling a series of load versus deflection design curves to be drawn for any beam with any geometrical cross-section in any bending configuration. Future commercial prospects for the cellular structure have been anticipated by filing patent applications worldwide. Mechanical tests have been undertaken to establish the originality of the cellular material. The energy absorption capacity of the cellular composite structure was assessed. It was shown that the structure has an unusually high specific energy absorption capacity in comparison to single composite cylinders of equivalent geometric ratios. It was also demonstrated that the energy absorption, which is rate independent, is dependent on cell geometry and the orientation of the reinforcing fabric.

No description available.

Thesis (M.S.M.E.)--University of Delaware, 2006. / Principal faculty advisors: Suresh G. Advani, Dept. of Mechanical Engineering; and Shridhar Yarlagadda, Shridhar Yarlagadda, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

The performance of a deep water composite production riser from a system perspective is presented, and its advantages are articulated through comparisons with a typical steel riser under identical service conditions. The composite riser joints in this study were considered to be a part of a single Tension Leg Platform (TLP) riser string to be installed at a depth of 6000 ft in Gulf of Mexico. A series of numerical analyses –burst, collapse, fatigue, global and local – have been performed, and the capacities of the composite riser have been determined utilizing long-term strength properties. The capacities associated with the hoop direction, i.e., burst and collapse, are limited by the presence of a steel internal liner whose function is to ensure pressure and fluid tightness. The collapse capacity of the riser can be drastically impaired by the presence of a debond between the liner and composite. Due to the high strength to weight ratio of the carbon/epoxy composite, its response under combined axial tension and bending moment showed great safety margins, favoring pursuits of greater water depths. The study also constructed damage envelopes associated with axial tension and bending moment, which facilitate feasibility checks for expanding the use of the composite joints to other locations or systems. The fatigue life of the composite body is expected to greatly exceed its design life, and the most critical element is the welds between the liner and metal end pieces. Since there is wide dispersion of S-N relationships for carbon/epoxy composites depending on the combinations of constituent materials, a parametric study was carried out in this study to suggest the range of acceptable S-N relationships. The composite riser is estimated to offer only moderate damping, due primarily to its specially orthotropic lay-up. The study also demonstrates that the use of Rayleigh stiffness proportional damping may not be suitable for deep water risers. A series of forced excitation analyses show that the system in sea water does not show notable resonance due to fluid drag. When compared with the steel riser, vibration amplitudes at low elevations are much lower.

Nanocomposites show promise in various fields, ranging from aerospace vehicles to microelectronics. Specifically, electro-active nanocomposites would enable a whole new set of applications, where the nanocomposite material would exhibit strength, toughness, and electromechanical coupling. The broad goal of this thesis was to investigate potential electromechanical behavior in single walled carbon nanotube (SWNT)-polyimide (PI) composites. The specific objective was to measure and characterize the actuation response of SWNT–PI nanocomposites. Two different polyimides, non-polar CP2, and a weakly piezoelectric polymer (beta-CN) APB-ODPA are used in the study. Electrical and dielectric characterization of the nanocomposites were carried out to better understand the effect of SWNTs on the different physical properties of the composites, and to identify the electroactive mechanism in the resulting composites. (beta-CN) APB-ODPA composites show a higher increase in both conductivity and dielectric constant with SWNT content as compared to the CP2 composites. The effect of SWNTs on remnant polarization (PR) is quantified using the dielectric relaxation tests and Thermally Stimulated Current (TSC) experiments. Both experiments show an increase in the remnant polarization with SWNT content and a higher value for the (beta-CN)APBODPA nanocomposites over CP2 nanocomposites. Actuation tests employing a cantilever bending experiment were carried out on the nanocomposite samples while varying the SWNT content and electric field. The strains are seen to be proportional to the square of the electric field, indicating an electrostrictive response. Strain rate and the coefficient of electrostriction (M1333) values are seen to increase with SWNT content and are higher for (beta-CN) APB-ODPA nanocomposites than the CP2 nanocomposites. Electrostrictive strains can also be expressed as the square of polarization; hence the findings of the dielectric relaxation studies and TSC measurements can be correlated to the measured electrostrictive effect. The cause for the enhancement in dielectric, dielectric relaxation and actuation response of the nanocomposites with the increase in the SWNT content and polarity of the matrix was explored. Among different possible causes special emphasis was given to the importance of the interface between the SWNTs and the matrix and the resulting increase in polarization as the main factor driving the enhancement.

The performance of a deep water composite production riser from a system perspective is presented, and its advantages are articulated through comparisons with a typical steel riser under identical service conditions. The composite riser joints in this study were considered to be a part of a single Tension Leg Platform (TLP) riser string to be installed at a depth of 6000 ft in Gulf of Mexico. A series of numerical analyses –burst, collapse, fatigue, global and local – have been performed, and the capacities of the composite riser have been determined utilizing long-term strength properties. The capacities associated with the hoop direction, i.e., burst and collapse, are limited by the presence of a steel internal liner whose function is to ensure pressure and fluid tightness. The collapse capacity of the riser can be drastically impaired by the presence of a debond between the liner and composite. Due to the high strength to weight ratio of the carbon/epoxy composite, its response under combined axial tension and bending moment showed great safety margins, favoring pursuits of greater water depths. The study also constructed damage envelopes associated with axial tension and bending moment, which facilitate feasibility checks for expanding the use of the composite joints to other locations or systems. The fatigue life of the composite body is expected to greatly exceed its design life, and the most critical element is the welds between the liner and metal end pieces. Since there is wide dispersion of S-N relationships for carbon/epoxy composites depending on the combinations of constituent materials, a parametric study was carried out in this study to suggest the range of acceptable S-N relationships. The composite riser is estimated to offer only moderate damping, due primarily to its specially orthotropic lay-up. The study also demonstrates that the use of Rayleigh stiffness proportional damping may not be suitable for deep water risers. A series of forced excitation analyses show that the system in sea water does not show notable resonance due to fluid drag. When compared with the steel riser, vibration amplitudes at low elevations are much lower.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 246-256).

Thèse de docteur-ingénieur : Génie des matériaux : Villeurbanne, INSA : 2002. / Thèse : 2002ISAL0011. Titre provenant de l'écran-titre. Bibliogr. p175-190.

Reproduction de : Thèse de doctorat : Mécanique des multi-matériaux : Lyon 1 : 2007. / Titre provenant de l'écran titre. Bibliogr. p. 259-265.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 172-182).