A research program was conducted to investigate the application of composite materials in repairing corroded offshore risers, leading to the development of an optimized repair using a hybrid carbon/E-glass system. The objective of this research program was to investigate the feasibility of extending onshore composite repair techniques to offshore risers by developing integrated analytical and experimental methods. The study considered loads typical for offshore risers including internal pressure, tension, and bending. To fulfill this objective efforts included a state of the art assessment of current composite repair technology, designing a carbon-based composite repair system optimized by numerical simulation with prototype testing, and providing guidelines for industry in repairing and reinforcing offshore risers using composite materials. Research efforts integrated numerical modeling, as well as full-scale testing that included four composite repair manufacturers to assess the current state of the art on pipe samples with simulated corrosion reinforced with composite materials. Analysis and testing were also performed on the optimized carbon/E-glass system. The results of this program demonstrated that composite materials are a viable means for repairing corroded offshore steel risers as adequate reinforcement ensures that the steel risers are not loaded beyond acceptable design limits. For corroded risers, the results demonstrated through analysis and full-scale testing efforts that properly designed composite repair systems can provide adequate structural reinforcement to ensure that excessive strains are not induced in the steel when subjected to internal pressure, axial tension, and bending design loads. This was verified experimentally using strain gages placed beneath the composite repair. This program is the first of its kind and is thought to contribute significantly to the future of offshore riser repairs. It is likely that the findings of this program will foster future investigations involving operators by integrating their insights regarding the need for composite repair based on emerging technology. One of the most significant contributions to the existing body of work is the use of limit analysis in developing design limits for the repair of steel pipes using composite materials.

The effect of silica nanoparticles on corrosion of steel by molten carbonate eutectic (42.7 percent Li2CO3, K2CO3) was investigated. The experimental design was based on static coupon immersion methodology where a coupon (material under study, in this case a rectangular stainless steel specimen of SS304 with dimensions approximately 5X20X.6mm and weight .5gm) is exposed to a static corroding environment for predetermined periods of time. The testing times were 2, 4 and 6 weeks. The temperature during testing was maintained at a constant 520C. The instantaneous corrosion rates were determined by normalizing the mass loss with respect to time and area. The mass loss was determined by descaling the corroded steel coupons using concentrated hydrochloric acid. The instantaneous corrosion rates obtained from all three times showed a reduction in corrosion of steel by molten carbonate eutectics when doped with silica 1 percent by weight in comparison to the molten base carbonate eutectics. The results showed that doping the carbonate eutectic with silica nanoparticles (1 percent by weight) reduced the corrosion of steel by half in comparison to the corrosion without doping.

­^¤åºK­n The research is to investigate the dynamic behavior for the large undersea pipeline structure system subjected to the wave force. In this study, the primary structure is composed of two steel layers and one viscoelastic layer modeled as a three-layered pipeline structure in composite type. The theory of this study is based on Reddy¡¦s¡§High-order Shear Deformation Theory¡¨and continues Lee¡¦s research on VE materials applied in the engineering structures to discuss the dynamic behavior and the ability of VE materials to restrain the vibration. Based on the theory derived, the analytical results of vibration, deformation of the pipeline and the dynamic behavior for the whole pipeline system are obtained and discussed, in order to improve the dynamic performance for pipeline system and eventually to upgrade the durability of the system. This thesis is divided into two parts for pipeline structures ¡X the general pipeline structures and the undersea pipeline structures. For the general pipeline structures, the study focuses on the effect of the vibration mitigation due to the variation of the diameter of pipelines, length of pipelines and thickness of the viscoelastic material. Besides, the external forces of high-frequency loading and low-frequency loading are both applied. For the undersea pipeline structures, the depth of water, loading types (include the in-line force and the lift force), the periods of wave and the wave length of environmental effects are taken into account.

The purpose of thesis is aimed to analyze fracture and fatigue behaviors of notched composite laminates by numerical method. Types of notch are both central notch 4mm£rand double-edged crack. We employed finite element method analysis with ANSYS to perform the numerical analysis. We adopted Tsai-Wu failure criterion to approach failure of central notch laminates by a step increment method and considered the effect of failure area gradually expanded, thus we obtained the ultimate stress of a laminate. In the work of fatigue testing and evaluation, we used Miner¡¦s rule to predict the extension of fatigue damage zone, and compared it with experimental results. In the analysis of a double-edged crack laminate, it is first assumed mix mode failure. Then, we calculated the stress intensity factors of various crack length by extrapolation, and developed a function of configuration correction factor. Finally, this study can be concluded as follows. The accuracy of ultimate stress prediction with step-by-step increment analysis is satisfactorily well. The outcome failure area of a laminate is closely corresponding with the observation of experiment. In predicting the fatigue damage zone, the predicted initial damage zone is close to experimental observation, but it is inconsistent with the actual damage extension due to crack propagation. Stress intensity factors and configuration correction factors are directly in proportion to the square root of crack length. It is corresponding with fracture mechanics. However there are some errors in quasi-isotropic laminates due to the existing of ¡Ó45¢Xplies.

A research object of this study is a extrusion of the composite rods. As the condition of the incompressibility, a set of stream functions was proposed by this study to construct analysis model of the conventional and the hydrostatic extrusion. The upper-bound approach was applied to investigate the plastic deformation behavior during composite rods extrusion. The topical subject of this study was consisted of conventional extrusion, hydrostatic extrusion and the instability of composite materials during conventional extrusion. This study proposes a set of stream functions to investigate the plastic deformation behavior of the rods during axisymmetric extrusion of composite rods through a conical die. The velocity field and the rigid-plastic boundaries can be obtained from the proposed stream functions immediately. Relative slip at the interface of the rods is allowed. The friction factor between the metal and die is determined by a ring compression test. By using the upper-bound approach, the radius ratio of the core layer at the exit of the die and the plastic region within the die are determined by the minimization of the total power. Experiments on extrusion of composite rods composed of aluminum (core layer) and copper (sleeve layer) are also carried out. The predicted force, final radius ratio and flow pattern of the rods within the die are compared with the experimental results. Being different with conventional extrusion, a condition that has relative slip at the interface of the rods at the exit of the die was modified to become no relative slip. The same set of stream functions with that of the conventional extrusion was also applied to simulate the flow behavior of the composite rods through a conical die during hydrostatic extrusion. This model is used to predict the hydrostatic extrusion pressure for various process parameters via the upper bound theorem. Experiments are also carried out using composite rods composed of copper as the sleeve layer and commercial aluminum as the core layer. The experimental results are compared with the theoretical calculations. A plastic instability criterion under a tri-axial stress state was developed in this study to predict the occurrence of plastic instability in the hard core layer during axisymmetric composite rod extrusion. Stress states in the hard core layer at the exit of the die, where plastic instability is most likely to occur, were employed to formulate the plastic instability criterion. The effects of various extrusion conditions, such as the initial radius ratio and yield stress ratio of the composite rods, etc., upon the critical area reduction, under which plastic instability can be avoided, were discussed systematically. Furthermore, experiments on composite rod extrusion were also conducted by employing aluminum and lead as layers of composite rods. It was found that the theoretical predictions of the critical area reduction were in good agreement with the experimental measurements with the initial area of 0.15.

Abstract Organically modified montmorillonite by a long chain alkylammonium surfactant was used to prepare polyimide/clay nanocomposites in this study. Several attempts were made in an effort to achieve fully exfoliated nanocomposites. These included the one-step method, two-step method and in-situ polymerization method. At the same time, the effects of polyimide structures and clay contents were studied. Two dianhydrides and two diamines were used to prepare polyimide/clay nanocomposites via the two-step method. The polyimide/clay nanocomposites with various clay contents from 1.5 ~ 10 wt % were prepared via the two-step method too. The structure of polyimides and the dispersion level of clay were identified by Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). Thermogravimetric analysis (TGA) was performed to demonstrate the thermal stability of the nanocomposites. TGA and XRD results indicate the surfactants are intercalated into the layers of clay. FTIR results indicate the all polyimides in the nanocomposites are formed successfully. XRD results indicate the BPDA-ODA/clay nanocomposite within 3 % by weight of clay via the two-step method is shown to have the best dispersion level of clay. These results are consistent with observations from TGA. The temperature at 10 % by weight loss of the nanocomposite is 31 ¢J greater than that of pure BPDA-ODA. The formation mechanism of polyimide/clay nanocomposites via the two-step method can be described by three distinct steps. A polyamic acid/clay mixture with an exfoliated morphology is first formed. A portion of solvents and intercalated surfactants are then either degraded or expelled from the clay gallery under thermal imidization, resulting in a reduced gallery height of 1.32 nm. On the other hand, portion of the clay layers show an exfoliated morphology due to the effective surfactant and polyimide molecules. As a result, a partially exfoliated polyimide/clay nanocomposite is obtained.

In this study, the CVD diamond films were grinded using composite electroplating in-process sharpening (CEPIS). At an applied load of 4.2 kg, a rotation speed of 200 rpm and 20 rpm for the upper and lower spindles, the effects of NiCl2 (nickel chloride) content of electrolyte (in the range of 5-75 g/l) and cathode current density (in the range of 0-7.5 ASD) on the structure of the nickel-diamond composite coating and its grinding ability were investigated. Based on the experiment results, the coating structure became porous and the coating thickness increased with decreasing NiCl2 content of electrolyte during the composite electroplating process. During CEPIS process, the material removal rate of diamond film has no obvious concern with the NiCl2 content at low cathode current density (below 2.5 ASD). However, its material removal rate rapidly increased to a saturated value with increasing NiCl2 content at high cathode current density (above 5 ASD). The NiCl2 content to achieve a saturated material removal rate increased with increasing cathode current density. In this study, the maximum removal rate of diamond film is about 0.093 mg/min at the NiCl2 content of 75 g/l and the cathode current density of 5 ASD.

Many golf firms of carbon fiber golf shafts are much concerned about for standard measurement of shafts for their specific needs. To achieve the purpose, the present study was conducted. Flex¡GThe researcher first hanged a mass on the tip with the butt fixed, and then he hanged a mass on the butt with the tip fixed for measuring the deflection of the shaft. Torque¡GThe degree of torsion is measured by applying the twisting moment 0.126 (kgf•m) to the tip. Vibration¡GThe cycle per minute is measured by adding a mass to the tip of a shaft and shaking it. The mechanical performance of carbon fiber composite is modeled and solved by the finite element software ¡§ANSYS¡¨ in static and modal analysis. The errors between the simulations and experiments were compared and discussed. Finally, the angles of in, middle, and out layers of the shaft were changed to see how they affect the mechanical performance of golf shafts. In this study, the errors of the results for deflection, degree of torsion, and cycle per minute of golf shafts between experiments and simulations are less than 10%. The results solved by the finite element software ¡§ANSYS¡¨ are reliable. The results of simulations also show that a close relationship between the mechanical performance of golf shafts and the fiber angles. Eventually, a series of data bases and trend pictures were provided for golf firms' reference and application.

Thesis (M.S.) in Mechanical Engineering--University of Maine, 2002. / Includes vita. Includes bibliographical references (leaves 76-83).

Thesis (Ph. D.) in Forest Resources--University of Maine, 2000. / Includes vita. Includes bibliographical references (leaves 135-141).