SYNOPSISIn pursuing the new polymers that could provide high mechanical properties and good thermal stabilities, a series of naphthoxazines are synthesized from different hydroxynaphthalenes with aniline and formaldehyde. The molecular structures are confirmed by NMR spectroscopy. After being polymerized in an autoclave, the naphthoxazine derived from 1,5dihydroxynaphthalene is successfully cured to form the void-free resin. The density and tensile properties of these polynaphthoxazines are measured. Dynamic mechanical tests are performed to determine the TR, crosslink density, and the activation enthalpy of the glass transition process for the polynaphthoxazines postcured in air a t different temperatures. The effect of postcure temperature on the Tgs of the polynaphthzoxazines is investigated and discussed in terms of crosslink density. The polynaphthoxazine shows a T, higher than the cure temperature. Fourier transform IR spectroscopy is applied for the molecular characterization of the curing systems. Thermal properties of these polynaphthzoxazines are studied in terms of the weight loss after isothermal aging in static air, the decomposition temperature from thermogravimetric analysis, and the change of dynamic storage moduli at high temperatures.

To develop high‐performance composites with high temperature resistance, two newly synthesized polybenzoxazines were successfully cured with carbon fiber to obtain composites with 60 vol% fiber. Results from differential scanning calorimetry studies were used to modify the benzoxazine monomers to improve processability in terms of melting point and solubility. The density and void content of these composites were measured. Dynamic mechanical tests were performed to determine the glass transition temperature (Tg) and the activation enthalpy of the glass transition process for these two composites. The effect of cure temperature on the Tg of the composites was investigated. Thermal characteristics were studied by means of dynamic mechanical analysis in terms of isothermal aging, decomposition temperature from thermogravimetric analysis, and storage moduli change at high temperatures. Mechanical evaluations of these composites were conducted by flexural and interlaminar shear tests. The mechanical and thermal properties of these two composites exceed bismaleimide composites and compete with polyimide composites, while exhibiting easier processability than polyimides.

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Utilizing the SMART Layer technology as a basis, a real-time active pipeline integrity detection (RAPID) system is developed for built-in in situ assessment of the health of new and existing pipelines. The RAPID system consists of a sensor network permanently mounted on the host pipeline, portable electronic hardware and diagnostic software. Three moduli, including image display, damage sizing, and corrosion depth, are built into the diagnostic software to help in visualization of the approximate location and the extent of corrosion, and to quantify the corrosion sizing and depth. The main advantages of the RAPID system include: (1) ease of use, (2) ability to provide a well-defined resolution, (3) reliability with self-diagnostic and environmental compensation, and (4) quantified corrosion sizing. To verify the detection capability of the RAPID system, a series of tests have been conducted on a 6.7 m long steel pipe with a diameter of 610 mm and a wall thickness of 7.14 mm with ten different types of corrosion flaws. Test results demonstrated that the depth detection limit could be as low as 0.125 mm for general corrosion with an area of 60 mm × 60 mm under laboratory conditions, while a pinhole with 6.35 mm diameter and 3.5 mm depth can be detected with the given sensor density. Some practical issues for field applications of the RAPID system are also discussed.