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The behavior of a highly fluorinated epoxy resin used as a composite matrix material with AS-4 fibers and as an AS-4 fiber coating was studied. The composite mechanical properties were obtained, and the adhesion of the matrix to the fibers was evaluated. Comparisons of uncoated and fluoropolymer coated AS-4 fibers using single fibers embedded in an Epon 828 matrix were made. Substantial improvement in fiber critical length, and therefore fiber-matrix adhesion, was observed.

The effect of fiber-coating thickness on retained in-situ fiber strength and the resulting mechanical properties of composites was investigated. Flexure tests in a four-point-bend mode were used to evaluate ultimate strength and work-of-fracture of the composites with various fiber-coating thicknesses. Retained in-situ fiber strength in the fractured composites was evaluated by fractographic techniques. Retained in-situ fiber strength, ultimate strength, and work-of-fracture of the composites increased with increasing fiber-coating thickness, reaching a peak value at a coating thickness of {approximately}0.3{mu}m. Further increases in coating thickness did not improve the mechanical properties of either the fibers or the composites. A direct correlation between retained in-situ fiber strength and mechanical properties of the composites suggests that retained in-situ fiber strength has a significant influence on the mechanical properties of composites.

International audience; Optical fibers are key components in telecommunication technologies. Apart from optical specifications, optical fibers are expected to keep most of their physical properties for 10-20 years in current operating conditions. The reliability and the expected lifetime of optical links are closely related to action of the chemical environment on the silica network. However, the coating also contributes largely to the mechanical properties of the fibers. The aim of this work was to study the strength and the mechanical behavior of the silica optical fibers in an acid environment and with a permanent deformation. A container with ammonium bifluoride acid salt was plunged into hot water at different temperatures (55 and 75 °C). This emitted acid vapors which attacked the optical fibers for a period of 1-18 days. An aging study was performed on silica optical fibers with standard polyacrylate coating and with hermetic carbon coating. A dynamic two-point bending bench at different faceplate velocities (100, 200, 400 and 800 μm/s) was used. For comparison, the same dynamic measurements were also carried out on non-aged fibers. After acid vapor condensation, salt crystal deposits on the fibers were displayed using an electron scanning microscope. These crystals became visible to the naked eye from the seventh day.

Giant unilamellar vesicles (GUVs) are deposited on glass microfibers. The vesicles adopt the classical “onduloidal” shape of liquid droplets on fibers. They spread by two simultaneous mechanisms: envelopment and emission of a precursor film. This film spreads faster than on a uniform plane surface and eventually stops, signaling the presence of defects on the rod. This fast spreading tenses the vesicles; transient pores open on the GUVs and the internal liquid leaks out. This process leads to a new technique for fiber coating.

SUMMARY AND FUTURE WORKAnti-cortisol antibodies were immobilized using sol-gel encapsulation techniques and used as probes forcortisol detection. Calibration curves were constructed with monoliths and thin films as the sensing element. Our futuregoals include development of a fiber-optic system. Using a bifurcated fiber, fluorescence signals in the fiber coating canbe directed into a portable spectrophotometer for signal detection. The proposed system is designed to be small andcompact, suitable for use in space. ACKNOWLEDGEMENTS This project is funded by NASA under Grant No. NAG9- 1252. References 1 Brinker CJ, Scherer GW. The Physics and Chemistry ofSol-Gel Processing. Academic Press, mc: San Diego, 1990.2 Rickus, JL, Dunn, B, Zink, JI "Chapter 14: Optically Based Sol-Gel Biosensor Materials." Optical Biosensors:Present and Future. Ed. F. Ligler and C. Rowe-Taitt, Elsevier, Amsterdam. 2002.3 Lan EH, Dave BC, Fukuto JM, Dunn B, Zink JI, Valentine JS, "Synthesis of sol-gel encapsulated heme proteins withchemical sensing properties." J. Mater. Chem. 9, p45. 1999.4 Yamanaka SA, Nishida F, Ellerby LM, Nishida CR, Dunn B, Valentine JS, Zink JI, "Enzymatic Activity of GlucoseOxidase Encapsulated in Transparent Glass by the Sol-Gel Method", Chem. Mater. 4, p1. 1992.5 Lan EH, Dunn B, Zink JI, "Sol-Gel Encapsualted Anti-Trinitrotoluene Antibodies in Immunoassays for TNT", Chem.Mater. 12, p1874. 2000.

The effect of oxidation of the carbonaceous fiber coating on the intermediate temperature stress-rupture behavior of a Nicalon{trademark}/C/SiC continuous fiber composite was modeled. The model, that was reduced to the analysis of a general ideal bundle composed of classical fibers subjected to constant loading, predicts that the oxidation of the fiber coating triggers a sequence of processes that can lead, under certain conditions, to composite failure. These processes involve loss of stress transfer between the fiber and the matrix, fiber overloading, and fiber failure. The implications of the model predictions are discussed in relation to experimental measurements at 425 C in air that show that Nicalon{trademark}/C/SiC exhibits time-dependent loss of strength.

This report gives progress made on the following milestones: demonstrate Ti and Nb monitoring at 3M site, demonstrate Al monitoring at LLNL, complete baseline melt and vapor plume model for the metal matrix process (3M fiber coating process), prototype a laser at LLNL to monitor Cu, ZrO{sub 2} monitoring demonstration at LLNL, Se monitoring demonstration, and process scale-up study for YBCO high-temperature superconductor.

Optical microfibers (OMs) are good alternatives in the field of sensing. In this letter, a simple and effective miniature temperature sensor based on OM is proposed and experimentally verified. Using pure water and fiber coating as the OM clad, an additional loss will occur due to the absorption of outer medium. The temperature of the outer environment can be estimated by monitoring the change in additional loss. In the demonstrated experiments, a series of OM with different diameters, waist lengths, and constructions are used as sensing elements. The correlation coefficients between the experimental results and the linear fittings are better than 0.99, and the temperature sensitivity obtained by the linear fittings can achieve -0.151 dB/oC (in pure water) and -0.405 dB/oC (covered by fiber coating). Moreover, higher sensitivity can be obtained by decreasing the diameter, increasing the waist length of the OM, or choosing the proper operating wavelength.

The interfacial chemical behavior of two candidate coating systems for use on fine diameter (∼10 μm) Al2O3 in TiAl is presented. The performance of the Nb/Y2O3 system appears to be related to the transport rate of Ti through the Y2O3 layer. Interfacial reaction is then observed at points where the Y2O3 thickness is less than about 1 μm. The main reaction product formed appears to be an oxygen saturated TiAl phase. An alternative system, C/TiN/Y2O3 is then presented as a solution to the Ti transport problem and may offer more desirable interfacial mechanical properties.

A transducer continuum is integrated to the fiber coating by means of a sequence of on-line sputtering, electro-plating, photolithography and periodical etching processes. Applications to the distributed sensing of temperature, strain and pressure are reported.

Adhesiveless mechanical fiber optic splices may provide pullout resistance by gripping onto the bare fiber or by gripping onto the fiber coating. The possibility of creep and thermal expansion mismatch in the plastic coating makes gripping onto the stripped fiber attractive. We have determined that damage to the fiber by a gripping mechanism is measurable but not severe, particularly by comparison to mechanical stripping damage and handling damage. We have also observed fiber failures within such splices when using 900 micron diameter, tight buffered fiber. Torque, generated when the fiber is arranged into loops in an organizer tray, propagates into the bare fiber inside the splice. This torque can cause a fiber to break in torsion after a period of time.

Significant degradation of the fiber coatings occurred in an optical fiber cable that was aged for five days at 85°C. Incompatibility between the coating and the surrounding buffer tube gel was the suspected cause. To investigate this problem, fiber samples were aged in several gels, the compositions of which were determined using a variety of analytical techniques. Coating degradation occurred as cracking or discoloration in all but one of the gels. These degradations were found to have a strong temperature dependence and to be closely related to the molecular weight distributions of the gel components. Compatibility screening was identified as a necessary procedure to avoid future recurrences of this problem

A technique has been implemented to measure and control the eccentricity of lightguide fiber in transparent polymer coating materials. It is based upon a model which describes the characteristics of a forward-scattered light pattern generated by transversely illuminating coated fiber with a laser beam. The model predicts the behavior of the principal characteristics of the pattern as a function of fiber eccentricity within the coating. The implementation automatically detects and controls the position of the dominant pattern feature to maintain an average fiber-coating concentricity within 2 μn over multikilometer lengths of fiber.

This paper describes the temperature dependence of chromatic dispersion in single-mode fibers for a temperature range of -60°- 250°C. Highly accurate dispersion measurements demonstrated a linear relationship (0.025 nm/°C) between the zero dispersion wavelength and temperature for tests conducted below 150°C. Further tests in the high-temperature range showed an increase in this dependence. For both temperature ranges, the results were independent of fiber coating and structure.

Low profile in-line partially reflecting splices have been developed to allow the nondestructive internal measurement of strain in advanced composite materials. The splices consist of stripped and cleaved fiber ends spaced a few tens of microns apart and rejacketed with fiber coating material. This paper reviews the use of optical time domain methods for internal materials evaluation, the development of such splices, and their system performance.

The transthickness tensile strength (TTS) of 2-D CVI-SiC/SiC composites reinforced with Tyranno SA fibers was evaluated by the diametral compression test. The effect of specimen size and specimen shape on the magnitude of the TTS were studied and the results were analyzed using Weibull statistics. Specimens failed along an interlaminar plane adjacent to the line of action of the applied load and fractographic analyses revealed that the crack had propagated through matrix pores and along interfaces between the fiber, fiber coating and matrix. The magnitude of the TTS was found to be independent of specimen size or shape for the range of specimen dimensions investigated, although the amount of scatter was largest for the results obtained from the evaluation of the smallest specimens. The characteristic value of the TTS and the Weibull modulus for the distribution of TTS values were 24.9 MPa and 6.48, respectively.

The SiC fiber reinforced Ti55 composite (SiC f /Ti55) was fabricated by Fiber Coating Method (FCM) and Hot Isostatic Pressing (HIP). After the composites were thermally exposed in vacuum under different conditions, the study on the order of interfacial reaction products and the kinetics of interfacial reaction was performed. The results show that only C, Ti and Si elements take part in the interfacial reaction. The order of interfacial reaction products of SiC f /Ti55 composite exposed at 1000 °C can be identified as SiC | Ti 3 SiC 2 | Ti 5 Si 3 +TiC | TiC | Ti55. However, the Ti 3 SiC 2 does not exist in the composites exposed at low temperature. The interfacial reaction layer growth is controlled by diffusion and follows a role of parabolic rate, and the activation energy Q k and the pre-exponential factor k 0 of SiC f /Ti55 composite are 198.16 kJ·mol −1 and 1.79×10 −3 m·s −1/2 , respectively. Compared with the SiC f /Ti composite and SiC f /Ti 2 AlNb composite, there is an interface with higher stability in SiC f /Ti55 composite. However, the interfacial reaction between SiC fiber and matrix takes place easier in SiC f /Ti55 composite than in the SiC f /Ti600 composite and SCS-6 SiC f /super a 2 composite.

The pressure sensitivity of the induced phase modulation in fiber optic acoustic sensors is studied both analytically and experimentally. The elastic parameters of commonly used coatings (thermoset plastics and acrylate based U. V. curable coatings), which govern the sensitivity, have been studied in bulk samples as a function of frequency (102–104 Hz) and temperature (0°–35 °C). The analysis, which takes into account the exact composition and geometry of multilayer fibers, is utilized to identify coatings which optimize the fiber acoustic sensitivity. The analytically predicted frequency dependence of the acoustic sensitivity is found to be in agreement with that obtained experimentally using fibers with various coatings.