Zero-stress Aging Research Articles

Zero Stress Aging of Glass and Carbon Fibers in Water and Oil—Strength Reduction Explained by Dissolution Kinetics

Understanding the strength degradation of glass and carbon fibers due to exposure to liquids over time is important for structural applications. A model has been developed for glass fibers that links the strength reduction in water to the increase of the Griffith flaw size of the fibers. The speed of the increase is determined by regular chemical dissolution kinetics of glass in water. Crack growth and strength reduction can be predicted for several water temperatures and pH, based on the corresponding dissolution constants. Agreement with experimental results for the case of water at 60 °C with a pH of 5.8 is reasonably good. Carbon fibers in water and toluene and glass fibers in toluene do not chemically react with the liquid. Subsequently no strength degradation is expected and will be confirmed experimentally. All fiber strength measurements are carried out on bundles. The glass fibers are R-glass.

Zero stress aging in notched multi‐component glass fibers

AbstractDegradation of glass under zero applied load in the presence of humidity at ambient temperature is of great interest to the container and fiber glass industries. The phenomenon is well documented for fused silica used in optical fibers, but has not been studied in detail for multi‐component glasses. In this work notches of varying length (500‐1500 nm) were placed with a focused ion beam into two types of multi‐component glass fibers, E‐glass (48 μm diameter) and soda‐lime‐silicate (35 μm diameter). Notched specimens were exposed to dry and humid conditions for up to 32 days. Transmission electron microscopy revealed the presence of extensive reaction products within the root of the notch, even after only 1 day of aging in the nominally dry environment for the soda‐lime‐silicate glass. Surprisingly, the extensive reactions have no measurable effect on the fiber strength. The uniaxial tensile strength of the notched glass fibers, measured with the fracture surface mirror radius method, does not follow a classic fracture mechanics prediction, implying that the notches are not classic Griffith flaws. Fracture mechanics is applied to show that sharpness at the notch base may be important, especially when subcritical crack growth is present during the strength measurement.

DETERMINATION OF 850 NM AND 1 DB/KM AT 1300 NM, 9/125 SINGLE MODE LOSES 0.4/0.25 DB/KM AT 1310/1550 NM. FOR INSULATING SUBMARINE CABLES FOR UNDERSTANDING VARIATION IN HIGH DIELECTRIC CONSTANT.

Optical fibers are very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions. There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues, and zero-stress aging.

Effects of silica nanoparticle addition to the secondary coating of dual-coated optical fibers

The mechanical and optical properties of dual-coated optical fibers with silica nanoparticles added to the secondary (outer) coating have been investigated. Incorporation of silica nanoparticles in the secondary coating is shown to enhance the resistance of optical fibers to fatigue and zero stress aging. In contrast to the properties of single-coated fibers containing the silica additive, this beneficial effect is obtained without degrading the tensile strength. Pretreatment of the nanoparticles to improve their dispersion in the coating is also investigated. Two dispersants studied do not significantly improve dispersion and result in reduced efficiency of the mechanical reliability enhancing effect. However, improving the mechanical mixing process does produce coatings with well-dispersed nanoparticles; as a consequence a significantly reduced optical loss and a more dramatic improvement of mechanical reliability result.

Phenomenological Prediction of Tensile Strength of E-Glass Composites from Available Aging and Stress Corrosion Data

A simple model to predict the time- and environment-dependent degradation of tensile strength of unidirectional E-glass fiber composites is presented. The model is phenomenological; that is, based on curve-fits of data for the individual time- and environment-dependent behavior, for which data is available in the literature. These include stress corrosion, zero-stress aging, interphase aging, and moisture-dependent matrix stiffness. The ineffective length at fiber break sites is corrected for debonding length. The average strength of the fiber is reduced to account for zero-stress aging. The concept of inert aged strength is proposed to be able to use data developed under different environmental exposure and load-testing conditions. The conditions for which exposure and aging affect the composite significantly are discussed. Different exposure and loading times are accounted for in the model. Model predictions are compared with available experimental data.

Interaction between Static Fatigue and Zero-Stress Aging in E-glass Fiber Composites

Interaction between static fatigue and zero stress aging of E-glass fiber composites is investigated. A comprehensive gathering of available experimental data for E-glass fibers and unidirectional composites is presented. A methodology is proposed that allows us to utilize seemingly ill-assorted data developed under noncomparable environmental exposure conditions. This is made possible by using the concept of inert aged strength, which allows us to homogenize all aging data regardless of the conditions of exposure by shifting it to the inert condition. Such inert aged data is then used to generalize the static fatigue model. Models for the two phenomena, static fatigue and zero-stress aging, acting separately and jointly are presented. Conditions are established for proper determination of the static fatigue susceptibility. Available experimental data of fibers and unidirectional composites is used to support the arguments made for an interacting model. The conditions for which aging becomes significant are outlined.

In-situ Strength Degradation of Glass Fibers in a Pultruded Composite by Environmental Aging

The problem of long-term environmental degradation of ®ber-reinforced composites has been receiving more attention in recent years because of the need to repair and retro®t rapidly deteriorating infrastructures using such materials. It has long been known that the residual tensile strength of glass ®bers decreases after stress corrosion and zero-stress aging [1±4], and in situ ®ber strength degrades in polymerbased composites under environmental aging [5]. Establishing a relationship between the aging process and the statistical ®ber-strength distribution will enable one to more accurately predict the long-term performance of the composite. Using a sub-critical crack growth model, the rate of crack growth on glass ®bers can be described by [1, 6]

Environmental effects on the mechanical integrity of optical fibers

The use of optical fibers is of particular interest to the telecommunications industry, due to the many striking advantages over traditional copper lines. These advantages cannot be realized, however, unless the mechanical integrity of the fibers is guaranteed. Therefore, the fact that certain environments can have detrimental effects on the mechanical properties of optical fibers is of great concern. In this investigation, both zero stress aging tests and two-point bending static fatigue tests were performed. The environments tested include buffer solutions of pH 4, 7, and 10, sodium chloride solution, unleaded gasoline, wasp killer, and deionized water. Zero stress aging in these environments had varying effects on the fibers, ranging from mild to severe reductions in fiber strength. Aging in the high-pH alkaline solutions produced severe reductions in fiber strength, whereas aging in the wasp killer, gasoline, and low-pH acidic environments resulted in relatively mild reductions in fiber strength. The static fatigue tests produced similar results, with stress corrosion parameters ranging from 5.5 for the pH 10 environment to 25.4 for the unleaded gasoline environment. ‘‘Fatigue knees’’ were also observed in the NaCl and pH 7 environments. Because of the fatigue knees, the stress corrosion parameters dropped from 25.3 to 3.7, and 19.7 to 3.1 for the NaCl and pH 7 environments respectively.

Degradation of Stressed Optical Fibers in Water: New Worst‐case Lifetime Estimation Model

Simultaneously determined results from zero‐stress aging and static fatigue measurements in water at 65°, 80°, and 95°C have been combined into a worst‐case fiber lifetime model which shows good agreement between predicted and observed failure times. The model shows that the lifetime in a wet environment of the largest crack at normal service strain (0.1%) is nearly identical to the lifetime of the pristine fiber and that the initial strength and the stress corrosion exponent are of minor importance for the lifetime. In a separate experiment, it is shown that degradation in a water‐saturated, jelly‐filled cable is significantly slower than when fibers are directly immersed in water. For a fast‐degrading fiber, evidence of a strength‐increasing mechanism is presented.

Mechanical durability of ZBLAN and aluminum fluoride-based optical fiber

Zero stress aging and static fatigue experiments were performed on fluoride glass fibers of ZBLAN and aluminum fluoride-based compositions to examine the mechanical durability in aqueous solutions. ZBLAN fiber, which has the higher initial strength, becomes weaker than initially lower strength aluminum fluoride-based fiber in less than one hour in pH 7 buffer solution at 30/spl deg/C. This is shown to be due to dissolution of the glass and precipitation of crystals at the glass/coating interface. In 1N NaOH the solubility is higher, resulting in less precipitation and hence less strength degradation. Although ZBLAN fiber degrades more quickly when a high strain is applied, at low applied strain the residual strength is higher than is observed when do strain is applied. These results indicate that future work on fluoride glass fibers for use in aqueous environments should focus on optimization of the as-drawn strength of durable glass, such as aluminum fluoride-based material, rather than on making small strength improvements to already strong but less durable glass, since such improvements will be quickly lost in aggressive environments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scanning Tunneling Microscopy of Optical Fiber Corrosion: Surface Roughness Contribution to Zero‐Stress Aging

Strength, fatigue resistance, and zero‐stress aging behavior control the long‐term mechanical reliability of optical fibers. Zero‐stress aging refers to the loss of strength of high‐strength glass fibers after exposure to some corrosive environments in the absence of stress. Understanding the effect of the chemical environment under zero stress on the subsequent fracture strength of optical fibers is important because optical fibers in service will probably encounter water and other chemical species while exposed to zero‐ or low‐stress conditions. In this work, the strength of fibers aged under zero‐stress conditions at 80°C in deionized water has been measured. Scanning tunneling microscopy was also used to measure the roughening of the fibers from corrosion at intervals during the aging. The product of the median inert strength of fibers aged for various times and the square root of the roughness depth of fibers was constant within experimental error. The results show that surface roughening contributes to zero‐stress aging in silica fibers.

Predicted Static Fatigue Behavior of Specially Coated Optical Glass Fibers

Long‐term static fatigue behavior of optical glass fibers is controlled by their strength, fatigue resistance, and zerostress aging behavior. The effectiveness of four special coatings in preventing the long‐term static fatigue deterioration of optical glass fibers was evaluated by determining the dynamic fatigue behavior and the effects of zero‐stress aging on strength of the four specially coated optical glass fibers in water from 25° to 85°C. The results clearly show that the strength, fatigue resistance, and aging behavior varied significantly between these specially coated fibers. By analysis of these experimental results in terms of fracture mechanics principles, the predicted static fatigue behaviors of the four fibers were compared. Ideally the optimum fiber is one that exhibits a high strength, low strength variability, high fatigue resistance, and high aging resistance. Each of these specially coated fibers had a deficiency in at least one of these properties.