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.     

Temperature Dependence of Static Fatigue of Optical Fibers Coated with a Uv-Curable Polyurethane Acrylate

The static fatigue of fused silica optical fibers coated with a uv-curable polyurethane acrylate was measured, in water, from 40° to 90°C in 10° C intervals. The usual log (time-to-failure) vs log (applied stress) plotting of the data gives a bilinear fit at all test temperatures examined. By assuming exponential temperature dependence for static fatigue parameters, empirical static fatigue equations are generated for the two straight-line segments. These equations are then used to generate a static fatigue design diagram at a given temperature. In view of the possible coating effects on static fatigue, these results should be cautiously applied to optical fibers coated with other polymers.     

Dynamic and Static Fatigue of Silicate Glasses

Fatigue of silicate glasses was studied using both static and dynamic tests. Static fatigue data for acid-etched soda-lime silicate glass determined at 74°F in 50 and 100% rh can be represented by a single universal fatigue curve (UFC). The UFC for acid-etched glass does not lie on the UFC of Mould and Southwick, which was determined for abraded soda-lime silicate glass; the acid-etched glass was less susceptible to static fatigue. The susceptibility of acid-etched soda-lime silicate glass to static fatigue differed little from that of pristine E-glass and fused SiO₂ fibers. Dynamic fatigue data for soda-lime, E, borosilicate, and fused quartz glasses agreed well qualitatively and quantitatively with fundamental crack velocity data for these glasses; the dynamic fatigue theory of Charles was used in the comparison. The theoretical implications of these results are discussed.     

High-Temperature Fatigue Behavior of Polycrystalline Alumina

The strength and fatigue behavior of a 99.5% polycrystalline alumina were measured as a function of temperature. Both the strength and fatigue behavior remained essentially constant up to 500°C; from 800° to 1100°C the strength and fatigue resistance decreased markedly and at >1100°C macroscopic creep was observed. It is believed that the decrease in strength and fatigue resistance is caused by a grain-boundary glassy phase enhancing subcritical crack growth. Proof-testing at room temperature was effective in improving the strength distributions at both room temperature and 1000°C; however, at 1000°C it was not effective, due to crack growth during the proof test. The good agreement between proof-test results and fracture-mechanics theory indicates that the same flaws control the strength at room temperature and at high temperatures.     

Strength and Fatigue of Fluoride Glass Optical Fibers

Strength and fatigue characteristics of fluoride glass optical fibers, used as a new infrared transmission medium, were examined. A correlation parameter between mirror size and tensile strength of 0.826 MPa.m¹² was obtained, and a fatigue parameter of 16.2 was determined from a dynamic fatigue test at 20°C and 60% rh .     

Strength and Static Fatigue of Abraded Glass Under Controlled Ambient Conditions: III, Aging of Fresh Abrasions

The effect of aging under various conditions on the strength and static fatigue of freshly abraded specimens has been studied. For both grit-blast and emery cloth abrasions the liquid nitrogen (fatigueless) strength increased with storage time after formation of the abrasions for specimens stored in liquid water or in an atmosphere containing water vapor. After 1 day of storage in water the strength increase was about 60% of the freshly abraded value for emery cloth abrasions and about 30% for grit-blast abrasions. The aging depended strongly on the medium in which the specimens were stored and on the relative humidity when they were stored in air. In very dry air or vacuum the aging effect appeared to be eliminated. Static fatigue curves (strength vs. load duration) in water were measured for specimens containing fresh abrasions and aged abrasions. Ordinary aging did not change the static fatigue behavior of fresh abrasions. The liquid nitrogen strength and static fatigue also were studied for specimens which had been baked at 470°C. in high vacuum after being abraded. This treatment increased the fatigueless strength by approximately the same amount as aging in water. The rate of static fatigue, however, which was unaffected by ordinary aging, was reduced by a factor of approximately 25 for vacuum-baked as compared with fresh abrasions. Possible mechanisms for aging are discussed in some detail. It is proposed that the observed aging effects on the fatigueless strength can be accounted for by an increase of the radii of the tips of the abrasion cracks in the surfaces of the specimens. The suppression of fatigue for the vacuum-baked specimens is believed to be related to the non-wettability of their surfaces which was observed in the course of the experiments.     

Fatigue behavior and relation between fatigue resistance and tensile properties of poly(para-phenylene-co-3,4'-oxydiphenylene terephthalamide) fiber

The poly(para-phenylene-co-3,4′-oxydiphenylene terephthalamide) (PPODTA) fiber is one of the high strength organic fibers, and it has been reported that the PPODTA fiber has superior fatigue resistance. The high strength fibers are used in the applications to utilize their high mechanical properties in general. Therefore, the long-term durability of these fibers is also required. In this study, the fatigue tests were conducted for the PPODTA fibers. As a result, it was found that the PPODTA fibers were able to be fractured by the cyclic tensile stress, and the fatigue behavior was influenced by the stress conditions. In addition, the single fiber tensile tests were also conducted for the PPODTA fibers, and the relation between the tensile properties and the fatigue resistance of the PPODTA fiber was investigated. The fatigue resistance of the PPODTA fiber was increased with the decrease of the fiber diameter and the increase of the tensile modulus.     

浅谈高强玻璃纤维的发展和应用

介绍了高强玻璃纤维和普通无碱玻璃纤维相比具有的拉伸强度高、弹性模量高、抗冲击性能好、化学稳定性好、耐高温、抗疲劳性好等优良特征,高强玻璃纤维在国内外发展的情况,高强玻璃纤维及其制品纱及织物的主要技术性能,它在航空航天、国防工业、一般工业、体育休闲器材等高性能的增强材料方面的广泛应用。     

Interfacial bonding and optical transmission for transparent fiberglass/poly(methyl methacrylate) composites

Evidence is presented relating the interfacial bonding strength and the optical transmission of transparent glass fiber reinforced PMMA composites. The temperature dependent (20° to 50°C) optical transmission of composites that contained uncoated 13 μm glass fibers and 13 μm glass fibers coated with divinyltetramethyl disilazane or 3-(trimethoxysilyl)propyl methacrylate was found to decrease in the same order as the bond strength of the PMMA/glass fiber interface, namely, trimethoxy silane coated fiber, disilazane coated fiber, and uncoated fiber. SEM photographs showed similar fracture surfaces, clean fiber pull-out, and no apparent bonding of the glass fiber to the PMMA for the composites containing uncoated and disilazane coated fiber, whereas, the composite containing trimethoxy silane coated fiber showed virtually no clean fiber pullout. Additional evidence for differences in the bonding strength is seen in the degradation (penetration of water and fiber whitening) on aging at 23°C in air or water for composites containing uncoated fiber (most degradation), disilazane coated fiber (slight degradation), and trimethoxy silane coated fiber (no degradation). The optical transmission between 20° and 30°C at 600 to 800 nm for the composite containing trimethoxy silane coated fiber decreased the least with increasing temperature (from ∼85% to 70%) while the composite containing uncoated fiber decreased the most (from ∼85% to 32%).     

Effects of water and moisture on strengths of optical glass (silica) fibers coated with a UV-cured epoxy acrylate

Furnace-drawn optical silica fibers coated with a uv-curable epoxy acrylate (V1F) were subjected to long-term tests in water and in humid environments. Results of stress-free aging tests showed a progressive reduction of strength both in water and in the atmosphere of 90% r.h. at 32.6°C. Stressing the fibers up to 517 MN/m² (75 kpsi) during aging did not result in additional loss of strength. Static fatigue tests in 90% r.h., 32.6°C, showed that the fatigue strength decreased monotonically with time of exposure in accordance with the power law of Charles. However, there were indications that Charles' theory might not be obeyed over an extended test period.     

Fatigue and Durability of Silane-Bonded Epoxy/Glass Interfaces

Fatigue (slow) crack growth in epoxy/glass interfaces bonded with the silane coupling agent 3-aminopropyltriethoxysilane was studied under static and cyclic loading at 23°C, 95% RH using the double cleavage drilled compression test. Crack growth rates under cyclic loading were significantly greater than under static loading, in contrast to crack growth rate results in monolithic glass. After aging up to 34 h at 94°C in distilled water, the silane-bonded epoxy/glass specimens exhibited somewhat greater resistance to fatigue crack growth than the unaged samples; however, after aging at 98°C in distilled water and at 70°C in an aqueous KOH solution at pH 10, crack growth became cohesive and exhibited fractal behavior. Mechanisms for fatigue crack growth at silane-bonded epoxy/glass interfaces are proposed.     

Fatigue and Durability of Silane-Bonded Epoxy/Glass Interfaces

Fatigue (slow) crack growth in epoxy/glass interfaces bonded with the silane coupling agent 3-aminopropyltriethoxysilane was studied under static and cyclic loading at 23°C, 95% RH using the double cleavage drilled compression test. Crack growth rates under cyclic loading were significantly greater than under static loading, in contrast to crack growth rate results in monolithic glass. After aging up to 34 h at 94°C in distilled water, the silane-bonded epoxy/glass specimens exhibited somewhat greater resistance to fatigue crack growth than the unaged samples; however, after aging at 98°C in distilled water and at 70°C in an aqueous KOH solution at pH 10, crack growth became cohesive and exhibited fractal behavior. Mechanisms for fatigue crack growth at silane-bonded epoxy/glass interfaces are proposed.     

Effect of hydrothermal aging on the thermo‐mechanical properties of a composite dental prosthetic material

The aim of this investigation was to evaluate the long‐tern effects of aging in water on the physical properties of a new class of commercially available dental polymer composites. The selected product consists of a bisphenol a glycidyl methacrylate (Bis‐GMA) resin diluted with triethylene glycol dimethacrylate (TEGDMA) and reinforced with long E‐glass fibers, specifically developed for prosthetic dental bridges. Samples were prepared according to a standard procedure suggested by the producer, and aged in water at 37°C and 70°C up to 32 weeks. Samples were periodically tested in order to assess their mass variation, static flexural modulus and strength, fatigue resistance, and dynamic mechanical thermal behavior. Experimental results evidenced that aging caused two simultaneous phenomena, having opposite effects on the specimen mass. In fact, composites absorbed a certain amount of water (up to 0.8 wt% at 37°C and 1.2 wt% at 70°C) but at the same time a mass loss was detected, which could be attributed to a release of unreacted monomeric species and fragments generated by polymer chain degradation (especially at 70°C). Flexural strength strongly decreased during aging in water, reaching 80% and 45% of the initial value for samples aged for 32 weeks at 37 and 70°C, respectively. Aging practically does not affect flxural modulus, while a sensible reduction of the material fatigue life was observed. Glass transition temperature and the relative activation energy were markedly influenced by the aging in water with effects related to the water uptake and mass loss phenomena.     

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.     

Fatigue behavior of glass-fiber fortified thermoplastics

This investigation deals with the fatigue behavior of a group of thermoplastics fortified with discontinuous glass fibers dispersed by an injection molding process. The thermoplastics included nylon, polystyrene and polyethylene reinforced with short (1/8 in.) and long (1/2 in.) glass fibers. Several aspects of the fatigue behavior are included in the study. First, classical S–N curves were generated under fluctuating tension with R = 0.05 to show the loss of strength due to cyclic load application. Next, the extent of progressive fatigue damage was established by measuring the residual strength after cyclic loading. Finally, hypotheses pertaining to the fatigue mechanisms operative in all four materials were made based on microscopic examinations of sections removed from fatiguedamaged specimens.     

Effect of Moist Ammonia on the Strength of Polymer-Coated Optical Fibers

The tensile strength of polymer-coated fused silica optical fibers aged in a moist ammonia environment at 23°C was drastically reduced compared to that of fibers aged under ammonia-free high-humidity conditions. However, most of the strength lost on aging in ammonia was recoverable by ambient desorption of the ammonia, in analogy to the strength recovery which occurs when fibers aged in water are dried.     

Cyclic-Fatigue Behavior of SiC/SiC Composites at Room and High Temperatures

Tension-tension cyclic-fatigue tests of a two-dimensional-woven-SiC-fiber-SiC-matrix composite (SiC/SiC) prepared by chemical vapor infiltration (CVI) were conducted in air at room temperature and in argon at 1000°C. The cyclic-fatigue limit (10⁷ cycles) at room temperature was ∼160 MPa, which was ∼80% of the monotonic tensile strength of the composite. However, the fatigue limit at 1000°C was only 75 MPa, which was 30% of the tensile strength of the composite. No difference was observed in cyclic-fatigue life at room temperature and at 1000°C at stresses >180 MPa; however, cyclic-fatigue life decreased at 1000°C at stresses < 180 MPa. The fracture mode changed from fracture in 0° and 90° bundles at high stresses to fracture mainly in 0° bundles at low stresses. Fiber-pullout length at 1000°C was longer than that at room temperature, and, in cyclic fatigue, it was longer than that in monotonic tension. The decrease in the fatigue limit at 1000°C was concluded to be possibly attributed to creep of fibers and the reduction of the sliding resistance of the interface between the matrix and the fibers.     

Coating of Fine-Grained Silicon Nitride Whiskers on Fiber-like Silicon Nitride

Fine-grained silicon nitride (Si3N4) whiskers were coated on Si3N4 fibers through a vapor-liquid-solid mechanism under the following process. After the oxide glass of a Si-Al-Y-O system was coated on seed Si3N4 fibers, the coated fibers were heated at 1490°C and 700° in the vapor of the Si-N system which was generated by decomposition of amorphous Si3N4. The resulting specimens looked just like rose twigs. The Si3N4 whiskers were precipitated by nucleation in a liquid phase generated by melting of the oxide glass layers on the Si3N4 fibers.     

Experimental assessment of the improved properties during aging of flax/glass hybrid composite laminates for marine applications

The investigation for natural fibers composites in terms of performance, durability, and environmental impact for structural applications in marine environments is a relevant challenge in scientific and industrial field. On this context, the aim of this work is to assess the durability and mechanical stability in severe environment of epoxy/glass–flax hybrid composites. For the sake of comparison, also full flax and glass epoxy composites were investigated. All samples were exposed to salt–fog environmental conditions up to 60 aging days. Wettability behavior during time was compared with water uptake evolution to assess water sensitivity of hybrid composite configurations. Moreover, quasi-static flexural and dynamic mechanical analysis were carried to evaluate as aging conditions, laminate configuration influence the surface and mechanical performances stability of the hybrid composites. The addition of glass fibers on flax laminate allows to enhance both flexural strength by 90%, and modulus by 128%, even if these properties are lower than those of full glass laminates. The results evidenced that the hybridization of flax fibers with glass ones is a practical approach to enhance the aging durability of epoxy/flax composite laminates in marine environmental conditions, obtaining a suitable compromise among environmental impact, mechanical properties, aging resistance, and costs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47203.     

High-Temperature Fatigue Strength of Crack-Healed Al2O3 Toughened by SiC Whiskers

Al₂O₃ reinforced by SiC whiskers (Al₂O₃/SiC-W) was hot-pressed to investigate the fatigue strength of crack-healed specimens at high temperature. Semielliptical surface cracks of 100 μm surface length were introduced on each specimen surface. These specimens were crack-healed at 1300°C for 1 h in air, and static and cyclic fatigue strengths were systematically investigated at room temperature, 900° and 1100°C by three-point bending. The static and cyclic fatigue limits of the crack-healed specimens were more than 70% of the average bending strength at each testing temperature. Crack-healed specimens of Al₂O₃/SiC-W were not sensitive to static and cyclic fatigue at room temperature and high temperatures. Therefore, the combination of crack-healing and whisker reinforcement can play an important role in increasing static and cyclic fatigue strengths at high temperature.