Tensile performance of packaged optical fibers

The tensile testing of packaged optical fibers involves the measurement of elastic strains in the range 2-10%. Under these conditions slippage at the tensile grips can produce erroneous results when a nonextensometric method of measurement (e.g., in positive production testing) is used. Slippage of packaged silica fibers (polypropylene/silicone resin-coated silica fibers) observed when using standard pneumatic parallel-faced jaws has been eliminated by using 50-mm-diameter pulley grips with suitable clamps to hold the fiber ends. With this arrangement clean fiber failures are obtained within the gauge length. A correction factor has been estimated for the measured strain values by a theoretical analysis of the measured tension/extension curves for the composite polypropylene/silicone resin-coated fibers. Statistical data have also been obtained for polypropylene-(PP) coated lead silicate fibers and PP-coated “plastic clad” silica fibers. In the latter case, true failure had been obscured by the onset of fiber slippage within the PP jacket.     

Tensile performance of packaged optical fibers

Abstract

The tensile testing of packaged optical fibers involves the measurement of elastic strains in the range 2–10%. Under these conditions slippage at the tensile grips can produce erroneous results when a nonextensometric method of measurement (e.g., in positive production testing) is used. Slippage of packaged silica fibers (polypropylene/silicone resin-coated silica fibers) observed when using standard pneumatic parallel-faced jaws has been eliminated by using 50-mm-diameter pulley grips with suitable clamps to hold the fiber ends. With this arrangement clean fiber failures are obtained within the gauge length. A correction factor has been estimated for the measured strain values by a theoretical analysis of the measured tension/extension curves for the composite polypropylene/silicone resin-coated fibers. Statistical data have also been obtained for polypropylene-(PP) coated lead silicate fibers and PP-coated “plastic clad” silica fibers. In the latter case, true failure had been obscured by the onset of fiber slippage within the PP jacket.     

Determination of thermal residual strain in cabled optical fiber with high spatial resolution by Brillouin optical time-domain reflectometry

The thermal residual strain induced in the cabled optical fiber is a very important factor for evaluating the reliability of optical fiber cables. In order to determine the distributed thermal residual strain in cabled optical fiber, a measurement method based on Brillouin optical time-domain reflectometry (BOTDR) system is proposed in the article. Thermal characteristics of residual strain along cabled optical fibers are investigated theoretically and experimentally based on Brillouin frequency shift (BFS) detection. The thermal residual strain along the cabled fiber, if any, can be determined with a high spatial resolution that is equal to that of the BOTDR system and can be less than a few meters. A double-coated fiber in loose optical cable was used as the test cabled optical fiber, and the experimental results were in good agreement with those predicted from the theory. It has been found that the fiber residual strain increases linearly with decreasing temperature in the range from 50 to ?50 °C.     

单轴应变对氮化铟电子结构及光学性质的影响

采用密度泛函理论框架下的第一性原理平面波赝势方法,计算单轴应变下闪锌矿氮化铟的电子结构及光学性质.结果表明：施加应变会使带隙变窄.对于拉应变,随着应变增大带隙减小程度增大;对于压应变,随应变增大带隙减小程度减弱;且拉、压应变对带隙调控都是线性的.在能量区间4 eV~12 eV范围内施加应变时,氮化铟的吸收光谱发生红移,随拉应变程度增加,吸收光谱的红移进一步加大;随压应变增加,吸收光谱红移减弱;在该范围内,氮化铟的折射率、反射率随拉应变的增大而增加,随压应变增加减小;施加拉应变时能量损失函数峰值增大,施加压应变后能量损失函数峰值减小.通过施加单轴应变能有效调节氮化铟材料的电结构及光学性质.     

Effect of uniaxial strain on adatom diffusion across {1 1 1}-faceted step

Diffusion of Pt adatom across the strained {1 1 1}-faceted step is studied by embedded atom method along with nudged elastic band method. For adatom on the flat (1 1 1) surface, the anisotropic diffusion behavior is found as the uniaxial strain is imposed. For the strained {1 1 1}-faceted step, our results show that the maximum energy barrier for adatom crossing step edge remains approximately constant as the strain varied from −1.0% to 1.0%, and there is a rise as the larger uniaxial strain is applied. The calculated energy barrier for adatom diffusion along the step edge increases with increasing tensile strain, and the slope of the straight line is small.     

Mechanical and optical properties of silver-halide infrared transmitting fibers

This article presents a review of the optical and mechanical properties of infrared transmitting fibers extruded from single crystals of silver-halides at the Applied Physics Group in Tel-Aviv University during the last decade. The optical properties of Agcl_xBr_1-x crystals and fibers include the spectral transmission window, laser power transmission, the change of the power distribution traveling along the fiber, and the laser-induced breakdown. The mechanical properties include the investigation of the ultimate tensile strength (UTS), hardness, and the elastic strain limits of these fibers and their composition dependence. The mechanical properties that involve single and multiple bending of fibers in the plastic and the elastic strain limits are also described.     

Enhancing the interfacial strength of glass/epoxy composites using ZnO nanowires

This paper investigated the application of ZnO nanowires (ZnO NW) to enhance the interfacial strength of glass/epoxy composites. ZnO NW were grown on glass fibers by hydrothermal method, tensile properties of bare and ZnO NW coated fibers were measured by single fiber tensile testing, wettability of fiber with resin was studied by contact angle measurements and finally the interfacial strength and mechanisms were determined by single fiber fragmentation testing of glass/epoxy composites. The surface coverage of ZnO NW on glass fibers was fairly uniform without formation of major clusters. The coating of ZnO NW slightly reduced the tensile strength and improved the tensile modulus of fibers. Wettability tests showed reduction in contact angles for ZnO NW coated fibers because of enhanced wetting and infiltration of epoxy resin into nanowires. In fragmentation testing of microcomposites, smaller and concentrated interfacial debonding zones for ZnO NW coated fibers indicated good stress transfer and strong interfacial adhesion. A new form of crossed and closely spaced stress patterns were observed for nanowires of high aspect ratios. The interfacial strength of ZnO NW coated fibers increased by at least 109% and by 430% on average, which was attributed to the increased surface area and mechanical interlocking provided by ZnO NW.     

Band gap of carbon nanotubes under combined uniaxial–torsional strain

Within tight-binding model, the band gaps of armchair and zigzag carbon nanotubes (CNTs) under both uniaxial tensile and torsional strains have been studied. It is found that the changes in band gaps of CNTs depend strongly on the strain type. The torsional strain can induce a band gap for armchair CNTs, but it has little effect on band gap of the zigzag CNTs. While the tensile strain has great effect on band gap of zigzag CNTs, but it has no effect on that of the armchair CNTs. More importantly, when both the tensile and torsional strains are simultaneously applied to the CNTs, the band gap changes of armchair CNTs are not equal to a simple sum over those induced separately by uniaxial tensile and torsional strains. There exists a cooperative effect between two kinds of strains on band gap changes of armchair CNTs. But for zigzag CNTs, the cooperative effect was not found. Analytical expressions for the band gaps of armchair and zigzag CNTs under combined uniaxial–torsional strains have been derived, which agree well with the numerical results.     

Optimization of mechanical strength of titania fibers fabricated by direct drawing

Nanostructured polycrystalline titania (TiO₂) microfibers were produced by direct drawing from visco-elastic alkoxide precursors. The fiber crystallinity and grain size were shown to depend on post-treatment calcination temperature. Tensile tests with individual fibers showed strong sensitivity of the elastic modulus and the tensile strength to microstructural details of the fibers. The elastic modulus of as-fabricated fibers increased about 10 times after calcination at 700 ^°C, while the strain at failure remained almost the same at ～1.4 %. The highest tensile strength of more than 800 MPa was exhibited by nanoscale grained fibers with a bimodal grain size distribution consisting of rutile grains embedded into an anatase matrix. This structure is believed to have reduced the critical defect size, and thus increased the tensile strength. The resultant fibers showed properties that were appropriate for reinforcement of different matrixes.     

New method for strength improvement of silica optical fibers

The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers, a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a long optical fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending insensitivity, especially during handling and in-service installation. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new method for increasing fiber strength.The silica optical fibers used were 125 μm in diameter, with a 62.5 μm thick epoxy-acrylate coating. Fibers were rolled up around two similar cylinders. Using a screw, these cylinders moved away from one another and thus subjected the fibers to stretching. Submitted to this mechanical loading, the distended fibers were plunged into hot water at 65 or 85 °C and aged for several days. Then, the fibers were removed from the water and various weights were suspended on the fiber ends. Thus, the fibers were subjected to a tensile loading in static fatigue for several days. Just before fiber rupture, the fibers were unloaded and subjected to dynamic tensile tests at different velocities.Result analysis proved that the aging in hot water increased the fiber strength. The Weibull's diagram study shows a bimodal dispersion of defects on the fiber surface and the important role of polymer coating.     

Plastic coating of glass fibers and its influence on strength

Sodium borosilicate glass fibers pulled from the melt were plastic coated “on-line” to preserve the fiber strength. By the use of tapered nozzles within the coating applicator the coating could be made concentric around the fiber, and a 40-μm concentric coating was found to be sufficient for the fiber to withstand a mild abrasion test with no deterioration in strength. Strength measurements made in ambient conditions showed that the fiber had a uniform breaking strain of 4% elongation. The same fiber measured at liquid nitrogen temperatures had a breaking strain of 14%, even after extensive handling, which is close to the theoretical glass cohesive strength.     

Effect of temperature on inhomogeneous elastic deformation and negative stiffness of NiAl and FeAl alloy nanofilms

The uniaxial tension of NiAl and FeAl intermetallic alloy nanofilms at different temperatures has been investigated by the molecular dynamics method. It was previously shown that nanofilms at 0 K are elastically deformed by almost 40% and that, under strain-controlled tension, there is a region in the stress—strain curves, where an increase in the strain is accompanied by a decrease in the tensile stress, i.e., the stiffness of nanofilms is negative. Deformation of the films in the thermal instability region is associated with the appearance of domains with different elastic strains. The influence of the temperature on these effects is investigated. Particularly, it is shown that as the temperature increases, both the elastic strain and the negative stiffness of nanofilms decrease. The inhomogeneous elastic strain and negative stiffness for FeAl films are observed in a broader temperature range (to 1000 K) than for NiAl films (to 300 K), which constitutes 0.16 and 0.65 of the melting point of these materials, respectively.     

Plastic coating of glass fibers and its influence on strength

Abstract

Sodium borosilicate glass fibers pulled from the melt were plastic coated “on-line” to preserve the fiber strength. By the use of tapered nozzles within the coating applicator the coating could be made concentric around the fiber, and a 40-μm concentric coating was found to be sufficient for the fiber to withstand a mild abrasion test with no deterioration in strength. Strength measurements made in ambient conditions showed that the fiber had a uniform breaking strain of 4% elongation. The same fiber measured at liquid nitrogen temperatures had a breaking strain of 14%, even after extensive handling, which is close to the theoretical glass cohesive strength.     

Strain-tunable electronic,elastic, and optical properties of CaI2 monolayer: first-principles study

ABSTRACT

The effects of biaxial strain on the electronic structure and the elastic and optical properties of monolayer CaI₂ were studied using first-principles calculations. The two-dimensional (2D) equation of state for monolayer CaI₂ as fit in a relative area of 80–120% is more accurate. The band gap can be tuned under strain and reached a maximum at a tensile strain of 4%. Under compressive strains, the absorption spectrum showed a significant red shift at higher strains. The static reflectance and static refractive index decreased in the strain range of ?10% to 10%.     

Anisotropic elastic behaviour and one‐dimensional metal in phosphorene

Using first‐principles calculations, we investigate the mechanical and electronic properties of phosphorene nanosheets under tensile strains. It is found that phosphorene possesses a prominent anisotropic elasticity with the large anisotropic factor of 15.5. Along the armchair direction, the phosphorene sheet exhibits a high tensile ductility, characterized by a large elastic strain limit of 0.31. While in the zigzag direction, the critical strain of phosphorene is dictated by the phonon instability and the in‐plane soft mode occurs beyond the 0.22 strain. Under uniaxial strains, the band gaps of phosphorene can be modulated continuously, whose band features are also altered accordingly. A Dirac‐like band structure appears in phosphorene under adequate strains along the zigzag direction. More interestingly, these Dirac cones of phosphorene display evident anisotropy, which have high Fermi velocities up to (6 – 7) × 10⁵ m/s along the armchair direction but drop to zero along the zigzag direction. With such a characteristic, the strained phosphorene sheet acts as an intriguing one‐dimensional metal, which enables the system many potential applications in power‐efficient and ultrafast nanodevices. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Velocities of sound and the densities of phonon states in a uniformly strained flat graphene sheet

The effect of elastic strain on the mechanical and physical properties of graphene has been intensively studied in recent years. Using the molecular dynamics method, a surface has been built in the three-dimensional space of components of the plane strain tensor bounds the region of the structural stability of a flat graphene sheet without considering thermal vibrations and the influence of boundary conditions. The velocities of sound and the densities of phonon states in graphene subjected to an elastic strain within the region of the structural stability have been calculated. It has been shown that one of the velocities of sound becomes zero near the stability boundary of a flat graphene sheet. During biaxial tension of graphene, there is no gap in its phonon spectrum; however, it forms under uniaxial tension along the zigzag or armchair directions and also under combined tensile and compressive strains.     

Influence of material processing and interface on the fiber fragmentation process in titanium matrix composites

The objective of this work is to study the effect of composite processing conditions on the nature of the fiber–matrix interface in titanium matrix composites and the resulting fragmentation behavior of the fiber. Titanium matrix, single fiber composites (SFCs) were fabricated by diffusion bonding and tensile tested along the fiber axis to determine their interfacial load transfer characteristics and the resulting fiber fragmentation behavior. Two different titanium alloys, Ti-6Al-4V (wt%) and Ti-14Al-21Nb (wt%), were used as matrix material with SiC (SCS-6) fibers as reinforcement. The tensile tests were conducted at ambient temperature and were continuously monitored by acoustic emission. It was observed that the Ti-6Al-4V/SCS-6 composite system exhibited a greater degree of fiber–matrix interfacial reaction, as well as a rougher interface, compared to Ti-14Al-21Nb/SCS-6 composites. Acoustic emissions during tensile testing showed that most of the fiber fractures in Ti-6Al-4V/SCS-6 occurred at strains below ～5% and the fragmentation ceased at ～10% strain corresponding to specimen necking. In contrast, the Ti-14Al-21Nb/SCS-6 composite deformed without necking and fiber fractures occurred throughout the plastic range until final fracture of the specimen at about 12% strain. The markedly different fragmentation characteristics of these two composites were attributed to differences in the fiber–matrix interfacial regions and matrix deformation behavior.     

Creep deformation measurement using quartz optical fiber

This paper describes an optical system for high temperature creep strain measurement using quartz optical fiber, super long working distance microscope and digital image processing techniques. In this system one end of the quartz optical fibers is arrayed in a small area on the specimen surface and the other end is illuminated by a laser beam. The fiber ends on the specimen surface form the spot array. The small optical spots on the specimen are tracked by a CCD camera and the images are processed by digital image processing software. The diameter of each quartz fiber is 100 μm and the fibers can be arrayed in a small area. The local strains are determined by measuring the variety of relative distance between two spots. Experimental results of local creep strain on the welding joints of 15CrMo and HK40 at 850°C are obtained.     

形变多晶氧化铝纤维的荧光R谱线

使用自制拉伸装置和显微拉曼系统测定了形变下多晶氧化铝纤维的荧光R1和R2谱线,发现两条谱线均随纤维拉伸应变的增大而变宽,并获得了纤维应变与谱线宽化值之间的定量关系。从纤维的结晶晶格结构和形态学微结构定性地解释了谱线的宽化行为。也测定了谱线频率与多晶氧化铝纤维温度间的定量关系,频率温度系数值近似等同于单晶氧化铝的值。最后,研究了激发光偏振方向相对于纤维轴向的不同夹角对谱线频率的影响,并由此得出,氧化铝晶粒有相对纤维轴向取向的倾向。     

Electronic structure and optical properties of CuAlO2 under biaxial strain

An ab initio calculation has been carried out to investigate the biaxial strain ( - 10.71% < ε < 9.13%) effect on elastic, electronic and optical properties of CuAlO(2). All the elastic constants (c(11), c(12), c(13), c(33)) except c(44) decrease (increase) during tensile (compressive) strain. The band gap is found to decrease in the presence of tensile as well as compressive strain. The relative decrease of the band gap is asymmetric with respect to the sign of the strain. Significant differences between the parallel and perpendicular components of the dielectric constant and the optical properties have been observed due to anisotropic crystal structure. It is further noticed that these properties are easily tunable by strain. Importantly, the collective oscillation of the valence electrons has been identified for light polarized perpendicular to the c-axis. From calculations, it is clear that the tensile strain can enhance the hole mobility as well as the transparency of CuAlO(2).