Fiber ring laser with a feedback mirror

We describe the spectral and power features of a ytterbium-doped double-clad photonic crystal fiber laser that is operated in a ring configuration with an external mirror that feeds back only one of its two output beams. We compare the operation of the laser with and without an external feedback mirror. We find that the feedback mirror reduces significantly the spectral and power fluctuations. It is also responsible for an interesting spectral phenomenon: The laser frequency is drifting periodically over 9 nm at a rate of 2 nm/s from a short wavelength to a longer wavelength and vice versa.     

Fiber reinforcement of a biomimetic bone cement

In this study we investigated the influence of electrospun polymer fibers on the properties of a α-tricalcium phosphate/gelatin biomimetic cement. To this aim, we added different amounts of poly(L-lactic acid) and poly(lactide-co-glycolide) fibers to the cement composition. Fibers enrichment provoked a significant reduction of both initial and final setting times. Moreover electrospun polymer fibers slowed down the conversion of α-tricalcium phosphate into calcium deficient hydroxyapatite. As a result, the final cements were more compact than the control cement, because of the smaller crystal dimensions and reduced crystallinity of the apatitic phase. The compressive strength, σ(b), and Young's modulus, E, of the control cement decreased significantly after 40 days soaking in physiological solution, whereas the more compact microstructure enabled fiber reinforced cements to maintain their mechanical properties in the long term.     

Preparation of a SiC Fiber Textile Material

A textile material consisting of SiC fibers has been produced by siliciding carbon cloth in a gaseous SiO atmosphere. The reactive SiO source used was a mechanical mixture of silicon and silicon dioxide. The process was run at a temperature of 1400°C under dynamic vacuum. The results demonstrate the conceptual feasibility of using the process for producing SiC cloth reproducing the dimensions and shape of the parent carbon cloth.     

Fiber characterization in a stationary ultrasonic field

An instrument has been developed to characterize the mean dimensions of softwood fiber samples. It is based on the phenomenon that particles of cylindrical shape diluted in water and shorter than one fourth of the acoustic wavelength migrate to nodal planes of acoustic radiation pressure and reorient parallel to these planes when subjected to a stationary ultrasonic field. As the resonator operating frequency is 72 kHz, fibers up to 5 mm in length can be measured. The time evolution of the fiber suspension during ultrasonic excitation is monitored with a collimated beam of light. Scattered light signals collected off-axis in the plane perpendicular to the acoustic nodal planes are shown to be a function of the weighted average fiber length. Results are presented for pulp samples in the average fiber length range of 0.2 to 3 mm. It was found that there is a region where the scattered light is linearly related to concentration. Acoustooptical measurements obtained at initial concentration in this linear region, for all fractions, have shown that the longer the average length from screen classifier is, the faster the layer formation is. Since the fiber length the radius are proportional for a wood species, this observation is in agreement with the theoretical prediction.     

熔融纺丝过程优化制备细直径碳化硅纤维及其对力学性能的影响

强度、模量和柔顺性作为碳化硅(SiC)纤维重要的力学性能受到纤维直径大小的影响, 而制备工艺中的熔融纺丝过程对纤维直径起决定作用。本工作研究了纺丝温度、纺丝压力和卷绕速度对聚碳硅烷(Polycarbosilane, PCS)原纤维直径的影响, 分析了纺丝过程中纤维断裂的原因, 并初步探究了SiC纤维直径与力学性能的关系。结果表明, 在一定范围内降低纺丝温度、降低纺丝压力和提高卷绕速度均能显著减小原纤维的直径。在连续纺丝的前提下, 最优纺丝工艺下得到的PCS原纤维直径为13.5 μm。随着PCS纤维直径由18.3 μm减小至13.5 μm, SiC纤维直径则由13.8 μm减小至9.5 μm, 而SiC纤维的强度与模量分别由1.7、181 GPa提高至2.9、233 GPa, 强度分布更为集中, 柔顺性得到显著提高。     

一种新型的棉纤维校准塞在SJ175棉纤维气流仪中的应用

本文介绍了一种新型的专门针对SJ175棉纤维气流仪的校准而研制的棉纤维校准塞,论述了其结构组成、调试过程、使用方法及注意事项.该校准塞具有操作简单、使用方便的特点,利于准确测定棉花的马克隆值.     

Hybrid Wavelength-Time-Domain Interrogation System for Multiplexed Fiber Bragg Sensors Using a Strain-Tuned Erbium-Doped Fiber Laser

A system for the interrogation of fiber Bragg grating (FBG) sensors using a strain-tuned EDF laser with linear cavity is described. An optical switch is spliced to one end of the laser cavity and connects one of two high-strength draw-tower fiber Bragg gratings (DTGs). The gratings are simultaneously tuned by a stretching device and act as the end reflector of the laser cavity. By applying a ramp signal to the actuator synchronized to the optical switch, the laser signal sweeps over two different wavelength intervals, depending on the connected DTG. This approach represents a hybrid wavelength-time-domain interrogation for multiplexed sensors and doubles the number of sensors that may be addressed when compared with single DTG scanning. In addition, the use of the DTG allows a fivefold increase in the strain tuned wavelength interval over standard fiber Bragg gratings. An example application is demonstrated where temperature inside an electrical motor is measured during operation.     

Constitutive Model for a Fiber Tow Bridging a Delamination Crack

A simple model is introduced for a fibrous tow, stitch, or rod that bridges a delamination crack in a laminate. The model is introduced for mode II delamination cracks but is intended for general mixed-mode cracks. Modeling is guided by prior observations and measurements on laminates reinforced through the thickness by stitches or short rods. Salient phenomena include shear deformation of the bridging tow, its debonding from and sliding relative to the surrounding laminate, and its sideways displacement through the laminate. The tow is represented as a beam that can shear and extend axially. Its axial displacement relative to the laminate is resisted over its debonded periphery by friction. The forces associated with its sideways displacement are estimated by regarding it as a punch being driven through a plastic medium (the laminate). Thus the mechanics of the whole problem are reduced to a set of one-dimensional equations. The distinction between continuous stitches and discontinuous rod reinforcement consists of a boundary condition. With realistic values assigned to undetermined parameters, experimental data for stitches are reproduced over the whole range of displacements up to ultimate failure of the stitch. The model generates a bridging traction law that can be used for optimal design of through-thickness reinforcement for damage tolerance in a wide variety of structures.     

Spreading of Annular Droplets on a Horizontal Fiber

This paper investigates an annular droplet on a horizontal fiber. The static state and the dynamic spreading process of the droplet is analyzed. A full model describing the profile of a static droplet is derived from the energy variation principle. To study the dynamical spreading of the droplet, we derive a lubrication model which is verified by the full model. It indicates that the lubrication model is valid for a thin droplet. Results of the static droplet reveal that, when the fiber radius is very small, the droplet tends to have a spherical shape; if the fiber radius is very large, the droplet approaches to a parabolic profile. Furthermore, the time-evolution study is carried out to investigate the dynamical spreading of the droplet. It is highlighted that when the fiber radius is small, the droplet can breakup into small droplets or contract into a sharp shape. For a large fiber radius, the droplet spreads to a steady profile. In addition, the liquid viscosity is found to retard the deformation of the droplet and the motion of the contact lines.     

四通道单模光纤旋转连接器的研制

设计了一种基于道威棱镜的光传输特性的四通道单模光纤旋转连接器,采用锥齿轮行星轮结构实现光信号的旋转耦合,并设计了耦合调整方案;分析道威棱镜光轴与旋转轴不重合带来的耦合损耗,确定道威棱镜的装调精度。最终使四通道单模光纤旋转连接器的技术指标达到了国外同类产品水平,且道威棱镜的通光孔径大,可在结构尺寸不变的情况下直接扩展为八通道单模光纤旋转连接器。     

Fiber reinforced vessel design with a damage criterion approach

Current design codes for the design of fiber reinforced vessels are generally based on a quadratic interaction criterion which relies on failure testing of laminas with different fiber orientations. A stress ratio is then imposed for purposes of design. This approach appears to be overly conservative for certain resins and does not account for the onset of damage.

An experimental investigation has been conducted to determine the stress at onset of damage in small coupon specimens. The results from the coupon testing were used to develop a damage based design approach that differs from the existing failure based approach. The damage approach was used for the design of a new manway and nozzle on a 2.13 m diameter by 6.55 m tall (7.0 ft diameter by 21.5 ft tall) glass fiber reinforced polymer pressure vessel. The vessel was subsequently tested with acoustic emission to verify the adequacy of the new designs. This paper focuses on the design of these discontinuity regions and provides comparisons between finite element model predictions and measured strain gage data.     

Fiber pullout based on a one-dimensional model of decohesion

An analytical solution is given for the fiber pull-out problem. To make the problem tractable, the following assumptions are invoked: (1) the problem is axisymmetric, (2) the effect of the deformable medium surrounding the fiber and the actual interface behavior is reflected through an interface constitutive equation with the surrounding medium considered to be rigid, and (3) the interface constitutive equation is a bilinear elastic-softening relation between interface traction and fiber displacement. The result is that there are only two derived dimensionless parameters. One dimensionless parameter identifies two distinct regimes for the evolution of detachment. These same regimes identify different force–displacement features. In one instant there is a progressive failure; in the other there is a load reversal which may be associated with “catastrophic” behavior from an experimental viewpoint. Finally, the effect of size on the maximum pull-out force is a natural consequence of the analysis.     

一种光纤化学二氧化碳传感器的研制

研究开发了一种基于指示剂的二氧化碳光纤化学传感器,采用具有高气体可透过性和低折射率的无定型聚四氟乙烯(Teflon AF)材料作为液芯波导管,高灵敏度微型CCD分光光度计作为检测器,溴百里酚蓝(BTB,bromothymol blue)和Na2CO3为指示剂缓冲溶液。在0～194 ppm的CO2浓度范围内,传感器最佳精度为±1.21ppm,响应时间(99％)约为2 min。传感器具有体积小,能耗低等特点,适于现场长期自动监测。     

一种植物纤维发泡材料的静态力学性能研究

目的研究某植物纤维发泡材料的力学性能,建立粘弹塑性力学模型。方法用万能材料试验机进行静态压缩实验,得到该植物纤维发泡材料的应力-应变曲线,并建立其力学模型,用SPSS软件对实验数据回归分析和参数识别,最后对比分析模型曲线与实验数据的吻合度。结果该植物纤维发泡材料变形有3个阶段,即弹性阶段、粘塑性阶段和压溃阶段。该植物纤维发泡材料的粘弹塑性模型可由1个线性弹簧元件、1个非线性弹簧元件、1个粘性元件和1个塑性元件组合而成。在弹性阶段,该植物纤维发泡材料的弹性模量参数为5.873 MPa;在粘塑性阶段,该植物纤维发泡材料的力学模型可用三次函数来表示,三次项、二次项、一次项和常数项的参数分别为9.155,-9.1,3.608,0.136。结论该植物纤维发泡材料是一种粘弹塑性材料,其理论模型可用三次函数表示,实验数据与理论模型吻合度高。     

Fiber anemometer

Summary The described fiber anemometer permits measuring small constant and variable discharges and velocities of liquid and gas, direction of currents, and the characteristics of turbulence. The lower limit of measurable velocities is fractions of mm · sec^–1. The special features of this anemometer are insensitivity to electrical and magnetic disturbances, and the possibility of taking measurements in chemically agressive media. It can be useful for measurements in hydrodynamics, meterology, oceanography, pneumatics, chemical technology, and low-speed aerodynamics.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 42–44, June, 1968.     

Tamarind Fruit Fiber and Glass Fiber Reinforced Polyester Composites

Polyester-based hybrid composites were developed by combining the tamarind fruit (Tf) and glass fibers into a polyester matrix. Hardness, impact strength, frictional coefficient, and chemical resistance of hybrid composites with and without alkali treatments were studied. Variation of the aforementioned mechanical properties and chemical resistance was studied with different fiber lengths, such as 1, 2, and 3 cm. A 9 vol% of the tamarind and glass fibers was reinforced into the polyester matrix. The aforementioned mechanical properties were optimally improved at 2-cm fiber length when compared with 1- and 3-cm fiber lengths. Chemical resistance was also significantly improved for all chemicals except toluene. A 3°C rise in decomposition temperature while a 2°C rise in glass transition temperature was observed from TGA and DSC micrograms, respectively.     

Simulation of SiC Deposition in a Fiber Coating CVD Reactor

A simulation was carried out to study the Chemical Vapor Deposition (CVD) of SiC on a thin cylindrical substrate in a hot wall reactor. The results of this simulation are expected to apply to the process of fiber coating for interface control in fiber reinforced composites. The reactant in this study is methyltrichlorosilane (CH₃SiCl₃) in a background of hydrogen. The simulation was carried out using a commercial code (FLUENT). The simulation results compared well with experimental data from a hot wall reactor. It was determined that the temperature profiles tend to be uniform in the radial direction, and the deposition process is dominated by reaction kinetics.     

Fiber reinforced plastics using a new heat-resistant silicon based polymer

Fiber reinforced plastics (FRPs), reinforced with carbon fiber, SiC fiber and glass fiber, were prepared by using a new thermosetting silicon-containing polymer, poly[(phenylsilylene) ethynylene-1,3-phenyleneethynylene](MSP), as a matrix resin. In MSP composite processing, no solvent is needed, no by-products are generated, and the curing temperature is low (150–210°C). The FRPs (MSP composite) showed high heat-, burn- and radiation-resistant properties. Bending strengths (110–140 MPa) and modulus (30 GPa) at 200°C and 400°C were almost equal with those at room temperature, and were not affected by 100 MGy of irradiation. Dynamic viscoelasticity and creep properties of MSP composite were also determined and compared with those of a polyimide composite.