Fiber Preforms Research Articles

Realizing 0.7 dB/m gain in O + E band by promoting BACs-P formation in bismuth-doped phosphosilicate fiber with double-pass configuration.

The long fiber length required for the amplification of bismuth-doped fiber (BDF) has hindered its practical application. In this paper, we propose and demonstrate a feasible method to improve the active absorption of bismuth active centers (BACs) by optimizing the drawing conditions, achieving a high gain with a short fiber length. The bismuth-doped phosphosilicate fiber (BPSF) preform was fabricated by the modified chemical vapor deposition (MCVD) process and drawn into fiber under nine different conditions. The results indicate that the active absorption of BACs increases as the drawing temperature increases and the drawing speed decreases within these drawing parameters. Meanwhile, the corresponding gain per unit length is improved. Furthermore, a maximum gain of 31.6 dB at 1350 nm with the >20 dB gain wavelength range of 1311-1401 nm was achieved in a double-pass double-pump configuration, using only 45 m BPSF. Meanwhile, the -3 dB bandwidth was 1328-1370 nm. The gain per unit length is 0.7 dB/m, which, to the best of our knowledge, is the highest gain per unit length reported for the BPSF.

Influence of the surface energy of a basalt fiber on capillary wicking and in-plane permeability of reinforcements

This study evaluates the influence of a thermal treatment of a basalt fiber on capillary wicking tests and in-plane permeability experiments, under several pressure differences. The impact of the treatment was characterized at three scales: microscopic, to determine the fiber surface energy; mesoscopic, to estimate an equivalent capillary pressure (Pcap) of the fabric in spontaneous impregnation; and macroscopic, to determine the saturated (Ksat) and unsaturated (Kunsat) permeability of the fibrous preform at the process scale. Results at the microscopic scale showed that the thermal treatment increased the polarity of the fiber by 22% and decreased its surface roughness. Capillary wicking tests showed that the treated fabric presents a better affinity with water, increasing Pcap by 68%. At the process scale, permeability experiments showed the increase of Ksat and Kunsat after treatment. Finally, results of capillary pressure (ΔPγ) showed a dominance of capillary effects under the negative pressure difference.

4D-XCT monitoring of void formation in thick methacrylic composites produced by infusion

Void formation in fibre-reinforced polymer composites processed by liquid moulding is a persistent issue in composite research and development. Not only may several void formation mechanisms come into play, but these defects can also accumulate and grow over the course of the manufacturing process. Mitigation methods can be applied once the underlying causes of voiding are identified, which is impossible through post-mortem characterisation. Here, void formation is dynamically monitored in miniaturised glass fibre-reinforced thermoplastic polymer composite samples manufactured by vacuum infusion and in-situ polymerisation, using laboratory-based X-ray computed tomography (XCT). The method allows the characterisation of the evolution of void patterns as the resin polymerises and cools down within the fibre preform. With a time resolution of 2 min and a voxel size close to 20 µm, this first-of-a-kind XCT experiment provides insights into the evolution of the void volume fraction, void size and location. The root causes leading to void formation in the system of interest were successfully identified as a combination of flow-related air entrapment during preform filling and, mostly, of chemical shrinkage of the matrix upon polymerisation. Additionally, thermal shrinkage during the cooling of the preform results in a slight decrease in the final void volume fraction.

Coupled heat and fluid transport in pulled extrusion of optical fiber preforms

In the fabrication of optical fibers, the viscosity of the glass varies dramatically with temperature so that heat transfer plays an important role in the deformation of the fiber geometry. To date, models of fiber drawing processes have either assumed isothermal conditions or that advection is the dominant heat-transfer mechanism, with conduction therefore neglected. While advective heat transfer and neglect of conduction are valid in the fast process of drawing a preform to a fiber, heat conduction is also important in the slow process of extruding a fiber preform. In this paper, we derive and solve, in the context of pulled extrusion, a coupled heat and fluid flow model that incorporates heat conduction. The dramatic variation of viscosity with temperature means that this problem is extremely challenging to solve via standard numerical techniques and we therefore develop a novel finite-difference numerical solution method that proves to be highly robust. We use this method to show that conduction significantly affects the size of internal holes at the exit of the device and hence has important consequences for the process of manufacturing optical fibers.

An experimental study of ultrasonic-knife cutting for a woven carbon fiber preform by an industrial robot

This study investigates the effect of the cutting process parameters on the cutting forces and the quality parameters of a woven carbon fiber preform during robotic ultrasonic-knife cutting. An ultrasonic cutting device, with a power of 1200 W, a frequency of 24 kHz, and an amplitude of 60 µm, mounted on the end effector of a six-axis degree of freedom industrial robot to make linear cuts. A three-level factorial experimental design was used to examine the effect of the feed rate (1 m/min to 5 m/min) and the knife’s attack angle (45° to 75°) on the cutting forces, the dimensional accuracy of the machined preform coupons, and the damage on the machined preform edges. The cutting force analysis results show that the increasing feed rate resulted in increasing feed force and thrust force. However, the increase of the attack angle increases the feed force but decreases the thrust force. The average width and damage of the ultrasonic knife cut preform coupons are highly related to the process conditions. The combination of the low feed rate, 1 m/min, and the low attack angle, 45°, resulted in dimensional errors ranging from 253 μm to 365 μm oversized from the programmed 15.0 mm width with no damage. When the feed became 3 m/min and 5 m/min at the attack angle of 75°, the preform coupons’ dimensional accuracy and damage formation worsened. In these conditions, the ultrasonic knife attached to the industrial robot arm could not cut the preform plate effectively, so the tows on the preform were unevenly cut or dislodged.

Dynamic damage behavior of auxetic textile reinforced concrete under impact loading

To investigate the dynamic compression behavior of Textile-reinforced concrete (TRC) under impact load, low speed and high speed impact tests were performed using a ball drop test and a split Hopkinson pressure bar (SHPB) with ϕ50mm, respectively. In view of the advantages of auxetic materials in impact resistance and energy absorption, the auxetic fiber preforms with negative Poisson's ratio effect were woven into meshes and added to the cement-based materials to obtain the auxetic textile-reinforced concrete. Thus, the auxetic textile reinforced cement-based material is obtained. In this paper, TRC with different textile types, laying layers and surface treatments were prepared, and impact tests with different impact speeds were carried out to evaluate the impact resistance of TRC. The impact damage behavior of TRC was analyzed through the method of digital scattering analysis, and then the impact damage mechanism of TRC was investigated. The results show that the auxetic effect of auxetic textiles can still be stabilized under impact loads of different velocities, which provides better control of deformation and energy consumption in the matrix material. Under different impact heights of falling balls, the impact fracture energy of cementitious materials reinforced with auxetic textiles was increased by up to 22.5 and 20 times, respectively, compared with that of blank samples.

Effects of crosslinker concentration on curing process and performances of needled fiber preform reinforced phenolic aerogel composite using process simulation and comprehensive experiments

A kind of needled quartz/carbon fiber preform reinforced phenolic aerogel composite (NQCF/PR) was fabricated through impregnating needled fiber preform with phenolic resin precursor solution, followed by sol–gel polymerization and solvent drying. The needled fiber preform serves as lightweight quasi-three-dimensional reinforcement, while phenolic aerogel matrix provides high porosity and low thermal conductivity. During fabrication of aerogel composite part using vacuum-assisted resin infusion process, distribution of crosslinker hexamethylenetetramine (HMTA) in precursor solution can be problematic, as precipitated crosslinker particles may be filtered by fibrous preform. In this study, the impact of HMTA filtration induced heterogeneous structure on subsequent curing process was investigated using process simulation. Temperature effects of sol–gel polymerization and solvent evaporation were considered through establishment of corresponding kinetic models. Impacts of heterogenous structure on distribution of temperature, resin curing degree and solvent conversion degree in large hemispherical aerogel composite structure were investigated. This leads to variations in gel network and pore structure of aerogel, thereby affecting final material performance. Based on experimental results, as HMTA concentration increases, compressive performance of NQCF/PR obviously increases. Among these, NQCF/PR with 4.7 wt% HMTA provides a balance of lightweight nature (0.25 g/cm3), excellent thermal insulation property (0.052 W·m−1·K−1) and compressive performance (strength of 0.35 MPa).

Self-healing carbon fiber/epoxy laminates with particulate interlayers of a low-melting-point alloy

In order to prolong the service life of fiber-reinforced polymer composites, the implementation of self-healing ability with the micro-encapsulated healing agent has been extensively studied. However, such microcapsule-based self-healing composites typically suffer from degraded mechanical properties due to the liquid-phase inclusions, thereby limiting their proliferation. Here, a low-melting-point alloy is utilized as the particulate inclusions of carbon fiber/epoxy laminated composites. Field's Metal particles (melting point: 62 °C) are distributed between woven carbon fiber preforms followed by the resin impregnation to realize laminated composites with a Field's Metal-enhanced interlayer(s). The resulting laminated composites demonstrate the autonomic repair of interlaminar failure with a 40 % of healing efficiency. Most of all, the mechanical properties of these self-healing laminated composites are comparable to the conventional laminated composites attributed to the rigid inclusions that can be compressed to increase the fiber volume. Since the Field's Metal particle inclusions can bestow polymer composites with self-healing ability and the potential increase in mechanical properties, Field's Metal-enhanced fiber-reinforced polymer composites are expected to unlock the practical utility of self-healing composites.

Watt-level cladding-pumped bismuth-doped fiber laser operating near 1.31 [formula omitted]m

We report, to the best of our knowledge, the first CW bismuth-doped fiber laser operating at around 1.31 μm with an output power of >1 W utilizing a cladding-pumping configuration with multimode semiconductor laser diodes emitting at a wavelength of 793 nm. The Bi-doped fiber (BDF) serving as an active medium of the laser was based on a pedestal-index design, where P2O5−SiO2 glass core surrounded by P-doped cladding. The BDF construction offers advanced gain characteristics and an increased mode size (∼13 μm). The fiber preform was fabricated by the conventional modified chemical vapor deposition (MCVD) method combined with all gas-phase doping technique. The BDF with low-index polymer coating provided sufficient cladding peak absorption at 750 nm belonging to bismuth active centers associated with phosphorus atoms (BACs-P) that allowed to develop a continuous-wave laser with a linear cavity configuration and enable a maximum slope efficiency of ∼ 4% with respect to the absorbed pump power. In addition, near-field spatial intensity distribution of optical beam has good quality (M2<1.13) and close to Gaussian mode profile in x and y directions. The perspectives for optimization of BDF design and laser system configurations based on such fibers for further power scaling are discussed.

Impact of process parameter on the behavior of pyrocarbon deposition in chemical vapour infiltration (CVI) process

Carbon-carbon composite manufactured by deposition of pyrocarbon (PyC) through chemical vapor infiltration (CVI) has the key issue of being process parametric sensitive which necessitates the detailed study of the effect of process parameters on the rate of PyC deposition. Conventional method of studying the parametric effect by changing one variable at a time keeping the other variables constant has a limitation of more number of experiments and missing the interaction effect among the variables. Here, the effect of process parameters including temperature, pressure, methane gas flow rate, and nitrogen gas flow rate on the mass gain and PyC deposition was studied by Taguchi method, a statistical optimization method, which has the advantage of very few experiments performed at specific pairs of process parameters only. The experiments were performed at three levels of the process parameters. Carbon-Carbon composite material is processed through the CVI process where PyC was deposited on porous carbon fiber preforms at various process conditions as per the Taguchi method. The impact of gas residence time, Reynolds number, Prandtl number, and Peclet number were also investigated. It was observed that the CVI process parameters significantly affect the rate of PyC deposition. Optimized CVI process parameters are essential for achieving a high rate of PyC deposition to reduce the processing time. The findings have revealed that a higher PyC deposition rate arises under high temperatures, pressure, methane gas flow rate, and optimal nitrogen gas flow rate. The effect of the critical interaction of the CVI process parameters on the rate of PyC deposition was also obtained. Based on the experimental studies, process guidelines are proposed for the densification of carbon fibers preform to realize C/C composite products.

Processing and properties of 3D woven SiC/SiC composites with hybrid matrix

3D woven SiC/SiC composites with Sylramic™-iBN SiC fibers have been fabricated by first partially infiltrating 3D woven fiber preforms with SiC by chemical vapor infiltration (CVI) and then by polymer infiltration and pyrolysis (PIP) of SiC-yielding polymer. The influence of fiber architecture on damage evolution and failure mechanisms during tensile loading, in-plane tensile properties, transverse thermal conductivity, and interlaminar tensile strength of the composites has been investigated. Wherever possible, the data are compared with those of 2D woven melt infiltrated (MI), CVI, and (CVI+PIP) hybrid SiC/SiC composites. The composites exhibit 300-hr creep durability at 1482 °C in air at stresses up to 138 MPa and show potential for elevated-temperature applications. Further improvements in composite properties are possible by optimizing composite constituents and fiber architecture.

Processing and performance of ultra high temperature ceramic matrix composite (UHTCMCs) using radio frequency assisted chemical vapour infiltration (RF-CVI)

Ultra-high temperature ceramic matrix composites (UHTCMCs) have been produced using a radio frequency assisted chemical vapour infiltration (RF-CVI) process. The composites were based on 2.5D carbon fibre preforms with a 0 / 90° (out of plane) fibre orientation and containing 23 % fibre volume fraction. These were initially impregnated with zirconium diboride (ZrB2) powder in the form of a slurry and then, after solvent removal, the majority of the porosity filled with pyrolytic carbon (PyC) using the RF-CVI process at 1273 K and 0.5 kPa chamber pressure. The latter resulted in a uniform rough laminar texture with good interfacial bonding. As intended, an inverse temperature profile was achieved using the RF heating, enabling uniform densification of the preform from the inside out, with no entrapped porosity and achieving 90 % of theoretical density in only 24 h, at least a tenfold reduction in processing time compared to the conventional CVI process and a fivefold reduction compared to other modified CVI processes such as forced flow or pressure gradient CVI. The resulting UHTCMCs displayed good mechanical strength and thermo-ablative behaviour.

Response of short jute fibre preform based epoxy composites subjected to low-velocity impact loadings

This work aimed to investigate the low velocity impact behaviour of short jute fibre non-woven preform epoxy matrix composites experimentally. Dry fibre preforms were developed using an optimised process and a laboratory made preforming device. The effects of alkali and poly vinyl alcohol (PVA binder) treatments on impact performances of jute composites were investigated and compared at 3 J and 6 J impact energy levels. To identify the failure modes of tested composites, the X-ray µCT tomography was employed. The results demonstrated that the developed untreated short jute fibre preform reinforced composites absorbed a higher impact energy, when they were compared to treated (alkali or PVA binder) composites. For untreated composites, maximum impact forces at 3 J and 6 J energies, were found as ⁓2478 N and ⁓2319 N, respectively; for the PVA treatment these values were measured as ⁓2457 N and ⁓2216 N, while, at same energy levels, alkali treated composites showed the lowest values as ⁓1683 N and ⁓1440 N, respectively. Untreated jute fibre contains natural matrices such as hemicellulose, lignin and waxes, which ensured a positive response to absorb more energy upon impact loading. In contrast, the alkali treatment facilitates a highly fibre packed composite structure, which accelerated the impact crack propagation in tested composites, resulting in lower resistance to impact energy. Although, PVA treated composites showed reduced impact properties compared to untreated composites due to the PVA polymer brittleness on the treated fibre surface during the impact incidents, this treatment demonstrated better impact responses over the alkali treatment. The application of PVA binder on alkali-treated fibres provided an extra support to fibres and a better fibre/matrix interface and hence, this combined treatment demonstrated a slightly better impact resistance (⁓2027 N and ⁓1874 N impact forces at 3 J and 6 J respectively) compared to only alkali treated fibre composites. The SEM fracture images and the X-ray µCT damage analysis revealed different impact damage modes, which supported the observed impact results. The obtained results from this investigation could be helpful for using short jute fibre composites in various load demanding applications where impact incidents are likely to be happened.

Sustainable Jute Fiber Sandwich Composites with Hybridization of Short Fiber and Woven Fabric Structures in Core and Skin Layers

AbstractSustainable hybrid composites, made of two different natural plant fiber types, are increasingly being attracted by composite researchers, for their cost effectiveness and ability to control mechanical performances through varying weight ratios of different fibers. In contrast, their lower mechanical properties are reported in the literature, because of strength variations of different fiber types and an improper fiber‐matrix stress distribution. Therefore, it is aimed to develop sustainable hybrid composites from two dry fiber preforms—woven fabric and short fiber preform—originated from same fiber type (jute). A highly packed short fiber preform is used as the core layer, while woven fabrics (plain/twill–rib/twill–diamond) are used in the skin layers for producing sandwiched hybrid jute composites. Mechanical tests and scanning electron microscopy images show that hybridized plain fabric/short fiber preform composites have better mechanical properties (≈58 MPa tensile strength/≈117 MPa flexural strength/≈112.12 kJm−2 impact strength with an ≈487.4% improvement) compared to other fabric structures hybrid/nonhybrid composites. This enhancement is related to the interlocking of short fibers with long plain fabric leading to a strong fiber‐matrix interfacial bonding. Thus, this developed hybrid composites, can be applied in many semi‐structural applications, wherein composites’ low cost and mechanical performances are primary concerns.

A microscale modeling method for predicting the compressive behavior of 3D needled nonwoven fiber preforms

The through-thickness compressive mechanism of 3D needled nonwoven fiber preforms is complicated due to the complex fiber structure and enormous fiber-to-fiber contacts. This work developed a microscale modeling method to predict compressive behavior of carbon fiber nonwoven preforms. A newly-developed virtual fiber is proposed based on the generalized beam elements, for which the low bending stiffness of the fiber is calibrated by experimental data and decoupled from the high tensile stiffness. The feasibility of the proposed virtual fiber method is demonstrated through a simulation example of three-point bending of 6 k carbon fiber yarn. Influence of modeling parameters including amount of virtual fibers in the yarn and the element length of virtual fibers on the simulations is analyzed. High precision model of 3D needled preform is then generated using the proposed virtual fiber method. Through-thickness and axial compressive deformations of the preform are simulated. The predicted load–displacement curves agreed well with the experimental results.

Preparation and mechanical properties of Cf/SiC composites via pressure-assisted gel impregnation and PIP

Non-uniform shrinkage of SiC precursors will lead to cracking and thus weaken the mechanical properties of the Cf/SiC composites. This study used the pressure-assisted gel impregnation method to introduce SiC particles (SiCp) into the carbon fiber preform and combined the PIP technique to fabricate Cf/SiC composites. The mechanism of enhancing the mechanical properties of composites was studied. Results showed that SiCp effectively eliminated matrix cracking, and the PyC interface layer inhibited interfacial crack propagation. The combined effect of the two resulted in a significant improvement in the mechanical properties of the composites. Specifically, the maximum flexural strength of the Cf/SiC composites was 360.63±26.02 MPa, and the maximum fracture toughness was 8.57±1.82 MPa·m1/2.

Terahertz time-domain spectroscopy for the inspection of dry fibre preforms

Liquid moulded polymer matrix composites (LM-PMCs) are increasingly used in aerospace, automotive and other industrial applications. Liquid moulding processes featuring dry fibre preforms provide flexibility and enable cost reductions for secondary load-bearing structures. However, preform variability and manufacturing reproducibility remain major obstacles to wider use in primary structures. The open literature records only marginal use of non-destructive inspection (NDI) methods for dry multilayer preforms due to technological limitations and cost of NDI methods. In this work, terahertz time-domain spectroscopy (THz-TDS) is used for inspecting three dry multilayer glass fibre preforms featuring different defects, for the first time. A novel time-domain enhancement method is compared with classical image processing methods, aiming at improving image contrast and detecting potential defects. Furthermore, THz B-Scan is used for verifying the accuracy of interply defect detection. Finite difference time domain is simulated for analyzing THz magnitude variation in time-domain. Finally, quantitative evaluation is applied to further illustrate the significant potential of THz-TDS for the inspection of dry fibre preforms. The results show that the errors on defects lengths, widths, angles, and diameters for THz-TDS are in the ranges 8.2 %–34.3 %, 18.67 %–75 %, 0.29 %–6.67 %, and 1.33 %–10 % respectively.

Comparing the laser-induced damage distribution in POFs with raytracing simulations

The understanding of the laser-induced damage behavior in polymer optical materials is of high interest to prevent their damage and to increase the laser damage resistance of optical components. Moreover, compared with optical components made from high-quality glass materials, nanosecond laser-induced damage for wavelengths in the visible and near-infrared (NIR) occurs inside the bulk material of PMMA and not at its surface. This phenomenon complicates the determination of the laser-induced damage threshold (LIDT) in PMMA fibers. Since the bulk material itself determines the LIDT, knowledge of the intensity distribution in the multimode fiber is of utmost importance. Our fibers were irradiated at a wavelength of 532 nm with an ns-pulsed laser system with a 10 Hz repetition rate. To investigate the damage behavior in polymer optical fibers, we applied different imaging and analysis techniques. To our knowledge, those techniques are used here for the first time in order to study damaged polymer materials. With the help of a Nomarski microscope, axial and radial damage distributions within the multimode PMMA fibers were determined and compared with ray-tracing simulations of the intensity distribution within the optical fiber. Moreover, extruded PMMA plates were irradiated with the aim of comparing the damage behavior of materials with different manufacturing. In addition, the planar geometry of the plates allows for a more reliable application of the different measurement methods. Overall, investigations with a thermal imaging camera and EDX analysis indicate that the damage behavior of polymer optical material is thermally driven during the ns-pulsed irradiation. Furthermore, voids are formed during the damaging process within the polymer optical fibers and plates, as indicated by both SEM images and X-ray computed microtomography (µ-CT) investigations. Finally, we investigated the damages in fiber preforms and PMMA plates using two photon-microscopy. By doing this, we detected fluorescence signals from the damaged material, indicating that the damage process leads to a major modification of the polymer.

A novel Nd3+-doped fiber fabricated by curable nanocomposites for 916 nm laser

In this work, a novel Nd3+-doped silica fiber preform was fabricated by the UV-curable nanocomposite technology combined with the solution doping method. The preform sample had a great homogeneity with a doping concentration of 1.14 wt% Nd3+ ions and 2.51 wt% Al3+ ions. The obtained Nd3+-doped core glass provided a relatively large emission cross section (∼0.84 pm2) and a long lifetime (373 μs) of 916 emission. On this basis, by using an 808 nm laser diode as the pump source, lasing at 916 nm was achieved from a 4 cm long fabricated Nd3+-doped silica fiber, with the corresponding slope efficiency of ∼13.6 %. Notably, only 2 cm-short created fiber alone was enabled for 916 nm lasing generation. Our results indicated that the created Nd3+ doped fiber by the novel approach has unique advantages and potential for compact short-cavity 0.9 μm laser applications.

Advances in laser‐based manufacturing techniques for specialty optical fiber

AbstractAs demand for customized specialty fibers grows, standardized production methods face challenges. This article reviews industry standards and discusses potentially disruptive techniques that enable rapid prototyping and fabrication of optical fiber devices. Furthermore, we showcase laser powder deposition's (LPD) potential for additive manufacturing (AM) of customized glass structures. In the case of, for example, fiber preforms, although the feasible size is smaller than the industry standard, utilizing laser‐based manufacturing techniques for a small batch production presents an attractive avenue for rapid prototyping and expedites material and design optimization. In the realm of AM of glass, LPD offers numerous benefits, including minimal shrinkage, high densification, and the ability to tailor glass composition to achieve desired optical properties. The article reviews the latest achievements and highlights future directions in this technology.