Fiber Geometry Research Articles

Assessing flexural and permeability performance of roller-compacted concrete pavement (RCCP) reinforcing with different types of synthetic fibres and crimped steel fibre

ABSTRACT The ever-increasing use of fibres in roller-compacted concrete pavement (RCCP) necessitates fully identifying the mechanical and permeability properties of RCCPs. Incorporating fibres in RCCP with different properties leads to a better comparative investigation that helps discover the unique effects of each fibre on the RCC characteristics. This aim was achieved via analyzing the test results of compressive and flexural strengths, flexural toughness, drying shrinkage, porosity, and water sorptivity. The reinforced RCCs were prepared by incorporating 0.5% and 1% of steel, Barchip, Kortta, and polypropylene fibres in a plain mixture. The plain mixture was chosen between nine mixtures, the differences of which were defined in w/c ratio, volume of cement content, and type of aggregate grading curve. The results indicated that increase in the volume of fibres from 0.5% to 1% could reduce the drying shrinkage rate and enhances the flexural toughness of FR-RCC. Furthermore, the water sorptivity and porosity were found to increase with the substitution of fibres in the RCC mixtures. Here, the water sorptivity of the specimens was highly dependent on the type and surface geometry of fibres. However, apart from other characteristics of fibres, the porosity was significantly increased, using fibres with a high aspect ratio.

Study and modeling of photonic crystal fibers

"Optical fiber is a light guide which today constitutes the preferred medium for the transport of information. But, in order to meet the increasing needs generated by the development of the Internet in particular, it was necessary to always improve the propagation characteristics in the fibers. A new generation of fibers has been designed with the aim of obtaining lower losses and better performance than classical fibers. This work presents a design of hexagonal photonic crystal fiber (PCF) geometry for analyzing different optical properties with respect to wavelength ranging. This geometry has been used for analyzing effective refractive index, dispersion, effective mode area, nonlinear coefficient and birefringence. Silica glass is chosen as background material and the cladding region is made of air hole layers. This work is based on the modeling and analysis of the propagation characteristics of waves in a photonic crystal fiber."

Optimizing Evanescent Efficiency of Chalcogenide Tapered Fiber.

Evanescent wave absorption-based mid-infrared chalcogenide fiber sensors have prominent advantages in multicomponent liquid and gas detection. In this work, a new approach of tapered-fiber geometry optimization was proposed, and the evanescent efficiency was also theoretically calculated to evaluate sensing performance. The influence of fiber geometry (waist radius (Rw), taper length (Lt), waist deformation) on the mode distribution, light transmittance (T), evanescent proportion (TO) and evanescent efficiency (τ) is discussed. Remarkably, the calculated results show that the evanescent efficiency can be over 10% via optimizing the waist radius and taper length. Generally, a better sensing performance based on tapered fiber can be achieved if the proportion of the LP11-like mode becomes higher or Rw becomes smaller. Furthermore, the radius of the waist boundary (RL) was introduced to analyze the waist deformation. Mode proportion is almost unchanged as the RL increases, while τ is halved. In addition, the larger the micro taper is, the easier the taper process is. Herein, a longer waist can be obtained, resulting in larger sensing area which increases sensitivity greatly.

Exceptional-point-induced asymmetric mode conversion in a dual-core optical fiber segment

The engineering of exceptional points (EPs) in open optical systems has lately attracted much attention for developing future all-optical devices. However, investigation of the fascinating features of EPs in fiber geometries is lacking. We design a fabrication feasible dual-core optical fiber segment, where non-Hermiticity in terms of a symmetric customized gain-loss profile is introduced to modulate the interaction between two corresponding coupled modes toward hosting a dynamical EP encirclement scheme in the gain-loss parameter space. An asymmetric conversion process between two supported modes is reported by exploiting the chirality of the encountered EP. The proposed scheme can lead to an advanced platform to design mode-manipulative all-optical components in communication and all-fiber photonic devices.

Quantum-inspired multicore optical fiber

We introduce a new, to the best of our knowledge, type of multicore optical fiber having a quantum-inspired network topology and unique spectral features. Particularly, the connectivity between the cores is generated by unfolding a circular array of coupled quantum oscillators in Fock space. We show that in such a fiber geometry, the eigenvalues of the optical supermodes exhibit partial degeneracy and form a ladder. In turn, this leads to revival dynamics, allowing for a periodic re-imaging of the input intensity. As an example, we present a realistic design with six cores in silica glass platforms.

Investigations on high-reflective Fiber-Bragg-Gratings in multimode fibers

Due to the large core diameter and high number of guided modes in fibers with large core diameters, increasing the reflectivity of Fiber-Bragg-Gratings (FBG) in these multimode (MM) fibers is technically challenging. To increase the homogeneity and reflectivity of FBG in MM fibers, we analyze the impact of laser inscription parameters onto the FBG dimensions. Limitations of the processable core volume due to the cylindrical fiber geometry are observed. A new inscription strategy is developed, utilizing the rotational symmetry of the fiber to make a larger core volume accessible. In combination with a chirp of the FBG’s grating period a maximum reflectivity of 61% is archived in a 105 µm core diameter fiber.

Critical investigation on the effect of fiber geometry and orientation on the effective mechanical properties of fiber-reinforced polymer composites

In this study, finite element method is used to investigate the effect of combined geometry and orientation of the fiber on the elastic properties of fiber-reinforced composites. The finite element models were developed using COMSOL Multiphysics. Representative volume elements consisting of circular, square and elliptical cross-section of fibers were used in the case of combined geometry while 0°, 15°, 30°, 45°,60°, 75°, 90° and 135° were angles considered for the fiber orientation. Results from the study show that the combined geometry and fiber orientation angle has significant effect on the performance of fiber reinforced composites.

Simple Strategies for Enhancement of the Strength of Lignin‐Based Nanofibrous Aerogels

AbstractSolvent fractionated lignin and cellulose nanocrystals (CNCs) are used to create highly resilient nanofiber‐based aerogel materials. Two fractions of softwood kraft lignin (SKL) are combined and subsequently electrospun into nanofibers composed of 99% lignin. Additionally, 5 wt.% of CNCs is added into the fiber, based on the solid lignin weight, to enhance the physical properties of the nanofiber materials. The manufacturing process involves dispersing the fibers in water followed by freeze‐drying and subsequent heat treatment. The heat treatment process, with carefully chosen blends of fractionated lignin with specific glass transition temperatures, provides an initial thermoplastic behavior that results in the physical cross‐linking of entangled fibers upon heat treatment. This tailored morphology shows four times higher compressive strength compared to lignin nanofiber materials that only contain high molecular weight fractions. Moreover, CNC is a critical additive that helps maintain fiber geometry by reducing significant softening of lignin under elevated temperatures. Therefore, the fibers with CNC additives ensure the 3D shape after heat treatment, resulting in enhanced physical connections at fiber junctions. As a result, lignin/CNC nanofibers are transformed into 3D structured, lightweight materials that can undergo near full recovery after repeated compressive strain matching the performance of some carbonized analogs.

Numerical modelling of steel fibers pull-out from cementitious matrixes

The improvements of cementitious matrixes due to fibers addition are directly related to fibers’ pull-out mechanism and hence the proper simulation of this phenomenon is essential for the numerical simulation of fiber reinforced cementitious composites behavior.A steel fiber pull-out model is proposed in this paper. The model takes into account the matrix properties, the fibers shape, properties and orientation and uses parameters that can be obtained from pull-out tests of straight fibers. The paper includes calibration with experimental results, application examples and comparison with other experimental results that show the ability of the model to reproduce steel fibers pull-out behavior from different types of concrete matrix. The variation of the model parameters with concrete type and strength and fiber type and geometry is also included. It is shown that the model is able to describe not only fibers pull-out process but also matrix and fibers failure for different fiber geometries and orientations.

Influence of two phase flow on cake layer resistance and flux enhancement in spiral wound and submerged flat sheet microfiltration membrane modules

<p>Gas sparging has emerged as an effective technique for control of particle fouling in different microfiltration membrane processes. However most of the research work carried out has been pertinent to hollow fiber and tubular membrane geometries. A little attention has been paid to evaluate the potentails of gas-liquid two-phase for control of particle fouling in spiral wound and submerged flat sheet microfiltration membranes. This study focuses on control of particle fopuling by gas sparging in open channel spiral wound and submerged flat sheet microfiltration membranes. Commercial yeast was used as test suspension. The Effect of gas sparging on membrane fouling and permeate flux was studied by analysing the cake layer characteristics like cake mass deposition, cake layer thickness and cake porosity. The filtration flux and cake properties under various operating conditions, such as cross-flow velocity, filtration pressure, particle concentration, and sparging intensity are analyzed based on hydrodynamics. The results of this study show that gas sparging is very effective in control of particle fouling for both membrane module geometries. It was found that gas bubbling reduced the deposition of particles on the membrane surface due to which cake layer thickness decreases and resultantly permeate flux increased substantially. The permeate flux increased with increase in gas sparging intensity. A maximum flux enhancement of 170 % and 284 % were observed for spiral wound and flat sheet membranes respectively when gas sparging was applied to the process.</p>

Towards reference-grade multi-mode fiber connectors — Impact of fiber geometry on attenuation and encircled flux

The connection attenuation for perfectly aligned graded-index multi-mode fiber connections with dissimilar core diameter (CD) and numerical aperture (NA) is derived in analytical form for spatially large intensity patterns that include target encircled-flux (EF) compliant launches and overfilled (OF) launches. The launches are spatially stable in that it is possible to describe the ray density distribution (and hence the EF), the intrinsic connection attenuation and the redistribution of the rays in the receiving fiber by means of the ray turning points. This has enabled us to derive the analytical formulation. Although imposing an EF compliant launch significantly reduces the sensitivity of the attenuation due to fiber geometry mismatch by about a factor of three for the NA and a factor of six for the CD as compared to an OF launch, we show that tightening the tolerance of the CD to 50±0.5μm (instead of ±2.5μm) and the tolerance of the NA to 0.2±0.002 (instead of ±0.015) is necessary to ensure <0.1 dB attenuation among reference-grade connectors (instead of ≤1.2 dB).

Time-Resolved Radioluminescence Dosimetry Applications and the Influence of Ge Dopants In Silica Optical Fiber Scintillators

The quality of treatment delivery as prescribed in radiotherapy is exceptionally important. One element that helps provide quality assurance is the ability to carry out time-resolved radiotherapy dose measurements. Reports on doped silica optical fibers scintillators using radioluminescence (RL) based radiotherapy dosimetry have indicated merits, especially regarding robustness, versatility, wide dynamic range, and high spatial resolution. Topping the list is the ability to provide time-resolved measurements, alluding to pulse-by-pulse dosimetry. For effective time-resolved dose measurements, high temporal resolution is enabled by high-speed electronics and scintillator material offering sufficiently fast rise and decay time. In the present work, we examine the influence of Ge doping on the RL response of Ge-doped silica optical fiber scintillators. We particularly look at the size of the Ge-doped core relative to the fiber diameter, and its associated effects as it is adjusted from single-mode fiber geometry to a large core-to-cladding ratio structure. The primary objective is to produce a structure that facilitates short decay times with a sufficiently large yield for time-resolved dosimetry. RL characterization was carried out using a high-energy clinical X-ray beam (6 MV), delivered by an Elekta Synergy linear accelerator located at the Advanced Medical and Dental Institute, Universiti Sains Malaysia (USM). The Ge-doped silica optical fiber scintillator samples, fabricated using chemical vapor deposition methods, comprised of large core and small core optical fiber scintillators with high and low core-to-cladding ratios, respectively. Accordingly, these samples having different Ge-dopant contents offer distinct numbers of defects in the amorphous silica network. Responses were recorded for six dose-rates (between 35 MU/min and 590 MU/min), using a photomultiplier tube setup with the photon-counting circuit capable of gating time as small as 1 μs. The samples showed linear RL response, with differing memory and afterglow effects depending on its geometry. Samples with a large core-to-cladding ratio showed a relatively short decay time (&lt;1 ms). The results suggest a contribution of Ge-doping in affecting the triplet states of the SiO2 matrix, thereby reducing phosphorescence effects. This is a desirable feature of scintillating glass materials that enables avoiding the pulse pile-up effect, especially in high dose-rate applications. These results demonstrate the potential of Ge-doped optical-fiber scintillators, with a large core-to-cladding ratio for use in time-resolved radiation dosimetry.

Measuring Strain in Diffusion-Weighted Data Using Tagged Magnetic Resonance Imaging.

Accurate strain measurement in a deforming organ has been essential in motion analysis using medical images. In recent years, internal tissue's in vivo motion and strain computation has been mostly achieved through dynamic magnetic resonance (MR) imaging. However, such data lack information on tissue's intrinsic fiber directions, preventing computed strain tensors from being projected onto a direction of interest. Although diffusion-weighted MR imaging excels at providing fiber tractography, it yields static images unmatched with dynamic MR data. This work reports an algorithm workflow that estimates strain values in the diffusion MR space by matching corresponding tagged dynamic MR images. We focus on processing a dataset of various human tongue deformations in speech. The geometry of tongue muscle fibers is provided by diffusion tractography, while spatiotemporal motion fields are provided by tagged MR analysis. The tongue's deforming shapes are determined by segmenting a synthetic cine dynamic MR sequence generated from tagged data using a deep neural network. Estimated motion fields are transformed into the diffusion MR space using diffeomorphic registration, eventually leading to strain values computed in the direction of muscle fibers. The method was tested on 78 time volumes acquired during three sets of specific tongue deformations including both speech and protrusion motion. Strain in the line of action of seven internal tongue muscles was extracted and compared both intra- and inter-subject. Resulting compression and stretching patterns of individual muscles revealed the unique behavior of individual muscles and their potential activation pattern.

High-energy Q-switched 16-core tapered rod-type fiber laser system.

High-energy Q-switched master oscillator power amplifier systems based on rod-type 4 × 4 multicore fibers are demonstrated, achieving energy up to 49 mJ in ns-class pulses. A tapered fiber geometry is tested that maintains low mode order in large multimode output cores, improving beam quality in comparison to a similar fiber with no taper. The tapered fiber design can be scaled both in the number of amplifying cores and in the dimensions of the cores themselves, providing a potential route toward joule-class fiber lasers systems.

A Numerical Simulation of Electrical Resistivity of Fiber-Reinforced Composites, Part 2: Flexible Bituminous Asphalt

Asphalt concrete pavements are vulnerable to freeze-thaw cycles. Consecutive cracking and penetration of corrosive agents can expedite the degradation of asphalt pavements and result in weight loss and reduced strength. Fiber reinforcement in flexible bituminous asphalt bridge cracks limits the crack width and enhances the toughness of the composite. Furthermore, steel fibers facilitate asphalt heating during maintenance and repair operations. Electrical resistivity is a vital parameter to measure the efficiency of these operations and to identify the state of degradation in fiber-reinforced asphalt concrete. The significant difference between conductivities of steel fibers and bituminous matrix warrants in-depth investigations of the influence of fiber reinforcement on the measured surface electrical resistivity of placed pavements. Numerical simulations endeavor to predict the resistivity and associated deviations due to randomly distributed fiber reinforcement. Results and discussions reveal the sources and magnitudes of fiber geometry and content adjustments. Outcomes investigate associated errors for practical applications.

Experimental Database on pullout bond performance of steel fiber embedded in ultra-high-strength concrete

The bond strength between the steel fiber and the ultra-high performance concrete (UHPC) matrix plays a significant role in improving the behavior of plain UHPC. This paper compiles the existing experimental research database on the pullout bond performance of steel fibers embedded in UHPC. The variations of key parameters in the database are the steel fiber type and geometry, fiber volume fractions, and fiber embedded length. The effects of these parameters are analyzed and discussed in detail. Based on the analysis of the results, it was found that the deformed steel fibers, i.e., the hooked-end, half-hooked-end, and twisted steel fibers clearly provided higher average bond strengths than that straight fibers. The average pullout bond strength was obtained by increasing of fiber volume fraction in the UHPC matrix up to 2% (11.21MPa) with an increment of 20.4%. When the steel fiber volume fractions increase beyond 2%, the average bond strength decreases. Additionally, it was also found that using smaller embedded lengths in deformed steel fibers could result in the improvement of bond strength. This could be due to the fact that the bond is controlled by the mechanical anchorage of the end-hook rather than the physio-chemical bond in the straight portion. Conversely, increasing the embedded length of steel fiber could greatly contribute to the enhancement of pullout resistance resulting in increased bond strength between the UHPC matrix and steel fibers.

Design and fabrication of dispersion controlled highly nonlinear fibers for far-detuned four-wave mixing frequency conversion.

We report on the conception, fabrication and characterization of a new concept of optical fiber enabling a precise control of the ratio between the 2nd and 4th-order of chromatic dispersion (respectively β2 and β4) at 1.55 µm which is at the heart of the Four-Wave-Mixing (FWM) generation. For conventional highly nonlinear fiber the sensitivity of this ratio to fiber geometry fluctuations is very critical, making the fabrication process challenging. The new design fiber reconciles the accurate control of chromatic dispersion properties and fabrication by standard stack and draw method, allowing a robust and reliable method against detrimental fluctuations parameters during the fabrication process. Experimental frequency conversion with FWM in the new design fiber is demonstrated.

A stereological approach to estimation of fibre distribution in concrete

Steel fibre reinforced concrete (SFRC) continues to gain popularity as a sustainable construction material with enhanced strength and durability properties. These mechanical properties are dependent on the distribution and orientation of steel fibres achieved during casting, the determination of which is challenging. Three-dimensional X-ray micro-CT scanning is currently the only technique that yields the true three-dimensional (3D) dispersion of fibres, but the technology is applicable only to small samples at laboratory settings. In this study, a mathematical framework is developed to utilize 2D probing, like X-ray projectional radiography, which is more practical for in situ nondestructive characterization of fibre dispersion in SFRC members. For the first time, fibres are treated as finite-sized inclusions, developing the appropriate mathematical formulations consistent with published research in the field of stereology and practically applying them to digitized X-ray projected images of SFRC and UHPFRC. Stereological principles were employed to establish the volume fraction of fibres (3D property) from their areal fraction in images. The method was developed and tested for both X-ray slices and projected images. Tests were performed on UHPFRC cores as well as SFRC dogbones with different nominal fibre dosages. It is shown that accurate estimation of fibre volume fraction and their spatial distribution can be robotically achieved from 2D imaging using the developed algorithms. The influence of parameters such as fibre geometry and thickness of structural members on the applicability of the stereological equations and accuracy of estimated results is investigated, with a comprehensive discussion of the stereology approach.

A generalized shear-lag theory for elastic stress transfer between matrix and fibres having a variable radius

A generalized shear-lag theory for fibres with variable radius is developed to analyse elastic fibre/matrix stress transfer. The theory accounts for the reinforcement of biological composites, such as soft tissue and bone tissue, as well as for the reinforcement of technical composite materials, such as fibre-reinforced polymers (FRP). The original shear-lag theory proposed by Cox in 1952 is generalized for fibres with variable radius and with symmetric and asymmetric ends. Analytical solutions are derived for the distribution of axial and interfacial shear stress in cylindrical and elliptical fibres, as well as conical and paraboloidal fibres with asymmetric ends. Additionally, the distribution of axial and interfacial shear stress for conical and paraboloidal fibres with symmetric ends are numerically predicted. The results are compared with solutions from axisymmetric finite element models. A parameter study is performed, to investigate the suitability of alternative fibre geometries for use in FRP.

Effect of Electrolyte and Electrode Configuration on Cu‐Catalyzed Nitric Oxide Reduction to Ammonia

AbstractReduction of nitric oxide was investigated using Cu electrodes in acid and neutral pH conditions. Analysis of Cu discs in stagnant electrolyte by Electrochemical Mass Spectrometry (EC‐MS), revealed the favorable formation of ammonia (and hydrogen) in acidic electrolyte, while N2O and N2 are formed in significant quantities at neutral conditions. Additional performance evaluation of Cu electrodes in hollow fiber geometry, was performed using 10 vol % NO in Ar supplied through the porous electrode structure and off‐line determination of ammonia by 1H NMR spectroscopy. The pH dependent performance of the Cu hollow fiber is in agreement with EC‐MS data at low gas flow rates, showing the highest ammonia selectivity in acidic conditions. However, at relatively high gas flow rates, almost 90 % faradaic efficiency and a NH3 production rate of 400 μmol h−2 cm−2 were obtained in neutral electrolyte at −0.6 V vs RHE, likely due to enhanced availability of NO at the electrode surface, suppressing the hydrogen evolution reaction. This approach shows conversion of waste NO gas to valuable green fertilizer components is possible.