Random Fiber Research Articles

Polymer composites with short recycled glass fibres manufactured by vacuum infusion

Recycling glass fibre reinforced thermoset composites remains a challenge despite years of research in the field. Among the barriers for a successful recycling, the properties of the recycled materials and their application in new products represent the main ones. With a pyrolysis recycling process, clean glass fibres can be extracted and separated from the polymer matrix. In this paper, recycled glass fibres are incorporated in a new polymer composite structure using both virgin and recycled glass fibres. Recycled glass fibres have a Young’s modulus comparable to virgin glass fibres. The objective is to identify a composite lay-up using virgin and recycled glass fibres, and where the Young’s modulus of recycled fibres is beneficial for the resulting composites mechanical properties. To do so, a sandwich structure composite with virgin fibres on the outer layer and recycled fibres in the inside is designed and manufactured. In order to produce flat panels despite the short and random fibres, a manufacturing procedure ensuring a good dispersion of the fibres and controlling the thickness of the panel is developed. Panels are produced incorporating two different weight fraction of recycled glass fibres. The quality of the panels are characterized using microstructure observations, fibre porosity analysis and mechanical testing. Results shows that the sandwich composites have a low porosity content and achieves higher bending stiffness than a composite only made of unidirectional virgin glass fibres.

Comparative Study of Ultra-Narrow-Mode Generation in Random Fiber Lasers Based on Different Fiber Types

We studied the properties of ultra-narrow spectral modes, appearing in random distributed feedback Raman fiber lasers, for different fibers building up a laser cavity. Fibers with different nonlinear coefficients and dispersion were employed to obtain the generation. Ultra-narrow modes were observed in all fibers except those with the smallest dispersion. We measured the mode parameters, such as the average lifetime, as well as the maximum averaged output power that can support the ultra-narrow generation. The comparison revealed that the modes were more pronounced in high-dispersion fibers. Based on this comparative study, we conclude with the importance of the nonlinearity-dispersion interplay for regime stability.

Ultra-Wide Bandwidth Brillouin-Raman Random Fiber Laser With Augmented Synergistic Nonlinearity

We propose a Brillouin-Raman random fiber laser with enhanced synergistic nonlinearity for ultra-wide bandwidth Brillouin comb generation. The augmented synergistic nonlinearity, including enhanced Rayleigh scattering (RS) effect, stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), is achieved in a hybrid fiber (a fiber combination of a 7.2-km dispersion compensation fiber and a 10-km single-mode fiber) under a strong Raman pumping condition. Under the strong Raman pumping condition, more Stokes lines are generated due to the enhanced RS-induced oscillations of Brillouin Stokes lines at short wavelength band, thus suppressing self-lasing cavity mode oscillations at long wavelength band. In the experiments, the multi-wavelength Brillouin comb with an ultra-wide bandwidth of 63.5 nm (1513 nm-1576.5 nm) with frequency spacing of double Brillouin frequency shift, which is the largest bandwidth from Brillouin fiber lasers, to the best of our knowledge, has been achieved. The proposed ultra-wide bandwidth Brillouin-Raman fiber laser has potential applications in optical communication, optical wavelength division multiplexing, and fiber sensing.

Mesoscale numerical investigation of dynamic spalling fracture in toughness concrete

This study presents a two-phase mesoscale numerical model to investigate the dynamic spalling fracture behaviour of hybrid fibre ultra-high toughness cementitious composites (UHTCC). The model simulated the presence of random steel fibres and ductile UHTCC independently, and accurately incorporated the fibre-matrix bond-slip relationship, with carefully considering the influence of the inclination angle of the steel fibres on the pullout behaviour. Validation of the numerical model involved a meticulous comparison between numerical outcomes and results from spallation tests, encompassing strain-time and velocity-time histories, failure modes, and locations of cracking or fracture. Subsequently, the developed model was employed to analyse the impact of fibre inclination, stress wave amplitude, and waveform (based on the impulse equivalence principle) on the dynamic spalling fracture behaviour of hybrid fibre UHTCC. Evaluation of spalling fracture performance was based on both maximum velocity and pullback velocity of resulting fragments or free surfaces. Findings revealed that fibres parallel to the stress wave propagation direction exhibited optimum performance. It was also observed that stress waveforms with rectangular and sinusoidal shapes presented the highest risk of spalling fracture, while exponentially attenuated waves were comparatively safer. Additionally, stress waveforms with either rise time or duration at maximum pressure were deemed hazardous. Further, the hybrid fibre UHTCC demonstrated multiple spalling cracking/fracture behaviours under all stress waves except rectangular ones. This comprehensive exploration provided insights for the utilization of hybrid fibre UHTCC in impact engineering.

Spectral dynamics of pseudo-distributed erbium gain in Raman random fiber laser

This work explores the spectral dynamics of pseudo-distributed erbium gain in a Raman-based open cavity hybrid random fiber laser (RFL) and compares it to two other schemes; without erbium-doped fiber (EDF) and with EDF integrated mid-cavity. The pseudo-distribution of erbium gain is simulated by splicing short segments of EDF in between single-mode fiber (SMF) spools. The three schemes have similar total SMF lengths of 78 km, and a total of 30 m EDF if any. It was established that the laser wavelength shifts significantly from 1555.936 nm to 1565.904 nm simply by the insertion of EDF mid-cavity, while the distribution of EDF segments along the cavity allowed the generation of dual-wavelength lasing at 1559.964 and 1565.236 nm. The distribution of EDF also generated a higher maximum output power of 485.60 mW compared to the schemes with lumped EDF and without EDF of 409.17 mW and 352.02 mW output powers, respectively. However, the increment came at the expense of a longer instability event from homogenous gain broadening of SBS induced Stokes and a delayed onset of laser threshold condition. We discuss the formations of these different laser schemes and its dynamics permitted solely due to the uniqueness of random fiber lasers. The scheme presents an interesting opportunity in the development of hybrid random fiber lasers, and the analysis of this structure offers insights for better designed dual-wavelength random fiber lasers and the role that rare-earth Erbium dopant plays in the formation of laser in a Raman-based fiber cavity.

Review of Random Fiber Lasers for Optical Fiber Sensors.

A random fiber laser does not need a traditional resonant cavity and only uses the multiple scattering of disordered media to provide feedback to achieve laser output. Therefore, it has the advantages of a simple structure, narrow linewidth, and low noise and is particularly suitable for fiber optic sensors. This paper provides an introduction to the categories and corresponding principles of random fiber lasers. The research progress of random fiber lasers in the sensing field in recent years, including various aspects of random fiber lasers as low-noise light sources or sensitive elements for fiber sensing systems, is the main focus. Finally, the future development trend of random fiber lasers for optical fiber sensors is explored.

Ultra-narrow linewidth and a low-noise cascading Brillouin random fiber laser with a dual pump.

A cascading Brillouin random fiber laser with a dual pump (DP-CBRFL) is proposed and demonstrated. The DP-CBRFL can improve the Brillouin gain significantly to achieve an ultra-narrow linewidth (95.5 Hz) with 200 mW pump power, due to two cascading Brillouin gain fibers with an identical Brillouin frequency shift. Compared with the general Brillouin random fiber laser, the proposed random fiber laser has a more stable Brillouin gain spectrum and a lower mode density, which makes it have a lower intensity noise and frequency noise, especially in the low-frequency range. Meanwhile, it exhibits a high slope efficiency of 28% even if the pump power has reached 1.1 W due to the strong suppression ability of the high-order Stokes light.

Transient replica symmetry breaking in Brillouin random fiber lasers

Replica symmetry breaking (RSB), as a featured phase transition between paramagnetic and spin glass state in magnetic systems, has been predicted and validated among random laser-based complex systems, which involves numerous random modes interplayed via gain competition and exhibits disorder-induced frustration for glass behavior. However, the dynamics of RSB phase transition involving micro-state evolution of a photonic complex system have never been well investigated. Here, we report experimental evidence of transient RSB in a Brillouin random fiber laser (BRFL)-based photonic system through high-resolution unveiling of random laser mode landscape based on heterodyne technique. Thanks to the prolonged lifetime of activated random modes in BRFLs, an elaborated mapping of time-dependent statistics of the Parisi overlap parameter in both time and frequency domains was timely resolved, attributing to a compelling analogy between the transient RSB dynamics and the random mode evolution. These findings highlight that BRFL-based systems with the flexible harness of a customized photonic complex platform allow a superb opportunity for time-resolved transient RSB observation, opening new avenues in exploring fundamentals and application of complex systems and nonlinear phenomena.

Study on Mechanical Properties of Pineapple Leaf-Glass Fiber Hybrid Composites for Car Body Applications

The purpose of this study was to determine the mechanical properties of glass fiber composites and fiber, orientation and variations pineapple with a different composition of the main tarik.Bahan tests used are glass fiber, pineapple fiber, lye (NaOH), epoxy resin and hardener. Specimens composites made by the method of hand lay up with variations in the composition of the glass fiber 6%: pineapple fiber 4%, the glass fiber 9%: pineapple fiber 6%, glass fibers 12%: pineapple fiber 8%, glass fibers 15%: pineapple fiber 10% and with random fiber orientation and horizontal. Making the specimens was performed by reference to standard ASTM D 638.Hasil this test shows that the highest tensile strength in horizontal fiber orientation with the volume fraction of 25% sebesar143.98 MPa, while the lowest occurred in a random fiber orientation of 10% amounting to 13.45 MPa. Fault Composite glass fiber and epoxy pineapple fiber bermatrik average can be classified as a single fracture type.

Impact of Fiber Characteristics on the Interfacial Interaction of Mammalian Cells and Bacteria

An imperative requisite of tissue-engineered scaffolds is to promote host cell regeneration and concomitantly thwart microbial growth. Antibacterial agents are often added to prevent implant-related infections, which, however, aggravates the risk of bacterial resistance. For the first time, we report a fiber-based platform that selectively promotes the growth of mammalian cells and alleviates bacteria by varying fiber size, orientation, and material of polymeric yarns. The interactions of Gram-positive and -negative bacterial species with mammalian mesenchymal stem cells (MSC) were investigated on poly-€-caprolactone (PCL) yarns, polyethylene terephthalate (PET), poly-L-lactic acid (PLLA), and cotton. Various yarn configurations were studied by altering the fiber diameter (from nano- to microscale) and fiber orientations (aligned, twisted, and random) of PCL yarns. PCL nanofibrous yarn decreased the adhesion of S. aureus and E. coli, with a 2.7-fold and 1.5-fold reduction, respectively, compared to PCL microfibrous yarn. Among different fiber orientations, nanoaligned fibers resulted in an 8-fold and 30-fold reduction of S. aureus and E. coli adhesion compared to random fibers. Moreover, aligned orientation was superior in retarding the S. aureus adhesion by 14-fold compared to nanotwisted fibers. Our data demonstrate that polymeric yarns comprising fibers with nanoscale features and aligned orientation promote mammalian cell adhesion and spreading and concomitantly mitigate bacterial interaction. Moreover, we unveil the wicking of cells through polymeric yarns, facilitating early cell adhesion in fibrous scaffolds. Overall, this study provides insight to engineer scaffolds that couple superior interaction of mammalian cells with high-strength fibrous yarns for regenerative applications devoid of antibacterial agents or other surface modification strategies.

Efficient generation of random fiber distribution by combining random sequential expansion and particle swarm optimization algorithms

Representative volume elements (RVEs) with random fiber distribution are widely used in micro-mechanics for determining the properties of unidirectional fiber-reinforced composites from their microstructure. In this paper, the random sequential expansion (RSE) and particle swarm optimization (PSO) algorithms are combined to develop an efficient methodology for generating such RVEs. This methodology can successfully eliminate the biased regions of dense fiber population and unreal matrix-rich corners that usually appear in created RVEs and resolve the complications in selection of the input parameters in the RSE algorithm. Statistical analysis of the generated microstructures and two- and three-dimensional finite element analyses are performed to validate the capability of the proposed algorithms.

Flexible generation of broadly wavelength- and OAM-tunable Laguerre-Gaussian (LG) modes from a random fiber laser.

Broadband wavelength tunable Laguerre-Gaussian (LG) mode with flexibly manipulated topological charge is greatly desired for large-capacity optical communication. However, the operating wavelengths achieved for the current LG modes are significantly restricted either by the emission spectrum of the intracavity gain medium or by the operation wavelengths of mode-conversion or modulation components. Here, broadband wavelength-tunable LG modes with a controllable topological charge are generated based on a random fiber laser (RFL) and a digital micromirror device (DMD). The RFL can produce broadly wavelength-tunable laser emissions spanning from 1044 to 1403 nm with a high spectral purity and an excellent beam quality, benefiting from the cascaded random Raman gain starting from a ytterbium fiber based active gain. A commercially available broadband DMD is then utilized to excite the LG modes with a flexibly tunable topological charge of up to 100 order through the super-pixel wavefront shaping technique. The combination of the RFL and the DMD greatly broadens the operating wavelength region of the LG modes to be achieved, which facilitates the capacity scaling-up in the orbital angular momentum multiplexed optical communication application.

Effect of random fiber distribution on the performance of counter-flow hollow fiber membrane-based direct evaporative coolers

The counter-flow hollow fiber membrane-based direct evaporative cooler (MDEC) was proposed as an energy-efficient and hygienic air cooling solution. The random sequential addition algorithm was used to simulate the randomness of fiber distribution within the MDEC in engineering practice. 3D numerical models were developed with a computational domain determined as a hexagonal prism containing multiple fibers. The experimentally validated model depicted the air state variation along the path under regular and random fiber distributions. The differences in wet-bulb effectiveness (εwb) and coefficient of performance (COP) of MDEC with two configurations, regular and random fiber distributions, were compared for different packing fractions and air flow rates. Furthermore, dimensionless correlations for the shell-side friction factor (f), Nusselt number (Nu), and Sherwood number (Sh) were derived to generalize the results to other hollow fiber membrane modules employed in liquid/gas systems. The results showed that the channel flow effect and dead zone under the random configuration worsened the heat and moisture handling performance of MDEC. Compared with the regular configuration, both Nu and Sh were degraded by 11.6–55.6%, but f was desirably reduced by 28.8–49.8%. Balancing cooling capability and energy efficiency, a regular configuration with moderate packing fraction was more beneficial for engineering practice.

Effect of Rayleigh backscattering on the multiwavelength random fiber laser bandwidth

We investigated the effect of Rayleigh backscattering on the bandwidth of a multiwavelength random fiber laser (MWRFL). This MWRFL is based on an erbium-doped fiber amplifier (EDFA) as the gain medium and a Lyot filter as the wavelength-selective device. A high number and stable lasing line is generated with the assistance of a nonlinear polarization rotation effect induced by highly nonlinear fiber (HNLF) and optimized by a polarization controller. Longer single-mode fiber (SMF) produces wider multiwavelength bandwidth as compared to shorter SMF lengths, as 10 km, 3 km, and 0.1 km obtained 6.24 nm, 5.76 nm, and 2.75 nm wavelength bandwidth, respectively. When the SMF is removed from the setup, no Rayleigh backscattering is provided in the cavity, which led to a narrower multiwavelength bandwidth of 2.69 nm. Subsequently, the alteration of EDFA power, half-wave plate (HWP) angle, and quarter-wave plate (QWP) angles affected the degradation of multiwavelength performance. The best output spectrum is achieved at an EDFA power of 18 dBm, a HWP angle of 60°, and a QWP angle of 105°. The laser stability over a period of 120 min was excellent with a peak power deviation of 1.33 dB.

Stable Triple-Wavelength Random Fiber Laser Based on Fiber Bragg Gratings

We demonstrate a generation of three lasing wavelengths with the assistance of Rayleigh backscattering as the stabilizer of peak power variations. The proposed laser consists of a combination of the semiconductor optical amplifier (SOA) and erbium-doped fiber amplifier (EDFA) as the amplifying media. Three fiber Bragg gratings are employed as the selective wavelength selectors at 1544, 1547 and 1550 nm. At 110 mA SOA current and 18 dBm EDFA output power, a flattened output spectrum with 0.9 dB peak power variation is attained. In terms of stability, the maximum peak power fluctuation for the individual laser is 0.24 dB within 120 minutes observation period. Without the Rayleigh backscattering effect, the peak power flatness is severely degraded. This shows that the weakly distributed photons can be utilized as peak power stabilizers in fiber laser systems.

Anisotropic reinforcement in polymer nanocomposites using dielectric-magnetic difunctional fibers

One-dimensional (1D) functional fibers have been widely used for the property enhancement of polymer nanocomposites. Modulating the orientations of fibers is crucial to maximizing the performances of the nanocomposites. In this work, we report anisotropic polymer nanocomposites enabled by dielectric-magnetic difunctional ceramic fibers, where the magnetic Fe2O3 nanoparticles (FO nps) were confined inside the dielectric ceramic fibers, to produce concurrent strong magnetism and high dielectric/piezoelectric responses. The difunctional fibers can rotate well along the direction of the external magnetic field during the nanocomposite processing, producing notable anisotropic enhancements of polymer nanocomposites. By computing the difference in magnetic and gravitational potential energy versus the internal thermal energy of the fibers that serve the alignment, we determined the optimal content of magnetic FO nps for producing a desirable alignment of fibers, while maintaining the high insulativity of nanocomposites. Finally, the resultant anisotropic polymer nanocomposites with aligned fibers present a maximum 85% enhancement in dielectric constant (ϵr) and 50% enhancement in piezoelectric coefficient (d33), compared to the nanocomposites with random fibers, while maintaining excellent elastic modulus and transmittance. Our work provides an effective strategy for the development of fiber-reinforced polymer nanocomposites with anisotropy and multi-functionality.

Carbonization at Varying Temperatures of PVA-Derived Nanofibers Fabricated by Electrospinning

This research was conducted to determine the morphology, dimensions, and structure of carbon-nanofibers, using polyvinyl alcohol (PVA) as a source of polymer fibers fabricated by electrospinning technique, and given variations in carbonization temperature. Variations in temperature during the carbonization process are carried out to see changes in the structure and morphology of the carbon nanofibers formed. characterization by conducting XRD and SEM tests to determine the structure and morphology of the carbon nanofibers produced, it is seen that the amorphous carbon structure of the nanofibers produced is in the shape of random fibers and tends to be straight without beads. The results obtained from the XRD test, it appears that the structure is amorphous with two peaks that appear during the test, the two peaks are typical of amorphous carbon peaks, so that the fiber that has been formed, then with the carbonization process changes its structure to carbon nanofiber. Unique results were obtained when PVA nanofibers were characterized by SEM, namely the diameter of the fibers formed before and after the carbonization process had sizes in the range of 40 to 50 nanometers, these results were influenced by the process of initial formation of nanofibers using an electrospinning system.

Engineered Interleaved Random Glass Fiber Composites Using Additive Manufacturing: Effect of Mat Properties, Resin Chemistry, and Resin-Rich Layer Thickness.

Standard lay-up fabrication of fiber-reinforced composites (FRCs) suffer from poor out-of-plane properties and delamination resistance. While advanced manufacturing techniques (e.g., interleaving, braiding, and z-pinning) increase delamination resistance in FRCs, they typically result in significant fabrication complexity and limitations, increased manufacturing costs, and/or overall stiffness reduction. In this work, we demonstrate the use of facile digital light processing (DLP) technique to additively manufacture (AM) random glass FRCs with engineered interleaves. This work demonstrates how vat photo-polymerization techniques can be used to build composites layer-by-layer with controlled interleaf material, thickness, and placement. Note that this engineering control is almost impossible to achieve with traditional manufacturing techniques. A range of specimens were printed to measure the effect of interleaf thickness and material on tensile/flexural properties as well as fracture toughness. One important observation was the ≈60% increase in interlaminar fracture toughness achieved by using a tough resin material in the interleaf. The comparison between AM and traditionally manufactured specimens via vacuum-assisted resin transfer molding (VARTM) highlighted the limitation of AM techniques in achieving high mat consolidation. In other words, the volume fraction of AM parts is limited by the wet fiber mat process, and engineering solutions are discussed. Overall, this technique offers engineering control of FRC design and fabrication that is not available with traditional methods.

Spectral characteristic of multi-wavelength random fiber laser using a microfiber knot resonator

We demonstrate a U-band multi-wavelength random Raman fiber laser (RRFL) based on a microfiber knot resonator (MKR). The RRFL has a forward-pump half-open cavity, wherein a 10-km single mode fiber provides both Rayleigh backscattering feedback and Raman gain. A MKR with a 0.18 nm free spectral range is used as the broadband comb filter. Up to 40 and 38 wavelength channels within 3 dB bandwidth were achieved from the intracavity and the end of the RRFL, respectively. The laser showed a good stability with maximum 0.38 and 0.1 dB peak power fluctuation within an hour at the two outputs, respectively. The spectral evolution with two envelopes was observed, and the impact of the MKR was discussed. The MKR is a small-size all-fiber and wavelength-insensitive broadband filter, which suits well with the broadband operation of the RRFL. The proposed RRFL has a simple structure and good potential tunability and provides guidance for flexible multi-wavelength lasers in the U-band and other wavebands, which have great potential in applications.

The Synergy of Electrospinning and Imprinting for Faithful Replication of Fiber Structures

AbstractElectrospinning is a powerful method to fabricate structures resembling the fibrous texture of the native extracellular matrix. However, the random fiber deposition of the process hinders a faithful reproduction of the fiber mesh morphology on multiple samples, which raises difficulties in experimental designs to systematically test and assess cell response in vitro. A multi‐replication process to precisely reproduce the fiber morphology on different cell culture substrates is developed. The process involves a decoupling of the fiber structure, material, and porosity by combining the key advantages of electrospinning and imprinting. With this, fiber patterns having a diameter between 0.4 and 2.8 µm are replicated on polycarbonate, polystyrene, poly(methyl methacrylate), and cyclic olefin copolymer films. Identical fiber morphology is, then, obtained on porous films having a pore diameter between 2 and 12 µm. Having full control over these parameters allows the multireplication process to engineer well‐characterized cell microenvironments, which can potentially be used to further investigate complex cell–material interactions.