Fibers

23 pages, 10671 KiB

Open AccessArticle

Multi-Scale Toughening of UHPC: Synergistic Effects of Carbon Microfibers and Nanotubes

by J. D. Ruiz Martínez, J. D. Ríos, H. Cifuentes and C. Leiva

Fibers 2025, 13(4), 49; https://doi.org/10.3390/fib13040049 - 21 Apr 2025

This study investigates multi-scale reinforcement of Ultra-High-Performance Concrete through targeted modifications of its mechanical and fracture-resistant properties via carbon microfibers and carbon nanotubes. The research employed comprehensive characterization techniques including workability tests, mercury porosimetry for microscale porosity analysis, and X-ray tomography for macro-scale [...] Read more.

This study investigates multi-scale reinforcement of Ultra-High-Performance Concrete through targeted modifications of its mechanical and fracture-resistant properties via carbon microfibers and carbon nanotubes. The research employed comprehensive characterization techniques including workability tests, mercury porosimetry for microscale porosity analysis, and X-ray tomography for macro-scale pore evaluation. Mechanical performance was assessed through compression strength, tensile strength, and fracture energy measurements. Results demonstrated significant performance enhancements testing UHPC samples with 6 mm carbon microfibers (9 kg/m³) and varying carbon nanotubes dosages (0.11–0.54 wt%). The addition of carbon microfibres improved compressive strength by 12%, while incorporating 0.54 wt% carbon nanotubes further increased strength by 24%. Remarkably, the combined reinforcement strategy yielded a 313% increase in tensile strength compared to the reference mixture. The synergistic effect of carbon fibers and carbon nanotubes proved particularly effective in enhancing concrete performance. This multi-scale reinforcement approach presents a promising alternative to traditional steel fiber reinforcement, offering superior mechanical properties and potential advantages in corrosive environments. Full article

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21 pages, 21103 KiB

Open AccessArticle

Modelling Pore Size Distribution Function of Twist-Texturized Yarns and Single-Jersey Knitted Fabrics

by Leon Pauly, Lukas Maier, Sibylle Schmied, Albrecht Dinkelmann, Ulrich Nieken and Götz T. Gresser

Fibers 2025, 13(4), 48; https://doi.org/10.3390/fib13040048 - 16 Apr 2025

Abstract

Pore sizes on the micrometre scale are a critical factor influencing the fluid transport properties of textiles. Consequently, the pore size distribution function is a desirable parameter in the design of textiles for technical applications. However, the experimental determination of pore size and [...] Read more.

Pore sizes on the micrometre scale are a critical factor influencing the fluid transport properties of textiles. Consequently, the pore size distribution function is a desirable parameter in the design of textiles for technical applications. However, the experimental determination of pore size and its distribution can be challenging, costly, or impractical. Knitted fabrics offer a wide range of porosity and pore size distribution properties. While statistical models have shown reasonable accuracy in predicting pore size distributions in nonwovens and filter media, no equivalent model exists for twist-texturized yarns and single-jersey knitted fabrics. This study presents a hierarchical pore model for single-jersey fabrics. The model uses a log-normal distribution for the intra-yarn pores in the yarn and cylindrical pores for inter-yarn pores between the yarns in the fabric. With these two pore sizes, the model quantitatively characterises the porous structure of the fabric. Initial validation of the model for intra-yarn pores on four yarns of different fibre finenesses shows that the model can cover the influence of different fibre counts. For the validation on the fabric scale, two tomography datasets of single-jersey knitted fabrics show that the presented model can capture the effect of different fabric structures. A parameter study visualises the effects of both yarn and knitting parameters on the pore size distribution function of single-jersey knitted fabrics. The mean pore sizes of the fabrics are given. The results deepen the understanding of the porous properties of knitted fabrics and provide a valuable direction for structural fabric development on knitting machines. Full article

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18 pages, 3472 KiB

Open AccessArticle

A Controlled Study on Machine Learning Applications to Predict Dry Fabric Color from Wet Samples: Influences of Dye Concentration and Squeeze Pressure

by Warren J. Jasper and Samuel M. Jasper

Fibers 2025, 13(4), 47; https://doi.org/10.3390/fib13040047 - 15 Apr 2025

Abstract

Most dyeing occurs when a fabric is in a wet state, while color matching is performed when the fabric is in a dry state. As water is a colorless liquid, it has been difficult to analytically map these two states using existing color [...] Read more.

Most dyeing occurs when a fabric is in a wet state, while color matching is performed when the fabric is in a dry state. As water is a colorless liquid, it has been difficult to analytically map these two states using existing color theories. Machine learning models provide a heuristic approach to this class of problems. Linear regression, random forest, eXtreme Gradient Boosting (XGBoost), and multiple neural network models were constructed and compared to predict the color of dry cotton fabric from its wet state. Different models were developed based on squeeze pressure (water pickup), with inputs to the models consisting of the L*a*b* (L*: lightness; a*: red–green axis; b*: blue–yellow axis) coordinates in the wet state and the outputs of the models consisting of the predicted L*a*b* coordinates in the dry state. The neural network model performed the best by correctly predicting the final shade to under a 1.0 color difference unit using the International Commission on Illumination (CIE) 2000 color difference formula (CIEDE2000) color difference equation about 63.9% of the time. While slightly less accurate, XGBoost and other tree-based models could be trained in a fraction of the time. Full article

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18 pages, 3948 KiB

Open AccessArticle

Effect of Cenosphere Fillers on Mechanical Strength and Abrasive Wear Resistance of Carbon–Glass Polyester Composites

by K. H. Pulikeshi, Dayanand M. Goudar, R. V. Kurahatti and Deesy G. Pinto

Fibers 2025, 13(4), 46; https://doi.org/10.3390/fib13040046 - 14 Apr 2025

Abstract

Fabric-reinforced hybrid polymer composites are present in almost every sector of modern life, and most essential areas of research in recent years have focused on glass–carbon fabric with filler material composites. Fabric and fillers are employed in strengthening polymer composites with the aim [...] Read more.

Fabric-reinforced hybrid polymer composites are present in almost every sector of modern life, and most essential areas of research in recent years have focused on glass–carbon fabric with filler material composites. Fabric and fillers are employed in strengthening polymer composites with the aim of improving their mechanical and tribological properties. The primary objective of this investigation was to investigate thetribological and mechanical properties of unfilled and cenosphere-filled carbon–glass-reinforced polyester composite systems, utilizing two types of fabric (glass and carbon) with cenosphere filler in varying weight fractions (0, 2.5, 5, 7.5, 10, and 12.5 wt.%) for both carbon fabric and the cenosphere. The abrasive wear characteristics were evaluated using a stainlesssteel wheel abrasion tester, utilizing silica sand as the abrasive material. Tests were performed at various distances (360–1800 m) and loads (12 N and 24 N). The results show that the wear rate of carbon–glass fabric-reinforced polyester composites differs significantly, with and without cenosphere fillers. Notably, the unfilled composites exhibit the highest wear volume loss, indicating a substantial improvement in wear resistance with the addition of cenospheres. The results reveal that in carbon–glass fabric-reinforced polyester composites, specific wear rate decreases when more cenospheres are loaded. The wear rate was successfully reduced by cenospheresunder silica sand as an abrasive. Compared to unfilled composites, the mechanical properties of filled composites exhibit superior performance. These variations were explained by examining the worn-out surfaces under an SEM and correlating the features observed with the mechanical properties. Full article

(This article belongs to the Special Issue Mechanical Behaviour of Reinforced Thermosetting Polymers with Fibers: Analytical/Numerical Models and Experimental Evidence)

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17 pages, 5007 KiB

Open AccessArticle

Properties of Composites from Curauá Fibers and High-Density Bio-Based Polyethylene: The Influence of Processing Methods

by Daniele O. de Castro, Rachel P. O. Santos, Adhemar C. Ruvolo-Filho and Elisabete Frollini

Fibers 2025, 13(4), 45; https://doi.org/10.3390/fib13040045 - 11 Apr 2025

Abstract

The study examined composites composed of curauá fibers (10%) and a high-density bio-based polyethylene (HDBPE) matrix, emphasizing the effects of processing methods on their final properties. In addition, plant-derived oils were applied as compatibilizers to improve the interfacial adhesion between the hydrophilic fibers [...] Read more.

The study examined composites composed of curauá fibers (10%) and a high-density bio-based polyethylene (HDBPE) matrix, emphasizing the effects of processing methods on their final properties. In addition, plant-derived oils were applied as compatibilizers to improve the interfacial adhesion between the hydrophilic fibers and the hydrophobic HDBPE, thereby supporting the process’s sustainability. The comparative analysis of HDBPE/curauá fiber/plant-based oil composites utilized distinct methodologies: compounding with an internal mixer, followed by thermopressing and mixture composition using a twin-screw extruder with subsequent injection molding. Castor oil (CO), canola oil (CA), or epoxidized soybean oil (OSE) were employed as compatibilizers (5%). All composites displayed high levels of crystallinity (up to 86%) compared to neat HDBPE (67%), likely due to interactions with curauá fibers and compatibilizers. The use of twin-screw extruder/injection molding produced composites with higher impact and flexural strength/modulus-assessed at 5%(approximately 222 J/m to 290 J/m; 22/700 MPa to 26/880 MPa, respectively), considerably exceeding those formed via internal mixer/thermopressing (approximately 110 J/m to 123 J/m; 14/600 MPa to 20/700 MPa). Micrographs of the composites indicated that the extruder separated the fiber bundles into smaller-diameter units, which may have facilitated the transfer of load from the matrix to the fibers, optimizing the composite’s mechanical performance. As a compatibilizer, CO enhanced both properties and, when combined with the twin-screw extruder/injection technique, emerged as the optimal choice for HDBPE/curauá fiber composites. Full article

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15 pages, 2675 KiB

Open AccessArticle

The Effect of Stabilization Conditions on Fibers from Polylactic Acid and Their Properties

by Mária Petková, Anna Ujhelyiová, Jozef Ryba, Veronika Hrabovská and Martin Kurtulík

Fibers 2025, 13(4), 44; https://doi.org/10.3390/fib13040044 - 11 Apr 2025

Abstract

In this work, we investigated the influence of stabilization on polylactic acid (PLA) fibers. Biodegradable plastics have a significantly lower environmental impact because they are produced from renewable resources and can break down through the action of microorganisms. Considering the issues of polymer [...] Read more.

In this work, we investigated the influence of stabilization on polylactic acid (PLA) fibers. Biodegradable plastics have a significantly lower environmental impact because they are produced from renewable resources and can break down through the action of microorganisms. Considering the issues of polymer waste production and accumulation, PLA, being a biodegradable material derived from renewable sources, represents a promising solution for the future. Nowadays, several studies on PLA evaluate its properties for various applications. However, we focused on improving the user properties of PLA fibers. Different thermal stabilization processes simulate the use of PLA fibers and their impact on the behavior and properties of PLA fibers exposed to these conditions. The thermal behavior of PLA fibers (the melting temperatures, the crystallization temperatures, and enthalpies), mechanical (tenacity and elongation at the break, Young’s modulus), and thermomechanical (the shrinkage and the temperature of first distortion) properties of PLA fibers have been investigated in detail. Our research results show that the PLA fibers can achieve better properties (as mechanical and dimensional) by stabilization. It is about the dimensional stability of the fibers for applications such as knitting and weaving. Under the monitored stabilization conditions, shrinkage was reduced (especially at higher stabilized temperatures above 85 °C), which can improve the next process of textile processing (knitting and weaving). Thermal stabilization after drawing is one possibility. The stabilization conditions will depend on the potential use of the PLA fibers. Full article

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11 pages, 1951 KiB

Open AccessArticle

Kinetic Analysis of Cement–Asbestos Materials’ Thermal Decomposition Process by an Ex Situ Technique

by Robert Kusiorowski, Anna Gerle and Magdalena Kujawa

Fibers 2025, 13(4), 43; https://doi.org/10.3390/fib13040043 - 10 Apr 2025

Abstract

For many years, countries around the world have been struggling with the problem of storing asbestos waste, especially in, those countries where the production and use of asbestos products have been legally banned. Following the adoption of plans for cleaning up asbestos waste, [...] Read more.

For many years, countries around the world have been struggling with the problem of storing asbestos waste, especially in, those countries where the production and use of asbestos products have been legally banned. Following the adoption of plans for cleaning up asbestos waste, countries are struggling with the problem of its disposal, which mainly involves storing it in specialist landfills. At the same time, scientists are looking for alternatives to this type of “disposal” of asbestos by developing methods for degrading the harmful fibers. Particular attention has been paid to methods based on the thermal treatment of this waste, which results in hazardous asbestos fibers being thermally decomposed. This work focuses on the kinetic study of the thermal decomposition process of cement–asbestos using an exsitu thermal treatment. The results obtained made it possible to interpret this thermal transformation kinetically. Kinetic analysis of the isothermal data using an Avrami–Erofeev model yielded values for the overall reaction order. On this basis, the value of the apparent activation energy of the thermal decomposition process of the tested cement–asbestos samples was obtained, which was approximately 140–180 kJ mol⁻¹. Full article

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13 pages, 3903 KiB

Open AccessArticle

Polyaniline-Coated Electrospun Polyacrylonitrile Nanofibers for Effective Short-Chain PFAS (GenX) Removal from Water

by Israt Jahan, Easmin Ara Tani, Harsh V. Patel, Renzun Zhao and Lifeng Zhang

Fibers 2025, 13(4), 42; https://doi.org/10.3390/fib13040042 - 9 Apr 2025

Abstract

A 6-carbon short-chain per- and polyfluoroalkyl substance (PFAS), GenX, also known as hexafluoropropylene oxide dimer acid (HFPO-DA) and its ammonium salt, has been manufactured in recent years as a replacement for perfluorooctanoic acid (PFOA), a traditional long-chain PFAS, due to the increasing environmental [...] Read more.

A 6-carbon short-chain per- and polyfluoroalkyl substance (PFAS), GenX, also known as hexafluoropropylene oxide dimer acid (HFPO-DA) and its ammonium salt, has been manufactured in recent years as a replacement for perfluorooctanoic acid (PFOA), a traditional long-chain PFAS, due to the increasing environmental regulation of PFAS compounds in recent years. GenX has received significant attention because of the fact that it is more toxic than people originally thought, and it is now one of the six PFAS compounds that are placed under legally enforceable restrictions in drinking water, i.e., 10 ppt, by the United States Environmental Protection Agency (US EPA). In this research, we extended the use of polyacrylonitrile (PAN) nanofibers from electrospinning for GenX removal from water by coating them with polyaniline (PANI) through in situ polymerization. The obtained PANI-coated electrospun PAN nanofibrous adsorbent (PANI-ESPAN) demonstrated excellent GenX adsorption capability and could remove nearly all GenX (>98%) from a 100 ppb aqueous solution. This research provided valuable insights into short-chain PFAS remediation from water by designing and developing high-performance adsorbent materials. Full article

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16 pages, 1840 KiB

Open AccessArticle

Cotton Fiber Micronaire and Relations to Fiber HVI and AFIS Qualities Between Deltapine^® and PhytoGen Upland Varieties

by Yongliang Liu and Doug J. Hinchliffe

Fibers 2025, 13(4), 41; https://doi.org/10.3390/fib13040041 - 3 Apr 2025

Abstract

Cotton micronaire (MIC) is an essential fiber quality index that characterizes both fiber maturity and fineness components. This study compared how MIC affects the fiber high volume instrument (HVI) and advanced fiber information system (AFIS) qualities between Deltapine^® and PhytoGen upland varieties. [...] Read more.

Cotton micronaire (MIC) is an essential fiber quality index that characterizes both fiber maturity and fineness components. This study compared how MIC affects the fiber high volume instrument (HVI) and advanced fiber information system (AFIS) qualities between Deltapine^® and PhytoGen upland varieties. There were noticeable differences among HVI and AFIS qualities from Deltapine^® fiber samples and PhytoGen samples, with significant differences om HVI strength and elongation. MIC development benefited fiber HVI strength enhancement and also HVI short fiber index (SFI), AFIS neps, AFIS short fiber contents, and AFIS immature fiber content (IFC) reduction, all of which were desired. Adversely, MIC evolution could cause undesired HVI Rd lowering, HVI +b boosting, and AFIS UQL(w), and a decrease in L5%(n) in fiber. Further, MIC values were not related with lint turnout, but they were positively and greatly correlated with algorithmic M_IR values of the attenuated total reflection in Fourier transform infrared (ATR FT-IR) spectra. The results demonstrated the applicability of the ATR FT-IR technique combined with the M_IR approach for rapid laboratory MIC assessment at early MIC testing in remote/breeding locations. Full article

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23 pages, 7172 KiB

Open AccessArticle

Properties of Medium-Density Fiberboards with Different Contents of Recycled Fibers and Urea–Formaldehyde Resin

by Viktor Savov, Petar Antov, Viktoria Dudeva and Christian Panchev

Fibers 2025, 13(4), 40; https://doi.org/10.3390/fib13040040 - 3 Apr 2025

Abstract

Recycling wood-based panels is essential for promoting the cascading use of wood, advancing the transition to a circular economy, and maximizing the efficient use of natural resources. While recycling particleboard has become a well-established industrial practice, recycling medium density fiberboard (MDF) panels presents [...] Read more.

Recycling wood-based panels is essential for promoting the cascading use of wood, advancing the transition to a circular economy, and maximizing the efficient use of natural resources. While recycling particleboard has become a well-established industrial practice, recycling medium density fiberboard (MDF) panels presents challenges, particularly in preserving material quality. The aim of this research work was to investigate and evaluate the combined effect of recycled MDF fibers and urea–formaldehyde (UF) resin content on the performance characteristics of the panels. MDF recycling was conducted using hydrothermal hydrolysis and hammer mill refinement. Preliminary experiments revealed that the degradation of properties in recycled MDF panels is not uniform with the addition of recycled fibers. The panels retained their properties significantly with up to 20% recycled fiber content, while formaldehyde emissions decreased by 1.2%. Based on these findings, the optimization of recycled fiber and UF resin content was performed, revealing that the maximum allowable recycled fiber content through hydrothermal hydrolysis and hammer mill refinement is 24%, with a minimum UF resin content of 12%. This study highlights the potential for integrating recycled MDF fibers into new panels, contributing to more sustainable production practices. By optimizing the balance between recycled fiber content and UF resin, it is possible to produce MDF panels that meet industry standards while reducing the environmental impact. Full article

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17 pages, 5419 KiB

Open AccessArticle

Fiber/Free-Space Optics with Open Radio Access Networks Supplements the Coverage of Millimeter-Wave Beamforming for Future 5G and 6G Communication

by Cheng-Kai Yao, Hsin-Piao Lin, Chiun-Lang Cheng, Ming-An Chung, Yu-Shian Lin, Wen-Bo Wu, Chun-Wei Chiang and Peng-Chun Peng

Fibers 2025, 13(4), 39; https://doi.org/10.3390/fib13040039 - 2 Apr 2025

Abstract

Conceptually, this paper aims to help reduce the communication blind spots originating from the design of millimeter-wave (mmW) beamforming by deploying radio units of an open radio access network (O-RAN) with free-space optics (FSOs) as the backhaul and the fiber-optic link as the [...] Read more.

Conceptually, this paper aims to help reduce the communication blind spots originating from the design of millimeter-wave (mmW) beamforming by deploying radio units of an open radio access network (O-RAN) with free-space optics (FSOs) as the backhaul and the fiber-optic link as the fronthaul. At frequencies exceeding 24 GHz, the transmission reach of 5G/6G beamforming is limited to a few hundred meters, and the periphery area of the sector operational range of beamforming introduces a communication blind spot. Using FSOs as the backhaul and a fiber-optic link as the fronthaul, O-RAN empowers the radio unit to extend over greater distances to supplement the communication range that mmW beamforming cannot adequately cover. Notably, O-RAN is a prime example of next-generation wireless networks renowned for their adaptability and open architecture to enhance the cost-effectiveness of this integration. A 200 meter-long FSO link for backhaul and a fiber-optic link of up to 10 km for fronthaul were erected, thereby enabling the reach of communication services from urban centers to suburban and remote rural areas. Furthermore, in the context of beamforming, reinforcement learning (RL) was employed to optimize the error vector magnitude (EVM) by dynamically adjusting the beamforming phase based on the communication user’s location. In summary, the integration of RL-based mmW beamforming with the proposed O-RAN communication setup is operational. It lends scalability and cost-effectiveness to current and future communication infrastructures in urban, peri-urban, and rural areas. Full article

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17 pages, 8952 KiB

Open AccessArticle

Machine Learning for Identifying Damage and Predicting Properties in 3D-Printed PLA/Lygeum Spartum Biocomposites

by Khalil Benabderazag, Moussa Guebailia, Zouheyr Belouadah, Lotfi Toubal and Salah Eddine Tachi

Fibers 2025, 13(4), 38; https://doi.org/10.3390/fib13040038 - 31 Mar 2025

Abstract

This paper offers an experimental approach that integrates acoustic emission (AE) monitoring with machine learning (ML) to identify damage mechanisms and predict the mechanical properties of 3D-printed biocomposites. Specimens were fabricated using a bio-filament composed of a PLA matrix reinforced with 10% wt. [...] Read more.

This paper offers an experimental approach that integrates acoustic emission (AE) monitoring with machine learning (ML) to identify damage mechanisms and predict the mechanical properties of 3D-printed biocomposites. Specimens were fabricated using a bio-filament composed of a PLA matrix reinforced with 10% wt. of Lygeum spartum fibers and were subjected to tensile and flexural tests. The processed dataset, comprising six normalized features (cumulative rise, duration, count, frequency, energy, and amplitude) was used to train four ML models: Random Forest Regression (RFR), Support Vector Regression (SVR), Artificial Neural Networks (ANN), and Decision Trees (DT) implemented in Python using libraries such as scikit-learn, pandas, and numpy. The prediction models were developed using an 80/20 train–test split and further validated by 5-fold cross-validation, with performance evaluated by R-squared (R²) and Mean Squared Error (MSE) metrics. Our results demonstrate robust prediction capabilities, with the RFR model achieving the highest accuracy (R² > 0.98 and MSE as low as 0.013 for tensile stress prediction). Additionally, unsupervised clustering using K-means was applied to group AE signals into distinct clusters corresponding to different damage modes. This comprehensive methodology not only enhances our understanding of damage evolution in composite materials but also establishes a data-driven framework for non-destructive evaluation and structural health monitoring. Full article

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24 pages, 8460 KiB

Open AccessArticle

Influence of Coated Steel Fibers on Mechanical Properties of UHPC Considering Graphene Oxide, Nano-Aluminum Oxide, and Nano-Calcium Carbonate

by Seyed Sina Mousavi, Khatereh Ahmadi, Mehdi Dehestani and Jung Heum Yeon

Fibers 2025, 13(4), 37; https://doi.org/10.3390/fib13040037 - 29 Mar 2025

Abstract

The addition of high volume fractions of fibers in ultra-high-performance concrete (UHPC) presents specific durability-based challenges due to the high content of interfacial transition zones (ITZ) between the fibers and surrounding mortar, along with the production cost. Hence, this study explored a novel [...] Read more.

The addition of high volume fractions of fibers in ultra-high-performance concrete (UHPC) presents specific durability-based challenges due to the high content of interfacial transition zones (ITZ) between the fibers and surrounding mortar, along with the production cost. Hence, this study explored a novel coating approach on the surface of micro steel fibers, considering various nanomaterials, including graphene oxide (GO), nano-aluminum oxide, and nano-calcium carbonate. Poly(vinyl alcohol) (PVA) was employed as a coupling agent. UHPC mixtures containing coated fibers were compared with reference uncoated fiber-reinforced UHPC and UHPC containing GO. The proficiency of the proposed technique was measured through compressive strength, direct tensile, and flexural tests. A microstructure analysis was conducted using scanning electron microscope (SEM) images to determine the ITZ depth surrounding the coated fibers. Findings indicated improvements ranging from 10.7% to 21% for compressive strength, 11.2% to 38% for tensile strength, and 26.6% to 60% for flexural capacity. Full article

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16 pages, 1742 KiB

Open AccessArticle

Modeling and Analysis of the Transverse Surface Roughness in Hollow-Core Fibers

by Federico Melli, Kostiantyn Vasko, Lorenzo Rosa, Fetah Benabid and Luca Vincetti

Fibers 2025, 13(4), 36; https://doi.org/10.3390/fib13040036 - 27 Mar 2025

Abstract

The corrugation of the interfaces of the cross-section of hollow core fibers based on the inhibited coupling waveguiding mechanism is modeled and the impact on propagation loss analyzed. The proposed model is based on a combined use of coupled-mode theory and Azimuthal Fourier [...] Read more.

The corrugation of the interfaces of the cross-section of hollow core fibers based on the inhibited coupling waveguiding mechanism is modeled and the impact on propagation loss analyzed. The proposed model is based on a combined use of coupled-mode theory and Azimuthal Fourier Decomposition. It shows that such transverse roughness causes coupling between the core modes and the dielectric modes of the cladding and consequently an increase of the fiber loss. The model is validated by comparing theoretical and numerical results obtained by applying both deterministic and stochastic corrugations to tubular lattice and nested fibers. Scaling laws and impact of the fibers’ parameters are discussed. The model shows that the loss increase is not directly correlated to the root mean square of the stochastic roughness but only to the value of the power spectral density in specific spatial frequency ranges. In particular, the spectral components characterized by a periodicity lower than

10^{- 1}

of the tube circumference must have a power spectral density value lower than 0.2 nm² to ensure a negligible effect of the transverse roughness on fibers with losses lower than 0.1 dB/Km. Full article

(This article belongs to the Special Issue Characterization and Applications of Specialty Optical Fibers)

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18 pages, 2385 KiB

Open AccessArticle

Buckling Solution of Fixed–Free Anisotropic Laminated Composite Columns Under Axial Loading

by Rund Al-Masri, Hayder A. Rasheed and Bacim Alali

Fibers 2025, 13(4), 35; https://doi.org/10.3390/fib13040035 - 27 Mar 2025

Abstract

A generalized buckling solution for anisotropic laminated composite fixed–free columns under axial compression is developed using the critical stability matrix. The axial, coupling, and flexural equivalent stiffness coefficients of the anisotropic layup are determined from the generalized constitutive relationship through the static condensation [...] Read more.

A generalized buckling solution for anisotropic laminated composite fixed–free columns under axial compression is developed using the critical stability matrix. The axial, coupling, and flexural equivalent stiffness coefficients of the anisotropic layup are determined from the generalized constitutive relationship through the static condensation of the composite stiffness matrix. The derived formula reduces down to the Euler buckling equation for isotropic and some special laminated composites. The analytical results are verified against finite element solutions for a wide range of anisotropic laminated layups yielding high accuracy. A parametric study is conducted to examine the effects of ply orientations, element thickness, finite element type, column size, and material properties. Comparisons with numerical results reveal a very high accuracy across the entire parametric profile and a linear correlation between the percentage error and a non-dimensional condensed parameter is extracted and plotted. Full article

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32 pages, 5714 KiB

Open AccessArticle

Polynomial Modeling of Noise Figure in Erbium-Doped Fiber Amplifiers

by Rocco D’Ingillo, Alberto Castronovo, Stefano Straullu and Vittorio Curri

Fibers 2025, 13(3), 34; https://doi.org/10.3390/fib13030034 - 14 Mar 2025

Abstract

Erbium-Doped Fiber Amplifiers (EDFAs) are fundamental to optical communication networks, providing signal amplification while introducing noise that affects system performance. Accurate noise figure estimation is critical for optimizing link budgets, monitoring optical Signal-to-Noise Ratio (OSNR), and enabling real-time network optimization. Traditional analytical models, [...] Read more.

Erbium-Doped Fiber Amplifiers (EDFAs) are fundamental to optical communication networks, providing signal amplification while introducing noise that affects system performance. Accurate noise figure estimation is critical for optimizing link budgets, monitoring optical Signal-to-Noise Ratio (OSNR), and enabling real-time network optimization. Traditional analytical models, while computationally efficient, often fail to capture device-specific variations, whereas machine-learning-based approaches require large training datasets and introduce high computational overhead. This paper proposes a polynomial regression model for real-time EDFA noise figure estimation, striking a balance between accuracy and computational efficiency. The model leverages Generalized Least Squares (GLS) regression to fit a multivariate polynomial function to measured EDFA noise figure data, ensuring robustness against measurement noise and dataset variations. The proposed method is benchmarked against experimental measurements from multiple EDFAs, achieving prediction errors that are within the measurement uncertainty of Optical Spectrum Analyzers (OSAs). Furthermore, the model demonstrates strong generalization across different EDFA architectures, outperforming analytical models while requiring significantly less data than deep-learning approaches. Computational efficiency is also analyzed, showing that inference time is below 0.2 ms per evaluation, making the model suitable for real-time digital-twin applications in optical networks. Future work will explore hybrid modeling approaches, integrating physics-based regression with Machine Learning (ML) to enhance performance in high-variance spectral regions. These results highlight the potential of lightweight polynomial regression models as an alternative to complex ML-based solutions, enabling scalable and efficient EDFA performance prediction for next-generation optical networks. Full article

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38 pages, 9959 KiB

Open AccessArticle

Application of Carbon-Fiber-Reinforced Polymer Rods and Ultra-High-Performance Fiber-Reinforced Concrete Jackets with Mechanical Anchorage Systems to Reinforced Concrete Slabs

by Firas Hassan Saeed and Farzad Hejazi

Fibers 2025, 13(3), 33; https://doi.org/10.3390/fib13030033 - 13 Mar 2025

Abstract

The aim of this experimental study was to develop and evaluate the effectiveness of a new strengthening system for reinforced concrete slabs employing external jackets consisting of ultra-high-performance fiber-reinforced-concrete (UHPFRC) and mechanical anchor systems. The issue of debonding between old and fresh concrete [...] Read more.

The aim of this experimental study was to develop and evaluate the effectiveness of a new strengthening system for reinforced concrete slabs employing external jackets consisting of ultra-high-performance fiber-reinforced-concrete (UHPFRC) and mechanical anchor systems. The issue of debonding between old and fresh concrete layers, as well as the efficiency of utilizing CFRP rods, is the primary challenge of applying the UHPFRC jackets with embedded CFRP rods. In this study, we propose a novel retrofitting technique for implementing a mechanical anchor system to improve the binding of fresh UHPFRC jackets with old RC slabs. An experimental test was conducted by subjecting three slabs to cyclic loads by utilizing a dynamic actuator: a reference slab, a retrofitted slab with an external UHPFRC layer, and a retrofitted slab with an external UHPFRC layer incorporating CFRP bars. Furthermore, finite element models (FEMs) were utilized to investigate the responses of the retrofitted slabs and compare the novel method with traditional strengthening techniques, including near-surface-mounted (NSM) CFRP rods, externally bonded CFRP strips, and epoxy-bonded UHPFRC jackets, as well as two models that were the same as the experimental strengthened slab specimens except for the fact that they did not have a mechanical anchor system. Additionally, analytical mechanistic models were employed to determine the flexural moment capacity of the RC slabs. The experimental findings demonstrated that the proposed strengthening strategy considerably prevented premature debonding and enhanced the maximum load of retrofitted RC slabs by over 82%. Also, the FEM and analytical results are significantly consistent with the experimental outcomes. In conclusion, the newly suggested strengthening technique is a reliable system for enhancing the efficacy of slabs, effectively preventing early debonding between existing and new components. Full article

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16 pages, 5970 KiB

Open AccessArticle

Advanced Vibration of Functionally Graded Material Coupled Plates and Circular Shells with Four Layers

by Chih-Chiang Hong

Fibers 2025, 13(3), 32; https://doi.org/10.3390/fib13030032 - 12 Mar 2025

Abstract

This study is based on typical thermal studies on thick, functionally graded material (FGM)-coupled plates and circular shells. Numerical studies have been previously published by researchers on the linear first-order shear deformation theory (FSDT) model for thin-thickness and two-layer materials. The present relationship [...] Read more.

This study is based on typical thermal studies on thick, functionally graded material (FGM)-coupled plates and circular shells. Numerical studies have been previously published by researchers on the linear first-order shear deformation theory (FSDT) model for thin-thickness and two-layer materials. The present relationship was further studied by the author on the nonlinear third-order shear deformation theory (TSDT) model for thick-thickness and four-layer FGMs. The material properties of FGM layers deal with the effect of temperature. The novelty of this study is in its further consideration of four layers of FGMs and the non-dimensional shear coefficient. The stiffness and stiffness integrals of the four layers are studied. The material properties in the power law expression of the functions of the four layers are assumed for the first time. Under the conditions of a time sinusoidal, varied thermal loads and simply supported conditions for four layers are studied. Parametric case studies involving temperature, the standard power law form of the index, and the nonlinear term of the displacement theory and shear coefficient for the dynamic stresses and displacements are obtained and presented. Full article

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15 pages, 4088 KiB

Open AccessArticle

Durable Hydrophilic PVDF Hollow Fiber Membrane for Dissolved Organics Separation from High-Salinity Produced Water

by Samuel Oppong, Zongjie He, Gabriela Torres Fernandez, Guoyin Zhang and Jianjia Yu

Fibers 2025, 13(3), 31; https://doi.org/10.3390/fib13030031 - 11 Mar 2025

Abstract

Organic compounds are major constituents in produced water that have gained increasing attention due to their negative impacts on operations and the environment. In this study, a novel hydrophilic polyvinylidene fluoride (PVDF) hollow fiber (HF) membrane was formulated and fabricated for organics separation [...] Read more.

Organic compounds are major constituents in produced water that have gained increasing attention due to their negative impacts on operations and the environment. In this study, a novel hydrophilic polyvinylidene fluoride (PVDF) hollow fiber (HF) membrane was formulated and fabricated for organics separation (OS) from oilfield-produced water. The PVDF dope solution was formulated with lithium chloride (LiCl) and polyvinylpyrrolidone (PVP) as synergistic pore agents, and the obtained PVDF HF membranes showed a defect-free asymmetric structure with a stable hydrophilicity. The OS performance was studied in terms of permeate water flux, OS efficiency, and long-term membrane stability using both decanoic acid and real produced water as feed solutions. Specifically, the effects of operating parameters, such as pressure, total organic carbon (TOC), pH, and salinity, on the OS performance were examined in decanoic acid solution. The long-term membrane stability was evaluated through a 60 h continuous OS experiment using real produced water as the feed solution. The used membrane was thoroughly characterized to understand both scaling and fouling phenomena during the OS operation. The results indicated that the membranes showed promising permeate water flux (>500 kg/m²/h at 350 kPa) and OS efficiency (>92%). It also exhibited a near-100% recovery of organics separation efficiency during six cyclic OS experiments due to consistent membrane hydrophilicity. Full article

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