Fibers

19 pages, 2652 KiB

Open AccessArticle

The Effects of Polypropylene Fibres on the Shear Behaviour of a Concrete Crack: An Experimental Study

by Francisco Ortiz-Navas, Juan Navarro-Gregori and Pedro Serna

Fibers 2025, 13(7), 96; https://doi.org/10.3390/fib13070096 - 11 Jul 2025

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The objective of this study is to investigate the effects of macrosynthetic polypropylene fibres as shear reinforcement in a concrete crack. An experimental study was conducted using twenty push-off specimens with varying volumes of fibres, along with plain concrete specimens as a reference. [...] Read more.

The objective of this study is to investigate the effects of macrosynthetic polypropylene fibres as shear reinforcement in a concrete crack. An experimental study was conducted using twenty push-off specimens with varying volumes of fibres, along with plain concrete specimens as a reference. The testing methodology allowed for the analysis of crack kinematics by measuring the evolution of normal and shear stresses in relation to slip and crack opening. This facilitated the creation of diagrams similar to those presented by Walraven (1980) for crack interface shear transfer, but in this case, applied to concrete reinforced with macrosynthetic polypropylene fibres. The findings demonstrate that macrosynthetic polypropylene fibres significantly enhance shear behaviour, particularly when their volume exceeds 8 kg/m³. This study provides valuable insights into the behaviour of macrosynthetic polypropylene fibres under shear loading conditions and highlights their potential benefits as effective shear reinforcement. Full article

(This article belongs to the Special Issue Fracture Behavior of Fiber-Reinforced Building Materials)

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20 pages, 5375 KiB

Open AccessArticle

Quality of Plywood Bonded with Nanolignin-Enriched Cardanol-Formaldehyde Adhesive

by Maria Rita Ramos Magalhães, Felipe Gomes Batista, Ana Carolina Corrêa Furtini, Mário Vanoli Scatolino, Flávia Maria Silva Brito, Lourival Marin Mendes, Thiago de Paula Protásio and José Benedito Guimarães Junior

Fibers 2025, 13(7), 95; https://doi.org/10.3390/fib13070095 - 10 Jul 2025

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Abstract

Cardanol is a derivative of cashew nut shell liquid (CNSL) and has the potential to be used when developing adhesives for wood boards. Adding nanostructures to adhesive can increase its bonding and reduce formaldehyde emission. Therefore, this study aimed to evaluate the different [...] Read more.

Cardanol is a derivative of cashew nut shell liquid (CNSL) and has the potential to be used when developing adhesives for wood boards. Adding nanostructures to adhesive can increase its bonding and reduce formaldehyde emission. Therefore, this study aimed to evaluate the different concentrations of nanolignin (1, 2, and 3%) added to the cardanol-formaldehyde adhesive for gluing plywood, in comparison to the cardanol-formaldehyde adhesive without nanolignin (0%). The plywood’s physical, mechanical, and formaldehyde emission properties were assessed. Plywoods with nanolignin showed shear strength increases of around 160% in the wet condition. With the addition of nanolignin, the modulus of rupture and of elasticity increased by approximately 150% and up to 400% in the parallel direction, respectively. The resistance to combustion also significantly improved. Physical properties did not show statistically significant differences with the percentages of nanolignin. Despite the increase in formaldehyde emission with nanolignin, all treatments met the marketing requirements (≤80 mg of formaldehyde/kg), demonstrating the adhesive potential for indoor use in plywood industries. Natural adhesives using cardanol and nanolignin are an innovative and ecological alternative, combining sustainability and high potential to reduce environmental impacts, which is aligned with at least four sustainable development goals (SDGs). Full article

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14 pages, 7615 KiB

Open AccessArticle

Electrospun Silk Fibroin/Cyclodextrin Nanofibers for Multifunctional Air Filtration

by Papimol Mongyun and Sompit Wanwong

Fibers 2025, 13(7), 94; https://doi.org/10.3390/fib13070094 - 8 Jul 2025

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Abstract

Particulate matter (PM) and volatile organic compounds (VOCs) are major air pollutants that can cause significant risks to public health. To mitigate exposure, fibrous filters have been widely utilized for air purification. In this study, we developed electrospun silk fibroin/poly (ethylene oxide)/cyclodextrin (SF/PEO/CD) [...] Read more.

Particulate matter (PM) and volatile organic compounds (VOCs) are major air pollutants that can cause significant risks to public health. To mitigate exposure, fibrous filters have been widely utilized for air purification. In this study, we developed electrospun silk fibroin/poly (ethylene oxide)/cyclodextrin (SF/PEO/CD) nanofibers as multifunctional air filters capable of efficiently reducing PM_2.5 and degrading VOCs. The resulting SF/PEO/10CD demonstrated the best multifunctional filtration performance, achieving PM_2.5 capture efficiencies of 91.3% with a minimal pressure drop of 4 Pa and VOC removal efficiency of 50%. These characteristics highlight the potential of the SF/PEO/10CD nanofiber with effective, multifunctional properties and environmental benefits for sustainable air filtration application. Full article

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14 pages, 3260 KiB

Open AccessArticle

Performance of Hybrid Strengthening System for Reinforced Concrete Member Using CFRP Composites Inside and over Transverse Groove Technique

by Ahmed H. Al-Abdwais and Adil K. Al-Tamimi

Fibers 2025, 13(7), 93; https://doi.org/10.3390/fib13070093 - 8 Jul 2025

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Abstract

The use of a carbon-fiber-reinforced polymer (CFRP) for structural strengthening has been widely adopted in recent decades. Early studies focused on externally bonded (EB) techniques, but premature delamination of CFRP from concrete surfaces often limited their efficiency. To address this, alternative methods, such [...] Read more.

The use of a carbon-fiber-reinforced polymer (CFRP) for structural strengthening has been widely adopted in recent decades. Early studies focused on externally bonded (EB) techniques, but premature delamination of CFRP from concrete surfaces often limited their efficiency. To address this, alternative methods, such as Externally Bonded Reinforcement Over Grooves (EBROG) and Externally Bonded Reinforcement Inside Grooves (EBRIG), were developed to enhance the bond strength and delay delamination. While most research has examined longitudinal groove layouts, this study investigates a hybrid system combining a CFRP fabric bonded inside transverse grooves (EBRITG) with externally bonded layers over the grooves (EBROTG). The system leverages the grooves’ surface area to anchor the CFRP and improve the bonding strength. Seven RC beams were tested in two stages: five beams with varied strengthening methods (EBROG, EBRIG, and hybrid) in the first stage and two beams with a hybrid system and concrete cover anchorage in the second stage. Results demonstrated significant flexural capacity improvement—57% and 72.5% increase with two and three CFRP layers, respectively—compared to the EBROG method, confirming the hybrid system’s superior bonding efficiency. Full article

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13 pages, 2665 KiB

Open AccessArticle

Kapok-Derived Super Hollow Porous Carbon Fibers and Their Greenhouse Gases Adsorption

by Hun-Seung Jeong, Cheol-Ki Cho, Dong-Chul Chung, Kay-Hyeok An and Byung-Joo Kim

Fibers 2025, 13(7), 92; https://doi.org/10.3390/fib13070092 - 4 Jul 2025

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Abstract

Industrialization and modernization have significantly improved the quality of life but have also led to substantial pollution. Cost-effective technologies are urgently needed to mitigate emissions from major polluting sectors, such as the automotive and transport industries. In this study, we synthesized naturally derived, [...] Read more.

Industrialization and modernization have significantly improved the quality of life but have also led to substantial pollution. Cost-effective technologies are urgently needed to mitigate emissions from major polluting sectors, such as the automotive and transport industries. In this study, we synthesized naturally derived, kapok-based porous carbon fibers (KP-PCFs) with hollow structures. We investigated their adsorption/desorption behavior for the greenhouse gas n-butane following ASTM D5228 standards. Scanning electron microscopy and X-ray diffraction analyses were conducted to examine changes in fiber diameter and crystalline structure under different activation times. The micropore properties of KP-PCFs were characterized using Brunauer–Emmett–Teller, t-plot, and non-localized density functional theory models based on N₂/77K adsorption isotherm data. The specific surface area and total pore volume ranged from 500 to 1100 m²/g and 0.24 to 0.60 cm³/g, respectively, while the micropore and mesopore volumes were 0.20–0.45 cm³/g and 0.04–0.15 cm³/g, respectively. With increasing activation time, the n-butane adsorption capacity improved from 62.2% to 73.5%, whereas retentivity (residual adsorbate) decreased from 6.0% to 1.3%. The adsorption/desorption rate was highly correlated with pore diameter: adsorption capacity was highest for diameters of 1.5–2.5 nm, while retentivity was greatest for diameters of 3.5–5.0 nm. Full article

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14 pages, 4803 KiB

Open AccessArticle

Developing JMP and VBA Add-Ins for Finite Mixture Modeling of Cotton Fiber Length Distribution

by Mourad Krifa, Vinusha Garlapati, Vikki B. Martin and Neha Kothari

Fibers 2025, 13(7), 91; https://doi.org/10.3390/fib13070091 - 2 Jul 2025

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Abstract

In this study, software add-ins were developed and presented to allow data processing and statistical analysis of the unique shape of cotton fiber length distribution. The approach uses VBA coding in Excel to process the data, as well as the JMP 14-17 application [...] Read more.

In this study, software add-ins were developed and presented to allow data processing and statistical analysis of the unique shape of cotton fiber length distribution. The approach uses VBA coding in Excel to process the data, as well as the JMP 14-17 application and add-in builder tools to fit finite mixture models to empirical fiber length distributions. The resulting model derives a parametric expression for the fiber length probability density function. The analysis add-in was applied and validated on a wide range of empirical length distributions and proved to parameterize the complex distribution patterns with an excellent goodness of fit. Both tools were compiled into installable add-ins that extended the capabilities of MS Excel for the processing of AFIS distribution reports and the statistical toolbox of JMP using the Application Builder JSL coding. Installable add-ins, along with a user manual, are available for download by cotton researchers. Full article

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18 pages, 2909 KiB

Open AccessArticle

Recycling Particleboard by Acid Hydrolysis: Effects on the Physical, Thermal, and Chemical Characteristics of Recycled Wood Particles

by Gustavo E. Rodríguez, Rosilei Garcia and Alain Cloutier

Fibers 2025, 13(7), 90; https://doi.org/10.3390/fib13070090 - 2 Jul 2025

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Abstract

Acid hydrolysis can be more efficient than water hydrolysis, particularly in breaking down cured adhesives found in waste panels within a shorter reaction time, which could benefit large-scale industrial processes. This study evaluates the effects of various acid hydrolysis conditions on the thermal, [...] Read more.

Acid hydrolysis can be more efficient than water hydrolysis, particularly in breaking down cured adhesives found in waste panels within a shorter reaction time, which could benefit large-scale industrial processes. This study evaluates the effects of various acid hydrolysis conditions on the thermal, physical, and chemical properties of recycled particles intended for particleboard production. Particleboards were recycled using oxalic acid and ammonium chloride at different concentrations and reaction times at 122 °C. The thermal stability of the particles was determined by thermogravimetric analysis. Particle size distribution, particle morphology, nitrogen content, pH and acid/base buffer capacity were analyzed. The effect of the recycled particles on the urea-formaldehyde (UF) curing was assessed using differential scanning calorimetry and the gel time method. The recycled particles exhibited a higher thermal degradation beyond 200 °C, indicating their thermal stability for manufacturing new panels. The acid treatments did not damage the anatomical structure of the particles, preserving the prosenchymatous elements. The nitrogen content of recycled particles decreased by up to 90% when oxalic acid was used, compared to raw board particles. Recycled particles exhibited a lower pH, with a maximum reduction of 44%. They also showed a decreased acid buffer capacity and an increased base buffer capacity compared to raw board particles. This effect was particularly pronounced in treatments that included ammonium chloride. The recycled particles did not significantly affect the peak polymerization temperature of the UF adhesive. However, some treatments affected the gel time of the adhesive, particularly those using 30% ammonium chloride. The results indicate that particleboards can be effectively recycled through acid hydrolysis, mainly with oxalic acid, which provides better results than hydrolysis using water alone. Oxalic acid showed increased selectivity in eliminating the cured UF adhesive, resulting in recycled particles suitable for manufacturing new panels. Full article

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20 pages, 5421 KiB

Open AccessArticle

Influence of Encapsulation Size and Textile Integration Techniques on the Wash Durability of Textiles with Integrated Electronic Yarn

by Arash M. Shahidi, Parvin Ebrahimi, Kalana Marasinghe, Tharushi Peiris, Zahra Rahemtulla, Carlos Oliveira, Dominic Eberl-Craske, Tilak Dias and Theo Hughes-Riley

Fibers 2025, 13(7), 89; https://doi.org/10.3390/fib13070089 - 2 Jul 2025

Viewed by 550

Abstract

A crucial factor when developing e-textiles is ensuring their robustness and functionality during everyday activities, particularly washing. The ability to launder e-textile garments is not merely a matter of convenience but a necessity for widespread adoption. Incorporating electronics into textiles can lead to [...] Read more.

A crucial factor when developing e-textiles is ensuring their robustness and functionality during everyday activities, particularly washing. The ability to launder e-textile garments is not merely a matter of convenience but a necessity for widespread adoption. Incorporating electronics into textiles can lead to damage due to mechanical and chemical stresses, which most electronics are not designed to withstand. This work focuses on electronic yarn technology (e-yarn), in which electronic functionality is added to textiles by embedding small electronic components into a flexible yarn-like structure. First, the component is soldered onto thin conductive wires. The soldered component is then enclosed in a protective polymer resin (micro-pod). Micro-pods have different diameters depending on the size of the embedded electronic component. The ensemble is finally covered in a textile sheath. This study focuses on the wash durability of e-yarns integrated with textiles in three different ways: embroidered onto the surface of a woven fabric, within a knitted channel in a knitted fabric, and woven as a weft yarn. Further, the work studied the impact of using different sizes of micro-pods on the e-yarns’ wash durability. Ultimately, good wash durability was observed under all testing conditions. Full article

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19 pages, 1844 KiB

Open AccessArticle

Embedding 1D Euler Beam in 2D Classical Continua

by Armine Ulukhanyan, Luca Placidi, Anil Misra, Roberto Fedele, Raimondo Luciano and Francesco Fabbrocino

Fibers 2025, 13(7), 88; https://doi.org/10.3390/fib13070088 - 1 Jul 2025

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Abstract

In this contribution, the classical Cauchy first-gradient elastic theory is used to solve the equilibrium problem of a bidimensional (2D) reinforced elastic structure under small displacements and strains. Such a 2D first-gradient continuum is embedded with a reinforcement, which is modeled as a [...] Read more.

In this contribution, the classical Cauchy first-gradient elastic theory is used to solve the equilibrium problem of a bidimensional (2D) reinforced elastic structure under small displacements and strains. Such a 2D first-gradient continuum is embedded with a reinforcement, which is modeled as a zero-thickness interface endowed with the elastic properties of an extensional Euler–Bernoulli 1D beam. Modeling the reinforcement as an interface eliminates the need for a full geometric representation of the reinforcing bar with finite thickness in the 2D model, and the associated mesh discretization for numerical analysis. Thus, the effects of the 1D beam-like reinforcements are described through proper and generalized boundary conditions prescribed to contiguous continuum regions, deduced from a standard variational approach. The novelty of this work lies in the formulation of an interface model coupling 1D and 2D continua, based on weak formulation and variational derivation, capable of accurately capturing stress distributions without requiring full geometric resolution of the reinforcement. The proposed framework is therefore illustrated by computing, with finite element simulations, the response of the reinforced structural element under uniform bending. Numerical results reveal the presence of jumps for some stress components in the vicinity of the reinforcement tips and demonstrate convergence under mesh refinement. Although the reinforcement beams possess only axial stiffness, they significantly influence the equilibrium configuration by causing a redistribution of stress and enhancing stress transfer throughout the structure. These findings offer a new perspective on the effective modeling of fiber-reinforced structures, which are of significant interest in engineering applications such as micropiles in foundations, fiber-reinforced concrete, and advanced composite materials. In these systems, stress localization and stability play a critical role. Full article

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16 pages, 2046 KiB

Open AccessArticle

Physical and Mechanical Characterization of Flax Fibers: From Elementary Fiber to Yarn

by Wafa Mahjoub and Omar Harzallah

Fibers 2025, 13(7), 87; https://doi.org/10.3390/fib13070087 - 30 Jun 2025

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Abstract

This study presents a multiscale characterization of flax fibers, from elementary fibers to technical bundles and yarns, to elucidate how fiber scale attributes influence yarn mechanics. Four yarn counts (111.11 tex, 100 tex, 90.9 tex, and 83.33 tex) were produced via dry spinning, [...] Read more.

This study presents a multiscale characterization of flax fibers, from elementary fibers to technical bundles and yarns, to elucidate how fiber scale attributes influence yarn mechanics. Four yarn counts (111.11 tex, 100 tex, 90.9 tex, and 83.33 tex) were produced via dry spinning, and tensile testing performed at each structural level. The results revealed a progressive decline in a specific modulus from elementary fibers (1.09 ± 0.62 N/tex) to short bundles (14.41 ± 9.59 N/tex), primarily due to fiber misalignment. Post hoc analysis confirmed that finer yarns (83.33 tex) exhibited higher stiffness (7.32 ± 1.69 N/tex, p < 0.001), attributed to advanced processing (GN4 combing). These findings highlight the critical role of fiber length and alignment in optimizing flax yarns for high-performance textiles. Full article

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23 pages, 9679 KiB

Open AccessArticle

Structure and Crystallization of Even–Odd Nylons Derived from Pimelic Acid: Influence of the Number of Methylene Groups in the Diamine Unit

by Matteo Arioli, Lourdes Franco and Jordi Puiggalí

Fibers 2025, 13(7), 86; https://doi.org/10.3390/fib13070086 - 27 Jun 2025

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Abstract

Nylons 6,7, 8,7 and 10,7 have been synthesized by interfacial polycondensation and characterized. Thermal properties and thermally induced structural transitions have been evaluated to complement the reported data on nylon 4,7. Therefore, the complete even–odd series derived from pimelic acid is here fully [...] Read more.

Nylons 6,7, 8,7 and 10,7 have been synthesized by interfacial polycondensation and characterized. Thermal properties and thermally induced structural transitions have been evaluated to complement the reported data on nylon 4,7. Therefore, the complete even–odd series derived from pimelic acid is here fully characterized, in order to insist on their peculiar structural polymorphism. Real-time WAXD synchrotron experiments were conducted during heating, cooling and reheating processes. Basically, three structures were involved: a modified α-form, a distorted pseudohexagonal form and a pseudohexagonal form. The modified α-form was stable up to relatively low temperatures (i.e., lower than 140 °C), was mainly produced by solution crystallization and was progressively disfavored when the number of methylene groups of the diamine moiety increased. A progressive transition from the modified α-form to the distorted pseudohexagonal structure was observed during heating. Also, a continuous reverse transition was detected on cooling, although the yield on the modified α-form was low. A Brill transition towards a pseudohexagonal structure was observed in all cases. This transition was reversible, although with some hysteresis degree. Oriented fiber patterns corresponding to the distorted pseudohexagonal structure were obtained by melt stretching. In all cases, the 00l reflections appeared with a meridional orientation and indicated a shortening close to 0.05 nm/amide group with respect to the expected values for fully extended conformations. Full article

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11 pages, 2369 KiB

Open AccessArticle

The Effect of a Carbon Fiber Layer Between the Cathode and the Current Collector on Battery Cell Performance

by Jaswinder Sharma, Runming Tao, Georgios Polizos, Ruhul Amin, Yue Feng, Junbin Choi, M. Shahriar and Jianlin Li

Fibers 2025, 13(7), 85; https://doi.org/10.3390/fib13070085 - 27 Jun 2025

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Abstract

Contact resistance between the cathode active material (CAM) and the Al current collector can be reduced by applying carbon coatings to the Al current collector surface. However, this process requires an additional step of carbon layer coating on the current collector, which increases [...] Read more.

Contact resistance between the cathode active material (CAM) and the Al current collector can be reduced by applying carbon coatings to the Al current collector surface. However, this process requires an additional step of carbon layer coating on the current collector, which increases both manufacturing costs and processing time. In the present work, an interlayer of continuous unsized carbon fibers aligned in one direction (CF interlayer), is introduced between the Al current collector and the NMC811 cathode during cathode deposition on the Al current collector. This single-step approach eliminates the need for the additional carbon layer coating on the current collector. Additionally, this approach removes the use of toxic solvents and insulative polymers used for making the carbon coating. The CF interlayer improves the rate capability at higher C-rates. The CF interlayer lowers the contact resistance between the cathode particles and the current collector while improving the activation energy of charge transfer. The peel test showed that the CF interlayer does not affect the adhesion strength of the cathode layer with the current collector. Full article

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35 pages, 10135 KiB

Open AccessArticle

Constitutive Model for Plain and Steel-Fibre-Reinforced Lightweight Aggregate Concrete Under Direct Tension and Pull-Out

by Hasanain K. Al-Naimi and Ali A. Abbas

Fibers 2025, 13(7), 84; https://doi.org/10.3390/fib13070084 - 23 Jun 2025

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Abstract

In the present study, a programme of experimental investigations was carried out to examine the direct uniaxial tensile (and pull-out) behaviour of plain and fibre-reinforced lightweight aggregate concrete. The lightweight aggregates were recycled from fly ash waste, also known as Pulverised Fuel Ash [...] Read more.

In the present study, a programme of experimental investigations was carried out to examine the direct uniaxial tensile (and pull-out) behaviour of plain and fibre-reinforced lightweight aggregate concrete. The lightweight aggregates were recycled from fly ash waste, also known as Pulverised Fuel Ash (PFA), which is a by-product of coal-fired electricity power stations. Steel fibres were used with different aspect ratios and hooked ends with single, double and triple bends corresponding to 3D, 4D and 5D types of DRAMIX steel fibres, respectively. Key parameters such as the concrete compressive strength f_lck, fibre volume fraction V_f, number of bends n_b, embedded length L_E and inclination angle ϴ_f were considered. The fibres were added at volume fractions V_f of 1% and 2% to cover the practical range, and a direct tensile test was carried out using a purpose-built pull-out test developed as part of the present study. Thus, the tensile mechanical properties were established, and a generic constitutive tensile stress–crack width σ-ω model for both plain and fibrous lightweight concrete was created and validated against experimental data from the present study and from previous research found in the literature (including RILEM uniaxial tests) involving different types of lightweight aggregates, concrete strengths and steel fibres. It was concluded that the higher the number of bends n_b and the higher the volume fraction V_f and concrete strength f_lck, the stronger the fibre–matrix interfacial bond and thus the more pronounced the enhancement provided by the fibres to the uniaxial tensile residual strength and ductility in the form of work and fracture energy. A fibre optimisation study was also carried out, and design recommendations are provided. Full article

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Fibers, Volume 13, Issue 7 (July 2025) – 13 articles

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