Fibers

Open AccessArticle

Multimode Graded Index Fiber with Random Array of Bragg Gratings and Its Raman Lasing Properties

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Alexey G. Kuznetsov

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Alexey A. Wolf

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Zhibzema E. Munkueva

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Alexander V. Dostovalov

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Sergey A. Babin

Fibers 2023, 11(6), 48; https://doi.org/10.3390/fib11060048 - 24 May 2023

Abstract

Light propagation in multimode fibers is known to experience various nonlinear effects, which are being actively studied. One of the interesting effects is the brightness enhancement at the Raman conversion of the multimode beam in graded index (GRIN) fiber due to beam cleanup [...] Read more.

Light propagation in multimode fibers is known to experience various nonlinear effects, which are being actively studied. One of the interesting effects is the brightness enhancement at the Raman conversion of the multimode beam in graded index (GRIN) fiber due to beam cleanup at Raman amplification and mode selective feedback in the Raman laser cavity based on fiber Bragg gratings (FBGs) with special transverse structure. It is also possible to explore random distributed feedback based on Rayleigh backscattering on natural refractive index fluctuations in GRIN fibers, but it is rather weak, requiring very high power multimode pumping for random lasing. Here, we report on the first realization of femtosecond pulse-inscribed arrays of weak randomly spaced FBGs in GRIN fibers and study Raman lasing at its direct pumping by highly multimode (M²~34) 940-nm laser diodes. The fabricated 1D–3D FBG arrays are used as a complex output mirror, together with the highly reflective input FBG in 1-km fiber. Above threshold pump power (~100 W), random lasing of the Stokes beam at 976 nm is obtained with output power exceeding 28 W at 174 W pumping. The beam quality parameter varies for different arrays, reaching M²~2 at the linewidth narrowing to 0.1–0.2 nm due to the interference effects, with the best characteristics for the 2D array. Full article

(This article belongs to the Special Issue Multimode Nonlinear Optical Fibers)

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Open AccessArticle

The Exothermic Effects of Textile Fibers during Changes in Environmental Humidity: A Comparison between ISO:16533 and Dynamic Hot Plate Test Method

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Faisal Abedin

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Emiel DenHartog

Fibers 2023, 11(5), 47; https://doi.org/10.3390/fib11050047 - 22 May 2023

Abstract

The exothermic effects of high regain fiber types have been described before; yet, there have not been reliable tests to demonstrate these effects on the human body. Most test methods focus on steady-state measurements; therefore, these exothermic effects during changes in environmental humidity [...] Read more.

The exothermic effects of high regain fiber types have been described before; yet, there have not been reliable tests to demonstrate these effects on the human body. Most test methods focus on steady-state measurements; therefore, these exothermic effects during changes in environmental humidity are typically not analyzed or quantified. We have conducted a set of fabric tests that shows the connection between the exothermic effect of water vapor uptake and its consequence for heat loss through the fabric in transient conditions. We have performed the ISO:16533 standard test, a dynamic hot plate test developed by Naylor to measure the exothermic property of the fabric, and dynamic regain tests to connect the dots between these tests and the water vapor uptake phenomenon. Although the ISO:16533 test method tends to show the temperature increase in fibers, it cannot differentiate between the hygroscopic fiber (wool, viscose, cotton) types (p > 0.001). In addition, sensor size and sample folding techniques could impact the temperature increase. On the other hand, the Naylor hot plate test showed a greater difference in heat release among the fiber types (wool showed 20% higher heat release than viscose, 50% more than cotton), although the relative humidity changes in the chamber take time, which might not reflect a step-wise change in humidity. So far, these test methods have proven to be the most reliable for determining the exothermic behavior of textile fiber. However, these test methods still have limitations and cannot simulate realistic environmental conditions considering an instantaneous change in the environment. This paper reflects the comparison between the two test methods and recommends directions to accurately address the theory of water vapor uptake under dynamic conditions. Full article

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Open AccessArticle

High-Temperature Behavior of Polyethylene-Terephthalate-Fiber-Reinforced Sand Concrete: Experimental Investigation

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Fibers 2023, 11(5), 46; https://doi.org/10.3390/fib11050046 - 16 May 2023

Abstract

At ambient temperature, concrete exhibits excellent mechanical properties. However, understanding the behavior of concrete under high-temperature conditions is crucial, especially for civil engineering applications during fire incidents. The growing use of plastic-based products has led to a significant increase in polymer waste, posing [...] Read more.

At ambient temperature, concrete exhibits excellent mechanical properties. However, understanding the behavior of concrete under high-temperature conditions is crucial, especially for civil engineering applications during fire incidents. The growing use of plastic-based products has led to a significant increase in polymer waste, posing environmental challenges. The valorization of this plastic waste in the form of fibers presents both economic and environmental advantages. This study focuses on the study of the behavior of sand concrete incorporating polyethylene terephthalate (PET) fibers with percentages of 1% and 2% at high temperatures (100, 300, 500 and 700 °C). Specimens are tested for residual mass loss, residual compressive and tensile strength. A complementary analysis of SEM makes it possible to confirm and better clarify the morphology of the concretes of sand before and after the rise in temperature. The results obtained from this study indicate that the residual resistance is reduced with the rise in temperature for all the concretes studied, except in the temperature range of 300 °C, in which a slight improvement in resistance is noticed. The incorporation of PET fibers in the test concretes does not enhance their residual behavior significantly. However, it does serve as an effective solution by reducing the susceptibility to spalling, by preventing cracking and by fulfilling a similar role to that of polypropylene fibers. Full article

(This article belongs to the Special Issue The Use of Fibers in the Field of Structural and Earthquake Engineering: Experimental Measurements and Numerical Simulations)

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Open AccessArticle

Elementary Liber Fibres Characterisation: Bias from the Noncylindricity and Morphological Evolution along the Fibre

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Marie Grégoire

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Emmanuel De Luycker

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Pierre Ouagne

Fibers 2023, 11(5), 45; https://doi.org/10.3390/fib11050045 - 15 May 2023

Abstract

In this work, we investigate the influence of noncircularity along with cross-sectional area evolution on the measurement of the mechanical properties of elementary fibres. First, we focus on the cross-sectional area measurement and compare the circular assumption with the elliptical one using an [...] Read more.

In this work, we investigate the influence of noncircularity along with cross-sectional area evolution on the measurement of the mechanical properties of elementary fibres. First, we focus on the cross-sectional area measurement and compare the circular assumption with the elliptical one using an ombroscopic device that allows the measurement of the projected diameters along the fibre as the fibre rotates around its axis, the fibre dimensional analysis system (FDAS). The results highlight important approximations to the cross-sectional area evaluation for fibres with noncircular cross sections, leading to reduced elastic modulus and stress at failure evaluated by the standard method. Additionally, results from the FDAS are used to evaluate the twist inside an individual fibre when the cross sections are sufficiently elliptical. A numerical model based on the real measured dimensions of the fibres is developed to illustrate and visualize this nonuniformity and to more accurately identify the elastic modulus. The results obtained lead us to an analytical approach that takes into account the evolution of the cross-sectional area along the fibre for a better identification of the stiffness and modulus of elasticity, which maximizes the identified mechanical properties on average by 12% for the modulus and 200% for the stress at failure. Finally, recommendations are formulated to better account for the variability along a fibre in order to evaluate the cross-sectional area. Full article

(This article belongs to the Special Issue Fiber Composite Process)

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Open AccessArticle

Advanced Study of Columns Confined by Ultra-High-Performance Concrete and Ultra-High-Performance Fiber-Reinforced Concrete Confinements

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Rr. M. I. Retno Susilorini

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Yuliarti Kusumawardaningsih

Fibers 2023, 11(5), 44; https://doi.org/10.3390/fib11050044 - 10 May 2023

Abstract

The need for concrete with ‘super’ strength and ‘super’ ductility for greater sustainability has been answered by the existence of ultra-high-performance concrete (UHPC) and ultra-high-performance fiber-reinforced concrete (UHPFRC). Over the last decades, UHPFRC has been implemented in actual concrete structures, as well as [...] Read more.

The need for concrete with ‘super’ strength and ‘super’ ductility for greater sustainability has been answered by the existence of ultra-high-performance concrete (UHPC) and ultra-high-performance fiber-reinforced concrete (UHPFRC). Over the last decades, UHPFRC has been implemented in actual concrete structures, as well as used to retrofit structural elements, including columns. However, the use of UHPC and UHPFRC confinement to strengthen normal concrete columns is still limited. Therefore, this research aims to investigate the advanced performance of columns using UHPC and UHPFRC confinement in the context of the strength and ductility of such columns, such as load capacity, stress–strain behavior, and the crack pattern in the failure mode. This research is an advanced study of several investigations previously carried out by other authors on the characteristics of UHPC and UHPFRC, as well as columns confined by UHPC and UHPFRC. The methods used in this research are experimental and analytical. The experimental results were compared to analytical calculations for validation. This research produced 12 short-column specimens confined by UHPC (CF0 series) and UHPFRC (CF1 and CF2 series) that contained 0%, 1%, and 2% fiber and were also tested for axial loading and various eccentricities as follows: e = 0, 35, and 70 mm. The results found that the normal strength concrete (NSC) columns confined by UHPC and UHPFRC could sustain a higher maximum load and stress, and also sustain greater vertical deformation and strain compared to the control specimens. It was noted that specimen CF2-35 had the highest load capacity, vertical deformation, maximum stress, and maximum vertical strain compared to specimen C-0 (control column with no confinement). The specimen CF2-35 (column confined by UHPC with a 2% fiber volume with an eccentricity of 35 mm) also exhibited a ductile failure mode and very minor cracks. It was also found that 75% of the specimens had 0–39% errors and 25% had 0–13% errors. The research proved that the addition of a volume of 2% fiber to the UHPFRC minimizes the crack of the failure mode and prevents confinement spalling of the column. This research has led to the conclusion that UHPC and UHPFRC confinements will increase the strength and ductility of columns. Full article

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Open AccessReview

Targeted Pre-Treatment of Hemp Fibers and the Effect on Mechanical Properties of Polymer Composites

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Fibers 2023, 11(5), 43; https://doi.org/10.3390/fib11050043 - 09 May 2023

Abstract

Research on plant-fiber-reinforced composites has gained significant research interest since it generates composites with exceptional mechanical properties; however, the potential of hemp fibers can only be fully exploited if the fibers are well separated from the bundle to achieve cellulose-rich fibers. This is [...] Read more.

Research on plant-fiber-reinforced composites has gained significant research interest since it generates composites with exceptional mechanical properties; however, the potential of hemp fibers can only be fully exploited if the fibers are well separated from the bundle to achieve cellulose-rich fibers. This is because well-separated bast fibers that are long and exhibit higher fiber aspect ratio enhance the mechanical properties of the composite by influencing property translations upon loading. A key feature for successful implementation of natural fibers is to selectively remove non-cellulosic components of hemp fiber to yield cellulose-rich fibers with minimal defects. Targeted pre-treatment techniques have been commonly used to address the aforementioned concerns by optimizing properties on the fiber’s surface. This in turn improves interfacial bonding between the fibers and the hydrophobic polymer, enhances the robustness of hemp fibers by improving their thermal stability and increases resistance to microbial degradation. In this study, we comprehensively review the targeted pre-treatment techniques of hemp fiber and the effect of hemp fiber as a reinforcement on the mechanical properties of polymeric composites. Full article

(This article belongs to the Special Issue Fibers 10th Anniversary: Past, Present, and Future)

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Open AccessArticle

Performance of Rice Straw Fibers on Hardened Concrete Properties under Effect of Impact Load and Gamma Radiation

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Fibers 2023, 11(5), 42; https://doi.org/10.3390/fib11050042 - 08 May 2023

Abstract

Concrete is an essential artificial building material in modern society. However, because concrete structures have brittle characteristics, they have a limited service life when subjected to dynamic loads. Nuclear emissions and explosions threaten human lives and structures’ safety due to harmful radiation and [...] Read more.

Concrete is an essential artificial building material in modern society. However, because concrete structures have brittle characteristics, they have a limited service life when subjected to dynamic loads. Nuclear emissions and explosions threaten human lives and structures’ safety due to harmful radiation and dynamic effects. Since agriculture has revealed a large amount of by-products that require disposal, the use of such by-products in many sectors is a challenge for contemporary studies. One of the most important areas for the disposal of such waste is construction, and concrete in particular. The utilization of the agricultural by-product rice straw fiber was chosen in this study to replace the usage of artificial fibers in concrete production and present an eco-friendly prospective contender with enhanced static/dynamic performance and gamma shielding characteristics. Different concrete mixtures were proposed in this study to evaluate the aforementioned characteristics. The designed concrete mixtures were conventional concrete with variations in the volume fraction of rice straw fibers (RSF) of 0%, 0.25%, 0.5%, and 0.75%. The desired static properties were compressive strength, splitting tensile strength, and flexural strength. Additionally, the drop weight impact test was used in this study to investigate the impact resistance of RSF-reinforced concrete. Finally, the radiation-shielding characteristic of the produced concrete was tested using the linear attenuation test. The results show that adding agricultural by-products of RSF in concrete production slightly enhanced the compressive strength by up to 7.0%, while it significantly improved the tensile and flexural properties by up to 17.1% and 25.8%, respectively. Additionally, a superior impact resistance of concrete was achieved by up to 48.6% owing to RSF addition. Furthermore, it enhanced the gamma shielding capability of concrete by up to 7.9%. The achievements in this study pave the way for utilizing RSF-reinforced concrete in various non-traditional applications. Full article

(This article belongs to the Special Issue Development of Eco-Friendly Concrete-, Mortar- and Fiber-Reinforced Composite Systems for Building Applications: Experimental and Theoretical Studies)

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Open AccessArticle

On the Pressure and Rate of Infiltration Made by a Carbon Fiber Yarn with an Aluminum Melt during Ultrasonic Treatment

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Sergei Galyshev

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Bulat Atanov

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Valery Orlov

Fibers 2023, 11(5), 41; https://doi.org/10.3390/fib11050041 - 06 May 2023

Abstract

The effect of the infiltration time of a carbon fiber yarn in the range of 6 to 13.6 s on the infiltrated volume under the cavitation of an aluminum melt has been studied. When the infiltration time was more than 10 s, the [...] Read more.

The effect of the infiltration time of a carbon fiber yarn in the range of 6 to 13.6 s on the infiltrated volume under the cavitation of an aluminum melt has been studied. When the infiltration time was more than 10 s, the carbon fiber was completely infiltrated with the matrix melt, and a decrease in the infiltration time led to a monotonous decrease in the fraction of the infiltrated volume. Based on the experimental data, the infiltration rate and the pressure necessary to infiltrate a carbon fiber yarn with an aluminum melt were estimated. The infiltration rate was 20.9 cm³/s and was independent of the infiltration depth. The calculated pressure necessary for the complete infiltration of a carbon fiber yarn at this rate was about 270 Pa. A comparison of the pressure values calculated according to Darcy’s and Forchheimer’s laws showed that the difference between them did not exceed 0.01%. This indicates that a simpler Darcy’s law could be used to estimate pressure. Full article

(This article belongs to the Special Issue Fibers 10th Anniversary: Past, Present, and Future)

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Open AccessReview

A Review of Fibre Reinforced Polymer Bridges

by

Jawed Qureshi

Fibers 2023, 11(5), 40; https://doi.org/10.3390/fib11050040 - 04 May 2023

Abstract

Fibre-reinforced polymer composites (FRPs) offer various benefits for bridge construction. Lightweight, durability, design flexibility and fast erection in inaccessible areas are their unique selling points for bridge engineering. FRPs are used in four bridge applications: (1) FRP rebars/tendons in concrete; (2) repair and [...] Read more.

Fibre-reinforced polymer composites (FRPs) offer various benefits for bridge construction. Lightweight, durability, design flexibility and fast erection in inaccessible areas are their unique selling points for bridge engineering. FRPs are used in four bridge applications: (1) FRP rebars/tendons in concrete; (2) repair and strengthening of existing bridges; (3) new hybrid–FRP bridges with conventional materials and (4) all–FRP composite new bridges made entirely of FRP materials. This paper reviews FRP bridges, including all–FRP and hybrid–FRP bridges. FRP bridges’ history, materials, processes and bridge components—deck, girder, truss, moulded parts and cables/rebars are considered. This paper does not discuss the use of FRP as an architectural element and a strengthening system. While lack of design codes, material specifications and recycling are the major challenges, the high cost of FRPs still remains the most critical barrier to the progress of FRPs in bridges. Full article

(This article belongs to the Collection Review Papers of Fibers)

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Open AccessFeature PaperReview

Mechanical Properties and Morphological Alterations in Fiber-Based Scaffolds Affecting Tissue Engineering Outcomes

by

James Dolgin

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Samerender Nagam Hanumantharao

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Stephen Farias

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Carl G. Simon, Jr.

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Smitha Rao

Fibers 2023, 11(5), 39; https://doi.org/10.3390/fib11050039 - 29 Apr 2023

Abstract

Electrospinning is a versatile tool used to produce highly customizable nonwoven nanofiber mats of various fiber diameters, pore sizes, and alignment. It is possible to create electrospun mats from synthetic polymers, biobased polymers, and combinations thereof. The post-processing of the end products can [...] Read more.

Electrospinning is a versatile tool used to produce highly customizable nonwoven nanofiber mats of various fiber diameters, pore sizes, and alignment. It is possible to create electrospun mats from synthetic polymers, biobased polymers, and combinations thereof. The post-processing of the end products can occur in many ways, such as cross-linking, enzyme linking, and thermal curing, to achieve enhanced chemical and physical properties. Such multi-factor tunability is very promising in applications such as tissue engineering, 3D organs/organoids, and cell differentiation. While the established methods involve the use of soluble small molecules, growth factors, stereolithography, and micro-patterning, electrospinning involves an inexpensive, labor un-intensive, and highly scalable approach to using environmental cues, to promote and guide cell proliferation, migration, and differentiation. By influencing cell morphology, mechanosensing, and intracellular communication, nanofibers can affect the fate of cells in a multitude of ways. Ultimately, nanofibers may have the potential to precisely form whole organs for tissue engineering, regenerative medicine, and cellular agriculture, as well as to create in vitro microenvironments. In this review, the focus will be on the mechanical and physical characteristics such as porosity, fiber diameter, crystallinity, mechanical strength, alignment, and topography of the nanofiber scaffolds, and the impact on cell proliferation, migration, and differentiation. Full article

(This article belongs to the Special Issue Nanofibers: Biomedical Applications)

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Open AccessFeature PaperArticle

Production of Long Hemp Fibers Using the Flax Value Chain

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Fibers 2023, 11(5), 38; https://doi.org/10.3390/fib11050038 - 28 Apr 2023

Abstract

Hemp is finding a strong renewal of interest in the production of fine fibers for garment textiles. This resource of long-line fibers would come as a complement to the highly demanded flax fibers, whose large production in the north-west of Europe cannot be [...] Read more.

Hemp is finding a strong renewal of interest in the production of fine fibers for garment textiles. This resource of long-line fibers would come as a complement to the highly demanded flax fibers, whose large production in the north-west of Europe cannot be extended. In Normandy, where a complete industrial value chain exists for flax, it is intended to adapt it to hemp, and this was demonstrated from the field to the scutched fibers with a complete value chain. In this region, early harvesting is necessary to leave enough time for dew-retting and permit dry storage of stems before mid-September. An early-flowering variety (USO-31) was harvested using dedicated hemp equipment to obtain a 1 m parallel and aligned windrow that can be further processed by flax equipment. The scutching process as well as the fiber’s morphological and mechanical properties were particularly studied. Adapted scutching process parameters with reduced advancing speed and beating turbine velocity led to long fiber yields of about 18% of the stem mass. Stem yields were reaching about 6 tons/ha leading to a production of 1.1 tons/ha of long fibers. The tensile properties of the long fibers were highly sufficient for textile applications, and their thickness after hackling was in the range suitable for the production of fine yarns. Compared to other crops grown in Normandy, the hemp as produced in this 2020 case study provides good incomes to the farmer, higher than traditional crops such as wheat or barley, and the results of this study should encourage farmers to grow hemp for textile purposes. Full article

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Open AccessArticle

Shear Strength Prediction of Steel-Fiber-Reinforced Concrete Beams Using the M5P Model

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Nadia Moneem Al-Abdaly

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Mahdi J. Hussein

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Hamza Imran

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Sadiq N. Henedy

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Luís Filipe Almeida Bernardo

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Zainab Al-Khafaji

Fibers 2023, 11(5), 37; https://doi.org/10.3390/fib11050037 - 27 Apr 2023

Abstract

This article presents a mathematical model developed using the M5P tree to predict the shear strength of steel-fiber-reinforced concrete (SFRC) for slender beams using soft computing techniques. This method is becoming increasingly popular for addressing complex technical problems. Other approaches, such as semi-empirical [...] Read more.

This article presents a mathematical model developed using the M5P tree to predict the shear strength of steel-fiber-reinforced concrete (SFRC) for slender beams using soft computing techniques. This method is becoming increasingly popular for addressing complex technical problems. Other approaches, such as semi-empirical equations, can show known inaccuracies, and some soft computing methods may not produce predictive equations. The model was trained and tested using 332 samples from an experimental database found in the previous literature, and it takes into account independent variables such as the effective depth d, beam width b_w, longitudinal reinforcement ratio ρ, concrete compressive strength f_c, shear span to effective depth ratio a/d, and steel fiber factor F_sf. The predictive performance of the proposed M5P-based model was also compared with the one of existing models proposed in the previous literature. The evaluation revealed that the M5P-based model provided a more consistent and accurate prediction of the actual strength compared to the existing models, achieving an R² value of 0.969 and an RMSE value of 37.307 for the testing dataset. It was found to be a reliable and also straightforward model. The proposed model is likely to be highly helpful in assessing the shear capacity of SFRC beams during the pre-planning and pre-design stages and could also be useful to help for future revisions of design standards. Full article

(This article belongs to the Special Issue Fibers 10th Anniversary: Past, Present, and Future)

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Open AccessArticle

Effective Strengthening of RC Beams Using Bamboo-Fibre-Reinforced Polymer: A Finite-Element Analysis

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Fibers 2023, 11(5), 36; https://doi.org/10.3390/fib11050036 - 22 Apr 2023

Abstract

This paper presents a finite-element model of the structural behaviour of reinforced concrete (RC) beams with and without openings externally strengthened with bamboo-fibre-reinforced composite (BFRC) plates. The simulation was performed using ABAQUS Unified FEA 2021HF8 software. The stress–strain relationship of the RC was [...] Read more.

This paper presents a finite-element model of the structural behaviour of reinforced concrete (RC) beams with and without openings externally strengthened with bamboo-fibre-reinforced composite (BFRC) plates. The simulation was performed using ABAQUS Unified FEA 2021HF8 software. The stress–strain relationship of the RC was modelled using a model code for concrete structures, whereas the concrete-damaged plasticity model was used to simulate concrete damage. The predicted crack pattern of the beams was comparable to that from experimental observations. The ultimate load-bearing capacity of RC beams in flexure was predicted with an error of up to 1.50%, while the ultimate load-bearing capacity of RC beams with openings in shear was predicted with an error ranging from 1.89 to 13.43%. The most successful arrangement for strengthening a beam with openings in the shear zone was to place BFRC plates perpendicular to the crack on both sides of the beam’s surface, which increased the beam’s original load-bearing capacity by 110.06% compared to that of the control beam (CB). The most effective method for strengthening RC beams in flexure is to attach a BFRC plate to the entire bottom soffit of the RC beam. This maximises the ultimate load-bearing capacity at the expense of the beam’s ductility. Full article

(This article belongs to the Special Issue Sustainable High Performance Fiber-Reinforced Cementitious Composites (HPFRCCs) and Fiber-Reinforced Polymers (FRPs))

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Open AccessArticle

Shear Strengthening and Repairing of Reinforced Concrete Deep Beams Damaged by Heat Using NSM–CFRP Ropes

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Ahmad Al-khreisat

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Mu’tasime Abdel-Jaber

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Ahmed Ashteyat

Fibers 2023, 11(4), 35; https://doi.org/10.3390/fib11040035 - 13 Apr 2023

Abstract

This study investigates experimentally the shear strengthening and repairing of reinforced concrete (RC) deep beams damaged by heat utilizing near-surface mounted carbon fiber reinforced polymers (NSM-CFRP) ropes. The main parameters adopted in this research are rope orientation (45°, 90°) and rope spacing (150 [...] Read more.

This study investigates experimentally the shear strengthening and repairing of reinforced concrete (RC) deep beams damaged by heat utilizing near-surface mounted carbon fiber reinforced polymers (NSM-CFRP) ropes. The main parameters adopted in this research are rope orientation (45°, 90°) and rope spacing (150 mm, 200 mm). For this purpose, ten RC deep beams were cast and tested until failure was reached. The test results showed that using NSM-CFRP ropes with various configurations significantly enhanced the shear capacity for repaired and strengthened deep beams. All the tested beams enhanced the ultimate load capacity for the strengthened beams ranging between 19% to 46%, while for the repaired beams, the values ranged between 40.8% to 64.6%. The CFRP ropes oriented at 45° recorded the highest enhancement result in shear capacity. Notably, all tested beams had a satisfactory rise in the enhancement ratio. Consequently, the economic aspect should have priority. Full article

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Open AccessArticle

An Electromechanical Impedance-Based Application of Realtime Monitoring for the Load-Induced Flexural Stress and Damage in Fiber-Reinforced Concrete

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Maria C. Naoum

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George M. Sapidis

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Nikos A. Papadopoulos

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Maristella E. Voutetaki

Fibers 2023, 11(4), 34; https://doi.org/10.3390/fib11040034 - 11 Apr 2023

Abstract

Effective real-time structural health monitoring in concrete structures is paramount to evaluating safety conditions and the timely maintenance of concrete structures. Especially, the presence of discrete fibers in fiber-reinforced concrete restrains crack propagation into small and thin cracks, which increases the difficulty in [...] Read more.

Effective real-time structural health monitoring in concrete structures is paramount to evaluating safety conditions and the timely maintenance of concrete structures. Especially, the presence of discrete fibers in fiber-reinforced concrete restrains crack propagation into small and thin cracks, which increases the difficulty in detecting damage. In this study, an array of piezoelectric lead zirconate titanate (PZT) transducers was applied to study the effects of external load-induced flexural stress and damage in fiber-reinforced concrete beams using the electromechanical impedance (EMI) or electromechanical admittance (EMA) methods. Beams were subjected to a four-point bending test under repeatable loading, while PZTs evaluated corresponding flexural stress and induced damage simultaneously. Due to the influence of the medium’s stress fields in the different types of wave propagation in structural elements, PZT transducers measurements are accordingly affected under variable stress fields, in addition to the effect of the higher level of damage that occurred in the medium. According to the results of the tests, variation in EMA signatures, following flexural stress and gradual damage changes, provided convincing evidence for predicting stress and damage development. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement-Based Mortars in Repair/Strengthening Methods of Masonry and Reinforced Concrete Structural Members)

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Open AccessArticle

Improving the Physical and Mechanical Characteristics of Modified Aerated Concrete by Reinforcing with Plant Fibers

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Alexey N. Beskopylny

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Evgenii M. Shcherban’

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Fibers 2023, 11(4), 33; https://doi.org/10.3390/fib11040033 - 03 Apr 2023

Abstract

An urgent and promising direction in the development of building materials science is the improvement of the quality of non-autoclaved aerated concrete. In view of the obvious disadvantages of non-autoclaved aerated concrete compared to the autoclaved equivalent in terms of technology, it can [...] Read more.

An urgent and promising direction in the development of building materials science is the improvement of the quality of non-autoclaved aerated concrete. In view of the obvious disadvantages of non-autoclaved aerated concrete compared to the autoclaved equivalent in terms of technology, it can be significantly improved because of a rationally selected composition and other factors of a recipe-technological nature. The goal of the study was to search for complex compositions and technological solutions aimed at identifying rational combinations of recipe-technological factors as simultaneous modifications of aerated concrete with various additives and dispersed the reinforcement of it with various environmentally friendly and cost-effective types of plant fibers. Fly ash (FA), instead of part of the cement, proved to be more effective than the GGBS additive. The compressive strength (CS), bending strength (BS), and coefficient of construction quality (CCQ) were higher by 4.5%, 3.8%, and 1.7%, respectively, while the density and thermal conductivity (TC) were lower by 0.7% and 3.6%, respectively, compared with aerated concrete modified with ground granulated blast-furnace slag (GGBS). The additional reinforcement of modified aerated concrete with coconut fiber (CF) and sisal fiber (SF) in an amount of 0.6% of the total mass of cement and modifier increases the CS to 15%, BS to 22% and CCQ to 16%. The SF was more effective than the CF. Aerated concrete modified with FA and reinforced with SF showed the highest efficiency. Compared to the control composition without modifiers or fibers, the increase in the CS was up to 40%, BS up to 47%, and CCQ up to 43%, while the decrease in density was up to 2.6%, and TC up to 15%. Full article

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Open AccessArticle

Adsorption Studies of Ammonia, Protein, and Phytic Acid Using Chitosan Fiber Coated with Oxidized Cellulose Nanofiber

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Duangkamol Dechojarassri

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Fibers 2023, 11(4), 32; https://doi.org/10.3390/fib11040032 - 30 Mar 2023

Abstract

Herein, chitosan (CS) fibers coated with TEMPO-oxidized cellulose nanofibers (CS/TOCN fibers) were successfully prepared using a wet spinning technique; CS was dissolved in acetic acid to obtain a CS doping solution. The tensile strength and ammonia adsorption percentages increased with increasing TOCN concentration. [...] Read more.

Herein, chitosan (CS) fibers coated with TEMPO-oxidized cellulose nanofibers (CS/TOCN fibers) were successfully prepared using a wet spinning technique; CS was dissolved in acetic acid to obtain a CS doping solution. The tensile strength and ammonia adsorption percentages increased with increasing TOCN concentration. The maximum ammonia adsorption percentage (41.39%, 8.3 mg/g) was obtained when 2% NaOH and 0.01% TOCN were used as the coagulation solution. Additionally, the adsorption of model proteins, including lysozyme (Lz), cytochrome C (Cyt C), and bovine serum albumin (BSA), were studied. In water, the CS/TOCN fibers with negative charges adsorbed more Lz with positive charges than CS fibers containing positive charges. Contrastingly, CS fibers adsorbed more Cyt C and BSA containing negative charges in phosphate-buffered saline solutions than CS/TOCN fibers. Furthermore, the adsorption percentage of phytic acid using the CS/TOCN fibers reached 64.18% (288 mg/g) within 60 min. Thus, TOCNs improved the tensile properties of CS fibers and preferred positively charged materials contaminated in water, such as ammonia, Lz, and phytic acid. Full article

(This article belongs to the Special Issue Fibers 10th Anniversary: Past, Present, and Future)

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Open AccessArticle

Effect of Elevated Temperature on the Behavior of Amorphous Metallic Fibre-Reinforced Cement and Geopolymer Composites

by

Faiz Uddin Ahmed Shaikh

,

Narwinder Singh Kahlon

and

Attiq Ur Rahman Dogar

Fibers 2023, 11(4), 31; https://doi.org/10.3390/fib11040031 - 28 Mar 2023

Abstract

To improve the tensile, flexural, and ductility properties of geopolymer composites, amorphous metallic fibres (AMF) are used to reinforce these composites, and the behavior of these composites at elevated temperatures has been assessed in this study. Four types of composites, i.e., cement, reinforced [...] Read more.

To improve the tensile, flexural, and ductility properties of geopolymer composites, amorphous metallic fibres (AMF) are used to reinforce these composites, and the behavior of these composites at elevated temperatures has been assessed in this study. Four types of composites, i.e., cement, reinforced cement, geopolymer, and reinforced geopolymer composites have been prepared. The composites have been reinforced using AMF with a fibre volume fraction of 0.75%. The composites have been assessed for change in mass loss, cracking, compressive strength, and flexural strength at four elevated temperatures of 200 °C, 400 °C, 600 °C, and 800 °C, and conclusions have been drawn concerning these composites. The results have shown that an increase in temperature has an adverse effect on these composites, and geopolymer composites exhibit higher performance than their counterpart cement composites at elevated temperatures. The mass loss and surface cracking were significantly lower in geopolymer composites, and the fibre reinforcement had a negligible effect on mass loss. Also, the residual compressive and flexural strength of reinforced geopolymer composites was significantly higher than that of the reinforced cement composites. In addition, scanning electron microscopic images also showed that even at higher temperatures, the geopolymer matrix is present on the AMF fibre, which results in higher residual strength than the cement composites in which a negligible amount of matrix is present on the fibres. Full article

(This article belongs to the Collection Feature Papers in Fibers)

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Open AccessArticle

Damage Investigation on the Carbon Tows during Rewinding and Braiding Processes

by

,

,

and

Fibers 2023, 11(3), 30; https://doi.org/10.3390/fib11030030 - 22 Mar 2023

Abstract

During the manufacturing process, the fibrous materials used in composite reinforcements are subjected to many sources of damage that must be managed if the best possible quality is to be reached for the final product. More specifically, carbon fibers are subjected, during reinforcement [...] Read more.

During the manufacturing process, the fibrous materials used in composite reinforcements are subjected to many sources of damage that must be managed if the best possible quality is to be reached for the final product. More specifically, carbon fibers are subjected, during reinforcement manufacturing, to friction with mechanical components and with other tows and to excessive tensile loads due to specific configurations required by textile devices, which results in degradation that affects their mechanical properties and those of final products. While many studies have focused on carbon tow damage during the weaving process, roving quality control during the post-braiding steps, such as the rewinding or braiding processes, is less studied in the literature. In this study, an experimental approach was developed to quantify the damage inflicted on 12 K carbon tows during the rewinding and braiding processes using image analysis software. Based on these images, a damage criterion is defined to quantify the influence of the parameters associated with rewinding and braiding processes on degradation of carbon tows. During the rewinding stage, the influence of the process parameters on the degradation by friction of the tows was significant, but the properties (linear density and tenacity) of these carbon tows were little-modified. On the other hand, the great influence of the tension applied on tows on the inflicted damage was experimentally demonstrated, during both the rewinding and braiding steps, which may have resulted in a loss of tenacity of up to 27%. Full article

(This article belongs to the Special Issue Fibers 10th Anniversary: Past, Present, and Future)

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