Fibers

45 pages, 2664 KiB

Open AccessReview

Converging Electrospinning and 3D-Printing Technologies: From Innovative Design for Tissue Engineering to Global Patent Trends and Technology Transfer

by Karen J. Juarez-Navarro, Vincenzo Guarino and Marco A. Alvarez-Perez

Fibers 2025, 13(6), 83; https://doi.org/10.3390/fib13060083 - 19 Jun 2025

Viewed by 1095

Abstract

Electrospinning is a technique that enables the production of nano- and microfibrillar patterns that mimic the native extracellular matrix. However, these nanofibrous structures often lack mechanical properties suitable for reproducing the behavior of structurally complex tissues. Therefore, achieving more accurate and precise geometric [...] Read more.

Electrospinning is a technique that enables the production of nano- and microfibrillar patterns that mimic the native extracellular matrix. However, these nanofibrous structures often lack mechanical properties suitable for reproducing the behavior of structurally complex tissues. Therefore, achieving more accurate and precise geometric structures be-comes a key challenge. In this context, additive manufacturing techniques such as 3D printing may allow for the development of tailored structures with highly controlled ar-chitecture and improved mechanical strength. However, in contrast with electrospinning, these techniques are commonly considered “low-resolution” techniques, unable to ma-nipulate structural details at the submicrometric scale. Hence, this review aims to intro-duce and discuss recent technological approaches based on combining these technologies for scaffold development in tissue engineering, detailing some distinct integration strate-gies correlating the outcomes to the benefits and drawbacks. Finally, a comprehensive analysis of the current state of the art in the registered intellectual property related to these integrated approaches will be proposed, assessing their distribution by geographic region and analyzing the main trends over time and future fallouts. Full article

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11 pages, 1050 KiB

Open AccessArticle

Optimization of Process of Dyeing Alpaca Yarn Using Indigo Carmine (C.I. Natural Blue 2)

by Cristina M. Luque-Jacobo, Elizabeth Medrano de Jara, Jose Carrasco Bocangel and Edgar García-Hernández

Fibers 2025, 13(6), 82; https://doi.org/10.3390/fib13060082 - 18 Jun 2025

Viewed by 456

Abstract

As part of an implementation in the Peruvian textile industry, the use of different sources to obtain blue hues in alpaca fiber has taken on a prominent role. The present study investigated the optimization of the dyeing process of alpaca fibers using indigo [...] Read more.

As part of an implementation in the Peruvian textile industry, the use of different sources to obtain blue hues in alpaca fiber has taken on a prominent role. The present study investigated the optimization of the dyeing process of alpaca fibers using indigo carmine as dye. The methodology was based on a central composite design (CCD) and response surface methodology (RSM) with color strength (K/S) as response variable. The results demonstrate that the independent variables significantly affected the color strength (K/S). In this context, an increase in both mordant concentration (3.9887 g/L) and dyeing temperature (95 °C), coupled with lower exhaust time (30.0019 min), enhanced levels of superficial dye adsorption. Additionally, color fastness properties provided tolerable values according to the gray scale. In conclusion, the optimization of the dyeing process of alpaca fibers using indigo carmine enabled the achievement of a blue shade with satisfactory fastness properties in the fiber yarns. Full article

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24 pages, 2772 KiB

Open AccessArticle

Harnessing the Unique Nature of Evanescent Waves: Optimizing FOEW LSPR Sensors with Absorption-Focused Nanoparticle Design

by Omar Awad, AbdulRahman Ghannoum and Patricia Nieva

Fibers 2025, 13(6), 81; https://doi.org/10.3390/fib13060081 - 17 Jun 2025

Viewed by 507

Abstract

This work presents a novel and comprehensive framework for optimizing fiber optic evanescent wave (FOEW) localized surface plasmon resonance (LSPR) sensors by investigating the unique interaction between evanescent waves and plasmonic nanoparticles. Unlike propagating light, the evanescent wave is a localized, non-propagating field [...] Read more.

This work presents a novel and comprehensive framework for optimizing fiber optic evanescent wave (FOEW) localized surface plasmon resonance (LSPR) sensors by investigating the unique interaction between evanescent waves and plasmonic nanoparticles. Unlike propagating light, the evanescent wave is a localized, non-propagating field that interacts exclusively with absorbing media near the fiber surface. This characteristic highlights the importance of prioritizing nanoparticle absorption over total extinction in FOEW sensor design. The optical response of silver nanoparticles was modeled across a size range of 10–100 nm, showing that absorption increases with particle number. Among the sizes tested, 30 nm silver nanoparticles exhibited the highest absorption efficiency, which was confirmed experimentally. An analytical adsorption kinetics model based on diffusion transport further predicted that smaller nanoparticles yield higher surface coverage, a result validated through atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging. Refractive index (RI) sensitivity tests conducted on sensors fabricated with 10 nm, 20 nm, and 30 nm silver nanoparticles revealed that while smaller nanoparticles produced higher initial absorption due to greater surface density, the 30 nm particles ultimately provided superior RI sensitivity due to their enhanced absorption efficiency. These findings underscore the significance of absorption-centered nanoparticle design in maximizing FOEW LSPR sensor performance. Full article

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22 pages, 5134 KiB

Open AccessArticle

Experimental Investigation of the Behaviour of Short-Span FRP-Reinforced Glulam Beams with Hoops and Tension Anchoring

by Herry Chen, Yannick Vetter, Catherine Shrimpton and Daniel Lacroix

Fibers 2025, 13(6), 80; https://doi.org/10.3390/fib13060080 - 17 Jun 2025

Viewed by 300

Abstract

Past research has shown that for short-span glulam beams reinforced with a simple tension GFRP fabric can lead to undesirable failure modes at the reinforcement termination point. An experimental programme aimed at investigating alternative reinforcement schemes comprising hoops and tension anchoring as an [...] Read more.

Past research has shown that for short-span glulam beams reinforced with a simple tension GFRP fabric can lead to undesirable failure modes at the reinforcement termination point. An experimental programme aimed at investigating alternative reinforcement schemes comprising hoops and tension anchoring as an alternative to fan-type anchorage and full-length confinement was undertaken. Sixteen GFRP-reinforced glulam beams were tested to failure under four-point bending. Overall, the hoops and tension anchoring prevented premature debonding and stress concentration failures observed in beams reinforced with simple tension reinforcement. Improvements in the stiffness and strength were generally observed for all configurations with the average failure strain being on average 1.16 times larger than the unreinforced specimens. While hoops prevented undesirable failure modes, it had limited improvements when using bidirectional fabrics for the hoops. Conversely, the configurations with tension anchoring using bidirectional fabrics only resulted in improved performance with some level of post-peak resistance compared to the unreinforced specimens and those reinforced with simple tension reinforcement. For short-span beams, or any FRP-reinforced glulam beams where flexure is not the dominant failure mode, more robust modelling techniques are required to properly capture the distribution of the reinforcement. Full article

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20 pages, 5667 KiB

Open AccessArticle

Optimising Mechanical Performance of Additive Manufactured Composites for Biomedical Applications

by Abdul Qadir, Amadi Gabriel Udu and Norman Osa-uwagboe

Fibers 2025, 13(6), 79; https://doi.org/10.3390/fib13060079 - 13 Jun 2025

Viewed by 325

Abstract

The mechanical properties of additive manufactured (AM) short-fibre reinforced polymer (SFRP) composites are significantly influenced by infill patterns, fibre orientation, and fibre-matrix interactions. While previous studies have explored the role of process parameters in optimising AM components, the impact of infill geometry on [...] Read more.

The mechanical properties of additive manufactured (AM) short-fibre reinforced polymer (SFRP) composites are significantly influenced by infill patterns, fibre orientation, and fibre-matrix interactions. While previous studies have explored the role of process parameters in optimising AM components, the impact of infill geometry on anisotropy and mechanical performance remains underexplored, particularly in the context of machine learning (ML). This study develops an ML-driven framework to predict the tensile and flexural properties of AM SFRP composites with different infill patterns, including triangular, hexagonal, and rectangular. AM structures were fabricated and subjected to tensile and flexural tests, with the data used to train ML models, including LightGBM, XGBoost, and artificial neural networks (ANN). The results showed that the triangular infill pattern had the highest tensile strength and stiffness, the hexagonal infill had the lowest flexural properties, and the rectangular infill exhibited performance levels that fell between those of the triangular and hexagonal patterns. The ML models demonstrated high prediction accuracy, with R-squared values exceeding 0.95. XGBoost performed best for predicting tensile properties of hexagonal infill, while ANN excelled with triangular and rectangular configurations. This study demonstrates the potential of machine learning to enhance the mechanical performance of additively manufactured SFRP composites by capturing the complex interplay between infill geometry and fibre-matrix interactions. Thus, providing additional data for the design of high-performance materials in applications such as biomedical devices. Full article

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12 pages, 1291 KiB

Open AccessArticle

Non-Destructive Condition and Damage Assessment of Historic Weighted Silk

by Marta Anghelone, Caroline Dalhed and Tanja Kimmel

Fibers 2025, 13(6), 78; https://doi.org/10.3390/fib13060078 - 10 Jun 2025

Viewed by 638

Abstract

Silk weighting is a process used to compensate for the weight loss caused by degumming, achieved by adding agents such as metallic salts to enhance the hand feel and appearance of the fibers. With the development of tin weighting procedures (ca. 1870s), the [...] Read more.

Silk weighting is a process used to compensate for the weight loss caused by degumming, achieved by adding agents such as metallic salts to enhance the hand feel and appearance of the fibers. With the development of tin weighting procedures (ca. 1870s), the production of weighted silk tremendously increased, as the fast decay of such fabrics was attributed to the process itself. The weighted silk was largely used for evening wear and high-fashion garments, many of which nowadays are stored in textile collections, and often characterized by poor conservation conditions. Within the present work, a multi-analytical and interdisciplinary non-destructive protocol was established for studying the finishing techniques, characterizing the materials as well as the state of preservation of historic tin-weighted silk. The protocol involves a visual and haptic approach typical of conservation professionals, as well as analytical investigations such as X-Ray Fluorescence analyses, 3D digital microscopy, Scanning Electron Microscopy with Energy Dispersive Spectroscopy, and Fourier-transform Infrared Spectroscopy (FTIR) in Attenuated Total Reflection. Elemental analyses are effective for studying the technology of production, while FTIR emerged as a powerful tool for assessing the condition, through the carbonyl and crystallinity indices. Full article

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18 pages, 7815 KiB

Open AccessArticle

Short-Beam Shear Fatigue Behavior on Unidirectional GLARE: Mean Shear Stress Effect, Scatter, and Anisotropy

by Douglas G. Caetano, Hector G. Kotik, Juan E. Perez Ipiña and Enrique M. Castrodeza

Fibers 2025, 13(6), 77; https://doi.org/10.3390/fib13060077 - 9 Jun 2025

Viewed by 969

Abstract

This paper investigates the effect of mean shear stress on short-beam shear fatigue in a GLARE 1-3/2 commercial fiber–metal laminate (FML). This study explores three shear stress ratios (

R_{τ}

0.1, 0.3, and 0.5) and two material orientations (longitudinal and transversal) under [...] Read more.

This paper investigates the effect of mean shear stress on short-beam shear fatigue in a GLARE 1-3/2 commercial fiber–metal laminate (FML). This study explores three shear stress ratios (

R_{τ}

0.1, 0.3, and 0.5) and two material orientations (longitudinal and transversal) under constant amplitude fatigue. Different stress levels for each

R_{τ}

value were explored to obtain failures between 10³ and 10⁶ load cycles. The experimental results reveal anisotropy, with transversal specimens exhibiting lower performance and increased scatter. The mean shear stress effect is discussed herein, with insights into the critical role of mean shear of fatigue performance.

R_{τ}

0.1 was the most severe condition and

R_{τ}

0.5 was the least severe. The

R_{τ}

0.3 condition produced steeper S-N curves, indicating that the combined effect of mean shear stress and shear stress amplitude led to a higher rate of damage accumulation. The fractographic analysis investigated the failure modes and confirmed the damage dominated by Mode II, supporting the test methodology employed. Full article

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20 pages, 8651 KiB

Open AccessArticle

Hierarchical Modeling of Archaeological and Modern Flax Fiber: From Micro- to Macroscale

by Vasuki Rajakumaran, Johnny Beaugrand, Alessia Melelli, Mario Scheel, Timm Weitkamp, Jonathan Perrin, Alain Bourmaud, Henry Proudhon and Sofiane Guessasma

Fibers 2025, 13(6), 76; https://doi.org/10.3390/fib13060076 - 9 Jun 2025

Viewed by 882

Abstract

Flax fiber reinforcements weaken with aging and microstructural changes, limiting their applications. Here, we examine the effects of microstructure and aging on flax fiber elements’ performance by using 4000-year-old and modern Egyptian flax as references through multi-scale numerical modeling. This study introduces a [...] Read more.

Flax fiber reinforcements weaken with aging and microstructural changes, limiting their applications. Here, we examine the effects of microstructure and aging on flax fiber elements’ performance by using 4000-year-old and modern Egyptian flax as references through multi-scale numerical modeling. This study introduces a novel investigation into the tensile stress distribution behavior of archaeological and modern flax yarns. The finite element (FE) model is derived from 3D volumes obtained via X-ray microtomography and tensile testing in the elastic domain. At the microscale, fibers exhibit higher axial stress concentrations around surface defects and pores, particularly in regions with kink bands and lumens. At the mesoscale, fiber bundles show increased stress concentrations at inter-fiber voids and lumen, with larger bundles exhibiting greater stress heterogeneity, especially around pores and surface roughness. At the macroscale, yarns display significant stress heterogeneity, especially around microstructural defects like pores and fiber–fiber cohesion points. Aged fibers from ancient Egyptian cultural heritage in particular demonstrate large fiber discontinuities due to long-term degradation or aging. These numerical observations highlight how porosity, surface imperfections, and structural degradation increase stress concentration, leading to fiber rupture and mechanical failure. This insight reveals how aging and defects impact flax fiber performance and durability. Full article

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21 pages, 6582 KiB

Open AccessArticle

Experimental Study on the Effect of Abaca Fibers on Reinforced Concrete: Evaluation of Workability, Mechanical, and Durability-Related Properties

by Armando Arvizu-Montes, Stefany Alcivar-Bastidas and María José Martínez-Echevarría

Fibers 2025, 13(6), 75; https://doi.org/10.3390/fib13060075 - 4 Jun 2025

Cited by 1 | Viewed by 1497

Abstract

Interest in incorporating natural fibers as reinforcements in concrete has grown in parallel with the increasing need to reduce the environmental impact of construction. These fibers, known for their renewability, low cost, and life-cycle superiority, exhibit technical advantages such as light weight and [...] Read more.

Interest in incorporating natural fibers as reinforcements in concrete has grown in parallel with the increasing need to reduce the environmental impact of construction. These fibers, known for their renewability, low cost, and life-cycle superiority, exhibit technical advantages such as light weight and high tensile strength. This study experimentally evaluated the influence of abaca fibers (AF) previously subjected to alkaline treatment and incorporated in reinforced concrete on workability, mechanical behavior, and durability, with a particular focus on the mechanisms affecting steel rebar corrosion. The characterization techniques included compressive and flexural testing; porosity, capillary water absorption, ion chloride penetration, and carbonation depth measurements; and corrosion rate monitoring via electrochemical methods. The results indicated that the addition of AF did not compromise the fresh-state properties or compressive strength but improved the flexural strength by 7.3%. Regarding durability, the porosity and water absorption increased by 4.1% and 8.2%, respectively, whereas the chloride penetration and carbonation depth remained within the requirements. Notable effects were observed regarding steel corrosion performance, where the incorporation of AF led to higher variability and an increasing trend in the corrosion rate compared with that of the reference concrete. Nevertheless, estimations suggest that abaca-fiber-reinforced concrete can meet the 100-year service life. These findings support the potential of AF as a viable reinforcement material for mechanical improvement; however, their influence on long-term durability, particularly corrosion, requires further investigation to deepen their feasible application for sustainable construction. Full article

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13 pages, 2510 KiB

Open AccessArticle

Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing

by Javier Jimenez, Joseph A. Orlando, James E. Cilek and Jeffrey G. Lundin

Fibers 2025, 13(6), 74; https://doi.org/10.3390/fib13060074 - 4 Jun 2025

Viewed by 642

Abstract

Personal protection from mosquitos is dominated by topically applied aerosol sprays or lotions, which demonstrate efficacy durations of no longer than 10 h, thus encouraging the research and development of long-term insect-repelling devices. Repellent-loaded polymeric matrices have driven the development of insect-repelling apparel [...] Read more.

Personal protection from mosquitos is dominated by topically applied aerosol sprays or lotions, which demonstrate efficacy durations of no longer than 10 h, thus encouraging the research and development of long-term insect-repelling devices. Repellent-loaded polymeric matrices have driven the development of insect-repelling apparel fabrics; however, most efforts either fail to offer the tensile properties demanded from apparel applications or only demonstrate repellency durations for multiple days. This study utilizes poly-D,L-lactic acid (PDLLA) as a compatibilizer between Nylon 12 and nootkatone for enhanced nootkatone retention throughout fabric manufacturing processes. Nootkatone-infused Nylon 12/PDLLA composites demonstrate up to a 14% increase in nootkatone retention throughout fabric manufacturing compared to pure Nylon 12, underscoring the importance of polymer/substrate miscibility on substrate retention. Moreover, while nootkatone-infused Nylon 12 filaments demonstrate decreasing tensile stress at breaks with increasing nootkatone content, Nylon 12/PDLLA filaments exhibit similar tensile properties regardless of nootkatone content. The PDLLA domains are suspected to behave as reservoirs for excess nootkatone to prevent its role as a defect within the Nylon 12 matrix. The resulting knits exhibit significant mosquito repellencies over 24 h dependent on the nootkatone concentration, thus demonstrating potential to embed insect repellent within high-performance polymeric filaments with effective mosquito repellencies. Therefore, the incorporation of PDLLA as a compatibilizer holds significant potential for enhanced nootkatone retention during Nylon 12 fabric manufacturing. Full article

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25 pages, 3711 KiB

Open AccessArticle

Eco-Friendly Extraction of Curcumin from Turmeric and Dyeability of Textile Fibers

by Vasilica Popescu, Ana-Diana Alexandrescu, Gabriel Popescu and Viorica Vasilache

Fibers 2025, 13(6), 73; https://doi.org/10.3390/fib13060073 - 4 Jun 2025

Viewed by 1611

Abstract

Classical and modern methods are used to release curcumin by degrading the polysaccharides found in the turmeric powder matrix. Classical methods use chemicals as acids (HCl, H₂SO₄, CH₃COOH), oxidants (H₂O₂, kojic acid), and [...] Read more.

Classical and modern methods are used to release curcumin by degrading the polysaccharides found in the turmeric powder matrix. Classical methods use chemicals as acids (HCl, H₂SO₄, CH₃COOH), oxidants (H₂O₂, kojic acid), and enzymes (amylase type) that can degrade amylose and amylopectin from starch. The modern applied methods consist of the degradation of the polysaccharides in the turmeric powder during eco-friendly processes assisted by ultrasound or microwaves. The extraction medium can consist of only water, water with a solvent, and/or an oxidizing agent. The presence of curcumin in turmeric powder is confirmed by FTIR analysis. The UV–VIS analysis of the extracts allows the determination of the efficiency of modern extraction processes. The release of curcumin from turmeric is highlighted quantitatively by colorimetric measurements for the obtained extracts, using a portable DataColor spectrophotometer. The comparison of the results leads to the conclusion that microwave-assisted extractions are the most effective. These extracts are able to dye many types of textile fibers: wool, cotton, hemp, silk, polyacrylonitrile, polyamide, polyester, and cellulose acetate. CIELab and color strength (K/S) measurements indicate that the most intense yellow colors are obtained on polyacrylonitrile (b* = 86.32, K/S = 15.14) and on cellulose acetate (b* = 90.40, K/S = 14.17). Full article

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22 pages, 1950 KiB

Open AccessArticle

Mechanical Properties and Structural Design of PVA Fiber-Reinforced Cementitious Composites with Fly Ash Replacement for Natural Sand Aggregates

by Camelia Maria Negrutiu, Pavel Ioan Sosa, Cristina Mihaela Campian and Maria Ileana Pop

Fibers 2025, 13(6), 72; https://doi.org/10.3390/fib13060072 - 3 Jun 2025

Viewed by 1130

Abstract

This paper investigates nine PVA fiber-reinforced cementitious composites with varying fiber content (1–2.5%) and types (oil-coated and non-coated). The experimental compositions utilize locally available cement, high volumes of fly ash, silica fume, PVA fibers, and a superplasticizer, entirely omitting natural aggregates. Key parameters [...] Read more.

This paper investigates nine PVA fiber-reinforced cementitious composites with varying fiber content (1–2.5%) and types (oil-coated and non-coated). The experimental compositions utilize locally available cement, high volumes of fly ash, silica fume, PVA fibers, and a superplasticizer, entirely omitting natural aggregates. Key parameters evaluated include bulk density, compressive strength, secant modulus of elasticity, flexural tensile strength, fracture energy, and structural design applicability. The results show that FRCs without natural aggregates achieves significantly lower densities (1500–1720 kg/m³). Compressive strength is influenced by matrix density, with the highest value recorded at 30.98 MPa. The high fly ash content reduces the secant modulus of elasticity, while flexural tensile strength follows a similar pattern to compressive strength. Oil-coated fibers generally lower fracture energy, except for the 1.5% PVA content, where the 2.5% composition performs best. All specimens exhibit tension softening rather than the strain-hardening behavior of ECCs. Structural design equations were developed, though experimental validation is necessary. The 2.5% PVA composition increases the compression zone height by 7% while requiring 2% more reinforcement. As a sustainable alternative to conventional concrete, the composites offer promising mechanical properties and structural viability for construction applications. Full article

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27 pages, 2272 KiB

Open AccessArticle

Application of L-Shaped Zigzag Steel Fibers with Different Parameters in Asphalt Mixtures

by Qingguo Yang, Wujing Yin, Jiawei Cheng, Ya Li, Yu Zhou, Kelin Chen and Yunhao Li

Fibers 2025, 13(6), 71; https://doi.org/10.3390/fib13060071 - 2 Jun 2025

Viewed by 570

Abstract

Taking AC-13 asphalt mixture as the matrix, this research delves into the impacts of assorted steel fibers on AC-13 asphalt mixture, especially the influence of 17.5 mm × 17.5 mm L-shaped steel fibers. A gradient design with mass dosages of 0%, 1%, 2%, [...] Read more.

Taking AC-13 asphalt mixture as the matrix, this research delves into the impacts of assorted steel fibers on AC-13 asphalt mixture, especially the influence of 17.5 mm × 17.5 mm L-shaped steel fibers. A gradient design with mass dosages of 0%, 1%, 2%, and 3% was employed to evaluate the reinforcement effect of L-shaped steel fiber-reinforced asphalt mixture compared with conventional mixture. Also, comparative analysis between L-shaped and straight steel fibers was conducted through comprehensive mechanical performance tests, including the Marshall stability test, high-temperature wheel tracking test, low-temperature beam bending test, freeze–thaw splitting strength test, and immersion Marshall test. The results demonstrate that L-shaped steel fibers significantly improve the comprehensive mechanical properties of asphalt mixture compared to conventional asphalt mixture, showing remarkable improvements in high-temperature stability, low-temperature crack resistance, and water stability. The overall performance enhancement effect increases by approximately 20%. Compared with straight steel fibers, the performance improvement of the mixtures is slightly greater, with the optimal performance achieved at 2% mass dosage. The standard deviation and coefficient of variation are used to reflect the degree of data dispersion. The results show that the data of L-shaped steel fibers have relatively smaller fluctuations, being more uniform and stable. Full article

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15 pages, 1952 KiB

Open AccessArticle

Influence of Geometric Non-Linearities on the Mixed-Mode Decomposition in Asymmetric DCB Samples

by Jorge Bonhomme, Victoria Mollón, Jaime Viña and Antonio Argüelles

Fibers 2025, 13(6), 70; https://doi.org/10.3390/fib13060070 - 27 May 2025

Viewed by 657

Abstract

The Asymmetric Double Cantilever Beam (ADCB) is a common test configuration used to produce mixed mode I/II in composite materials. It consists of two sublaminates with different thicknesses or elastic properties, a situation that usually occurs in bimaterial adhesive joints. During this test, [...] Read more.

The Asymmetric Double Cantilever Beam (ADCB) is a common test configuration used to produce mixed mode I/II in composite materials. It consists of two sublaminates with different thicknesses or elastic properties, a situation that usually occurs in bimaterial adhesive joints. During this test, the sample undergoes rotation. In this work, the influence of this rotation on the calculation of the energy release rate (ERR) in modes I and II was studied using the Finite Element Method (FEM). Several models with different degrees of asymmetry (different thickness ratio and/or elastic modulus ratio) and different applied displacements were prepared to obtain different levels of rotation during the test. As is known, the concept of modes I and II refers to the components of the energy release rate calculated in the direction perpendicular and tangential to the delamination plane, respectively. If the model experiences significant rotation during the application of the load, this non-linearity must be considered in the calculation of the mode partition I/II. In this work, appreciable differences were observed in the values of modes I and II, depending on their calculation in a global system or a local system that rotates with the sample. When performing crack growth calculations, the difference between critical loads can be in the order of 4%, while the difference between mode I and mode II results can reach 4% and 14%, respectively, for an applied displacement of only 5 mm. Currently, this correction is not usually implemented in Finite Element calculation codes or in analytical developments. The purpose of this article is to draw attention to this aspect when the rotation of the specimen is not negligible. Full article

(This article belongs to the Topic Advanced Carbon Fiber Reinforced Composite Materials, Volume II)

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25 pages, 4065 KiB

Open AccessArticle

Selective Enrichment of Fibrous Fragments Formed from Milled Carbon Fibers by Means of Gravitational Settling in a Liquid

by Nicolas Rodriguez y Fischer, Kerstin Kämpf, Torben Peters, Nico Dziurowitz, Carmen Thim, Daniela Wenzlaff, Asmus Meyer-Plath and Daphne Bäger

Fibers 2025, 13(6), 69; https://doi.org/10.3390/fib13060069 - 26 May 2025

Viewed by 1029

Abstract

The aim to reduce health risks of workers related to inhalative exposure to potentially toxic dusts requires the selection of appropriate measures depending on the hazard classification of the dust-composing materials. Due to their biodurability, respirable carbon fibers and their fragments can impose [...] Read more.

The aim to reduce health risks of workers related to inhalative exposure to potentially toxic dusts requires the selection of appropriate measures depending on the hazard classification of the dust-composing materials. Due to their biodurability, respirable carbon fibers and their fragments can impose such health risks but are currently lacking hazard classification. Here, a method is presented for fragmenting carbon fiber materials and enriching fibrous fragments to a level that is expected to allow differentiating between fiber and particle overload-related toxic effects. The method was applied to a commercial polyacrylonitrile-based carbon fiber. It was ground in an oscillating ball mill, homogenized in a liquid using ultrasonication and left undisturbed for gravitational settling. This way, a vertical gradient in particle size and shape formed, from which the supernatant was collected. Fragment morphologies were characterized with large ensemble statistics by semi-automated evaluation of scanning electron microscopy images employing an artificial neural network for binary semantic segmentation. The number of fibrous fragments of respirable and thus critical fiber morphology was increased from

0.36 \times 10^{6}

to

6 \times 10^{6}

WHO-analog fibers per mg. This corresponds to a factor of about 15 compared to the initial ground material. Since the mass percentage of non-fibrous objects was also significantly reduced, the requirements for a subsequently scheduled toxicological study with intraperitoneal application were fulfilled. Intraperitoneal testing is an accepted method for assessing the carcinogenic potential of biopersistent fibers. The developed method allows enriching fibrous fractions of concern at acceptable throughput and enables testing fiber toxicological effects of respirable fragments from disintegrated polyacrylonitrile-based carbon fibers. Full article

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39 pages, 11665 KiB

Open AccessReview

Sustainable Masonry Retrofitting and Upgrading Techniques: A Review

by Arnas Majumder, Flavio Stochino, Monica Valdes, Giovanna Concu, Marco Pepe and Enzo Martinelli

Fibers 2025, 13(6), 68; https://doi.org/10.3390/fib13060068 - 23 May 2025

Viewed by 1485

Abstract

This study presents a comprehensive review of various advanced methodologies that have been used to enhance the structural and thermal performance of masonry walls through innovative and sustainable retrofitting/upgrading techniques. Focusing on three primary approaches—mechanical/structural retrofitting, thermal retrofitting, and integrated (structural and thermal) [...] Read more.

This study presents a comprehensive review of various advanced methodologies that have been used to enhance the structural and thermal performance of masonry walls through innovative and sustainable retrofitting/upgrading techniques. Focusing on three primary approaches—mechanical/structural retrofitting, thermal retrofitting, and integrated (structural and thermal) retrofitting, this paper critically examines various masonry-strengthening strategies. Retrofitting techniques are categorized by material use and objectives. Fiber-based solutions include insulation materials, fiber composite mortar for strength, FRP for high-strength reinforcement, and TRM for durability. According to the relevant objectives, retrofitting can enhance structural stability (FRP, TRM), improve thermal insulation, or combine both for integrated performance. Particular emphasis is placed on the effectiveness of TRM systems, with a comparative analysis of man-made (glass, steel textile) and natural fiber-based TRM solutions. Regarding integrating natural fibers into TRM systems, this study highlights their potential as eco-friendly alternatives that reduce environmental impact while maintaining or improving structural integrity. Furthermore, it highlights and examines techniques for testing masonry walls. In this context, this review highlights the applicability of natural fiber as a sustainable building material in various retrofitting/upgrading solutions. Full article

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Fibers, Volume 13, Issue 6 (June 2025) – 16 articles

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