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Volume 8, January

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Fibers, Volume 8, Issue 2 (February 2020) – 9 articles

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Cover Story (view full-size image) Disturbance of Mn oxyhydroxide deposits can generate the release of asbestiform todorokite as well [...] Read more.
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Open AccessEditorial
Fibrous Material Science: Extensive and Persistent
Fibers 2020, 8(2), 16; https://doi.org/10.3390/fib8020016 - 18 Feb 2020
Viewed by 129
Abstract
It is my absolute pleasure to take up the position of Editor-in-Chief (EiC) of <ext-link ext-link-type="uri" xlink:href="https://www [...] Full article
Open AccessArticle
Development and Multiscale Characterization of 3D Warp Interlock Flax Fabrics with Different Woven Architectures for Composite Applications
Fibers 2020, 8(2), 15; https://doi.org/10.3390/fib8020015 - 18 Feb 2020
Viewed by 118
Abstract
Multiscale characterization of the textile preform made of natural fibers is an indispensable way to understand and assess the mechanical properties and behavior of composite. In this study, a multiscale experimental characterization is performed on three-dimensional (3D) warp interlock woven fabrics made of [...] Read more.
Multiscale characterization of the textile preform made of natural fibers is an indispensable way to understand and assess the mechanical properties and behavior of composite. In this study, a multiscale experimental characterization is performed on three-dimensional (3D) warp interlock woven fabrics made of flax fiber on the fiber (micro), roving (meso), and fabric (macro) scales. The mechanical tensile properties of the flax fiber were determined by using the impregnated fiber bundle test. The effect of the twist was considered in the back-calculation of the fiber stiffness to reveal the calculation limits of the rule of mixture. Tensile tests on dry rovings were carried out while considering different twist levels to determine the optimal amount of twist required to weave the flax roving into a 3D warp interlock. Finally, at fabric-scale, six different 3D warp interlock architectures were woven to understand the role of the architecture of binding rovings on the mechanical properties of the dry 3D fabric. The results reveal the importance of considering the properties of the fiber and roving at these scales to determine the more adequate raw material for weaving. Further, the characterization of the 3D woven structures shows the preponderant role of the binding roving on their structural and mechanical properties. Full article
Open AccessArticle
Terahertz Hollow Core Antiresonant Fiber with Metamaterial Cladding
Fibers 2020, 8(2), 14; https://doi.org/10.3390/fib8020014 - 17 Feb 2020
Viewed by 116
Abstract
A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation [...] Read more.
A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation results show that broadband terahertz radiation can be guided with six times lower loss in such hollow core fibers with metallic inclusions, compared to tube lattice fiber, covering a single mode bandwidth (BW) of 700 GHz. Full article
(This article belongs to the Special Issue Microstructured Optical Fibers and Applications)
Open AccessArticle
U-Jacketing Applications of Fiber-Reinforced Polymers in Reinforced Concrete T-Beams against Shear—Tests and Design
Fibers 2020, 8(2), 13; https://doi.org/10.3390/fib8020013 - 17 Feb 2020
Viewed by 113
Abstract
The application of externally bonded fiber-reinforced polymer (EB-FRP) as shear transverse reinforcement applied in vulnerable reinforced concrete (RC) beams has been proved to be a promising strengthening technique. However, past studies revealed that the effectiveness of this method depends on how well the [...] Read more.
The application of externally bonded fiber-reinforced polymer (EB-FRP) as shear transverse reinforcement applied in vulnerable reinforced concrete (RC) beams has been proved to be a promising strengthening technique. However, past studies revealed that the effectiveness of this method depends on how well the reinforcement is bonded to the concrete surface. Thus, although the application of EB-FRP wrapping around the perimeter of rectangular cross-sections leads to outstanding results, U-jacketing in shear-critical T-beams seems to undergo premature debonding failures resulting in significant reductions of the predictable strength. In this work, five shear-critical RC beams with T-shaped cross-section were constructed, strengthened and tested in four-point bending. Epoxy bonded carbon FRP (C-FRP) sheets were applied on the three sides and along the entire length of the shear-strengthened T-beams as external transverse reinforcement. Furthermore, the potential enhancement of the C-FRP sheets anchorage using bolted steel laminates has been examined. Test results indicated that although the C-FRP strengthened beams exhibited increased shear capacity, the brittle failure mode was not prevented due to the debonding of the FRP from the concrete surface. Nevertheless, the applied mechanical anchor of the C-FRP sheets delayed the debonding. Moreover, the design provisions of three different code standards (Greek Code of Interventions, Eurocode 8 and ACI Committee 440) concerning the shear capacity of T-shaped RC beams retrofitted with EB-FRP jackets or strips in U-jacketing configuration are investigated. The ability of these code standards to predict safe design estimations is checked against 165 test data from the current experimental project and data available in the literature. Full article
(This article belongs to the Special Issue Steel Fibre Reinforced Concrete Behaviour)
Open AccessArticle
Development of a Thulium Fiber Laser for an Atomic Spectroscopy Experiment
Fibers 2020, 8(2), 12; https://doi.org/10.3390/fib8020012 - 15 Feb 2020
Viewed by 158
Abstract
A convenient thulium fiber laser source is described with 3 W of output power operating at a wavelength of 2059 nm with a slope efficiency of 49% with respect to input pump power and 60% with respect to absorbed pump power. The laser [...] Read more.
A convenient thulium fiber laser source is described with 3 W of output power operating at a wavelength of 2059 nm with a slope efficiency of 49% with respect to input pump power and 60% with respect to absorbed pump power. The laser was applied in an atomic helium spectroscopy experiment to quench 3He (2058.63 nm) and 4He (2058.69 nm) meta-stable singlets (21S0), allowing for further investigation of the helium fine structure. The customized laser effectively eliminates the singlet counts to well below a background level (1%). A simplified analysis describes the basic laser performance with fitted constants in reasonable agreement with previous work. Full article
(This article belongs to the Special Issue Fiber Laser Sources)
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Open AccessArticle
Analysis of the Behavior of FRCM Confined Clay Brick Masonry Columns
Fibers 2020, 8(2), 11; https://doi.org/10.3390/fib8020011 - 10 Feb 2020
Viewed by 167
Abstract
The behavior of FRCM (Fabric Reinforced Cementitious Mortar) confined clay brick
masonry columns is analyzed in this paper. The results of an experimental investigation conducted
on small‐scale columns made by clay brick masonry confined with steel‐FRCM (or Steel Reinforced
Grout, SRG), PBO (poly‐paraphenylene‐benzo‐bisoxazole) [...] Read more.
The behavior of FRCM (Fabric Reinforced Cementitious Mortar) confined clay brick
masonry columns is analyzed in this paper. The results of an experimental investigation conducted
on small‐scale columns made by clay brick masonry confined with steel‐FRCM (or Steel Reinforced
Grout, SRG), PBO (poly‐paraphenylene‐benzo‐bisoxazole) FRCM and basalt‐FRCM, tested under
monotonic compressive load, are described and discussed. Tests were conducted on thirteen
prismatic columns; eleven columns (two unconfined and nine confined) were tested under
concentric load while an eccentric load was applied on two confined columns. For each confinement
system, the parameters investigated were the ‘confinement ratio’, the ‘load eccentricity’ and the
‘overlap configuration of the fiber fabrics’. FRCM confinement improved the structural response of
masonry columns in terms of ultimate strength, ultimate strain and ductility. Some models from the
literature were also examined to evaluate their applicability in predicting the axial capacity of
confined columns. Full article
Open AccessArticle
Modeling the Behavior of CFRP Strengthened Concrete Beams and Columns at Different Temperatures
Fibers 2020, 8(2), 10; https://doi.org/10.3390/fib8020010 - 10 Feb 2020
Viewed by 170
Abstract
The bonding of thin fiber-reinforced plastics (FRP) composites on the surface of concrete members has emerged as an effective method to increase both the strength and stiffness of concrete members. Although a large volume of experimental and numerical research has performed on existing [...] Read more.
The bonding of thin fiber-reinforced plastics (FRP) composites on the surface of concrete members has emerged as an effective method to increase both the strength and stiffness of concrete members. Although a large volume of experimental and numerical research has performed on existing concrete structures to increase their load carrying capacity, there appears to be less work reported on simulating the influence of temperature on the behavior of concrete structures. This study intends to examine the effects of changing temperature on the mechanical properties of FRP composites as well as deteriorated composites on the structural performance of FRP bonded concrete structures. The overall approach consists of computations using finite element models to simulate the structural behavior of FRP bonded beams and columns. Three-dimensional-extended finite element modeling X-FEM using ABAQUS-CAE v.6.13 program was performed to explore the influence of temperature of (25 °C, 100 °C and 180 °C) on failure loads of FRP strengthened beams and columns with adhesive material. Additionally, the cohesive traction–separation damage model was use to model the delamination of FRP from the concrete. The flexural strength, mid-span deflection, crack patterns, failure loads, and mode of failure for the tested models were compared with the previous experimental study. The results show that a FEM results were in good agreement with experimental results. The flexural strength decreases with temperature rise for FRP strengthened concrete beams. The high temperature 180 °C has an adverse influence on the compressive strength of the specimens. The way of FRP rupture in the simulation was similar to the mode that was observed during the experimental tests. Full article
Open AccessArticle
Mineralogical and Geochemical Characterization of Asbestiform Todorokite, Birnessite, and Ranciéite, and Their host Mn-Rich Deposits from Serra D’Aiello (Southern Italy)
Fibers 2020, 8(2), 9; https://doi.org/10.3390/fib8020009 - 28 Jan 2020
Viewed by 334
Abstract
Manganese ores, especially the oxyhydroxides in their different forms, are the dominant Mn-bearing minerals that occur in marine and terrestrial environments, where they are typically found as poorly crystalline and intermixed phases. Mn oxyhydroxides have a huge range of industrial applications and are [...] Read more.
Manganese ores, especially the oxyhydroxides in their different forms, are the dominant Mn-bearing minerals that occur in marine and terrestrial environments, where they are typically found as poorly crystalline and intermixed phases. Mn oxyhydroxides have a huge range of industrial applications and are able to exert a strong control on the mobility of trace metals. This paper reports the results of a detailed study on the Mn oxyhydroxides occurring in the manganiferous deposit outcropping in the Messinian sediments from Serra D'Aiello (Southern Italy). Nine Mn samples were characterized in detail using X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), thermogravimetry (TG), transmission electron microscopy combined with energy dispersive spectrometry (TEM/EDS), and X-ray fluorescence (XRF). The results indicated that the Mn deposit included the oxyhydroxide mineral species birnessite, todorokite, and rancièite. The size, morphology, and chemical composition of Mn oxyhydroxide samples were investigated in order to define their impact on the environment and human health. Todorokite displayed asbestiform shapes and could disperse fibers of breathable size in the air. Furthermore, since in-depth characterization of minerals within Mn deposits may be the first step toward understanding the genetic processes of manganese deposits, hypotheses about the genesis of the Mn oxyhydroxide deposits were discussed. Full article
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Open AccessArticle
Experimental Investigation and Numerical Analysis of Bond Behavior in SRG-Strengthened Masonry Prisms Using UHTSS and Stainless-Steel Fibers
Fibers 2020, 8(2), 8; https://doi.org/10.3390/fib8020008 - 27 Jan 2020
Viewed by 294
Abstract
This paper deals with the experimental and numerical study of the bond behavior of two steel reinforced grout (SRG)-strengthened masonry systems. Ten shear bond tests were carried out on prismatic masonry specimens. The data of experimental tests are recorded and results are given [...] Read more.
This paper deals with the experimental and numerical study of the bond behavior of two steel reinforced grout (SRG)-strengthened masonry systems. Ten shear bond tests were carried out on prismatic masonry specimens. The data of experimental tests are recorded and results are given in terms of load/stress-global slip curves, failure modes, tables, graphs and photographic reports, comparing the results of the two strengthening systems. Two kinds of steel fibers available in marketplace were used: ultra-high tensile strength steel galvanized micro-cords and stainless-steel strands. The main target is to obtain information on the behavior of the bond between masonry surface and the two types of SRG composites, which are characterized by two substantial differences: tensile strength with a ratio of 2.4 and the corresponding surface mass density with a ratio of 0.30. Finally, the influence of the matrices coupled with the two systems is critically analyzed. The characterization of the bond behavior is necessary in order to confirm the performance of the SRG systems that have become increasingly used and attractive. It also aims to make a contribution to the existing knowledge especially in relation to the use of low resistance steel fibers (stainless steel) which are still few studied today. Furthermore, using a suitable interface law proposed in the literature, a numerical model is defined and employed to simulate the behavior of the specimens tested in the laboratory. The comparisons show a good agreement between numerical and experimental results in terms of the maximum load, load versus global-slip curves, and crack patterns. Full article
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