Fibers

15 pages, 8432 KiB

Open AccessArticle

Electrochemical Deposition of SiO₂-Coatings on a Carbon Fiber

by Sergei Galyshev and Evgeniya Postnova

Fibers 2021, 9(5), 33; https://doi.org/10.3390/fib9050033 - 7 May 2021

Cited by 7 | Viewed by 3844

Research on carbon fiber oxide coatings is primarily focused on metal matrix composites. Such coatings act as a diffusion barrier between a matrix and a fiber and, in addition, they can be weak boundaries that significantly increase the mechanical properties of metal matrix [...] Read more.

Research on carbon fiber oxide coatings is primarily focused on metal matrix composites. Such coatings act as a diffusion barrier between a matrix and a fiber and, in addition, they can be weak boundaries that significantly increase the mechanical properties of metal matrix composites. A simple and economical method of coating deposition is the sol-gel method. However, it does not allow for control of the thickness of the carbon fiber coating. To eliminate this limitation, a combined method is used that includes sol-gel technology and electrochemical deposition. The paper presents the results of studies on the production of SiO₂ coatings on carbon fibers by the above method. The effect of current density, deposition time, salt concentration, pH of the reaction medium, TEOS/H₂O molar ratio, and alcohol concentration in the reaction medium on the structure and thickness of the coatings was studied. Full article

(This article belongs to the Special Issue Smart Reinforced Composites Using Carbon and Carbon-Based Nanomaterials II)

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17 pages, 5055 KiB

Open AccessArticle

Statistical Analysis of Mechanical Stressing in Short Fiber Reinforced Composites by Means of Statistical and Representative Volume Elements

by Kevin Breuer, Axel Spickenheuer and Markus Stommel

Fibers 2021, 9(5), 32; https://doi.org/10.3390/fib9050032 - 6 May 2021

Cited by 9 | Viewed by 3667

Abstract

Analyzing representative volume elements with the finite element method is one method to calculate the local stress at the microscale of short fiber reinforced plastics. It can be shown with Monte-Carlo simulations that the stress distribution depends on the local arrangement of the [...] Read more.

Analyzing representative volume elements with the finite element method is one method to calculate the local stress at the microscale of short fiber reinforced plastics. It can be shown with Monte-Carlo simulations that the stress distribution depends on the local arrangement of the fibers and is therefore unique for each fiber constellation. In this contribution the stress distribution and the effective composite properties are examined as a function of the considered volume of the representative volume elements. Moreover, the influence of locally varying fiber volume fraction is examined, using statistical volume elements. The results show that the average stress probability distribution is independent of the number of fibers and independent of local fluctuation of the fiber volume fraction. Furthermore, it is derived from the stress distributions that the statistical deviation of the effective composite properties should not be neglected in the case of injection molded components. A finite element analysis indicates that the macroscopic stresses and strains on component level are significantly influenced by local, statistical fluctuation of the composite properties. Full article

(This article belongs to the Special Issue Simulation of Short-Fiber-Reinforced Polymers)

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4 pages, 682 KiB

Open AccessTechnical Note

Density Profile Analysis of Laminated Beech Veneer Lumber (BauBuche)

by Nick Engehausen, Jan T. Benthien, Martin Nopens and Jörg B. Ressel

Fibers 2021, 9(5), 31; https://doi.org/10.3390/fib9050031 - 5 May 2021

Cited by 5 | Viewed by 3864

Abstract

An irreversible swelling was detected in laminated beech veneer lumber within the initial moistening. Supported by the facts that the lay-up of the glued veneers is exposed to high pressure during hot pressing, and that the density of the finished material exceeds that [...] Read more.

An irreversible swelling was detected in laminated beech veneer lumber within the initial moistening. Supported by the facts that the lay-up of the glued veneers is exposed to high pressure during hot pressing, and that the density of the finished material exceeds that of solid beech, it was hypothesised that the wood substance is compressed. Laboratory X-ray density profile scans were performed to check this and to identify the part of the material cross section in which the densification has taken place. The higher density was found to be located in the area of the adhesive joints, uniformly over the cross section, while the density in the middle of the veneers corresponds to that of solid beech wood. Full article

(This article belongs to the Special Issue Wood Plastic Composites)

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20 pages, 3780 KiB

Open AccessArticle

Rammed Earth with Straw Fibers and Earth Mortar: Mix Design and Mechanical Characteristics Determination

by Maria Francesca Sabbà, Mariateresa Tesoro, Cecilia Falcicchio and Dora Foti

Fibers 2021, 9(5), 30; https://doi.org/10.3390/fib9050030 - 4 May 2021

Cited by 14 | Viewed by 5028

Abstract

Raw earth is one of the oldest building materials, which is suitable for various uses: from the construction of load-bearing walls to use for plasters and finishes. The presence of straw fibers can give different behavior to this material. The present paper illustrates [...] Read more.

Raw earth is one of the oldest building materials, which is suitable for various uses: from the construction of load-bearing walls to use for plasters and finishes. The presence of straw fibers can give different behavior to this material. The present paper illustrates preliminary sensory and qualitative analyses, and subsequent laboratory tests that allow the characterization of the raw earth material with straw fibers for rammed earth constructions through mechanized compaction and the identification of a compatible earth mortar. The raw material considered in this study is mainly clayey; for this reason, a mix design usable with the pisé (or clay) technique has been developed. Cylindrical samples have been made through a press and subject to unconfined compression and indirect tensile tests. The results of the tests showed consistent tensile and compressive strength values in the context of earth materials. At the same time, a study for the realization of a mortar with the same base soil was carried out considering four mixtures, in order to investigate the best compromise between workability, shrinkage and compressive strengths. The purpose of the study was to investigate the mechanical characteristics of the local material through preliminary and laboratory tests, to classify it according to the Unified Soil Classification System (USCS) and to verify its suitability for a possible use in the construction field. Full article

(This article belongs to the Special Issue Fibres in Construction: Mechanical Modelling and Characterisation)

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24 pages, 9416 KiB

Open AccessArticle

Seismic Performance Enhancement of RC Columns Using Thin High-Strength RC Jackets and CFRP Jackets

by George Kalogeropoulos and Alexander-Dimitrios Tsonos

Fibers 2021, 9(5), 29; https://doi.org/10.3390/fib9050029 - 3 May 2021

Cited by 6 | Viewed by 3705

Abstract

The existing non-ductile RC structures built prior to the 1960s–1970s were mainly conceived to carry only vertical loads. As a result, the columns of these structures demonstrate poor overall hysteresis behavior during strong earthquakes, dominated by brittle shear or/and premature excessive slipping of [...] Read more.

The existing non-ductile RC structures built prior to the 1960s–1970s were mainly conceived to carry only vertical loads. As a result, the columns of these structures demonstrate poor overall hysteresis behavior during strong earthquakes, dominated by brittle shear or/and premature excessive slipping of the inadequately lap-spliced reinforcement. In the present study, the effectiveness of two different strengthening systems (including either the wrapping of the columns by carbon-fiber-reinforced polymer textile or the use of thin high-strength reinforced concrete jackets), was experimentally and analytically investigated. The main variables examined were the strengthening material, the length of the lap splices and the amount of confinement provided by the jackets. Three cantilever column specimens were constructed without incorporating modern design code requirements for preserving seismic safety and structural integrity. Subsequently, the specimens were strengthened and subjected to earthquake-type loading. Their hysteresis performances were compared, while also evaluated with respect to the response of two similar original specimens and the behavior of a control one with continuous reinforcement, tested in a previous study. The predictions of the proposed analytical formulation for the hysteresis behavior of the strengthened specimens were satisfactorily verified by the experimental results. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymers and Fiber-Reinforced Cement Composites as Concrete Reinforcement)

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12 pages, 2709 KiB

Open AccessArticle

Formation of Polysulfone Hollow Fiber Membranes Using the Systems with Lower Critical Solution Temperature

by Tatiana V. Plisko, Alexandr V. Bildyukevich, Liang Zhao, Weiqing Huang, Vladimir V. Volkov and Zuohua Huang

Fibers 2021, 9(5), 28; https://doi.org/10.3390/fib9050028 - 2 May 2021

Cited by 15 | Viewed by 4354

Abstract

This study deals with the investigation of the phase state of the polymer systems from polysulfone (PSF) with the addition of polyethylene glycol (PEG-400, M_n = 400 g·mol⁻¹) and polyvinylpyrrolidone (PVP K-30, M_n = 40,000 g·mol⁻¹) in [...] Read more.

This study deals with the investigation of the phase state of the polymer systems from polysulfone (PSF) with the addition of polyethylene glycol (PEG-400, M_n = 400 g·mol⁻¹) and polyvinylpyrrolidone (PVP K-30, M_n = 40,000 g·mol⁻¹) in N,N-dimethylacetamide (DMA), which feature lower critical solution temperatures (LCSTs). A fragment of the phase state diagram of the system PSF —PEG-400—PVP K-30—DMA was experimentally constructed in the following range of component concentrations: PSF 20–24 wt.%, PEG-400—35–38 wt.% and PVP—0–8 wt.%. It has been established that PVP addition substantially reduces the phase separation temperature down to 50–60 °C. Based on the obtained phase diagrams, a method for preparation of highly permeable hollow fiber membranes from PSF, which involves the processing of the dope solution at a temperature close to the LCST and the temperature of the bore fluid above the LCST, was proposed. Hollow fiber membranes with pure water flux of 1200 L·m⁻²·h⁻¹ and a sponge-like macrovoid-free structure were obtained via LCST-thermally induced phase separation by free fall spinning technique. Full article

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17 pages, 8837 KiB

Open AccessFeature PaperArticle

Twisted Silica Microstructured Optical Fiber with Equiangular Spiral Six-Ray Geometry

by Anton V. Bourdine, Alexey Yu. Barashkin, Vladimir A. Burdin, Michael V. Dashkov, Vladimir V. Demidov, Konstantin V. Dukelskii, Alexander S. Evtushenko, Yaseera Ismail, Alexander V. Khokhlov, Artem A. Kuznetsov, Alexandra S. Matrosova, Oleg G. Morozov, Grigori A. Pchelkin, Francesco Petruccione, Airat Zh. Sakhabutdinov, Ghanshyam Singh, Egishe V. Ter-Nersesyants, Manish Tiwari, Elena S. Zaitseva, Vijay Janyani and Juan Yin Show full author list Hide full author list

Fibers 2021, 9(5), 27; https://doi.org/10.3390/fib9050027 - 2 May 2021

Cited by 16 | Viewed by 3615

Abstract

This work presents fabricated silica microstructured optical fiber with special equiangular spiral six-ray geometry, an outer diameter of 125 µm (that corresponds to conventional commercially available telecommunication optical fibers of ratified ITU-T recommendations), and induced chirality with twisting of 200 revolutions per minute [...] Read more.

This work presents fabricated silica microstructured optical fiber with special equiangular spiral six-ray geometry, an outer diameter of 125 µm (that corresponds to conventional commercially available telecommunication optical fibers of ratified ITU-T recommendations), and induced chirality with twisting of 200 revolutions per minute (or e.g., under a drawing speed of 3 m per minute, 66 revolutions per 1 m). We discuss the fabrication of twisted microstructured optical fibers. Some results of tests, performed with pilot samples of designed and manufactured stellar chiral silica microstructured optical fiber, including basic transmission parameters, as well as measurements of near-field laser beam profile and spectral and pulse responses, are represented. Full article

(This article belongs to the Special Issue Optical Fibers as a Key Element of Distributed Sensor Systems)

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Fibers, Volume 9, Issue 5 (May 2021) – 7 articles

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