Fibers, Volume 8, Issue 2 (February 2020) – 10 articles

The conventional chemical-based antistatic agents possess ecological and technological drawbacks, such as altering the bulk characteristics, flammability, and toxicity, but not the cost effective process. Recently, using conductive metal fibers in the woven structure also affects the mechanical properties of the fabric. To overcome these challenges, plasma treatment needs to be quite an effective method. In this study, polyester/cotton (P/C), 65/35%, blend fabric was treated in a vacuum-plasma-chamber using air, argon and oxygen. The electro-physical property of the samples were evaluated by measuring the surface and volume resistivities (ρ_s, ρ_v) using textile electrode Tera Ohmmeter (TO-3). Textile Softness Analyzer (TSA) has also been used to investigate hand-feel properties of the fabric. After treatment, the results revealed that the surface resistivity was reduced by 35.5% in the case of O₂, 27.3% for air and 18.4% for Ar, and also volume resistivity was decreased by 40.9%, 20.3% and 20% after O₂, air and Ar-plasma, respectively, whereas hand-feel properties are slightly affected at a higher power level and treatment time. Out of the three gases, oxygen had less effect on hand-feel properties and highly reduced the fabric resistivity. In addition, the SEM images showed that the surface morphology of the fibers changed to being rough due to the plasma. Full article

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

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

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

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

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

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

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

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