Internal Fiber Research Articles

Strengthening and Rehabilitating Structural Members by Carbon Fiber Reinforced Polymers (A Review)

The use of Carbon Fiber Reinforced Polymers CFRP in strengthening and rehabilitating structural members is one of the modern techniques which proved to be effective in different civil engineering applications. This review aims to provide the researchers and construction specialists with a detailed description on the practical application of External or Internal Carbon Fiber Reinforced Polymers in strengthening and rehabilitating concrete, steel, and composite members in flexure and shear.

Study on the Mechanical Properties and Thermal Conductivity of Cotton Stalk Fiber Heat-Insulating Shotcrete

In this study, heat-insulating shotcrete with excellent performance was developed to effectively reduce the thermal conductivity and meet the strength requirements of shotcrete in high ground temperature roadways. Ceramsite and pottery sand were used to replace 5% and 10% of sand and stone, respectively. The shotcrete was composed of cotton rod fiber treated with polyvinyl alcohol solution (SH adhesive) and other materials in a certain mix ratio. The working, mechanical, and heat insulation properties of the shotcrete were investigated by compressive strength, splitting tensile, thermal conductivity, electron microscope scanning, and X-ray diffraction tests. The results showed that the optimum content of the cotton stalk fiber was 2 kg/m3. The compressive strength and the splitting tensile properties were excellent, and the strength attained the maximum value. The performance of shotcrete increased with an increase in the cotton stalk fiber content. The thermal conductivity curve decreased smoothly when the cotton stalk fiber content exceeded 2 kg/m3. Furthermore, when the cotton stalk fiber content was 0–2 kg/m3, the internal cotton stalk fiber was tightly wrapped by the hydrate, and the mechanical properties were enhanced. Moreover, when the cotton stalk fiber content was 2-3 kg/m3, a clustering phenomenon occurred, and the compressive and tensile strengths were reduced. The hydration reaction of the cement mixed with cotton stalk fiber was normal, and the reinforced reticulated porous structure was formed with ceramsite in the concrete matrix, improving the strength of the concrete and reducing the thermal conductivity.

A Review of Optical Fibre Ethanol Sensors: Current State and Future Prospects

A range of optical fibre-based sensors for the measurement of ethanol, primarily in aqueous solution, have been developed and are reviewed here. The sensing approaches can be classified into four groups according to the measurement techniques used, namely absorption (or absorbance), external interferometric, internal fibre grating and plasmonic sensing. The sensors within these groupings can be compared in terms of their characteristic performance indicators, which include sensitivity, resolution and measurement range. Here, particular attention is paid to the potential application areas of these sensors as ethanol production is globally viewed as an important industrial activity. Potential industrial applications are highlighted in the context of the emergence of the internet of things (IoT), which is driving widespread utilization of these sensors in the commercially significant industrial and medical sectors. The review concludes with a summary of the current status and future prospects of optical fibre ethanol sensors for industrial use.

Reducing down-cycling of carbon fibre by fibre architecture preservation: Multi-layer fibre surface quality investigation

Carbon fibre has a high mechanical reinforcement capability associated with fibre architectures. However, it is significantly down-cycled in the current recycling practice as a result of a loss of fibre architecture. Without the use of chopping/shredding process, the architecture of carbon fibre can be preserved, but the surface cleanliness of recycled carbon fibre (rCF) is not clear. In this study, an investigation is carried out on the surface quality of architecture-preserved rCF obtained from multiple layers of a carbon fibre reinforced polymer (CFRP). Carbon fibre woven fabrics are manufactured into CFRP, recycled using a pyrolysis technique, and inspected using visual and microscopic techniques. The results indicate a good preservation of fibre architecture in all five layers of CFRP. Nonetheless, the residue from the pyrolysis of resin is increased in the internal layers (4th and 5th) of rCF in comparison to the external layers (1st to 3rd). The results suggest that fibre architecture preservation has a potential to reduce the down-cycling of carbon fibre, but the impact is limited in internal fibre layers due to reduced fibre surface cleanliness. The insights from this study provide a further understanding on the approach to reduce the down-cycling of carbon fibre and move the carbon fibre industry towards circular economy.

Methodical approach for manufacturing-oriented concept development for Tailored Textiles

Tailored Textiles (TT) are load-optimized fiber-based composites, providing a high potential for weight reduction as well as cost-saving compared to conventional composites. Compared to isotropic materials (e.g. most metals and plastics), anisotropic fiber-based composites require the definition of their internal fiber orientation. This additional development step results in strong interdependencies between the different disciplines: structural engineering, material engineering, and manufacturing planning. This provides a high complexity in the Product Development Process (PDP) and prevents the utilization of TT’s potential in industrial applications.This paper presents a customized PDP to develop TT structures, optimized for weight and cost reduction simultaneously. By linking the expert models for structural and cost engineering the necessity of iteration loops can be minimized. To meet the best compromise between a wide solution and the required development effort, customized model-fidelities are assigned to the different milestones during the PDP. This approach enables an early cost and performance evaluation and supports the engineer in his decisions in all phases of the PDP, such as the decision whether to design the component as a fiber-reinforced plastic (FRP) or the selection of the manufacturing technology for TT. Thus, based on this cost and performance evaluation, early decisions can be made about possible manufacturing technologies, reducing the complexity for the subsequent iterations of the detailed development process. Furthermore, the relevant development tasks and responsibilities of the involved entities are defined. The core entities are represented by project planning, production planning, structural engineer and manufacturing planning. The PDP’s scope covers the process from the initial definition of product requirements to manufacturing planning.

Utilization of natural sisal fibers to manufacture eco-friendly ultra-high performance concrete with low autogenous shrinkage

This study aims to explore a new method to reduce autogenous shrinkage of ultra-high performance concrete (UHPC) by incorporating natural sisal fibers. The water absorption and desorption behavior of sisal fibers were firstly determined. Then, flowability, setting time, hydration heat, autogenous shrinkage, internal relative humidity, mechanical properties, fiber distribution, hydration performance, and microstructure of UHPC mixtures incorporating various volume content of sisal fibers were evaluated. The results show that sisal fibers can release the absorbed water with decreasing relative humidity in UHPC specimens. The addition of sisal fibers can restraint the cement hydration process and delay the setting times. The 7 days autogenous shrinkage of UHPC was reduced by 71.4% by adding 1.5 vol% sisal fiber due to the internal curing and reinforcing effect induced by sisal fibers. Incorporating sisal fibers can promote late hydration of UHPC, so the 28 days compressive strength was reduced by only 7.7%∼8.2%. Moreover, the obvious gap between sisal fiber and concrete can be observed from the backscattered electron images, which is caused by the contraction of sisal fiber after releasing water. Finally, the environmental and cost evaluation shows that the use of renewable sisal fiber as a shrinkage-reducing material can reduce the production cost and carbon footprint of UHPC, so it is of great significance to the sustainable production of UHPC.

Fiber packing and morphology driven moisture diffusion mechanics in reinforced composites

Fiber reinforced polymer composite (FRPC) materials are extensively used in lightweight applications due to their high specific strength and other favorable properties including enhanced endurance and corrosion resistance. However, these materials are inevitably exposed to moisture, which is known to drastically reduce their mechanical properties caused by moisture absorption and often accompanied with plasticization, weight gain, hygrothermal swelling, and de-bonding between fiber and matrix. Hence, it is vital to understand moisture diffusion mechanics into FRPCs. The presence of fibers, especially impermeable like Carbon fibers, introduce tortuous moisture diffusion pathways through polymer matrix. In this paper, we elucidate the impact of fiber packing and morphology on moisture diffusion in FRPC materials. Computational models are developed within a finite element framework to evaluate moisture kinetics in impermeable FRPCs. We introduce a tortuosity factor for measuring the extent of deviation in moisture diffusion pathways due to impermeable fiber reinforcements. Two-dimensional micromechanical models are analyzed with varying fiber volume fractions, spatial distributions and morphology to elucidate the influence of internal micromechanical fiber architectures on tortuous diffusion pathways and corresponding diffusivities. Finally, a relationship between tortuosity and diffusivity is established such that diffusivity can be calculated using tortuosity for a given micro-architecture. Tortuosity can be easily calculated for a given architecture by solving steady state diffusion governing equations, whereas time-dependent transient diffusion equations need to be solved for calculating moisture diffusivity. Hence, tortuosity, instead of diffusivity, can be used in future composites designs, multi-scale analyses, and optimization for enabling robust structures in moisture environments.

Determining operating variables that impact internal fiber bonding using Wedge statistical analysis methods

In this study, Wedge statistical analysis tools were used to collect, collate, clean up, plot, and analyze several years of operational data from a commercial paper machine. The z-direction tensile (ZDT) and Scott Bond tests were chosen as representative of fiber bond strength. After analyzing thousands of operational parameters, the ones with the most significant impact upon ZDT involved starch application method, starch penetration, and the amount of starch applied. Scott bond was found to be significantly impacted by formation and refining. Final calendering of the paper web has also shown an impact on internal fiber bonding.

Multichannel Detection of Acoustic Emissions and Localization of the Source with External and Internal Sensors for Partial Discharge Monitoring of Power Transformers

The detection of acoustic emissions with multiple channels and different kinds of sensors (external ultrasound electronic sensors and internal optical fiber sensors) for monitoring power transformers is presented. The source localization based on the times of arrival was previously studied, comparing different strategies for solving the location equations and the most efficient strategy in terms of computational and complexity costs versus performance was selected for analyzing the error propagation. The errors of the acoustic emission source location (localization process) are evaluated from the errors of the times of arrival (detection process). A hybrid programming architecture is proposed to optimize both stages of detection and location. It is formed by a virtual instrumentation system for the acquisition, detection and noise reduction of multiple acoustic channels and an algorithms-oriented programming system for the implementation of the localization techniques (back-propagation and multiple-source separation algorithms could also be implemented in this system). The communication between both systems is performed by a packet transfer protocol that allows continuous operation (e.g., on-line monitoring) and remote operation (e.g., a local monitoring and a remote analysis and diagnosis). For the first time, delay errors are modeled and error propagation is applied with this error source and localization algorithms. The 1% mean delay error propagation gives an accuracy of 9.5 mm (dispersion) and a maximum offset of 4 mm (<1% in both cases) in the AE source localization process. This increases proportionally for more severe errors (up to 5% reported). In the case of a multi-channel internal fiber-optic detection system, the resulting location error with a delay error of 2% is negligible when selecting the most repeated calculated position. These aim at determining the PD area of activity with a precision of better than 1% (<10 mm in 110 cm).

Drying characteristics and processing optimization of combined microwave drying and hot air drying of Termitomyces albuminosus mushroom

Termitomyces albuminosus (termite mushroom) is an edible fungus growing from termitaries in certain parts of China. Recently, the mushroom has gained in popularity, but due to rapid post-harvest quality decay, novel processing techniques including drying are required. This study aimed to optimize the conditions of combined microwave and hot air drying for T. albuminosus. Factors including microwave density, air temperature, and moisture content at conversion point were investigated and optimized using the drying rate, protein content, color L*, DPPH scavenging ability, rehydration ratio (RR), texture, sensory, and overall score as responses. The results showed that the overall score dried at 1.83 W/g microwave density, 60°C hot air, and 50% moisture content at conversion point were 0.675, 0.575, 0.530, respectively. The optimum conditions of combined microwave and hot air drying were microwave density 2.0 W/g, moisture content 52% at conversion point, and hot air temperature 57 respectively. The optimum conditions of combined microwave and hot air drying L* was 54.16, DPPH clearance was 91.87%, RR was 2.41, pileus chewiness was 1,587.19 g, stipe chewiness was 4,457.28 g, sensory score was 7.3, and overall score was 0.793, while the sensory quality was very high. Therefore, microwave drying followed by hot air drying is an effective, suitable method to obtain dried T. albuminosus. Practical applications Termitomyces albuminosus is also known as Termitomyces and has a similar internal fiber structure, color, and flavor as chicken. Drying is one of the most important methods for edible fungi processing and the major aim is to decrease water activity, which in turn minimizes the chemical and physical modifications during storage. The conditions of combined microwave and hot air drying for T. albuminosus were investigated and optimized using the drying rate, protein content, color L*, DPPH scavenging ability, rehydration ratio, texture, sensory, and overall score as responses. The obtained process parameters were helpful, effective, and suitable for the application of combined microwave and hot air drying technology to preserve good quality, especially for T. albuminosus.

Micro-scale modeling of 3D needled nonwoven fiber preforms

This paper proposes a numerical modeling method for generating the virtual fiber structures of 3D needled nonwoven preforms. Microstructures of the preforms are investigated using Micro-CT technology. Geometric parameters of the fibers, including length, orientation and aggregation are statistically analyzed. Then the virtual fibers are generated based on the statistical parameters. Each virtual fiber is a flexible chain connected by truss elements with very short length. After that the virtual fibers are assembled together and compressed to a certain thickness. Deformations and contacts of the virtual fibers are simulated by finite element method using an explicit dynamics algorithm. Finally, 3D needled nonwoven preforms are modeled by numerical simulation of the needling process. The virtual fiber structures and the Micro-CT images are found to be in excellent agreement with each other. The modeling method of this study would be helpful for understanding internal fiber structures of 3D needled nonwoven preforms and provides a good basis to analyze the permeability for resin flow and mechanical properties of the composites.

Axial compressive behaviour of circular FRP-confined multi-tube concrete columns

A new form of hybrid structural column that has improved corrosion resistance and that can enhance the compressive strength and ultimate strain of concrete is the fibre-reinforced polymer (FRP)-confined multi-tube concrete column (MTCC) system. Existing research on MTCCs has been limited to glass FRP (GFRP) outer tubes with internal steel tubes and normal-strength concrete. This paper reports an experimental study on 22 circular MTCCs that are loaded under monotonic axial compression. Five main column parameters are investigated, namely internal tube material, internal tube configuration, concrete strength, fibre type, and FRP tube thickness. The test results show the excellent structural behaviour of MTCCs for both the normal- and high-strength concretes. The MTCCs with internal steel tubes outperformed those with aluminium internal tubes in terms of load carrying capacity. MTCCs confined with basalt FRP and GFRP jackets both performed well, while an increasing of FRP thickness improved the ultimate strength and axial strain capacity of the column. An analytical model based on the transformed section approach is also used to predict the axial load-strain behaviour of the MTCC specimens. The model provides satisfactory predictions of the test results.

Effects of Water and Alkaline Solution on Durability of Carbon-Glass Hybrid Fiber Reinforced Polymer Bars.

The glass fiber reacts with the hydroxyl owing to the concrete pore solution. A thin coat of carbon fiber wraps around the internal GFRP bars to improve the durability of internal GFRP bars in harsh environments. This paper investigates the effect of a thin carbon fiber coat on the durability of the carbon–glass hybrid fiber reinforced polymer bars (HFRP bars) in water, and compares the performance of FRP bars in alkaline solution. To this end, the water absorption behavior, interlaminar shear strength of both the GFRP bars and the HFRP bars was characterized in water and alkaline solution. The results indicate that the diffusivity coefficient of the carbon fiber coat is higher than that of internal GFRP in water. Compared to the GFRP bars in water, the HFRP bars have a higher diffusivity coefficient and saturation water absorption. It caused that the interlaminar shear strength of the HFRP bars aged in water at a temperature of 60 °C for 140 days decreases more markedly than that of the GFRP bars aged under similar conditions. Finally, it was proved that the thin carbon fiber coat does not slow the deterioration of the GFRP bars in water, while the carbon fiber coat significantly improves the retention of the interlaminar shear strength of the HFRP bars in the alkaline solution owing to the prevention of internal glass fiber reactivated by alkali ions.

Experimental Approach for Complex Optical Fiber Angular Orientation and Twist Measurement

Applications associated with complex, structured optical fibers having no circular symmetry often require information about their specific angular orientation. Such cases include, for example, splicing, sophisticated mode coupling, selective fiber Bragg gratings inscription, or direction‐sensitive sensing. Besides the external angular orientation of the fiber, additionally an intrinsic twist of the internal fiber structure has been identified as a critical parameter for applications. Such an intrinsic fiber twist might occur as a side effect of the fiber drawing process, or it may have been introduced intentionally as a special fiber property. In all such cases, a measurement of the local orientation along the fiber is highly desirable. A method for such measurements based on the analysis of the refractive–diffractive scattering patterns is presented. By comparing such measured patterns with reference patterns from modeling or from reference measurements, the orientation of the fiber can be identified with high accuracy and without measuring or reconstructing the detailed cross section of a fiber. The method, therefore, provides an approach for quick identification of a local angular fiber orientation status.

In-Tire Distributed Optical Fiber (DOF) Sensor for the Load Assessment of Light Vehicles in Static Conditions.

Modern vehicles are using control and safety driving algorithms fed by various evaluations such as wheel speeds or road environmental conditions. Wheel load evaluation could be useful for such algorithms, particularly for extreme vehicle loading or uneven loads. For now, smart tires are only equipped by tire pressure monitoring systems (TPMS) and temperature sensors. Manufacturers are still working on in-tire sensors, such as load sensors, to create the next generation of smart tires. The present work aims at demonstrating that a static tire instrumented with an internal optical fiber allows the wheel load estimation for every wheel angular position. Experiments have been carried out with a static tire loaded with a hydraulic press and instrumented with both an internal optical fiber and an embedded laser. Load estimation is performed both from tire deflection and contact patch length evaluations. For several applied loads from 2800 to 4800 N, optical fiber load estimation is realized with a relative error of 1% to 3%, almost as precisely as that with the embedded laser, but with the advantage of the load estimation regardless of the wheel angular position. In perspective, the developed methodology based on an in-tire optical fiber could be used for continuous wheel load estimation for moving vehicles, benefiting control and on-board safety systems.

Cyclic Thermal Shock Damage Behavior in CVI SiC/SiC High-Pressure Turbine Twin Guide Vanes.

In this paper, the SiC/SiC high-pressure turbine twin guide vanes were fabricated using the chemical vapor infiltration (CVI) method. Cyclic thermal shock tests at different target temperatures (i.e., 1400, 1450, and 1480 °C) in a gas environment were conducted to investigate the damage mechanisms and failure modes. During the thermal shock test, large spalling areas appeared on the leading edge and back region. After 400 thermal shock cycles, the spalling area of the coating at the basin and back region of the guide vane was more than 30%, and the whole guide vane turned gray, due to the formation of SiO2. When the thermal shock temperature increased from 1400 to 1450 and 1480 °C, the spalling area of the basin and the back region of the guide vane did not increase significantly, but the delamination occurred at the tenon, upper surface of the guide vane near the trailing edge of the guide vane. Through the X-ray Computed Tomography (XCT) analysis for the guide vanes before and after thermal shock, there was no obvious damage inside of guide vanes. The oxidation of SiC coating and the formation of SiO2 protects the internal fibers from oxidation and damage. Further investigation on the effect of thermal shock on the mechanical properties of SiC/SiC composites should be conducted in the future.

A numerical homogenization technique for unidirectional composites using polygonal generalized finite elements

The present study proposes a computational methodology to obtain the homogenized effective elastic properties of unidirectional fibrous composite materials by using the generalized finite-element method and penalization techniques to impose periodic boundary conditions on non-uniform polygonal unit cells. Each unit cell is described by a single polygonal finite element using Wachspress functions as base shape functions and different families of enrichment functions to account for the internal fiber influence on stresses and strains fields. The periodic boundary conditions are imposed using reflection laws between two parallel opposing faces using a Lagrange multiplier approach; this reflection law creates a distributed reaction force over the edges of the [Formula: see text]-gon from the direct application of a given deformation gradient, which simulates different macroscopic load cases on the macroscopic body the unit cell is part of. The methodology is validated through a comparison with results for similar unit cells found in the literature and its computational efficiency is compared to simple cases solved using a classic finite-element approach. This methodology showed computational advantages over the classic finite elements in both computational efficiency and total number of degrees of freedom for convergence and flexibility on the shape of the unit cell used. Finally, the methodology provides an efficient way to introduce non-circular fiber shapes and voids.

Muscle strain analysis from diffusion tractography and dynamic magnetic resonance imaging of the moving tongue

Strain estimation of a deforming human tongue is an important task in motor control studies. Various magnetic resonance imaging (MRI) modalities provided versatile acquisition tools, facilitating accurate strain computation and quantitative analysis. We report a method that combines data from diffusion and dynamic MRI to yield strain values along internal tongue muscle fiber directions. Dynamic MRI provides spatiotemporal muscle motion. Diffusion tractography provides muscle fiber geometry. Since the two datasets exist in different physical spaces and tractography is susceptible to numerical errors if spatially transformed, we transformed only muscle motion fields from the dynamic MRI space to the diffusion MRI space using diffeomorphic registration. Strain tensors were then computed and projected onto the fiber directions. Masks were used to extract strain of individual muscles. Three tongue motions while pronouncing two utterances and making a forward protrusion were processed. Resulting strain patterns on seven internal muscles showed that some muscles stayed stretched or compressed over all motion time while other muscles switched between stretches and compressions depending on specific tongue shapes. The proposed method enables accurate assessment of variations in muscle strains, which potentially reveals muscle activation patterns and provides insights into the tongue's detailed mechanics in speech motor control.

External sphincter-sparing anal fistulotomy (ESSAF): a simplified technique for the treatment of fistula-in-ano

Fistula-in-ano due to cryptoglandular disease is a common condition. While a simple anal fistula can be treated successfully by a fistulotomy, the risk of potential damage to the anal sphincters and subsequent poor functional outcomes persist in a large portion of patients with complex fistulae. Several sphincter-preserving treatment procedures have been described for complex fistulae over the past 3 decades, with variable results and complication rates, and no procedure is proven to be superior to the others. We developed external sphincter-sparing anal fistulotomy (ESSAF), a reproducible simple modification of the ligation of intersphincteric fistula tract (LIFT) technique for the treatment of complex fistula-in-ano.. The aim of the present study was to describe the technique and our outcomes. This was a retrospective review of all patients who underwent ESSAF for a complex anal fistula at our institution from January 2014 to December 2019. The primary outcome measure of this study was the primary fistula healing rate. Secondary outcome measures included fecal and/or gas incontinence and postoperative complications. During the ESSAF procedure, the mucosa and skin overlying the fistula tract are incised to allow complete exposure of the sphincter complex. Then the internal sphincter muscle fibers overlying the tract are divided and the tract is meticulously curetted and debrided. Next, the internal opening of the tract traversing the external sphincter muscle is suture-ligated with absorbable sutures. Then, a minimal amount of mucosa is advanced and the incision is partially closed with absorbable sutures, while its external portion is left open for drainage. Fifty-nine patients [43 males, median age was 50years (range 36-63years)] underwent ESSAF for complex anal fistula during the study period. Mean follow-up was 12 ± 14.7months. Of the 59 patients, 42 (71.2%) experienced fistula closure, with a median healing time of 8weeks (IQR 4-16weeks). None of the patients developed significant anal incontinence following the procedure. One patient (1.7%) suffered from soiling and another patient (1.7%) developed postoperative bleeding. There were no infectious complications. Of the 17 patients (28.8%) who failed to heal successfully, 9 (15.2%) did not heal primarily and 8 (16%) experienced recurrence after complete healing. Thirteen (76%) of these patients underwent reoperation with complete recovery after ESSAF (n = 4), fistulotomy (n = 8) or endorectal advancement flap (ERAF) (n = 1). Overall ESSAF initiated recovery in 93.2% of the patients. ESSAF is a feasible, safe, reproducible and effective sphincter-sparing procedure for the treatment of complex anal fistulae.

An optical fiber electric field sensor based on polarization-maintaining photonic crystal fiber selectively filled with liquid crystal

This paper presents a liquid crystal selective filling polarization-maintaining photonic crystal fiber (PMPCF) structure for electric field measurement. E7 liquid crystal (LC) is accurately filled into a large hole near the core of the PMPCF to form an internal fiber coupler. When an external voltage is applied, an electric field sensitivity of 1.1137 nm/Vrms is obtained. The device also responds to the frequency of the electric field, and when the frequency of the electric field increases, a blue shift of the transmitted spectrum occurs. The proposed structure has potential application value in the online measurement of electric field value and frequency.