Portion Of Fiber Research Articles

Composition of Active Oxidizing Species in Electrolyzed Sulfuric Acid for Resin Degradation of Carbon Fiber Reinforced Plastics

Peroxodisulfate ion produced by electrolytic oxidation of sulfuric acid is a powerful oxidant that can decompose only the resin portion of carbon fiber reinforced plastics (CFRP), and is expected to be used in technology for reproducing carbon fiber from waste CFRP. Sulfuric acid electrolysis using a boron-doped diamond (BDD) electrode produces mainly three active oxidizing species: peroxodisulfuric acid, hydrogen peroxide, and peroxomonosulfuric acid. The purpose of this study is to investigate the effect of electrolysis condition on the composition of active oxidizing species in the electrolyzed sulfuric acid. In addition, we investigated the relationship between composition of active oxidizing species and resin decomposition properties.30% and 50% sulfuric acid was electrolyzed by constant current electrolysis at BDD electrode. Concentration of the active oxidizing species in the electrolyzed sulfuric acid was estimated by a titration method. CFRP samples were immersed in the electrolyzed sulfuric acid with air bubbling to conduct a resin decomposition test. Concentration of active oxidizing species were investigated before and after the resin decomposition. In addition, changes in the concentration of active oxidizing species before and after resin decomposition of CFRP samples was examined for electrolyzed sulfuric acid with addition of hydrogen peroxide.10 mL of 30% and 50% sulfuric acid were electrolyzed at a constant current of 200 mA for 1 h to obtain electrolyzed sulfuric acid. Concentrations of peroxodisulfate, peroxomonosulfate and hydrogen peroxide were estimated to be 0.191, 0.073, and 0 mol/L for the electrolyzed 30% sulfuric acid, while those were 0.0213, 0.201, and 0.0117 mol/L for the electrolyzed 50% sulfuric acid, respectively. The composition of the active oxidizing species also varied with constant current. Thus, the result indicates that the composition of electrolyzed sulfuric acid can be controlled by the electrolysis condition. After the resin decomposition test, concentrations of peroxodisulfate and peroxomonosulfate decreased, indicating that these species contributed to the resin decomposition.Next, the CFRP samples before and after the resin decomposition test were observed by SEM. As a result, the electrolyzed 30% sulfuric acid was not so effective for resin decomposition, showing partial decomposition of resin in the CFRP. On the other hand, in the case of electrolyzed 50% sulfuric acid, almost no resin was found to remain leaving intact carbon fibers after the decomposition test. Since the total concentration of the active oxidizing species was comparable between these electrolyzed sulfuric acids, the composition of the active oxidizing species is considered to be important for effective resin decomposition. In addition, addition of hydrogen peroxide into the electrolyzed 30% sulfuric acid was found to activate the resin decomposition rate, which is considered to be based on the significant increase of peroxodisulfate and peroxomonosulfate concentrations even after the resin decomposition.

Effect of alkaline treatment on the thermo-physicochemical and mechanical properties of biochar powder/Washingtonia robusta fibers/PLA hybrid biocomposites

Replacing plastic products with fully biodegradable products remains a challenge in our daily lives. Biodegradable hybrid bio composites are designed for various structural and non-structural applications such as car interiors, filaments for 3D printers, biomedical, sports and electronic products, green building materials and food packaging. In this work hybrid composites fabricated using polylactic acid (PLA) matrix reinforced with short plant fibers from the Washingtonia robusta (WR) palm tree and biochar powder (BC) with grain diameters less than 0.6 μm obtained from WR palm waste after carbonization at 300 °C. Initially, a portion of the untreated plant fibers was retained, while the other portion was treated with NaOH (1, 2, 3%) for 15 h. Indeed, the untreated and alkali-treated fibers were observed by SEM and then characterized by thermogravimetric analysis/differential scanning calorimetry. Fourier transform infrared showed physical and chemical changes with surface degradation of the WR treated at higher concentrations (3% NaOH). In addition, establish the relationship between the alkali treatments of the biocomposite reinforcement fibers and the improvement of the mechanical performance of these materials. The best results obtained for the developed biocomposite hybrid products are those of BTR3, for mechanical characteristics such as traction, flexural strength and Izod, with values of 39.56 MPa and 74.43 MPa, and 3.26 kJ/m2 respectively; and 2.30 MPa as elastic stress, also for water absorption with a percentage of 8.3%. The percentages of the alkaline treatments used revealed that the BTR3 model presents the best physical-chemical and mechanical behavior of these new materials.

Ultra-low loss Rayleigh scattering enhancement via light recycling in fiber cladding

Rayleigh backscattering enhancement (RSE) of optical fibers is an effective means to improve the performance of distributed optical fiber sensing. Femtosecond laser direct-writing techniques have been used to modulate the fiber core for RSE. However, in-core modulation loses more transmission light, thus limiting the sensing distance. In this work, a cladding-type RSE (cl-RSE) structure is proposed, where the femtosecond laser is focused in the fiber cladding and an array of scatterers is written parallel to the core. The refractive-index modulation structure redistributes the light in the cladding, and the backward scattered light is recovered, which enhances the Rayleigh backscattered signal with almost no effect on the core light. Experimentally, it was demonstrated that in an effectual cl-RSE structure, the insertion loss was reduced to 0.00001 dB per scatterer, corresponding to the lowest value for a point scatterer to date. The cl-RSE structure accomplished measurements up to 800°C. In particular, the temperature measurement fluctuation of the cl-RSE fiber portion is only 0.00273°C after annealing. These results show that the cl-RSE structure has effective scattering enhancement, ultra-low loss, and excellent high-temperature characteristics, and has great potential for application in Rayleigh scattering-enhanced distributed fiber sensing.

Mechanical characterization and study on morphological properties: Natural and agro waste utilization of reinforced polyester hybrid composites

Eco-conscious products are currently garnering significant attention due to their abundant availability and versatile applications in various engineering contexts. The distinctive properties of natural fibers make them readily substitutable for synthetic fibers. A substantial one million tonnes of fiber waste, primarily composed of paddy straw fiber, is generated globally. The research emphasis revolves around the adoption of the Waste to Wealth technique, a highly efficient process aimed at repurposing waste materials. This approach plays a pivotal role in curbing air pollution, specifically by preventing the incineration of the residual portion of paddy straw fiber on agricultural lands. The study involves the collection of paddy straw fiber from agricultural fields, with subsequent extraction facilitated by an extracting machine. Employing a chemical treatment process enhances the adhesion properties between the fiber and matrix. Consequently, comprehensive fiber tests, including the single fiber test, fiber tenacity, and fiber fineness, were meticulously examined for both treated and untreated fibers. The reinforcements and matrix were taken by the weight percentage of 50:50 with different fiber length (25, 50, 75, 100 mm) using the compression moulding machine with 300 mm × 300 mm × 3 mm dimensions. After making the laminates, the samples were cut as per the ASTM standard. The mechanical and morphological behavior of the hybrid fiber-reinforced polyester composites were evaluated, and the water absorption property in the concerned laminates was studied.

Colonic fermentation of enzymatically treated cocoa bean shells (CBSs) and short chain fatty acids (SCFAs) production.

Cocoa bean shells (CBSs) are a by-product of the cocoa production chain characterized by a substantial dietary fiber (DF) content. The aim of this work was the evaluation of the prebiotic activity of DF from raw CBSs as well as defatted and dephenolized CBSs (polyphenols in their free form) treated with different enzymes mixtures to increase the fermentable fiber portion. Fermentability was tested through an in vitro model of colon fermentation using microbiota selectively adapted to more proximal and most distal compartments of the colon. Results showed a significant amount of short chain fatty acids (SCFAs) produced, particularly acetate, from fermentation of the lipid- and polyphenols-free CBS treated with the cellulase mixture. In both colonic regions, this sample boosted the production of SCFAs, suggesting the potential usefulness of this enzyme-driven processing to improve the prebiotic effect of CBS. Despite these findings, there was not a change in the DF content of the enzymatically treated samples, especially regarding the soluble dietary fiber (SDF) fraction. This outcome suggests that a structural change may have occurred in the fiber fraction increasing its fermentability. These outcomes open a new scenario in the bio-valorization of CBSs, in accordance with the concept of circular economy.

Femtosecond laser writing of robust waveguides in optical fibers with enhanced photosensitivity

We report the femtosecond laser writing of meter-long optical waveguides inscribed through the coating of specifically designed optical fibers. In order to improve the material photosensitivity and to ensure non-guiding optical fibers for subsequent laser processing of the waveguiding core, a depressed refractive index core design is implemented by co-doping a large portion of the optical fiber with germanium oxide and fluorine. The enhanced photosensitivity provided by further deuterium loading these fibers allows laser-writing of large refractive index contrast waveguides over wide cross sections. To mitigate the formation of photoinduced color centers causing high propagation losses in the photo-written waveguides, thermal annealing up to 400°C is performed on polyimide-coated laser-written fibers. Although the refractive index contrast decreases, the propagation losses are drastically reduced down to 0.08 dB/cm at 900nm allowing a robust single-mode guiding from visible to near infrared. Our results pave the way towards the development of a new generation of optical fibers and photonic components with arbitrarily complex designs.

Self Q-switched single-frequency all-fiber laser

Here, we propose a self Q-switched single-frequency (SF) all-fiber laser. The intra-cavity Er:Yb co-doped fiber serves not only as an active fiber for lasing but also as a fiber-type saturable absorber (SA). The self-Q-switching behavior is induced by the ground-state reabsorption of the unpumped portion of the active fiber. To achieve SF operation, double fiber loops constructed by two 3 dB optical couplers (OCs) form a cascade sub-cavity, which serves as a mode selector with a narrow bandwidth. Taking the advantage of a high damage threshold of the fiber-type SA, microjoule-level self-Q-switched SF pulses are obtained with a narrow linewidth of ∼252kHz. Combed with the measured pulse width of ∼1.766µs, the corresponding time-bandwidth product is ∼0.445, which is very close to the Gaussian transform limit. The maximum output power of the pulsed SF laser can reach ∼100mW. By stretching the fiber Bragg grating (FBG), the wavelength of the pulsed SF laser can be tuned.

A light-powered self-rotating liquid crystal elastomer drill

Self-oscillating systems can directly convert ambient energy to mechanical work, and new type self-oscillating systems are worth designing for applications in energy harvesters, engines, and actuators. Taking inspiration from the hand drill, we have developed a novel self-rotating drill system, which is consist of a turnplate and a liquid crystal elastomer (LCE) fiber under steady illumination. To investigate the self-rotating behaviors of the LCE drill, we have proposed a nonlinear theoretical model of the LCE drill under steady illumination based on the well-established dynamic LCE model. Numerical calculation reveals that the LCE drill can undergo a supercritical Hopf bifurcation between the static regime and the self-rotation regime. The self-rotation of drill originates from the contraction of winding portion of LCE fiber in illumination at winding state, and its continuous periodic motion is sustained by the interrelation between light energy and damping dissipation. The Hopf bifurcation conditions are also investigated in detail, as well as the vital system parameters affecting its frequency and amplitude. In contrast to the abundant existing self-oscillating systems, this self-rotating drill stands out due to its simple and lightweight structure, customizable dimensions, and high speed, and thus facilitates the design of compact and integrated systems, enhancing their applicability in microdevices and systems. This bears great significance in fields like micro-robotics, micro-sensors, and medical instruments, enabling the realization of smaller and higher-performance devices.

Supervised tractogram filtering using Geometric Deep Learning.

A tractogram is a virtual representation of the brain white matter. It is composed of millions of virtual fibers, encoded as 3D polylines, which approximate the white matter axonal pathways. To date, tractograms are the most accurate white matter representation and thus are used for tasks like presurgical planning and investigations of neuroplasticity, brain disorders, or brain networks. However, it is a well-known issue that a large portion of tractogram fibers is not anatomically plausible and can be considered artifacts of the tracking procedure. With Verifyber, we tackle the problem of filtering out such non-plausible fibers using a novel fully-supervised learning approach. Differently from other approaches based on signal reconstruction and/or brain topology regularization, we guide our method with the existing anatomical knowledge of the white matter. Using tractograms annotated according to anatomical principles, we train our model, Verifyber, to classify fibers as either anatomically plausible or non-plausible. The proposed Verifyber model is an original Geometric Deep Learning method that can deal with variable size fibers, while being invariant to fiber orientation. Our model considers each fiber as a graph of points, and by learning features of the edges between consecutive points via the proposed sequence Edge Convolution, it can capture the underlying anatomical properties. The output filtering results highly accurate and robust across an extensive set of experiments, and fast; with a 12GB GPU, filtering a tractogram of 1M fibers requires less than a minute.

Surface Plasmon Resonance (SPR)-Based Multimode Optical Fiber Sensors for Electrical Transformer Oil Aging Detection

I In this study, optical fibers were designed and implemented as a chemical sensor based on surface plasmon resonance (SPR) to estimate the age of the oil used in electrical transformers. The study depends on the refractive indices of the oil. The sensor was created by embedding the center portion of the optical fiber in a resin block, followed by polishing, and tapering to create the optical fiber sensor. The tapering time was 50 min. The multi-mode optical fiber was coated with 60 nm thickness gold metal. The deposition length was 4 cm. The sensor's resonance wavelength was 415 nm. The primary sensor parameters were calculated, including sensitivity (6.25), signal-to-noise ratio (2.38), figure of merit (4.88), and accuracy (3.2). In the current study, the refractive index values of sucrose and water solutions at different concentrations, which were used as a calibration method, were calculated to be (1.346, 1.359, 1.382, and 1.39). It was found that when the refractive index of the sensitive medium increases, the length of the resonant wavelength increases due to the decrease in energy.

PSIX-18 A Meta-Analysis on Undigestible Neutral Detergent Fiber as a Predictor for Feedlot Cattle Performance and Carcass Characteristics

Abstract Undigestible neutral detergent fiber (uNDF) is a non-nutritive component of the diet representing the portion of neutral detergent fiber (NDF) that is not digested. The uNDF amount affects ruminal fill, passage rate, diet digestibility, and cattle performance. Therefore, a meta-analysis was conducted to evaluate the potential use of dietary uNDF to predict finishing feedlot cattle performance and carcass characteristics. A specific search string was used to obtain 22 eligible experiments forming a database in which models were developed. The search string used was as follows “(feedlot OR beef) AND (forage OR roughage OR iNDF OR uNDF) AND (dressing percentage OR dressing %) AND (liver abscess) AND (feed efficiency OR GF OR FG) AND (DMI) AND (ADG) AND (rumen pH OR ruminal pH OR reticulo-ruminal pH)”. Due to the lack of measurement and reporting of uNDF in the literature, the dietary uNDF of each treatment included in the meta-analysis was estimated using data from the Cumberland Valley Analytical Services database. A comparison of uNDF and NDF as predictor variables of performance was also assessed. Models were developed using a mixed model approach, where experiment was modelled as a random effect. Models with dry matter intake (DMI), implant or tylosin as driving variables alongside uNDF concentration or uNDF intake lowered the root mean square prediction error (RMSPE) and improved the concordance correlation coefficient (CCC). The comparison of uNDF and NDF as predictors of outcomes demonstrated more accurate predictions with uNDF as the driving variable. Developed models from this meta-analysis can reasonably predict average daily gain, DMI, dressing percentage, final body weight, dressing percentage, feed efficiency, and hot carcass weight in healthy Bos taurus feedlot cattle. Results suggest there is still more to be discovered about uNDF and its impact in diets for finishing cattle and that uNDF may be a more informative metric than NDF alone. Further research to improve the characterization of forage in the diets of beef cattle is recommended.

Detection of biofuel adulterants using an optical fiber-based refractive index sensor

This study presents a Lossy Mode Resonance (LMR) based on fiber optic sensor for detecting biofuel adulteration. Tin Oxide (SnO2), coated over the clad removed portion of the optical fiber using the Radio Frequency Magnetron sputtering technique, was utilized as the sensing layer. The fabricated sensor probe was analyzed with various concentrations of the analytes that include methanol in ethanol, ethanol in methanol, methanol in water, ethanol in water, water in methanol, and water in ethanol. The absorption spectra of the fabricated sensor probe revealed two LMR peaks namely, LMR1 and LMR2 that exhibited wavelength shift under varying concentration of the analytes. The maximum sensor responses for the above combinations of the analytes were 4.95%, 3.30%, 3.00%, 3.56%, 2.91% and 3.57%, respectively. The sensitivities of the sensor probe towards these analytes were 0.46 nm/vol%, 0.17 nm/vol%, 0.49 nm/vol%, 0.58 nm/vol%, 0.08 nm/vol%, and 0.4 nm/vol%, respectively. The real time sample were examined using metal oxides coated sensors. The result exhibits SnO2 coated probe is sensitive than other probes.

Biotransformation of okara (soybean residue) through solid-state fermentation using probiotic Bacillus subtilis and Bacillus coagulans

Okara or soybean residue is a side-stream product of soybean processing generated in large quantities. However, okara is often underutilised as it is prone to spoilage and has a short shelf life. In this study, we explored the feasibility of biotransformation of okara through solid-state fermentation using probiotic Bacillus spp. to modify its nutritional value and flavour property. Two probiotic Bacillus species, namely Bacillus subtilis CU1 (CNCM I-2745) and R0179, and Bacillus coagulans IS-2 and 123 were firstly screened. Further analyses were performed on the B. subtilis R0179 and B. coagulans 123 fermented okara due to their better growth after 24 h (10.28 and 9.24 log colony forming units (CFU)/g respectively). Our results showed that B. subtilis R0179 converted a significant portion of okara insoluble dietary fibre into soluble dietary fibre after fermentation, but not B. coagulans 123. In addition, the samples fermented with B. subtilis R0179 showed higher amounts of maltose, hemicellulosic sugars as well as aromatic, branched-chain and hydrophobic amino acids. Furthermore, the B. subtilis R0179 transformed okara had greater amounts of acetoin, carboxylic acids, pyrazines and branched-chain fatty acids, which may contribute to characteristic natto-like and cheesy flavour. Overall, our study shed light on the possibility of using probiotic bacilli to transform okara with enhanced nutritional value and flavour property, which may increase okara usage in foods.

Study Explores Integration of Subsea Optical Distribution Systems

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 32645, “All-Optical Subsea Sensing and Communications,” by Glenn Wilson, SPE, Halliburton, and Mauricio Uribe and Sigurd Moe, TechnipFMC, et al. The paper has not been peer reviewed. Copyright 2023 Offshore Technology Conference. Reproduced by permission. _ Subsea control systems use electric or optical communication channels within subsea optical distribution systems for redundant, duplex telemetry between topside facilities and subsea control systems. Downhole fiber-optic sensing (DFOS) systems use the same subsea optical distribution systems for establishing transmission paths between the same topside facilities and downhole sensing fibers. At the time of writing, subsea fiber-optic control and sensing systems have been operated on independent subsea optical distribution systems. This redundancy introduces complexity and cost into the overall subsea optical distribution system required for subsea developments. In the complete paper, the authors describe the systems that combine fiber-optic communications for subsea control systems and DFOS systems into the same subsea optical distribution system. Need for Systems Integration While maturity of, and demand for, DFOS technology has grown for offshore projects with dry-tree installations, operators have expressed the need for solutions to address fiber-optic technology gaps for subsea development projects. To this end, the topside DFOS interrogation of subsea wells requires optical engineering solutions to compensate for the insertion losses and back-reflections accumulated through umbilicals, multiple wet- and dry-mate optical connectors, splices, optical feedthrough systems (OFS), and downhole-sensing-fiber and optical wet-mate connectors (Fig. 1). To obviate these problems for distributed acoustic sensing (DAS), the authors previously introduced a subsea fiber topology with two transmission fibers from the topside to a remote optical circulator deployed in the optical flying lead (OFL) at the subsea tree. This limits the sensing fiber portion of the total fiber length to the fiber located below the remote circulator and eliminates all back-reflections from the multiple subsea connectors in the subsea infrastructure above the remote circulator. The DAS pulse-repetition rate is constrained only by the fiber length below the remote circulator, thus enabling dry-tree equivalent pulse-repetition rates (i.e., acoustic bandwidth) regardless of the tieback distance. This yields significant signal-to-noise ratio improvement through stacking and selective amplification while further enabling sensing of high-frequency acoustic events occurring inside, or in the vicinity of, the wellbore. The initial application for subsea DAS was installing fiber from the tubing hanger to the production packer for vertical seismic profiling. The ability to maximize acoustic bandwidth irrespective of tieback distance, however, enables a wider range of interventionless reservoir diagnostic applications. This has increased operator demand for installing fiber across the reservoir section.

Exploiting the Advantages of Ag/ITO/Enzyme Trapped Gel Layers to Develop a Highly Sensitive and Selective Fiber Optic Plasmonic Urea Sensor

The fabrication and characterization of a surface plasmon resonance (SPR)-based urea biosensor, with thin silver (Ag), ITO (In2O3: SnO2), and enzyme-trapped gel over an unclad portion of plastic-clad silica fiber as a sensing element, is represented. The working principle is to identify changes in the refractive index of the enzyme (urease) entrapped gel layer following the interaction with the incoming analyte. This interaction causes swelling and shrinkage of the gel layer, which alters the effective refractive index of the sensing layer. The wavelength interrogation method is used, and the optimized sensor probe is characterized by urea samples having different pH values. Scanning electron microscopy confirmed the uniformity of the silver layer over the unclad core of the fiber. The sensor operates from 0 to 160 mM of urea concentrations to cover the physiological concentration range of blood urea normally present in the human body. The sensitivity and limit of detection (LOD) offered by the sensor are marked 0.59387 nm/mM near zero concentration of the urea sample and 0.56 mM, respectively, along with the provisions of high stability, remote sensing, and online monitoring of urea. The proposed sensor has proven to be one of a kind due to its fast response time.

Sympathetic components in left and right human cervical vagus nerve: implications for vagus nerve stimulation.

Cervical vagus nerve stimulation is in a great variety of clinical situations indicated as a form of treatment. It is textbook knowledge that at the cervical level the vagus nerve contains many different fiber classes. Yet, recently, several reports have shown that this nerve also may contain an additional class of potentially noradrenergic fibers, suggested to denote efferent sympathetic fibers. As such, the nature and presence of these fibers should be considered when choosing a stimulation protocol. We have studied human vagus material extracted from dissection room cadavers in order to further confirm the presence of this class of fibers, to study their origin and direction within the nerve and to determine their distribution and variability between subjects and pairs of left and right nerves of the same individual. Sections were studied with immunohistochemical techniques using antibodies against tyrosine hydroxylase (TH: presumed to indicate noradrenergic fibers), myelin basic protein and neurofilament. Our results show that at least part of the TH-positive fibers derive from the superior cervical ganglion or sympathetic trunk, do not follow a cranial but take a peripheral course through the nerve. The portion of TH-positive fibers is highly variable between individuals but also between the left and right pairs of the same individual. TH-positive fibers can distribute and wander throughout the fascicles but maintain a generally clustered appearance. The fraction of TH-positive fibers generally diminishes in the left cervical vagus nerve when moving in a caudal direction but remains more constant in the right nerve. These results may help to determine optimal stimulation parameters for cervical vagus stimulation in clinical settings.

Heating of thick continuous glass fiber reinforced thermoplastic plates via embedded metal mesh networks

A method is proposed to locally heat areas of thick (>25.4 mm) continuous glass fiber reinforced thermoplastic (C-FRTP) composites with embedded wire mesh resistive heating elements. Four test specimens including 10.6 cm wide nichrome mesh heating elements embedded in C-FRTP laminates were fabricated and used for heating trials, showing that the composite can be locally heated to near the thermoplastic forming temperature over its entire thickness in less than 1 hour. The heating trials were simulated using a purpose-built finite difference model to investigate detailed temperature distributions. The simulations show that the internal resistive heating elements are capable of locally increasing the temperature of the composite with negligible effect on the adjacent material. Heating efficiency is between 73% and 77%, with temperature differences in the z-direction at peak temperatures less than 35°C. Temperature uniformity can be improved by longer heating times and more heating elements. The local heating method does not cause deconsolidation of the part. The heating method was also experimentally assessed on a more complex cross-section laminate with varying thickness and a foam core using stainless steel mesh heating elements. Results from the first heating tests were applied to the experimental assessment of the more complex laminate to reduce z-direction temperature differences. Numerical simulation of the heating of the foam core laminate showed a z-direction temperature range of 15.5°C. The results of this study show that embedded resistive heating is a cost-effective and simple method for heating a local portion of a thick fiber reinforced thermoplastic composite.

Coir/glass hybrid fiber reinforced thermoset polymer composite laminates with room-temperature self-healing and shape memory functions

Natural fibers have a lot of potentials as renewable reinforcements for polymers. However, their lower load-carrying capacity compared with synthetic fibers made it a challenge to use them as polymer reinforcements. When a laminated composite beam is bent, the normal stress is the highest on the top and bottom layers and zero in the midplane due to the (non)linear distribution of normal strain. Even though the shear stress is the highest in the midplane, most polymers can tolerate the high shear stress. Therefore, hybrid composite laminates with strong synthetic glass fibers stacked over the core of weak natural coir fiber reinforcement have been designed. Even using a significant portion of coir fibers in the composites, the samples with hybrid fiber reinforcement showed almost similar mechanical properties compared with the samples with glass fiber reinforcement alone. Delamination and matrix crack induced by low velocity impact inside the composite panels were repeatedly healed at room temperature due to the self-healing capability of the diglycidyl 1,2-cyclohexanedicarboxylate (DCN) and polyethylenimine (PEI) polymer matrix. The healing efficiency was up to 99% for the first healing cycle and 72% for the fourth healing cycle. The composites also had good shape memory properties, with a shape fixity ratio up to 51% and a shape recovery ratio up to 93%, which were well maintained even after the several damage/healing cycles of the composites. This study opens new opportunities for applications of natural fibers in multifunctional load-bearing composites.

Fabrication and mechanical properties of metakaolin‐based geopolymer composites reinforced with auxetic fabrics

AbstractThis work presents a novel experimental study on the use of auxetic fabrics as the main reinforcement in geopolymer composites, aiming at higher energy dissipation in impact demanding applications. For this, a potassium‐based geopolymer was reinforced with an auxetic fabric consisting of basalt fiber fillings positioned between helical auxetic yarns (HAY) made of a thermoplastic polyester core, and a stiffer liquid‐crystal polymer wrap, which dispersed the load demands into several single elements having different capabilities. The composites were investigated under quasi‐static flexural and tensile loadings, in both longitudinal and transverse directions. The latter showed increased mechanical strengths, up to 26 MPa in tension, and 12.8 MPa in flexural strength. Each fiber portion was tested in tension separately, reaching flexible (core) and stiffer (wrap and basalt) responses, whereas HAYs displayed combined performances due to a suitable auxeticity effect, that is, a negative Poisson's ratio. The pullout investigation justified the cracking and delamination of the composites, due to its cyclic lateral area modification, which created a load demand much higher than what the brittle geopolymer can sustain in this type of solicitation. Thermogravimetric analyses helped to predict the use of such configurations under thermal exposure, pointing out that the geopolymer material could be a suitable thermal barrier to prevent sudden degradation of the fabric under these conditions.

REVIEW ON CONVENTIONAL CONCRETE AND NYLON FIBER REINFORCED CONCRETE BEHAVIOR

The addition of fibers to reinforced cement concrete enhances the suitability of structures under impacts and earthquake loads by boosting firmness or energy-consuming proficiency of the hardened concrete material. During cracking of concrete, one of the most relevant behaviors of fiber like “bridge effect” starts functioning. As a result of this, fiber blocks crack formation and propagation, and hence strength and ductility of concrete structure improve. The goal of this study is to compare the mechanical properties of reinforced cement concrete by mixing nylon fibers and without mixing nylon fibers. In this study, data from existing article are assessed to compare the strengths of nylon fiber reinforced concrete and conventional concrete by using concrete strength measuring test results such as compressive strength test, flexural strength test, and split tensile strength test. Adding fiber with concrete mix reduces the moisture content, thereby lessening the workability of concrete which produces fiber ball. Due to the obvious lack of homogeneity caused by fiber balling, the efficiency of fiber reinforced concrete is reduced. During the mixing of small portions of fibers with dry concrete the difficulty of fiber separation can prevent by providing good distribution and scattering within the mixtures which enhance concrete strength and thus the balling incident can escape. The dynamic transmission of stress between concrete mix and the fiber achieves by considering significant factors like aspect ratio, volume, and orientation of the fiber. Nylon fiber provides mechanical improvement of reinforced concrete by enhancing impact resistance and increasing flexural toughness, as a result the load-bearing capacity of concrete develops effectively. Introducing nylon fibers with concrete mixture promotes strong tensile comportment of concrete outstandingly after the post peak stage.