Fiber Constituents Research Articles

Fiber-reinforced composites: nonlinear elasticity and beyond

A fiber-reinforced material comprised of a soft polymeric matrix reinforced with polymeric filaments is often modeled as an equivalent anisotropic nonlinearly elastic solid. Although the response of a single constituent polymeric material can be modeled by nonlinear thermo-elasticity over a large range of deformations and temperatures, there can be conditions requiring a theory that extends the range of application to account for other features, such as nonlinear viscoelasticity and an evolving microstructure due to a combination of mechanical and nonmechanical factors. In a multi-constituent fiber-reinforced material these effects can be expected to occur with different initial triggering and ongoing potency in the separate polymer matrix and fiber constituents. This paper summarizes a number of constitutive models for fiber-reinforced materials that include these features, discusses the connection of these models to a nonlinearly elastic scaffold, provides a framework for the incorporation of these features into the constitutive theory for an equivalent general simple solid, and shows how certain terms in the mathematical structure can be associated with the matrix constituent while other terms can associated with the fibrous constituent.

Research on flexure and impact performance of functionally-graded two-stage fibrous concrete beams of different sizes

This research focuses on developing functionally-graded two-stage fibrous concrete (FGTFC) comprising steel and polypropylene fibres to enhance impact resistance and alleviate the damage. The FGTFC was developed based on the bionic-inspired impact resistance of turtle shells. This research examines the flexural and impact performance of FGTFC beams of three sizes. Three different beams were prepared of size 250 × 50 × 50 mm, 400 × 100 × 100 mm and 550 × 150 × 150 mm with a 2.4% average dosage of steel and polypropylene fibres. Additionally, steel and polypropylene used in this study are the new types of fibres which are not used by researchers and not found in the literature. Totally twelve mixtures were prepared; one was Two-Stage Concrete (TSC) and considered a reference specimen. Two-Stage Fibrous Concrete (TSFC) was another two with fully reinforced single layer cross-sectional beams, with their fibres constituents being dispersed evenly. The remaining were two and three-layered FGTFC beams with evenly dispersed fibre constituents. Uneven dispersion in the current research meant that the fibre dosage was more in the peripheral layers and less in the inner layers, despite the fibre dosage being used remains the same in all beams. The fabricated FGTFC beams were synchronously cast using cement grout and tested against the three-point bending and falling mass impact. All beams were tested through the falling mass impact as per the guidelines of ACI Committee 544. Compressive strength, first crack and peak stress, flexural toughness, initial crack impact number, failure impact number, impact ductility index, and failure patterns were examined. Findings indicated that the peak load, flexural toughness and impact strength increased significantly with increased beam size. Additionally, steel fibre significantly contributed to increasing flexural toughness and impact strength than the polypropylene fibre. Thus, the proposed three-layer FGTFC beams had greater efficacy and exceptional fiber usage in the peripheral layers, despite the exact fibre dosage in all TSFC beams.

Characterizing the autonomic neural connections between the abdominal aortic and superior hypogastric plexuses: A multimodal neuroanatomical study.

The aortic plexus serves as the primary gateway for sympathetic fibers innervating the pelvic viscera. Damage to this plexus and/or its associated branches can lead to an assortment of neurogenic complications such as bladder dysregulation or retrograde ejaculation. The neuroanatomy of this autonomic plexus has only recently been clarified in humans; as such, the precise function of its constituent fibers is still not clear. Further study into the functional neuroanatomy of the aortic plexus could help refine nerve-sparing surgical procedures that risk debilitating neurogenic complications, while also advancing understanding of peripheral sympathetic circuitry. To this end, the current study employed an in vivo electrostimulation paradigm in a porcine model, in combination with lipophilic neuronal tracing experiments in fixed, post-mortem human tissues, to further characterize the functional neuroanatomy of the aortic plexus. Electrostimulation results demonstrated that caudal lumbar splanchnic nerves provide primary control over the porcine bladder neck in comparison to other constituent fibers within the aortic plexus. Ex vivo human data revealed that the prehypogastric ganglion contains a significant number of neurons projecting to the superior hypogastric plexus, and that these neurons are arranged in a topographic manner within the ganglion. Altogether, these findings suggest that a pivotal sympathetic pathway mediating bladder neck contraction courses through the caudal lumbar splanchnic nerves, prehypogastric and inferior mesenteric ganglia and superior hypogastric plexus.

Suitability evaluation of untreated and surface-modified Eichhornia crassipes fibers for brake pad applications

ABSTRACT The current study investigated the suitability of untreated, alkali-treated, and silane-treated Eichhornia crassipes fibers as reinforcement in brake pads. The physio-chemical, thermal, crystalline properties of the untreated, alkali-treated, and silane-treated fibers were evaluated. Chemically modified fibers were utilized to develop brake pads and their properties were evaluated as per the industrial standards. The outcomes elucidated that silane treatment removed the extra lignin, hemicellulose, wax substances from the constituents of the Eichhornia crassipes fibers which increased the fiber bonding with the phenolic resin in brake pads. The silane-treated Eichhornia crassipes fibers had the higher thermal stability, maximum degradation temperature (338.2ºC), and crystallinity index (33.17%) than untreated and alkali-treated fiber. The brake pads with silane-treated Eichhornia crassipes fibers showed less acetone extraction value of 1.1%, proving its better curing and fade-recovery characteristics with the standard range as prescribed by industrial standards. Chase tested brake pads with silane-treated Eichhornia crassipes fibers had good fiber bonding and plateau formations as inferred from Scanning Electron Microscope.

Pasture and animal production in silvopastoral and open pasture systems managed with crossbred dairy heifers

The objective of this study was to evaluate the pasture traits and performance of crossbreed dairy heifers in a silvopastoral system (SPS) and open pasture (OP) of Urochloa decumbens, after 14-years of management. In the SPS, an average reduction of 46% in the photosynthetically active radiation (PAR) was calculated in relation to the OP. Experimental design was a randomized complete block, with three replications and two treatments (SPS and OP), evaluated in two seasons (summer and autumn), during three years. The paddocks were managed under continuous stocking with Holstein × Gyr heifers. The herbage mass was greater in OP, but a greater leaf and lower dead material percentages were observed in the SPS. The OP had higher tiller population than SPS only in the first year. The herbage accumulation was higher in the OP during autumn; however during summer only a trend was observed. The crude protein content was greatest in SPS, while the fiber constituents and forage digestibility did not vary with system. The stocking rate was greater in OP in the second year and similar between systems in the other years. Average daily gains were similar between systems, regardless of season and experimental year, while the OP showed a greater gain per area in the third experimental year. Despite of the difference in some variables, after 14–16 years of establishment, it was observed only a small decrease in the animal productive per area in SPS in the last year, in relation to OP, which indicates a high resilience of SPS, even under intense shading.

Identification of the Physical and Mechanical Properties of Moroccan Sisal Yarns Used as Reinforcements for Composite Materials

This work aims to investigate the physical and mechanical properties of sisal fiber and yarn of Moroccan origin. The cellulosic and non-cellulosic constituents of the Moroccan sisal fiber were identified by FTIR spectroscopy. The thermal properties were studied by thermogravimetric analysis. The hydrophilicity of the fiber was evaluated by the contact angle. The results show that the sisal fiber has a low thermal stability. The mechanical properties of the fiber analyzed by the Impregnated Fiber Bundle Test (IFBT) method show that the porosity of the impregnated yarns and the twist angle of the yarns influence the elastic modulus of the sisal fiber. The physical and mechanical properties of the manufactured sisal yarns were also characterized and analyzed. The obtained results reveal an interesting potential to use the Moroccan sisal fiber in development of bio-sourced composite materials.

Mechanical behavior and failure of glass/carbon fiber hybrid composites: Multiscale computational predictions validated by experiments

A comprehensive, novel and computationally low cost multiscale model based on finite element analysis is proposed which includes repeating unit cell micromechanics, material nonlinearity, and progressive damage analysis to predict the mechanical behavior and failure of glass/carbon fiber hybrid composites subjected to various loading conditions. The computational micromechanics is used to predict the homogenized properties of the composite from the mechanical properties of its constituents (fiber, and matrix), together with the volume fraction and spatial distribution of the fibers within it. Hashin’s failure criteria at the meso-scale is implemented to determine failure of lamina while nonlinearity of epoxy matrix is introduced to model through J2 deformation theory of plasticity. It is shown that the introduced multiscale model can be used for 3D macroscale structural analysis through a user defined material (UMAT) subroutine developed at the finite-element software ABAQUS/Implicit. The results of 3-point bending and tensile tests accompanied by acoustic emission, and in-plane shear tests with digital image correlation analysis, are used to validate the proposed multiscale model. It is shown that damage progress and strain distribution under various loading conditions can be predicted successfully, thus a reasonable correlation between the model and collected experimental data is achieved.

The chemical composition of oyster nut (Telfairia pedata) seeds and oil

In this paper, the chemical composition of Telfairia pedata seeds and oil is discussed. This crop belongs to the family of Cucurbitaceae. Unroasted seeds and oil obtained from roasted seeds were collected during a study trip in Tanzania. Oil from unroasted seeds was extracted in the lab using hexane. The seeds contain approximately 60 (% m/m) of oil and 30 (% m/m) of protein, being the remaining amount represented by crude fiber, carbohydrates and mineral constituents. The protein fraction contains glutamic acid, arginine, aspartic acid and leucine as the most representative amino acids. The fatty acid composition is a common one, being palmitic, linoleic, stearic and oleic acids, the most important fatty acids detected. No difference was found in fatty acid composition between oils extracted from roasted and unroasted seeds. On the contrary, the oil obtained from roasted seeds shows a higher concentration in sterols and tocopherols while the distribution between the different constituents remains the same.

Intelligent manufacturing of color blended yarn: Color matching algorithm and manufacturing process through computer numerically controlled ring spinning system

Yarn-dyed textiles complement digital printing textiles, which hold promise for high production and environmentally friendly energy efficiencies. However, the complicated structures of color-blended yarns lead to unpredictable colors in textile products and become a roadblock to developing nonpollution textile products. In the present work, we propose a framework of intelligent manufacturing of color blended yarn by combining the color prediction algorithm with a self-developed computer numerically controlled (CNC) ring spinning system. The S-N model is used for the prediction of the color blending effect of the ring-spun yarn. The optimized blending ratios of ring-spun yarn are obtained based on the proposed linear model of parameter W. Subsequently, the CNC ring-spinning frame is used to manufacture color-blended yarns, which can configure the constituent fibers in such a way that different sections of yarn exhibit different colors.

On the Ablation Behavior of Carbon Fiber-Reinforced Plastics during Laser Surface Treatment Using Pulsed Lasers

This contribution discusses the ablation phenomena observed during laser treatment of carbon fiber-reinforced plastics (CFRPs) with pulsed lasers observed employing laser sources with wavelengths of 355 nm, 1064 nm and 10.6 µm and pulse durations from picoseconds (11 ps) to microseconds (14 µs) are analyzed and discussed. In particular, the threshold fluence of the matrix material epoxy (EP) and the damage threshold of CFRP were calculated. Moreover, two general surface pretreatment strategies are investigated, including selective matrix removal and structure generation through indentation (ablation of both, matrix material and fibers) with a cross-like morphology. The surfaces obtained after the laser treatment are characterized by means of optical and scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy is employed for the analysis of composite and constituent materials epoxy and carbon fibers. As a result, different ablation mechanisms, including evaporation and delamination are observed, depending on the employed laser wavelength and pulse duration. For both 355 nm and 1064 nm wavelength, the laser radiation produces only partial ablation of the carbon fibers due to their higher absorption coefficient compared to the epoxy matrix. Although a selective matrix removal without residues is achieved using the pulsed CO2 laser. Differently, both constituent materials are ablated with the nanosecond pulsed UV laser, producing indentations. The sum of the investigations has shown that existing theories of laser technology, such as the ablation threshold according to Liu et al., can be applied to composite materials only to a limited extent. Furthermore, it has been found that the pronounced heterogeneity of CFRP mostly leads to an inhomogeneous ablation result, both when creating grooves and during selective matrix removal, where the carbon fibers influence the ablation result by their thermal conductivity, depending on fiber direction. Finally, despite the material inhomogeneity, a scanning strategy has been developed to compensate the heterogeneous ablation results regarding structure depth, width and heat affected zone.

Evaluation of Seven Oat (Avena sativa) Genotypes for Biomass Yield and Quality Parameters under Different Locations of Western Oromia, Ethiopia

Recognizing the potential and importance of cultivating improved forage crops as a means of tackling the recurrent feed shortage facing the study area, seven oat genotypes were tested in randomized complete block design with three replications across two locations for three growing seasons (2014, 2015, and 2016). The study was aimed to evaluate dry matter (DM) and digestible organic matter yield and nutrient composition of oat genotypes. The study revealed that oat genotypes responded differently for herbage dry matter (DM) and digestible organic matter (OM) yield, and quality parameters in both study locations. Averaged over the seven oat genotypes, herbage DM and digestible OM yield. recorded at Bako were higher than Boneya Boshe location across the study periods. The ash (P > 0.05) content did not vary among oat genotypes at both testing locations, while variation was observed for DM, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), in vitro digestibility, and metabolizable energy (ME) constituents. In general, genotypes ILRI 6710 and 5453 showed higher herbage DM and digestible OM yield. Moreover, the two genotypes are also higher in their in vitro digestibility value and ME, DM, and CP contents but relatively lower in NDF, ADF, and ADL fiber constituents, and thus, they are recommended for wider cultivation.

Anisotropic mechanical behaviour of calendered nonwoven fabrics: Strain-rate dependency

Calendered nonwovens, formed by polymeric fibres, are three-phase heterogeneous materials, comprising a fibrous matrix, bond-areas and interface regions. As a result, two main factors of anisotropy can be identified. The first one is ascribable to a random fibrous microstructure, with the second one related to orientation of a bond pattern. This paper focuses on the first type of anisotropy in thin and thick nonwovens under uniaxial tensile loading. Individual and combined effects of anisotropy and strain rate were studied by conducting uniaxial tensile tests in various loading directions (0°, 30°, 45°, 60° and 90° with regard to the main fabric’s direction) and strain rate (0.01, 0.1 and 0.5 s−1). Fabrics exhibited an initial linear elastic response, followed by nonlinear strain hardening up to necking and final softening. The studied allowed assessment of the extent the effects of loading direction (anisotropy), planar density and strain rate on the mechanical response of the calendered fabrics. The evidence supported the conclusion that anisotropy is the most crucial factor, also delineating the balance between the fabric’s load-bearing capacity and extension level along various directions. The strain rate produced a marked effect on the fibre’s response, with increased stress at higher strain rate while this effect in the fabric was small. The results demonstrated the differences of the mechanical behaviour of fabrics from that of their constituent fibres.

Water/moisture vapor permeabilities and thermal wear comfort of the Coolmax®/bamboo/tencel included PET and PP composite yarns and their woven fabrics

This study examined the water and moisture vapor permeabilities and the heat retention rate related to the wear comfort of the woven fabrics made from different types of composite yarn, the sheath/core composite yarn structure and non-circular cross-section of the constituent filaments (Coolmax®) in the core region played a very important role with high fabric porosity by including a capillary absorption in the wicking property. The fabric structures with high porosity composed of Coolmax® sheath/core yarns, and spun yarns with non-circular cross-sectional fibers (Coolmax®) affected strongly the fast drying rate due to moisture vapor diffusion of composite yarn fabrics. The moisture vapor permeability of the composite yarn fabrics was highly dependent on the porosity in the sheath/core yarn structures, In addition, the heat retention rate of the composite yarn fabric was strongly influenced by the high porosity due to the sheath/core and bulky staple yarn structures as well as the low thermal conductivity of the constituent fibers.

Dietary fiber components, microstructure, and texture of date fruits (Phoenix dactylifera, L.)

Date fruits vary widely in the hardness of their edible parts and they are classified accordingly into soft, semi-dry, and dry varieties. Fruit texture, a significant parameter in determining consumer acceptance, is related to the tissue structure and chemical composition of the fruit, mainly the ratio of sucrose to reducing sugars. This study aimed to understand the relationship between the chemical composition, microstructure, and texture profile of 10 major Emirati date fruits. The soluble sugars, glucose and fructose, represent ca 80 g/100 g of the fruits on the basis of dry weight (DW) while the dietary fiber contents varied 5.2–7.4 g/100 dg D.W. with lignin being the main determinant of the variability. The textures of the samples were studied using instrumental texture profile analysis. While no correlation was found between the soluble sugar and texture parameters in this study, the different fiber constituents correlated variably with the different parameters of date fruit texture. Lignin, arabinoxylan, galactomannan, and pectin were found to correlate significantly with fruit hardness and the related parameters, gumminess and chewiness. Both lignin and arabinoxylan correlated with resilience, and arabinoxylan exhibited a strong correlation with cohesiveness.

A practical ply-based appearance model of woven fabrics

Simulating the appearance of woven fabrics is challenging due to the complex interplay of lighting between the constituent yarns and fibers. Conventional surface-based models lack the fidelity and details for producing realistic close-up renderings. Micro-appearance models, on the other hand, can produce highly detailed renderings by depicting fabrics fiber-by-fiber, but become expensive when handling large pieces of clothing. Further, neither surface-based nor micro-appearance model has not been shown in practice to match measurements of complex anisotropic reflection and transmission simultaneously. In this paper, we introduce a practical appearance model for woven fabrics. We model the structure of a fabric at the ply level and simulate the local appearance of fibers making up each ply. Our model accounts for both reflection and transmission of light and is capable of matching physical measurements better than prior methods including fiber based techniques. Compared to existing micro-appearance models, our model is light-weight and scales to large pieces of clothing.

Lattice shells composed of two families of curved Kirchhoff rods: an archetypal example, topology optimization of a cycloidal metamaterial

A nonlinear elastic model for nets made up of two families of curved fibers is proposed. The net is planar prior to the deformation, but the equilibrium configuration that minimizes the total potential energy can be a surface in the three-dimensional space. This elastic surface accounts for the stretching, bending, and torsion of the constituent fibers regarded as a continuous distribution of Kirchhoff rods. A specific example of fiber arrangement, namely a cycloidal orthogonal pattern, is examined to illustrate the predictive abilities of the model and assess the limit of applicability of it. A numerical micro–macro-identification is performed with a model adopting a standard continuum deformable body at the level of scale of the fibers. A few finite element simulations are carried out for comparison purposes in statics and dynamics, performing modal analysis. Finally, a topology optimization problem has been carried out to change the macroscopic shear stiffness to enlarge the elastic regime and reduce the risk of damage without excessively losing bearing capacity.

Micromechanics based analytical model for estimation of stress distribution and failure initiation in constituents of UDFRP composites subjected to transverse loading

When a Unidirectional fiber reinforced polymer (UDFRP) composite is subjected to transverse loading, there is spatial variation of stresses in the constituents. The failure in matrix initiates at the location of maximum stress. Stress distribution and failure initiation in constituents of UDFRP composites is usually studied through finite element (FE) analysis of representative volume element (RVE) which is computationally expensive and time consuming. The present study proposes an analytical model through which stress variation and failure initiation in the constituents of UDFRP composite can be obtained in simple and reliable way and it can be readily used in designing. For this model, RVE is idealized in the form of springs arranged in parallel and series. These springs represent the stiffness of constituents (fiber and matrix). The results of analytical model are compared with FE simulations and good agreement is observed. Influence of fiber volume fraction on failure initiation of UDFRP composites is also studied through FE analysis of RVE and analytical model.

Parametric Study on Volume Fraction of Representative Volume Element (RVE) CFRP and GFRP Towards Tensile Properties

The properties such as fibre content, orientation, dimension of constituent fibres (diameter), level of intermixing of fibres, interface bonding between fibre and matrix, and arrangement of fibres between different types of fibres, influences the mechanical properties of hybrid composite.Representative Volume Element (RVE) for each constituent CFRP and GFRP assumed isotropic behavior for carbon fibre, glass fibre and epoxy resin matrix and assumed to be perfectly bonded interface between fibre and matrix region i.e. strain compatibility at the interface. The scope of study on the micro mechanical modelling via representative volume element (RVE) is limited only to unidirectional composites.

Achieving high porosity and large recovery strain in Ni-free high Zr-containing Ti-Zr-based shape memory alloy scaffolds by fiber metallurgy

Highly porous Ti-40Zr-8Nb-2Sn (at.%) shape memory alloy scaffolds were prepared by fiber metallurgy using rapidly solidified alloy fibers for the application of cancellous bone replacement. The phase constituents of alloy fibers and scaffolds were investigated by means of X-ray diffraction (XRD), superelastic behavior of alloy fibers was investigated by means of the dynamic mechanical analyzer (DMA), microstructures and mechanical properties of scaffolds were investigated by means of scanning electron microscopy (SEM) and compressive test, respectively. As-spun alloy fibers consisted of only β phase at room temperature. Clear superelastic behavior was observed in the as-spun alloy fibers at temperatures between 153 K and 298 K. The scaffolds showed three-dimensional networks with fiber-fiber bonds, whose porosity and pore size was about 80% and larger than 100 μm, respectively. The compressive yield stress and elastic modulus of the scaffold annealed at 973 K for 1.8 ks were about 4.0 MPa and 0.3 GPa, respectively, similar to those of cancellous bone. Recoverable strain in the scaffold was improved from 2.8% to 4.0% after annealed at 973 K due to the absence of α phase formed in the as-sintered scaffold. Stable cyclic superelastic behavior was observed in the annealed scaffolds at room temperature.

On collagen fiber morphoelasticity and homeostatic remodeling tone

A variety of biochemical and physical processes participate in the creation and maintenance of collagen in biological tissue. Under mechanical stimuli these collagen fibers undergo continuous processes of morphoelastic change. The model presented here is motivated by experimental reports of stretch-stabilization of the collagen fibers to enzymatic degradation. The fiber structure is modeled in terms of a fiber density evolution that is regulated by means of a fixed creation rate and a mechano-sensitive dissolution rate. The theory accounts for the possibly different natural configurations of the fiber unit constituents and the ground substance matrix. It also generalizes previous theoretical descriptions so as to account for finite survival times of the individual fiber units. Special consideration is given to steady state fiber-remodeling processes in which fiber creation and dissolution are in balance. Fiber assembly processes that involve prestretching the fiber constituents yield a homeostatic stress response with a characteristic fiber tone. Fiber density returns to homeostasis after mechanical disruption when sufficient time has passed.