Fuzzy Fibers Research Articles

The effect of fuzzy fiber-reinforced composite skin on bending stiffness and debonding growth between skin and polymeric foam core of sandwich structures

Progressive innovations in the field of nanotechnology demonstrate that through the radial growth of aligned carbon nanotubes (CNTs) on the circumferential surfaces of fibers known as fuzzy fibers, the transverse elastic properties of fiber-reinforced composites are notably improved. The main objective of the present work is to numerically examine the effects of using fuzzy fiber-reinforced composite (FFRC) skins on the flexural behavior of sandwich structures. Based on the considered two-stage analysis, in the first instance, the mechanical properties of FFRC are determined by the simplified unit cell (SUC) micromechanical model. Afterward, by simulating the three-point bending test via the finite element method (FEM), major assessments are accomplished to reflect the effects of microstructure-level features, including fiber and CNT volume fractions, CNT/polymer interphase, and CNT diameter, on the bending stiffness and debonding growth between the FFRC skin and polyvinyl chloride (PVC) foam core. The results reveal the satisfactory influence of employing FFRC skins on improving the flexural behavior of sandwich structures.

Recursive multiscale homogenization of multiphysics behavior of fuzzy fiber composites reinforced by hollow carbon nanotubes

Fuzzy fibers are fibers enhanced in terms of multiphysics properties with radially oriented carbon nanotubes grown on their surface through the chemical deposition process. For the first time, this paper attempts to present two generalized zeroth-order asymptotic homogenization schemes aimed at identifying the homogenized and local response of fuzzy fiber-reinforced composites, accounting for both multiphysics piezoelectric effect and cylindrically orthotropic material behavior. The unit cell problems are solved using the multiphysics finite-volume and the multiphysics finite-element techniques, respectively. While the former approach is based on the strong form solution of the equilibrium and conservation equations in an averaged sense in the discretized domain, the latter is based on the minimization of the total potential energy over the entire unit cell. A recursive multiscale analysis algorithm is developed wherein homogenized moduli (or local fields) obtained from the homogenization (or localization) analysis at one scale are utilized in the calculation of homogenized moduli (or local fields) at the next scale. Numerical examples indicate that good agreement of the homogenized properties and local field distributions generated by the two approaches is observed hence confirming the accuracy of the new homogenization methods for fuzzy fiber composites with multiphysics behaviors.

A hierarchical prediction scheme for effective properties of fuzzy fiber reinforced composites with two-scale interphases: Based on three-phase bridging model

In this paper, based on Huang's bridging model (Huang Z-M, 2001), an effective and concise analytical prediction scheme for effective elastic properties of fuzzy fiber reinforced composites' (FFRCs), is presented. The distinctive constructional feature of the FFRCs, herein, is that the fuzzy fibers are continuous, aligned, and having wavy nanofillers (like CNTs) grown radially on the circumferential surfaces. By means of the proposed approach, two-scale interphase effects on the overall properties of FFRCs are investigated, including the CNTs/matrix interphase and the fuzzy interphase surrounding the micro-fibers. Meanwhile, the size effect and the waviness effect of nanofillers are evaluated. The accuracy and effectiveness of this prediction scheme is validated by comparisons with the existing experimental data and analytical results. A thorough parametric study indicates that the introduction of slender nanofillers into the micro-fiber/matrix interfacial zone, indeed, leads to significant enhancement to the transverse and shear performance of the composite. Moreover, such enhancement depends on some major parameters, including the contents of the two-scale reinforcements, the stiffness of the two-scale interphase, CNT waviness, as well as the radius and length of CNTs. Those findings may have important implications in the future design of FFRCs.

Fracture toughness enhancement of fuzzy CNT-glass fiber reinforced composites with a combined reinforcing strategy

Low interlaminar mechanical properties is the foremost drawback of glass fiber reinforced composites (GFRPs). Hierarchical nanoparticles on fibers (e.g. carbon nanotubes (CNTs)) can improve interlaminar properties of composites with negligible weight increase because of excellent mechanical properties, and low density. Interlaminar properties of composites can be enhanced with the well-dispersed CNTs in polymer matrices as it facilitates load transfer from matrix to fibers. This paper investigates the mechanical properties of CNT-reinforced GFRPs. Two reinforcing strategies were studied as dispersion of CNTs in epoxy matrix and direct growth of CNTs onto glass fibers (GFs), simultaneously. The former is referred to as nanotube-reinforced composites (NRCs) while the latter is known as fuzzy architectures. Furthermore, the combination of NRCs and fuzzy glass fibers (F-GFs), also known as fuzzy nano-reinforced composites (F-NRCs), is used to fabricate composites and identify the reinforcing capabilities through both methods. Mechanical properties are investigated by Mode-I fracture toughness and unidirectional (UD) composite tensile tests. Even though NRCs and F-NRCs yield similar enhancements in the propagation fracture toughness as 113% and 119%, respectively, the tensile strength of F-NRCs is decreased by 24% due to heat treatment during the CNT synthesis.

Multiscale modeling accounting for inelastic mechanisms of fuzzy fiber composites with straight or wavy carbon nanotubes

This paper proposes a micromechanical approach aimed at identifying the response of unidirectional fuzzy fiber composites undergoing inelastic fields. Fuzzy fibers are reinforcement fibers coated with radially aligned straight or wavy carbon nanotubes grown through chemical deposition process (PVD or CVD). Due to this nature, the composite with fuzzy fibers is described by three scales: i) the microscale consisting of carbon nanotubes and their surrounding matrix, ii) the mesoscale containing the fiber, the nanocomposite and the matrix, and iii) the macroscale related to the overall fuzzy fiber composite. The developed framework considers for the mesoscopic scale an analytical formulation, based on the composite cylinders assemblage (CCA) method, combining the principles of the Transformation Field Analysis (TFA) technique. A numerical example that includes comparisons with full field homogenization strategies confirms the accuracy of the framework to predict the overall response, as well as the average local fields of the constituents.

Interface mechanics of carbon fibers with radially-grown carbon nanotubes

An atomistic modeling framework to investigate the interface/interphase of composite architecture with carbon fibers containing radially-grown carbon nanotubes (often called fuzzy fibers) is detailed in this paper. A polymeric functional coating for the carbon fiber surface, which also serves as a substrate for the CNT growth, is explicitly modeled. The tensile and transverse moduli of the fuzzy fiber/epoxy interphase is computed from virtual deformation simulations and compared to experimental values reported in literature, in order to validate the nanoscale model. Furthermore, the effect of the polymer substrate is studied by modeling the local interphase mechanics. Various modes of virtual loading provide the cohesive behavior of the local substrate/epoxy interphase. Conclusions are presented by comparing the material response of the interphase with and without the polymeric substrate. The integration of results from the nanoscale to an atomistically-informed subcell-based continuum level model is also demonstrated in the paper.

Modeling the effective mechanical properties of “fuzzy fiber” composites across scales length

Abstract We employ a variant of generalized Eshelby's homogenization method to deduce effective properties of multilayered nanostructured fiber composites where one layer is highly heterogeneous with respect to its mechanical response strain gradients. We focus on carbon (C) fibers coated by carbon nanotubes (CNT) embedded in polymeric matrix with the aid of CNT “blistered” interphase layer developed between the coating and the matrix during processing and/or use. Each of the three phases is treated for simplicity by classical elasticity, while the interphase layer around the coated fibers (“fuzzy fibers”) to provide adhesion, and is treated by the simple gradient elasticity (GradELa) model. The novelty of the work lies on the fact of treating the CNT “fuzzy” layer by the GradEla model, that consequently allows to consider the extra gradient coefficient or internal length (characterizing this model) in relation to other constitutive and geometric parameters of the composite to optimize its overall mechanical properties and functionality. The method is general and can apply to treat other types of “fuzzy fiber” composites.

Modeling of toughness enhancement mechanisms in graphene nanocomposites

ABSTRACTThe objective of this paper is to develop a mechanism-based theoretical model to explain fracture experiments conducted on nanographene platelet (NGP) reinforced thermoset polymer nanocomposite tested in pure Mode I and in mixed mode by the authors and other researchers. Remarkable improvement in fracture toughness, KIC (∼200%), and critical strain energy release rate, GIC (∼570%), was observed with only 0.5 wt% NGP addition to the EPON 862 polymer system. Interestingly, very large increase in ductility of the fracture specimens at peak load was observed with increasing NGP loading. Asymmetric four-point bend tests were also performed for three different mode mix (tan−1(KII/KI)) ratios (38°, 57°, and 89.5°). Significant enhancement in toughness as well as ductility for each mode mix case was observed with increasing NGP loading. Further, significant increases of 48% and 100% in delamination initiation toughness and resistance to crack propagation, respectively, were observed for 0.5-wt% NGP-reinforced IM7/EPON 862 unidirectional laminate. In this article, the reinforcement capacity of NGPs is explained through a length-scale based toughness enhancement mechanism, which is then employed to predict the critical length and orientation of nanoparticles for maximum fracture toughness improvement. It is envisioned that the application of this model could lead to significant toughness enhancement in composite laminates through (a) reduced intralaminar matrix cracks, (b) improved fiber/matrix interfacial toughening by controlling the size of nanoparticle growth on fuzzy fibers, and (c) improved delamination toughening as already demonstrated by the authors. For conclusive verification of our proposed model, there is a need for in-situ experiments to fully verify the nanoscale toughening effect by observing the process zone size near the tip of a nanoscale crack in a polymer thin film in-situ while it is being loaded, visualizing the brittle–ductile transition postulated by our theory and MD simulations. Work is currently underway in collaboration with the Air Force Research Laboratory to accomplish this objective.

Fusing multifocus images for yarn hairiness measurement

Yarn hairiness has been an important indication of yarn quality that affects weaving production and fabric appearance. In addition to many dedicated instruments, various image analysis systems have been adopted to measure yarn hairiness for potential values of high accuracy and low cost. However, there is a common problem in acquiring yarn images; that is, hairy fibers protruding beyond the depth of field of the imaging system cannot be fully focused. Fuzzy fibers in the image inevitably introduce errors to the hairiness data. This paper presents a project that attempts to solve the off-focus problem of hairy fibers by applying a new imaging scheme—multifocus image fusion. This new scheme uses compensatory information in sequential images taken at the same position but different depths to construct a new image whose pixels have the highest sharpness among the sequential images. The fused image possesses clearer fiber edges, permitting more complete fiber segmentation and tracing. In the experiments, we used six yarns of different fiber contents and spinning methods to compare the hairiness measurements from the fused images with those from unfused images and from the Uster tester. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this

Computational multiscale modeling and characterization of piezoresistivity in fuzzy fiber reinforced polymer composites

In this paper, the piezoresistive response (i.e. the change of resistance under the application of strain) of polymer composites reinforced by a novel material known as fuzzy fibers is characterized by using single tow piezoresistive fragmentation tests and modeled by using a 3D computational multiscale model based on the finite element analysis. In the characterization work, the fuzzy fiber tow is embedded in a dog-bone specimen infused by epoxy, with resistance and displacement measured simultaneously to obtain its piezoresistive response. An approximately linear and stable piezoresistive response is observed within the fuzzy fiber tow region yielding gauge factors on average of 0.14. Using a 3D multiscale mechanical–electrostatic coupled code and explicitly accounting for the local piezoresistive response of the anisotropic interphase region, the piezoresistive responses of the overall fuzzy fiber reinforced polymer composites are studied parametrically in an effort to provide qualitative guidance for the manufacture of fuzzy fiber reinforced polymer composites. It is observed from the model that the fuzzy fiber reinforced polymer composites with cylindrically orthotropic carbon nanotube interphase regions are dominated by the electrical tunneling effect between the nanotubes and can yield very large gauge factors while fuzzy fibers with randomly oriented carbon nanotubes in the interphase region yield smaller gauge factors as the material is electrically saturated by the carbon nanotubes. Finally, the modeling efforts provide plausible reasons for the observed small gauge factors in experiments in the form of a combination of high concentration randomly oriented carbon nanotube interphase regions separated by sparse nanotube regions along the fuzzy fiber length.

Shear Lag Model for Regularly Staggered Short Fuzzy Fiber Reinforced Composite

In this article, we investigate the stress transfer characteristics of a novel hybrid hierarchical nanocomposite in which the regularly staggered short fuzzy fibers are interlaced in the polymer matrix. The advanced fiber augmented with carbon nanotubes (CNTs) on its circumferential surface is known as “fuzzy fiber.” A three-phase shear lag model is developed to analyze the stress transfer characteristics of the short fuzzy fiber reinforced composite (SFFRC) incorporating the staggering effect of the adjacent representative volume elements (RVEs). The effect of the variation of the axial and lateral spacing between the adjacent staggered RVEs in the polymer matrix on the load transfer characteristics of the SFFRC is investigated. The present shear lag model also accounts for the application of the radial loads on the RVE and the radial as well as the axial deformations of the different orthotropic constituent phases of the SFFRC. Our study reveals that the existence of the non-negligible shear tractions along the length of the RVE of the SFFRC plays a significant role in the stress transfer characteristics and cannot be neglected. Reductions in the maximum values of the axial stress in the carbon fiber and the interfacial shear stress along its length become more pronounced in the presence of the externally applied radial loads on the RVE. The results from the newly developed analytical shear lag model are validated with the finite element (FE) shear lag simulations and found to be in good agreement.

Effective mechanical properties of “fuzzy fiber” composites

In this paper we investigate the mechanical behavior of carbon fiber composites, where the carbon fibers are coated with radially aligned carbon nanotubes. For this purpose we develop a general micromechanics method for fiber composites, where fibers are coated with radially aligned microfibers (“fuzzy fiber” composites). The mechanical effective properties are computed with a special extension of the composite cylinders method. The in-plane shear modulus is determined using an extended version of the Christensen’s generalized self consistent composite cylinders method. The proposed methodology provides stress and strain concentration tensors. The results of the method are compared with numerical approaches based on the asymptotic expansion homogenization method. The combination of composite cylinders method and Mori–Tanaka method allows us to compute effective properties of composites with multiple types of “fuzzy fibers”. Numerical examples of composites made of epoxy resin, carbon fibers and carbon nanotubes are presented and the impact of the carbon nanotubes length and volume fraction in the overall composite properties is studied.

Supramolecular Non-Amyloid Intermediates in the Early Stages of α-Synuclein Aggregation

The aggregation of α-synuclein is associated with progression of Parkinson's disease. We have identified submicrometer supramolecular structures that mediate the early stages of the overall mechanism. The sequence of structural transformations between metastable intermediates were captured and characterized by atomic force microscopy guided by a fluorescent probe sensitive to preamyloid species. A novel ∼0.3–0.6 μm molecular assembly, denoted the acuna, nucleates, expands, and liberates fibers with distinctive segmentation and a filamentous fuzzy fringe. These fuzzy fibers serve as precursors of mature amyloid fibrils. Cryo-electron tomography resolved the acuna inner structure as a scaffold of highly condensed colloidal masses interlinked by thin beaded threads, which were perceived as fuzziness by atomic force microscopy. On the basis of the combined data, we propose a sequential mechanism comprising molecular, colloidal, and fibrillar stages linked by reactions with disparate temperature dependencies and distinct supramolecular forms. We anticipate novel diagnostic and therapeutic approaches to Parkinson's and related neurodegenerative diseases based on these new insights into the aggregation mechanism of α-synuclein and intermediates, some of which may act to cause and/or reinforce neurotoxicity.

Electron microscopy of chromatin elimination in Cidaria (Lepidoptera).

Elimination chromatin observable in the middle of the bivalents in oogenesis of the geometrid moth species Cidaria variata (subgenus Thera) differs distinctly from the chromosomal chromatin by being less electron dense after uranyl acetate staining. Elimination chromatin is tightly packed in between the bivalent halves already at metaphase I, and is bursting out from between the bivalents leaving the centre of the bivalents as a hollow cavity. There is a distinct tendency for elimination chromatin to stick adjacent bivalents together. In the electron microscope it seems to have an unorganized, fibrillar appearance. The thickness of the fuzzy fibers is in the range of 100 a. Three possible hypotheses have been raised to account for the elimination of ribonucleoprotein material from chromosomes in lepidopteran oogenesis.

Reconstruction of the basement membrane in a cultured submandibular gland

In a rat submandibular rudiment on day 16, both laminin (LM) and type IV collagen (Col-IV) were found in all cases to colocalize not only in the basement membrane, but also in the rough endoplasmic reticulum of the epithelial cells, indicating that the synthesis of the components of basement membrane is greatly enhanced at this particular stage of extensive branch formation. Using the submandibular gland from a 16-day embryo, the model system was developed to determine the structural organization of the basement membrane. The pre-existing basement membrane was digested with collagenase and dispase, causing its complete disappearance. The subsequent gradual reconstruction of an authentic basement membrane was confirmed by electron microscopy and immunohistochemistry of LM and Col-IV. In the model system, this recovery started at 4 h of culture, and formation was complete by 8 h. During the recovery, thick bundles of actin filaments appeared transitionally in the basal cytoplasm. Electron microscopic analysis indicated two precursor structures, aggregated fuzzy fibers (type 1 extracellular matrix (ECM)) and 10-nm-thick strand piles (type 2 ECM), and an authentic basement membrane structure appeared during the course of membrane reconstruction. LM and Col-IV were always located together in these three structures. These observations clearly indicate that the precursors, containing LM, Col-IV and most likely heparan sulfate proteoglycan, appeared to form immediately following their secretion into the extracellular space, and assembled into the rigid structure of basement membrane within 8 h. The ultrastructural and immunohistochemical process of basement membrane reconstruction appeared to coincide closely with that of the glomerular basement membrane in developing kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

A unique cytoskeleton associated with crawling in the amoeboid sperm of the nematode, Ascaris suum.

Nematode sperm extend pseudopods and pull themselves over substrates. They lack an axoneme or the actin and myosins of other types of motile cells, but their pseudopods contain abundant major sperm protein (MSP), a family of 14-kD polypeptides found exclusively in male gametes. Using high voltage electron microscopy, a unique cytoskeleton was discovered in the pseudopod of in vitro-activated, crawling sperm of the pig intestinal nematode Ascaris suum. It consists of 5-10-nm fuzzy fibers organized into 150-250-nm-thick fiber complexes, which connect to each of the moving pseudopodial membrane projections, villipodia, which in turn make contact with the substrate. Individual fibers in a complex splay out radially from its axis in all directions. The centripetal ends intercalate with fibers from other complexes or terminate in a thickened layer just beneath the pseudopod membrane. Monoclonal antibodies directed against MSP heavily label the fiber complexes as well as individual pseudopodial filaments throughout their length. This represents the first evidence that MSP may be the major filament protein in the Ascaris sperm cytoskeleton. The large fiber complexes can be seen clearly in the pseudopods of live, crawling sperm by computer-enhanced video, differential-interference contrast microscopy, forming with the villipodia at the leading edge of the sperm pseudopod. Even before the pseudopod attaches, the entire cytoskeleton and villipodia move continuously rearwards in unison toward the cell body. During crawling, complexes and villipodia in the pseudopod recede at the same speed as the spermatozoon moves forward, both disappearing at the pseudopod-cell body junction. Sections at this region of high membrane turnover reveal a band of densely packed smooth vesicles with round and tubular profiles, some of which are associated with the pseudopod plasma membrane. The exceptional anatomy, biochemistry, and phenomenology of Ascaris sperm locomotion permit direct study of the involvement of the cytoskeleton in amoeboid motility.

Proposed structures and models for polymers crystallized in bulk

AbstractSince many publications have been concerned with polymers which have been crystalized in single crystals where chain‐folding represents the only way for explaining the arrangement of the long chain molecules, there are appearing increasingly more publications referring to chain‐folding also on polymers crystallized in bulk. Assuming that a polymer molecule is randomly coiled whether in solution or in bulk where actually sister molecules represent the “solvent,” then on crystallization of polymers in bulk, like chain sections will aggregate whether belonging to the same molecule or to a nearby sister molecule. In the latter case, regular chain‐folding should be very unlikely to occur. Using woolen yarn as a model substance which simulates both covalent and van der Waals binding forces (the latter by means of the fuzzy fibers), it is illustrated how bulk crystallization may be nicely imitated by parallel combing of randomly arranged yarn. This concept is also applied to explain changes in long‐period as occurring on annealing and the formation of macrostructures, mainly spherulites.

Response to Price in Production of Cotton and Cottonseed

A MONG the first studies of agricultural production responses to price changes was the one made by H. L. Moore, who demonstrated that there was a direct relationship between the percentage change in the acreage of cotton for any given year and the percentage change in the price of cotton lint the preceding year.' Similar results were obtained by Bradford B. Smith.2 A later study by T. B. Manny showed that farmers placed considerable emphasis on the price of cotton in the preceding crop year in deciding currently on the acreage to be planted to cotton.3 Except for the regression curves presented by Smith, no attempt was made in any of these studies to measure the elasticity of farmers' response to price changes in making production plans. That measurement is attempted here. In addition, special attention is paid to the possible effect of changes in the price of cottonseed on cotton acreage and production. Cottonseed is separated from cotton lint at the gin as a jointproduct of cotton production. The uses of cotton lint are well known. Cottonseed is an important source of vegetable oil used mainly for food. It also yields high-protein cake and meal used as a livestock feed. Cotton linters (short, fuzzy fibers adhering to the seed coat) are used in explosives, rayon, and felt and cottonseed hulls are used as livestock roughage and bedding. Until recently cottonseed provided the largest single source of vegetable oil and high-protein cake and meal in the'tnited States. This position is now challenged by soybeans, but cottonseed remains an important source of supply for these products. The relative importance of cottonseed appears to increase in war periods. Cash income from sales of cottonseed, which represented 10 percent of the total cash income from cotton and cottonseed in 1910-14, accounted for nearly 16 percent of the total in the follow-