Random Fiber Mats Research Articles

The influence of fabric architecture on impregnation behavior and void formation: Artificial neural network and statistical‐based analysis

AbstractThis work proposes an approach combining artificial neural networks (ANN) with statistical models to predict injection processing conditions for four reinforcement architectures: plain weave, bidirectional noncrimp fabrics, unidirectional fabrics (Uni) and random fiber mats (Random). Key results allow evaluating the velocity of the flow front by combining processing parameters and creating a three‐dimensional response surface based on a properly trained ANN. This investigation is based on a large number of experimental results. The key role played by some physical parameters was associated with predicting the impregnation behavior (velocity of the flow front) during resin injection. The main outcome aims to provide a better control of void content in terms of size and position to the four fibrous reinforcements considered.

Synthesis of developed rice straw sheets and glass fiber-reinforced polyester composites

In this study, a sheet of random rice straw fiber was developed. These rice straw sheets were used to reinforce polyester matrix. Synthesis of rice straw sheets and glass fibers as synthetic fibers-reinforced polyester composites were investigated. Several new stacking sequences were fabricated with random glass fiber mats with different areal densities (225 g/m2, 300 g/m2, and 450 g/m2) and rice straw sheets. The specific mechanical properties of these natural/synthetic fiber composites were investigated. Scanning electron microscopy was used to study the morphology of the fracture surfaces of the fabricated hybrid composites. Experimental results showed that specific tensile and flexural stiffness of rice straw fiber composite is better those obtained with glass fiber composites. The hybrid natural/synthesis composites with alternating glass fiber mat with areal densities 300 g/m2, and rice straw shows higher specific tensile strength than rice straw and other hybrid composites. Hybrid composites with high areal density on the outer surfaces yield a significant increase in flexural-specific strength and hardness as compared to other fabricated composites.

Tensile, Impact, and Thermal Properties of an Epoxynovolac Matrix Composites with Cuban Henequen Fibers

Composites based on an epoxy-novolac matrix and a Cuban henequen fiber reinforcement were investigated. A satisfactory reinforcing effect was observed for a composite material prepared by compression molding at room temperature using long random fiber mats. Tensile and impact experiments were run on the material, and its thermogravimetric analysis was performed. The breaking zone of the specimens tested in tension was examined by an electron sweep microscope. The results obtained are presented graphically and in photographs.

Effect of Natural Fiber Network on Permeability and Tensile Strength of Composites through Vacuum Infusion Process

ABSTRACTThis investigation is primarily focused to study the effect of fiber network on the permeability in vacuum infusion molding process. The unsaturated permeability of several natural fiber mats with different networks is measured. The experimental permeabilities are fitted by the Kozeny model and contact angle model. The outcome highlighted that the contact angle model shows more precise results as compared to kozeny model. The obtained permeability for the random fiber mats shows higher values than directional fiber mat. Furthermore, the maximum increase in tensile strength is observed in the unidirectional composites and the flow along the fiber direction.

3D printing of fiber-reinforced soft composites: Process study and material characterization

Fiber-reinforced soft composites (FrSCs) are composites that are made up of polymeric fibers with specific material properties and hierarchical length-scales, embedded within another soft-polymer matrix. This paper is aimed at systematically studying the effect of key processing parameters viz., fiber mat alignment, area coverage, and surface energy of the fiber carrier substrate, on the tensile properties and failure mechanisms seen in 3D printed FrSCs. A novel electrospinning-based “direct-write” system is used for creating the aligned and random nylon fiber mats. The fiber mats are then characterized for their diameter distributions, effective area coverage, number density, and tensile properties. The surface energy of the fiber carrier substrate is found to be critical to the fiber transfer efficiency of the stamping operation used in the 3D printing process, with polytetrafluoroethylene-coated aluminum films being more effective due to their low surface energy. Tensile testing results show that depending on the extent of alignment and the fiber content present in the 3D printed composite, it can have a 40–260% improvement in the elastic modulus over that of the base UV-curable polymer. The composites also show evidence of characteristic failure mechanisms seen in the domain of nanocomposite materials, viz., fiber-induced local plastic deformation (crazing), crack arrest and deflection, fiber strengthening, and fiber pull-out. The evidence of fiber pull-out also points to the formation of an interfacial polymer sheath around the fibers. The elastic modulus of this sheath is estimated to be an order of magnitude higher than the base polymer.

Characterization of textile permeability as a function of fiber volume content with a single unidirectional injection experiment

Textile permeability is a fundamental property to describe preform impregnation in Liquid Composite Molding (LCM) processes. It depends on textile architecture and fiber volume content (FVC). Conventional methods to measure in-plane permeability are based on radial or unidirectional injection experiments performed at fixed FVC. A complete characterization involves a series of tests and requires several material samples. This study presents a novel approach to characterize permeability as a function of FVC through a unique unidirectional injection experiment with a preform containing different FVC sections. The same experimental set-up as in conventional unidirectional unsaturated permeability measurements is used with a second pressure transducer embedded in the mold in addition to the one located at the inlet gate. A fast algorithm is developed to exploit the data from the two sensors and automatically derive the permeability distribution without any need of visual flow front observations. The methodology is validated with a random fiber mat and a woven fabric. Results show that accurate permeability characterization can be achieved for both kinds of textiles.

A Novel Multimaterial Additive Manufacturing Technique for Fabricating Laminated Polymer Nanocomposite Structures

The objective of this research is to develop a novel, multimaterial additive manufacturing technique for fabricating laminated polymer nanocomposite structures that have characteristic length-scales in the tens of millimeters range. The three-dimensional (3D) printing technology presented in this paper combines the conventional inkjet-based printing of ultraviolet (UV) curable polymers with the deposition of either aligned or random nanoscale fiber mats, in between each printed layer. The fibers are first generated using an electrospinning process that produces the roll of fibers. These fibers are then transferred to the part being manufactured using a stamping operation. The process has been proven to manufacture multimaterial laminated nanocomposites having different 3D geometries. The dimensional accuracy of the parts is seen to be a function of the interaction between the different UV-curable polymer inks. In general, the addition of the nanofibers in the form of laminates is seen to improve the mechanical properties of the material, with the Young’s modulus and the ultimate breaking stress showing the most improvement. The pinning and deflection of microcracks by the nanoscale fiber mats has been identified to be the underlying mechanism responsible for these improved mechanical properties. The thermogravimetric analysis (TGA) reveals that these improvements in the mechanical properties are obtained without drastically altering the thermal degradation pattern of the base polymer.

Modifying Fish Gelatin Electrospun Membranes for Biomedical Applications: Cross-Linking and Swelling Behavior

Development of suitable membranes is a fundamental requisite for tissue and biomedical engineering applications. This work presents fish gelatin random and aligned electrospun membranes cross-linked with glutaraldehyde (GA). It was observed that the fiber average diameter and the morphology is not influenced by the GA exposure time and presents fibers with an average diameter around 250 nm. Moreover, when the gelatin mats are immersed in a phosphate buffered saline solution (PBS), they can retain as much as 12 times its initial weight of solution almost instantaneously, but the material microstructure of the fiber mats changes from the characteristic fibrous to an almost spherical porous structure. Cross-linked gelatin electrospun fiber mats and films showed a water vapor permeability of 1.37 ± 0.02 and 0.13 ± 0.10 (g.mm)/(m2.h.kPa), respectively. Finally, the processing technique and cross-linking process does not inhibit MC-3T3-E1 cell adhesion. Preliminary cell culture results showed good cell adhesion and proliferation in the cross-linked random and aligned gelatin fiber mats.

Application of Multilayered Paper Processing to Hybrid Random Natural Fiber Mat

Fiber reinforced plastic composite (FRP) has gained remarkable development because of its excellent properties, such as low density, high stiffness, high strength, corrosion resistance, long fatigue life, and so on. However, as more and more products made of FRP, the rubbish of FRP is also increasing which has become an important problem to the environment. Recycling and reusing is a noticeable method to reduce trash discharge and to save resource. Although it is a more challenging work for FRP, many researchers have report their scores in this area, such as the group from The University of Nottingham who have developed a new technology to recycle the carbon fiber. The objective of this research is to make short fiber mat from recycled carbon fiber by paperboard making method. In this method the fiber can be made into very thin layers and be laid into mat. After that the mats were used to fabricate FRP and the tensile property of the materials was investigated. The property was evaluated between recycled carbon fiber and jute fiber as well as hybrid one. It was found that the hybrid one has better performance.

Directed differentiation and neurite extension of mouse embryonic stem cell on aligned poly(lactide) nanofibers functionalized with YIGSR peptide

End-functional PLLA nanofibers were fabricated into mats of random or aligned fibers and functionalized post-spinning using metal-free “click chemistry” with the peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). Fibers that were both aligned and functionalized with YIGSR were found to significantly increase the fraction of mouse embryonic stem cells (mESC) expressing neuron-specific class III beta-tubulin (TUJ1), the level of neurite extension and gene expression for neural markers compared to mESC cultured on random fiber mats and unfunctionalized matrices. Precise functionalization of degradable polymers with bioactive peptides created translationally-relevant materials that capitalize on the advantages of both synthetic and natural systems, while mitigating the classic limitations of each.

Processing and characterization of 100% hemp-based biocomposites obtained by vacuum infusion

Novel biocomposites made of an acrylated epoxidized hemp oil based bioresin reinforced with random hemp fiber mat were manufactured by the vacuum infusion technique. Mechanical properties (tensile, flexural, Charpy impact and interlaminar shear), dynamic mechanical properties (glass transition temperature, storage modulus and crosslink density) and moisture absorption properties (saturation moisture level and diffusion coefficient) were investigated and compared with samples manufactured under the same conditions but using a commercial synthetic vinylester resin as the polymeric matrix. Results showed that the 100% biocomposites mechanical performance is comparable to that of the hybrid composites made with the synthetic resin. Moisture absorption tests showed that acrylated epoxidized hemp oil based samples displayed both higher diffusion coefficient and saturation moisture content; however, fiber reinforcement was the dominant transfer mechanism. Vinyl ester based samples were found to have higher storage modulus, glass transition temperature and crosslink density than acrylated epoxidized hemp oil samples.

Properties of single electrospun poly (diol citrate)-collagen-proteoglycan nanofibers for arterial repair and in applications requiring viscoelasticity

Single nanofibers with chemical and functional properties consistent with artery extracellular matrix nanofibers were produced by electrospinning. Using weight ratios to mimic artery extracellular matrix, five materials were tested: (1) Collagen type I, (2) Collagen type I + Collagen type III, (3) Collagen type I + poly (diol citrate), (4) Collagen type I + Collagen type III + poly (diol citrate), and (5) Collagen type I + poly (diol citrate) + Decorin + Aggrecan. Fiber sizes for all materials ranged from 50 nm to 600 nm and random fiber mats had pore sizes from 21 to 40 = m(2) and porosities of 72-84%. Human embryonic palatal mesenchymal cells fibroblasts adhered to all fibers and proliferated over a 7-day study period. Mechanical properties of single fibers were investigated using a combined atomic force/optical microscope. Materials containing poly (diol citrate) showed elasticity increased 3.2 fold greater than composites without poly (diol citrate). Maximum stress was within functional range in comparison to decellularized artery extracellular matrix fibers. By incorporating poly (diol citrate) and proteoglycan along with collagen, a viscoelastic nanofibrous material was produced for use in tissues such as artery where viscoelasticity and tensile strength are required.

Large‐scale aligned fiber mats prepared by salt‐induced pulse electrospinning

AbstractIn this article, a new large‐scale aligned fiber mats formation method called salt‐induced pulse electrospinning was developed. By electrospinning salted solution in a humid environment, traditional continuous electrospinning changed into pulse electrospinning and aligned fibers were thus formed. The possible mechanisms for the occurrence of salt‐induced pulse electrospinning and the formation of fiber alignment were studied. The continuous electrospinning changing into the pulse electrospinning was due to the change of viscosity and conductivity of salted polymer solution in a wet electrospinning condition. Fishing net‐shaped whipping region of the electrospinning jet during pulse electrospinning process was considered as the key factor for the formation of fiber alignment. The mechanical properties of the aligned fiber mat increased significantly compared with that of the random fiber mat. This aligned fiber preparation method only requires a very low rotating drum speed as the receiver and can produce large‐scale aligned fiber mats for many applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Effect of Fiber Loading on the Mechanical Strength of NFR Hybrid Composites

Ortho-type UP resin is reinforced with long abaca and short bagasse fibers to produce a novel type of natural fiber-reinforced (NFR) hybrid composite material that is environment-friendly, has a long service life, possesses the properties of both long and short FRP’s, and has also acquired the advantages of utilizing two different types of natural fiber reinforcements. The abaca and bagasse fibers are treated in 5wt% NaOH(aq) solution at 80°C for 9 hours and pressed into continuous, unidirectional fiber sheets and random fiber mats, respectively. The fibers are then incorporated into the resin matrix by hand lay-up method, producing FRP laminates with the same uniform thickness but subjected to varying fiber loading conditions: (1) the stacking of long fiber sheets are done in cross-ply and parallel orientation; (2) the abaca and bagasse fibers are stacked in different alternating sequence patterns, and (3) the fibers are added into the ortho-UP matrix at increasing fiber fraction. The alkali-treated FRP laminates show an increase in fiber-matrix interfacial adhesion as compared to the untreated FRP’s, based on the overall improvement in the composite mechanical strength, as well as from the lesser visible fiber pull-out observed from SEM images on their fracture surfaces. Also, as expected, the tensile and flexural strengths of the abaca/bagasse hybrid FRP measures intermediate to those of abaca and bagasse FRP’s. The strength has also improved with increasing fiber content, although this increase has also caused an increased occurrence of void spaces that may consequently become detrimental to the NFR composite’s performance.

Fabrication of long and discontinuous natural fiber reinforced polypropylene biocomposites and their mechanical properties

Natural fiber reinforced polypropylene (PP) biocomposites were fabricated by blending long-and-discontinuous (LD) natural fibers (NF) with LD PP fibers. Firstly, random fiber mats were prepared by mixing NFs and PP fibers using a carding process. Then, heat and pressure were applied to the mats, such that the PP fibers dispersed in the mats melted and flowed out, resulting in the formation of consolidated sheets upon subsequent cooling. The effect of the fiber volume fraction on the mechanical properties of the bio-composites was scrutinized by carrying out tensile and flexural tests and observing the interface between the fiber and matrix. It was observed that the natural LD fiber content needs to be maintained at less than the nominal fiber fraction of 40 % by weight for the composites fabricated using the current method, which is quite low compared to that of continuous or short fiber reinforced composites. The limited fiber fraction can be explained by the void content in the biocomposites, which may be caused by the non-uniform packing or the deficiency of the matrix PP fibers.

Designed PCL Nanofibers Fabricated Using a Modified Electrohydrodynamic Process for Tissue Engineering

An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area, high porosity, and good interconnectivity of pores, electrospun micro-∕nanofibers have good potential as biomimic scaffolds. In this study, various poly(ε-carprolactone) webs consisting of uniaxially oriented micro-∕nanofibers were produced using an electrohydrodynamic process (electrospinning) with a conical electrode and two-axis collector. The oriented fibrous web showed mechanical orthotropic properties, which might be important for designing engineering scaffolds that mimic natural tissues, such as a blood vessel or ligament, which have orthotropic mechanical properties. In addition, the fabricated mats, which were electrospun using computer-assisted design, had good hydrophilic and good cellular behavior compared to a random fiber mat.

Three-dimensional features of void morphology in resin transfer molded composites

Detailed analyses of shape, size, and spatial variations of void morphology are presented for a disk-shaped, resin transfer molded (RTM), E-glass/epoxy composite. The disk is molded at constant injection rate and contains 17.5% E-glass random fiber mats. Voids throughout the composite are evaluated by microscopic image analysis of through-the-thickness and planar surfaces obtained from adjacent radial samples. The void content of 2.15% is obtained from the analysis of through-the-thickness images and believed to be representative of the actual void content in the studied part. Relatively large cylindrical voids are observed in cigar shapes in the planar surfaces, whereas these voids only appear as small irregular or elliptical voids on through-the-thickness surfaces. Along the radial direction, combined effects of void formation by mechanical entrapment and void mobility are shown to yield a complex radial void distribution. It is shown that fewer voids are trapped mechanically with increasing distance from the inlet and most of the medium and small voids that are mobile migrate towards the exit during resin injection. These findings are believed to be applicable not only to RTM, but generally to liquid composite molding processes with varying fluid front velocities.

Ideal Forming Analysis for Random Fiber Preforms

In resin transfer molding, the manufacture of the fiber preform controls many aspects of part quality. These include defects such as wrinkling and tearing, as well as spatial variations in fiber volume fraction and permeability. We develop a mathematical model and numerical method for analyzing preforming of random fiber mats. The model uses an ideal forming theory, which maps a fiber sheet to the mold surface by minimizing the integral of a formability function over the mold surface. The scalar formability function depends on the local deformation, and exhibits large values under conditions that promote either tearing or wrinkling of the mat. The model is implemented as a finite element simulation for arbitrarily shaped three-dimensional preforms. Results include the shape of the initial fiber sheet, and values of the formability function and the principal stretch ratios over the mold surface. This information is used to predict the presence of defects in the preform. Example calculations are shown for an axisymmetric hat shape and for a box with a flange. The calculation requires a modest amount of input data and, rather than predict the exact result of the forming operation, it shows the best result that is possible. Thus, it is a useful tool in the early stages of part and mold design.

Compaction of fiber reinforcements

AbstractIn resin transfer molding, dry fiber reinforcements are compacted as the mold closes before injection of a curable resin matrix. This paper presents experimental data of compaction pressure as a function of fiber volume fraction. Data are presented for woven roving mats, random fiber mats, loose fiber rovings for pultrusion, and uniaxial or biaxial roving mats. These data are fit to a mathematical model derived in an Appendix. Experimental data are also given for six combinations of reinforcements. We use the compaction model of each constituent layer to predict the average volume fraction assuming that fiber layers do not interact. However, we see that most combinations of reinforcements have fiber volume fractions greater than expected at pressures under 50 psi, indicating a synergistic packing between the layers of different composition.

Governing equations for unsaturated flow through woven fiber mats. Part 1. Isothermal flows

Correct modeling of resin flow in liquid composite molding (LCM) processes is important for accurate simulation of the mold-filling process. Recent experiments indicate that the physics of resin flow in woven (also stitched or braided) fiber mats is very different from the flow in random fiber mats. The dual length-scale porous media created by the former leads to the formation of a sink term in the equation of continuity; such an equation in combination with the Darcy's law successfully replicate the drooping inlet pressure history, and the region of partial saturation behind the flow-front, for the woven mats. In this paper, the mathematically rigorous volume averaging method is adapted to derive the averaged form of mass and momentum balance equations for unsaturated flow in LCM. The two phases used in the volume averaging method are the dense bundle of fibers called tows, and the surrounding gap present in the woven fiber mats. Averaging the mass balance equation yields a macroscopic equation of continuity which is similar to the conventional continuity equation for a single-phase flow except for a negative sink term on the right-hand side of the equation. This sink term is due to the delayed impregnation of fiber tows and is equal to the rate of liquid absorbed per unit volume. Similar averaging of the momentum balance equation is accomplished for the dual-scale porous medium. During the averaging process, the dynamic interaction of the gap flow with the tow walls is lumped together as the drag force. A representation theorem and dimensional analysis are used to replace this drag force with a linear function of an average of the relative velocity of the gap fluid with respect to the tow matrix for both the isotropic and anisotropic media . Averaging of the shear stress term of the Navier–Stokes equation gives rise to a new quantity named the interfacial kinetic effects tensor which includes the effects of liquid absorption by the tows, and the presence of slip velocity on their surface. Though the gradient of the tensor contributes a finite force in the final momentum balance equation, a scaling analysis leads to its rejection in the fibrous dual-scale porous medium if the permeability of flow through the gaps is small. For such a porous medium, the momentum equation reduces to the Darcy's law for single-phase flow.