Fiber Aspect Ratio Research Articles

Multi-fidelity modeling to predict the rheological properties of a suspension of fibers using neural networks and Gaussian processes

Unveiling the rheological properties of fiber suspensions is of paramount interest to many industrial applications. There are multiple factors, such as fiber aspect ratio and volume fraction, that play a significant role in altering the rheological behavior of suspensions. Three-dimensional (3D) numerical simulations of coupled differential equations of the suspension of fibers are computationally expensive and time-consuming. Machine learning algorithms can be trained on the available data and make predictions for the cases where no numerical data are available. However, some widely used machine learning surrogates, such as neural networks, require a relatively large training dataset to produce accurate predictions. Multi-fidelity models, which combine high-fidelity data from numerical simulations and less expensive lower fidelity data from resources such as simplified constitutive equations, can pave the way for more accurate predictions. Here, we focus on neural networks and the Gaussian processes with two levels of fidelity, i.e., high and low fidelity networks, to predict the steady-state rheological properties, and compare them to the single-fidelity network. High-fidelity data are obtained from direct numerical simulations based on an immersed boundary method to couple the fluid and solid motion. The low-fidelity data are produced by using constitutive equations. Multiple neural networks and the Gaussian process structures are used for the hyperparameter tuning purpose. Results indicate that with the best choice of hyperparameters, both the multi-fidelity Gaussian processes and neural networks are capable of making predictions with a high level of accuracy with neural networks demonstrating marginally better performance.

Shape evolution of long flexible fibers in viscous flows

The present work studies numerically the dynamics and shape evolution of long flexible fibers suspended in a Newtonian viscous cellular flow using a particle-level fiber simulation technique. The fiber is modeled as a chain of massless rigid cylindrical segments connected by ball and socket joints; one-way coupling between the fibers and the flow is considered while Brownian motion is neglected. The effect of stiffness, equilibrium shape, and aspect ratio of the fibers on the shape evolution of the fibers are analyzed. Moreover, the influence of fiber stiffness and their initial positions and orientations on fiber transport is investigated. For the conditions considered, the results show that the fiber curvature field resembles that of the flow streamline. It is found that the stiffer fibers experience not only a quicker relaxation phase, in which they transient from their initial shape to their “steady-state shape,” but they also regain their equilibrium shape to a larger extent. The findings also demonstrate that even a small deviation of fiber shape from perfectly straight impacts significantly the early-stage evolution of the fiber shape and their bending behavior. Increasing the fiber aspect ratio, when other parameters are kept fixed, leads the fiber to behave more flexible, and it consequently deforms to a larger extent to adjust to the shape of the flow streamlines. In agreement with the available experimental results, the fiber transport studies show that either the fiber becomes trapped within the vortices of the cellular array or it moves across the vortical arrays while exhibiting various complex shapes.

Instrument for tensile testing of individual collagen fibrils with facile sample coupling and uncoupling.

Collagen is the major structural protein in human bodies constituting about 30% of the entire protein mass. Through a self-assembly process, triple helical collagen molecules assemble into high aspect-ratio fibers of tens to hundreds of nanometer diameter, known as collagen fibrils (CFs). In the last decade, several methods for tensile testing these CFs emerged. However, these methods are either overly time-consuming or offer low data acquisition bandwidth, rendering dynamic investigation of tensile properties impossible. Here, we describe a novel instrument for tensile testing of individual CFs. CFs are furnished with magnetic beads using a custom magnetic tweezer. Subsequently, CFs are lifted by magnetic force, allowing them to be picked-up by a microgripper structure, which is mounted on a cantilever-based interferometric force probe. A piezo-lever actuator is used to apply tensile displacements and to perform tensile tests of tethered CFs, after alignment. Once the mechanical tests are finished, CFs are removed from the microgripper by application of a magnetic field. Our novel instrument enables tensile tests with at least 25-fold increased throughput compared to tensile testing with an atomic force microscope while achieving force resolution (p-p) of 10 nN at a strain resolution better than 0.1%.

Calibration of the PA6 Short-Fiber Reinforced Material Model for 10% to 30% Carbon Mass Fraction Mechanical Characteristic Prediction.

Short-fiber reinforced composites are widely used for the mass production of high-resistance products with complex shapes. Efficient structural design requires consideration of plasticity and anisotropy. This paper presents a method for the calibration of a general material model for stress–strain curve prediction for short-fiber reinforced composites with different fiber mass fractions. A Mori–Tanaka homogenization scheme and the J2 plasticity model with layered defined fiber orientation were used. The hardening laws: power, exponential, and exponential and linear were compared. The models were calibrated using experimental results for melt front, orientation tensor analysis, fiber length, and diameter and tension according to ISO 527-2, for samples of PA6 which were either non-reinforced, or reinforced with 10%, 15%, 20%, and 30% carbon fiber mass fractions. The novelty of this study lies in the transition from the strain–stress space to the strain–stress–fiber fraction space in the approximation of the material model parameters. We found it necessary to significantly reduce the fiber aspect ratio for the correct prediction of the mechanical characteristics of a composite using the Mori–Tanaka scheme. This deviation was caused by the ideal solution of ellipsoidal inclusion in this homogenization scheme. The calculated strength limits using Tsai–Hill failure criteria, based on strain, could be used as a first approximation for failure prediction.

Linear stability analysis of nonisothermal glass fiber drawing

We present a model of the draw resonance instability for glass fiber drawing including inertia, gravity, surface tension, and temperature. Using linear stability analysis, we have evidenced, through an alternative scaling, the crucial role of the fiber aspect ratio as a control parameter. It appears that a strong destabilization of the system occurs as this parameter increases. We also show the significant influence of nonhomogeneous ambient temperature on system stability. Contrary to the film casting problem, the high critical draw ratio in industrial applications could be rationalized only for a heat transfer coefficient dependent on both the velocity and cross-sectional area of the fiber.

Sodium Hydroxide/Silane Treated Kenaf Fibre in Unsaturated Polyester Matrix: Effects of Fibres Length and Fibres Loading Towards The Composites Flexural and Morphological Properties

The fibre behaviour is a critical aspect that will determine the deformation of the composite since it highly relies on its physical and chemical properties. This paper focus on the effect of similar fibres aspect ratio (L/D) with different length of untreated Kenaf fibre and SodiumHydroxide/silane treated Kenaf fibres on the flexural properties of the composites. The treated and untreated kenaf fibre at two different fibre lengths (A: 0.4 cm and B: 2.9 cm) were fabricated at low filler loadings (5,10,15%) and high filler loadings (45,50,55%). The results showed an improvement in the flexural stress (7-44 %) and modulus (6-46 %) with the application of treatments for both A- and B- fibre categories. The optimum result was achieved from the treated samples at a shorter A-fibre composite, although the aspect ratio between A and B-fibre samples are similar. The chemical treatment coalition might improve the surface interaction and, at shorter fibre length, it affects the fibres compact-ability that led to an improvement in stress distribution and low voids formation as supported by the observation on the composite's fractured surface where traces of matrix observed on the surface of pull-out fibres. From the fractographic analysis, the fibres morphological condition before the fabrication is one of the important factors to consider since it can affect the end-properties of the composites.

Experimental and numerical investigation of lightweight foamed reinforced concrete deep beams with steel fibers

This paper aims to experimentally and numerically study the effect of steel fiber on the behavior of Lightweight Foamed Reinforced Concrete (LWFRC) deep beams and its mechanism to improve the mechanical properties and crack control of concrete. In addition to this, steel fibers compensate for the lack of resistance due to the use of lightweight foamed concrete (LWFC). This paper will also address the effect of some variable parameters on the structural behavior such as: (1) volume of fiber; (2) fiber aspect ratio; (3) longitudinal reinforcement ratio.The experimental program consists of four groups; each group comprises two beams compared to the control specimen. All beams have an overall depth of 800 mm, width of 150 mm, and total length of 2200 mm with span of 2000 mm. Tests were performed under two points load with constant shear-span to depth ratio equal to one. The used LWFC has an average cubic, cylindrical compressive strength and splitting tensile strength of 33, 28 and 3.10 MPa, respectively. Hooked end steel fibers with length 40, 50, and 60 mm and 0.8 mm diameter were used with 0%, 0.5%, 0.75% and 1.0% volumetric ratio.The obtained results indicated that the cracking and the ultimate load has increased by 18.5% and 25.5%, respectively due to use steel fibers. Furthermore, the displacement ductility and toughness has increased by 38% and 56%, respectively. The failure mode of LWFRC deep beams is shear brittle failure.Shear capacity of all deep beams based on ECP 203–2017 (ECP-203, 2017) is calculated and compared with that from ACI 318–19 (ACI 318-19, 2018) which is based on strut and tie model (STM). Comparing the experimental results with STM results showed that ECP 203–2017 (ECP-203, 201) is slightly conservative in calculating the ultimate capacity than ACI 318–19 (ACI 318-19, 2018) for the range of the studied variables in this research and not in general. Finally, as the STMs are debatable, ANSYS 15 software was used to numerically study the behavior of LWFRC deep beams. Verification of numerical models has been done by comparing the results of the load deflection curves, cracks and ultimate loads with the experimental ones.

Prediction and developing of shear strength of reinforced high strength concrete beams with and without steel fibers using multiple mathematical models.

One of the methods to improve the structural design of concrete is by updating the factors given in standard codes, especially when non-conventional materials are used in concrete beams. Accordingly, this study focuses on the colorations between the compressive strength and shear strength of high-strength concrete beams with and without steel fibers. For that purpose, different models are proposed to predict shear strength of high-strength concrete beams, by taking different combinations of the main variables: beam cross-section dimension (width and effective depth), reinforcement index, concrete compressive strength, shear span ratio, and steel fiber properties (volumetric content, fiber aspect ratio, and type of steel fibers). Multi-linear and non-linear regression analyses are used with large database experimental results found in the literature. The predicted results from the proposed equations are composed with different available models from codes, standards, and literatures. The calculated results showed better correlations and were close enough to the experimental data. Based on the data given in the standard codes, the shear strength is proportional to compressive strength ([Formula: see text]) of the power 0.5. However, this value may not be adequate for modern cement and concrete containing steel fibers. Therefore, the mentioned power value must be reduced 5 times to 0.1.

Measuring orientation dynamics of carbon fibers by dielectric anisotropy in shear flows

Measuring orientation dynamics of carbon fibers is important for manufacturing high-performance composite materials, however, conventional methods fail to timely and non-destructively measure due to destructive sample preparation or complicated data processing from numerous fibers. Herein, we report a timely and non-destructive method that uses two pairs of interdigital electrodes to record dielectric anisotropy induced by carbon fibers orientation. As a proof-of-concept, orientation dynamics of carbon fibers is successfully characterized, the accuracy of which in measuring the final degree of orientation and dynamic orientation process is evidenced by theoretical calculations and optical observations. Experimental results reveal that increasing the fiber aspect ratios, viscosities of solvents and shear rates, could shorten orientation time or increase the final degree of orientation. Meanwhile, a modified model is proposed to explain orientation dynamics with a maximum error of 4.7%. This method has the potential for measuring the orientation dynamics of carbon fibers in the complex structure during processing.

Experimental Findings and Validation on Torsional Behaviour of Fibre-Reinforced Concrete Beams: A Review.

Fibres have long been utilized in the construction sector to improve the mechanical qualities of structural elements such as beams, columns, and slabs. This study aims to review the torsional behaviour of various forms of fibre reinforced concrete to identify possible enhancements and the practicability of concrete structural beams. Concrete reinforced steel fibre, synthetic fibre, and hybrid fibre are examples of fibre reinforced concrete. The review found that the mixing, orientation, and volume of fibres, the size of coarse particles, the aspect ratio of fibres, and the stiffness of fibres all affect the torsional strength of fibre reinforced concrete. Nevertheless, the application of fibres to recycled self-consolidating concrete of various forms needs to be explored and studied to ascertain its feasibility to facilitate greener concrete. Thus, with the results compiled in this review paper, it was possible to delimit advances and gaps on the effect of editing reinforcement fibres in relation to the torsion of structural elements.

Effect of Surface Modification on the Characteristics of Sisal Fiber Reinforced Concrete Treated with Na2CO3

Concrete with fiber as a reinforcing material is one of the important fields of research that is gaining traction in this upcoming green technology revolution. By adding fibers to concrete, the tensile strength properties are vastly improved without compromising the strength characteristics, and cost fluctuation is minimal. This research is being carried out to improve the qualities of concrete that have been infused with chemically treated sisal fiber in varied ratios. The paper investigates and describes the effects of sisal fiber when it is chemically treated and infused with concrete, comparing it to ordinary concrete in strength tests. Water absorption, workability, and other material characteristics of Sisal fiber reinforced concrete with 0.5 per cent, 1 per cent, 1.5 per cent, and 2 per cent fiber replacing cement by volume fraction and a sisal fiber aspect ratio of 1:100 are compared to the traditional M30 concrete grade. After being treated with an alkaline solution, 0.5 per cent and 1 per cent sisal fiber reinforced concrete increased tensile and compressive strength, as well as the formation of calcium carbonate deposits on the fiber interfaces; this also contributes to the concrete’s corrosion resistance and durability.

Ultra-high-strength engineered/strain-hardening cementitious composites (ECC/SHCC): Material design and effect of fiber hybridization

It is well known that an increase in the compressive strength of cementitious composites is usually accompanied by a loss of tensile ductility. Designing and developing ultra-high-strength cementitious composites (e.g., ≥200 MPa) with high tensile strain capacity (e.g., ≥3%) and excellent crack resistance (e.g., crack width ≤100 μm) remain challenging. In this study, a series of ultra-high-strength Engineered Cementitious Composites (UHS-ECC) with a compressive strength over 210 MPa, a tensile strain capacity of 3–6% (i.e., 300–600 times that of ordinary concrete), and a fine crack width of 67–81 μm (at the ultimate tensile strain) were achieved. Hybrid design of fiber reinforcement and matrix for UHS-ECC was adopted by combining the ECC and ultra-high-performance concrete (UHPC) design concepts, and the effect of fiber hybridization and aspect ratio on the mechanical behavior of UHS-ECC was comprehensively investigated. The overall performance of UHS-ECC was assessed and compared with the existing high-strength ECC and strain-hardening UHPC, and it was found that the currently designed UHS-ECC recorded the best overall performance among the existing materials. Finally, the multiple cracking behavior of UHS-ECC was analyzed and modeled based on a probabilistic approach to evaluate its critical tensile strain for durability control in practical applications. The results of this study have pushed the performance envelope of both ECC and UHPC materials and provided a basis for developing cementitious composites with simultaneously ultra-high compressive strength, ultra-high tensile ductility, and excellent crack resistance.

Analysis of Fracture and Toughness of a Denture Base with Polyvinyl Fibers

Fracture resistance of polymer reinforced with short fibers consists of a sum of contributions from matrix and fiber fracture, fiber de-bonding and pull-out. The existing models for predicting dependence of fracture toughness on structural variables were derived for the commercially important fiber volume fractions, i.e., for vf≥0.1. In this contribution, modification of the existing model for the dependence of the critical strain energy release rate, GIC, on the fiber type, length and aspect ratio, interfacial adhesion and volume fraction has been attempted to allow predictions at low vf < 0.10. The predictions based on the modified model were compared with experimental data on fracture toughness of lightly x-linked PMMA used to manufacture base of removable dentures toughened with short randomly oriented deformable fibers. The composite toughness was measured under impact loading to simulate typical mode of fracture of removable dentures. The GIC for composites containing short Kevlar 29, S2-glass and poly(vinyl alcohol) (PVOH) fibers were obtained using instrumented Charpy impact tests at room temperature and impact speed of 1.0 m/s. Theoretical prediction based on the proposed model and experimental results agreed reasonably well.

Analysis of Fracture and Toughness of a Denture Base with Polyvinyl Fibers

Fracture resistance of polymer reinforced with short fibers consists of a sum of contributions from matrix and fiber fracture, fiber de-bonding and pull-out. The existing models for predicting dependence of fracture toughness on structural variables were derived for the commercially important fiber volume fractions, i.e., for vf≥0.1. In this contribution, modification of the existing model for the dependence of the critical strain energy release rate, GIC, on the fiber type, length and aspect ratio, interfacial adhesion and volume fraction has been attempted to allow predictions at low vf < 0.10. The predictions based on the modified model were compared with experimental data on fracture toughness of lightly x-linked PMMA used to manufacture base of removable dentures toughened with short randomly oriented deformable fibers. The composite toughness was measured under impact loading to simulate typical mode of fracture of removable dentures. The GIC for composites containing short Kevlar 29, S2-glass and poly(vinyl alcohol) (PVOH) fibers were obtained using instrumented Charpy impact tests at room temperature and impact speed of 1.0 m/s. Theoretical prediction based on the proposed model and experimental results agreed reasonably well.

Exploring the applicability of a simplified fully coupled flow/orientation algorithm developed for polymer composites extrusion deposition additive manufacturing

Abstract Prior literature employed a finite element based fully coupled algorithm that solved the flow/orientation coupling effects in extrusion deposition additive manufacturing, i.e., a key component for identifying the material properties of solidified deposited polymer composites. However, the complex iterative solution protocol reduces the computational capability of the algorithm. This paper simplifies the finite element based fully coupled algorithm by employing a scalar representation of the fourth order orientation tensor affected viscosity tensor. The revised code predicts similar fiber orientation results as compared to a related prior study. With the simplified fully coupled algorithm, effects of material deposition rate and fiber aspect ratio on a 2D planar large area extrusion deposition flow are explored, where the power law rheology model is employed for the flow simulation. Computed results show that an increased material deposition rate reduces the extrudate-swell ratio of the melt front and varies the local fiber orientation of the deposited bead especially near the flow region in contact with the substrate. Higher fiber aspect ratio enhances the principal fiber alignment of the extrusion and deposition flows, where the maximum local difference of the principal A 11 component is 23% with increasing fiber aspect ratio from 10 to 25.

Concrete Blocks Reinforced with Arundo donax Natural Fibers with Different Aspect Ratios for Application in Bioarchitecture

In recent decades, the construction industry has advanced in its use of natural green resources, such as vegetable fibers (e.g., flax, hemp, jute, etc.) added in concrete mixtures, to create building materials that are both economically and environmentally sustainable. The pricing, low energy cost, and environmental sustainability of these natural fibers are driving this interest. The quantity of fibers and the ratio of fiber length to its transverse diameter (aspect ratio) are critical characteristics that have a decisive impact on concrete’s mechanical qualities. The influence of the aspect ratio of Arundo donax fibers on the tensile characteristics of concrete blocks was specifically investigated in this study. These fibers were collected from the outer section of the stem of this plant, which grows commonly in Mediterranean locations, but that is also found all over the world. Experiments were carried out on cylindrical concrete blocks with a constant amount of fiber (1 percent by weight) and different aspect ratios: 30, 50, and 70 (mm/mm) respectively, to assess their tensile strength, even when compared with concrete blocks without any fiber addition. Tensile tests on Arundo donax fibers were also conducted, with the aim to contribute to the analysis of their interaction with cementitious matrices, and to assess differences between the various compositions. The results showed a direct impact of the aspect ratio on the final tensile strength of concrete blocks, with higher aspect ratios producing superior tensile properties.

An efficient computational approach for three-dimensional modeling and simulation of fibrous battery electrodes.

Fibrous electrodes are a promising alternative to conventional particle‐based lithium‐ion battery electrodes. In this contribution, we propose an efficient computational approach for the modeling and simulation of electrochemical phenomena taking place in fibrous electrodes during battery charge/discharge processes. Since each fiber is explicitly modeled by means of a dimensionally reduced embedded fiber model, the framework enables simulations in a three‐dimensional setting with relatively modest discretization and computational requirements compared to simulations with fully resolved fiber discretizations. The approach is applied to electrodes with high volume fractions of high aspect ratio fibers. Various local and global quantities are analyzed and results are compared to those obtained with the standard finite element method and the pseudo‐2D model.

An FE-based orientation averaging model for elasto-plastic behavior of short fiber composites

A new micro-mechanical model for predicting the non-linear elasto-plastic behavior of short fiber reinforced composites is presented. The model is developed based on a two-step Orientation Averaging method, and is capable of accommodating a wide variety of micro-structural parameters. In the first step, Finite Element Analyses are performed on a unit cell (single fiber surrounded by matrix). Then, the unit cell response is up-scaled by calibrating its response to an elasto-plastic surrogate constitutive model. In a subsequent second homogenization step, a self-consistent interaction scheme is proposed. The predictive capability of the resulting two-step homogenization scheme is then evaluated, next to versions that adopt more traditional averaging schemes (Voigt and Reuss, providing upper and lower bounds, respectively), through comparisons to experiments and direct numerical simulations of realistic Representative Volume Elements. Results show that the model gives fairly good predictions. It is emphasized that the model is capable of accommodating any desired fiber orientation distribution, very large ranges of fiber aspect ratios and fiber volume fractions. Also, the model is computationally very efficient compared to the RVE computational homogenization approach, and thus, it could be conveniently used in applications possessing different fiber orientations at different points of a component.

A Review on Natural Fibre-Reinforced Biopolymer Composites: Properties and Applications

In ongoing decades, material researchers and scientists are giving more consideration towards the improvement of biobased polymer composites as various employments of items arranged by natural fibres and petrochemical polymers prompt natural awkwardness. The goal of this review paper is to provide an intensive review and applications of the foremost appropriate commonly used biodegradable polymer composites. It is imperative to build up the completely/incompletely biodegradable polymer composites without bargaining the mechanical, physical, and thermal properties which are required for the end-use applications. This reality roused to create biocomposite with better execution alongside the least natural effect. The utilization of natural fibre-reinforced polymer composites is concerned with the mechanical properties that are highly dependent on the morphology, hydrophilic tendency, aspect ratio, and dimensional stability of the natural fibre. With this in-depth consideration of eco-friendly biocomposites, structural application materials in the infrastructure, automotive industry, and consumer applications of the following decade are attainable within the near future.

Preparation and characterization of lightweight SiC frameworks by connecting SiC fibers with SiC joints

The increasing energy challenges and the rapidly developing astronautic technology require thermal insulators with low density and thermal conductivity, high–temperature thermal, chemical and mechanical stabilities. Herein, highly porous SiC frameworks were fabricated through procedures of assembling SiC fibers and formation of SiC joints by carbothermal reduction, which were named as SiC–bonded SiC fiber (SBSF) composites. The porosities were controlled in the range of 76–93% by varying aspect ratios of the SiC fibers. The SBSF composites exhibited outstanding corrosion resistance, oxidation resistance, and high–temperature thermal stability, as the inherent advantages of SiC ceramics. High strength and reversible compressibility were obtained in the out–of–plane compression load tests, and low thermal conductivity of 0.036–0.102 W/m · K at 25–800 °C was achieved. The results of this study suggest that the SBSF composites are a good candidate for high–temperature thermal insulators.