Effects Of Fiber Volume Fraction Research Articles

Preparation of continuous carbon fiber reinforced PA6 prepreg filaments with high fiber volume fraction

High-performance continuous carbon fiber prepreg filaments have been a research hotspot in the field of additive manufacturing in recent years, and are considered to be an effective option for improving the mechanical strength of thermoplastic composite parts. However, the effect of fiber volume fraction on the microstructure and tensile properties of 3D printed prepreg filaments remains miss. Therefore, this study selected suitable impregnation processes and materials to prepare prepreg filaments with different fiber volume fraction and investigated their mechanical properties and microscopic morphologies. The results show that the increase of fiber volume fraction effectively promoted the interface bonding between fiber and resin, and increased capacity for load transfer. When the fiber volume fraction was 54.0%, the tensile strength of the prepreg filaments and specimens reached 1977 MPa and 334 MPa, respectively. This study can provide a process optimization strategy for the preparation of more types of continuous fiber prepreg filaments with high fiber volume fraction, as well as a data reference for the preparation of high-performance 3D-printed thermoplastic composites.

Computational modeling and statistical analysis of buckling characteristics of polysilicon reinforced fiber

The purpose of this study is to evaluate the effect of volume fraction of continuous carbon fiber and sample length on buckling characteristics of polysilicon. A statistical design of 12 samples were formulated with constant cross-section area of 2500 mm2 using Design of Experiment software (DOE). The samples were sketched using ABAQUS 2019 software, and the total buckling force each sample was estimated. The estimated buckling forces were statically evaluated as a response using DOE. The estimated forces of 3.48776e07, 4.00652e07 and 5.78142e07 newton for the simulated samples of 100 mm in length and 0,15, and 25% volume fraction respectively, is an indication of positive effect of fiber volume fraction on the necessary force for buckling. In addition, similar tendency was found in other samples (the higher fiber volume fractions the higher buckling force). However, the estimated buckling force for each sample was negatively affected with length of the sample. The result indicated a value of 4.00652E+07, 5.00447E+06 and 1.80390E+06 newton at a constant fiber volume fraction and different length of 100, 300 and 500 mm respectively. The statistical analysis of the simulated buckling force showed a signification design, and the date of one factor effect is highly supported by the simulated buckling forces. The equation of a significant design can be used to estimate the buckling force at any fiber volume fraction and sample length.

Pengaruh Fraksi Volume Serat Terhadap Peningkatan Kekuatan Impak dan Kekuatan Tarik Komposit Berpenguat Serat Daun Nanas (Ananas Cosmosus)

A composite is a technical material that is made by combining two or more materials that have different properties to become a new material with different properties. Natural fibers used as composite reinforcement are more environmentally friendly and biodegradable. The use of natural fibers as composite reinforcement in recent years has experienced very rapid development. One of them is pineapple leaf fiber. The aim of this research is to determine the effect of fiber volume fraction and NaOH immersion on the mechanical properties (Tensile Strength and Impact Strength) of composites reinforced with pineapple leaf fibers with an epoxy matrix. In this research, woven composites were made with variations in volume fraction and NaOH immersion time for the fibers, then tensile tests according to ASTM D-3039 standards and impact tests according to ASTM D256 standards. Based on test results with varying fiber volume fractions of 15%, 20%, and 25%, the strength results increase and decrease. The tensile strength of the composite tends to increase with increasing fiber volume fraction and NaOH immersion. However, the longer the soaking time, namely 4 hours, the tensile strength of the composite tends to decrease. The most optimal average value of tensile strength is at a fiber volume fraction of 25% with fiber soaking for 2 hours with a value of 23.07 MPa and the lowest average value of tensile strength is at a fiber volume fraction of 15% with fiber soaking for 4 hours with value 11.31 MPa. Meanwhile, the highest average impact value was owned by a composite with a fiber volume fraction of 20% without soaking, namely 0.0589 j/mm2 and the lowest impact value was with a fiber volume fraction of 20% with fiber soaking for 4 hours, namely 0.0124 j/mm2.

A strength optimization approach for manufacturable 3D printed variable stiffness laminates with a strain-based approximation

The 3D printed continuous carbon fiber reinforced polymers (CFRP) are promising lightweight structures with outstanding mechanical performance. In this work, we propose a structure-manufacture integrated optimization approach for strength maximization of variable stiffness 3D printed CFRP composites by tailoring the steered printing paths. The rule of mixture is modified to evaluate material properties and strength of the printed laminates considering the effect of fiber volume fraction. To make this approach applicable to CFRP with asymmetric layups, a strain-based two-level convex approximation for the failure index based on the Tsai–Wu failure criterion is proposed, which can take the tension-bending coupling effect into consideration. The local failure indices are aggregated using the p-norm formula to reduce the size of the strength optimization model. In order to guarantee the manufacturability of the optimal design, the curvature of the steered printing fiber paths is constrained using a hybrid control method within the approach. The numerical cases show that the strength enhancement of the 3D printed variable stiffness laminates depends on the load, where an improvement between 35% and 46% can be achieved under the tension. Moreover, the proposed method can not only converge stably, but also be capable of optimizing structures with complex geometry.

Mechanical behavior of steel fiber reinforced concrete at cryogenic temperatures: Characterization with 3D meso-scale modelling

To investigate the mechanical properties of SFRC (Steel Fiber Reinforced Concrete) in low-temperature environments, a 3D mesoscale model approach was employed to simulate the mechanical behavior of SFRC specimens at cryogenic temperatures. The model considers SFRC a multiphase material composed of mortar, aggregate, ITZ (Interface Transition Zone), and steel fiber. Using the mesoscale modelling, the damage pattern, stress-strain curve, load-deformation curve, dissipated energy, strength under compressive and splitting-tensile loadings, strength prediction formula as well as the flexural toughness of SFRC specimens with different steel fiber content at low temperatures were obtained and analyzed. The results show that the compressive/splitting tensile strength significantly increases with the decrease in temperature. The splitting tensile strength, the peak deformation as well, and the dissipated energy increase in the case of a greater steel fiber volume fraction while the improvement effect of fiber content is weaker with the decrease in temperature. A prediction formula that considers the coupling effect of fiber volume fraction and temperature on the tensile strength of concrete was proposed. The effect of steel fiber on compressive strength is not obvious regardless of temperature. The flexural toughness index of SFRC increases significantly with increased steel fiber content but is insensitive to temperature changes.

Micromechanical characterization of Carbon/PEEK thermoplastic composite material in-situ consolidated by automated fiber placement: Stiffness prediction

Despite manufacturing challenges, Automated Fiber Placement (AFP) offers a viable alternative to conventional manufacturing methods, allowing for time and cost savings. Creating a Representative Volume Element (RVE) that realistically represents long-fiber-reinforced composites with high fiber volume fraction is a challenging task in modeling their response. The present research aims to predict effective stiffness properties of in-situ-consolidated Carbon/PEEK thermoplastic composite material by considering the effect of fiber volume fraction, void content, degree of crystallinity, and interlaminar resin pocket resulting from AFP in-situ consolidation manufacturing process. In this regard, two sets of samples were manufactured by AFP in-situ consolidation and autoclave re-consolidation methods. Both of them were evaluated by micrographic study and thermoanalytical Differential Scanning Calorimetry (DSC) technique to obtain inputs required for micromechanical analysis. The 2D RVEs on a micro-scale are developed to predict the transverse elastic modulus, out-of-plane Poisson's ratio and out-of-plane shear modulus of the composite material by applying Periodic Boundary Conditions (PBCs) and using Asymptotic Homogenization Theory (AHT). Results show that AFP in-situ consolidation may lead the transverse elastic and out-of-plane shear moduli of Carbon/PEEK thermoplastic composite material to be reduced by about 10 % and 20 %, respectively, compared to autoclave re-consolidation whereas the out-of-plane Poisson's ratio remains unchanged. The findings of the present work confirm that the mechanical performance of Carbon/PEEK thermoplastic composite material could be remarkably influenced by AFP in-situ consolidation manufacturing process, particularly in the transverse direction, which must be taken into account in finite element modeling, analyses, and design of AFP-manufactured composite laminates and structures.

Peridynamic study of fatigue failure of engineered cementitious composites

Fatigue crack propagation is crucial in studying fatigue in engineered cementitious composites (ECC). This paper established a peridynamics (PD)-based fatigue crack propagation model for ECC, incorporating the “cycle broken bonds number” to enhance calculation efficiency. First, the PD fatigue crack propagation model was constructed, and the validity of the model was verified by simulating the fatigue crack propagation path of an inclined edge crack in the plate. Secondly, an improved PMB model considering the strain softening stage was used to model the ECC cement matrix, and the fibers were modeled as one-dimensional cyclic dynamic rods to establish a PD fully discrete model of ECC. At the same time, an interface exponential friction attenuation model was introduced. Then, the effectiveness and validness of the fully discrete model were verified by simulating single fiber pull-out tests and uniaxial tensile tests of ECC specimens. Finally, the fatigue crack propagation forms of ECC beams with mid span Type I cracks under three-point bending fatigue loads were studied, and the effects of fiber volume fraction, stress level, and fiber length on the crack propagation forms and structural deflection of ECC beams under four-point bending fatigue loads were investigated.

Effect of fiber volume fraction on hybrid effects of tensile properties of unidirectional aramid/carbon fiber hybrid composites

AbstractAramid/carbon fiber hybrid reinforced polymer (A/CHFRP) composites were prepared via compression molding to obtain carbon‐fiber‐reinforced polymer (CFRP) composites with better toughness. Based on the existing theoretical model, the effects of the carbon fiber volume fraction on the properties of the A/CHFRP were studied using thermal gravimetric analysis (TGA), tensile tests, and scanning electron microscopy (SEM) analysis. According to the TGA results, the hybrid fiber improved the thermal stability of the CFRP. With increasing carbon fiber content, the thermal stability of the A/CHFRP composites also increased. The tensile results showed that the A/CHFRP composite with a carbon fiber volume fraction of 22.7% exhibited “pseudo‐ductility,” with the failure strain 54.09% higher than that of the CFRP composite. With increasing carbon fiber content, the ductility of the A/CHFRP composites decreased. The elastic modulus of the A/CHFRP composites conformed to the prediction model of the rule of mixtures (ROM). The strength was found to fall in the triangular area surrounded by the ROM and the bilinear ROM and exhibited a positive hybrid effect. The SEM results showed that the tensile failure modes of the A/CHFRP composites were mainly fiber and resin matrix debonding and fiber fracture. Brittle fracture of the carbon fibers was observed in the A/CHFRP composites, while aramid fibers appeared to peel off and silk crimp for ductile failure. Thus, this study provides a theoretical basis for toughening CFRPs.Highlights The volume ratio of the two fibers affects the hybrid effect of A/CHFRP. The thermal stability of A/CHFRP increases with increasing carbon fiber content. The carbon fiber volume ratio of 22.7% in A/CHFRP exhibited pseudo‐ductility. A/CHFRP exhibiting a failure strain 54.09% higher than that of the CFRP. The strength prediction of A/CHFRP depends on the failure mode.

Experimental Study on Direct Shear Strength of Fiber Reinforced Self Compacting Concrete under Acid and Sulfate Attack

This study primary is to investigate the shear strength of self-compacting concrete (SCC) reinforced by steel-fiber (SF) and polypropylene-fiber (PPF) in different environmental conditions: the air, sulfate (MgSO4 with a concentration of 5%) and acid (H2SO4 with a concentration of 5%). The study also examines the effect of fiber volume fraction on the workability, shear strength, compressive strength, and splitting tensile strength of fiber reinforced SCC. The article aims to determine the durability effects of both fibers and their resistance to aggressive environmental conditions. The contribution of this article is an experimental investigation on the shear strength of SCC reinforced by SF as well as PPF in 3 different environmental conditions after 30 days of exposure. The study also investigated the fresh and mechanical properties of 5 different mixtures of SCC with/out 0.1% and 0.2% fibers. The study also concluded that PPF decreased the workability of SCC badly, and special care must be taken when selecting its volume fraction. Also, it was found that generally shear strength of SCC mixes enhanced with increasing SF and PPF volume fraction. Moreover, it was found that both fibers have good durability effects, and resist aggressive environmental conditions, with the best results obtained from samples containing 0.2% SF. In the air condition, while the compressive strength, shear strength and tensile strength results were 52.6MPa, 6.43MPa and 3.91MPa, in the sulfate condition those were 46.37MPa, 6.55MPa and 3.59MPa, and in the acid condition those were 34.4MPa, 5.5MPa and 3.46MPa, respectively.

Effect of Macro Polyolefin Fibers on Bond Strength of Tension Lap Splices in RC Beams

The effect of macro synthetic polyolefin fibers on the bond strength of tension lap splices in reinforced concrete (RC) beams is investigated in this study. The bond between the reinforcement and concrete plays a vital role in the strength of RC beams. The presence of polyolefin fibers in the lap splice zone confines the concrete and enhances the bond strength of the steel bars. The use of synthetic fibers is preferable to steel ones since steel suffers from corrosion over time. Tests were conducted on 12 full-scale beam specimens to determine the effect of fiber volume fraction (Vf), bar diameter (db) and concrete cover-to-bar diameter (c/db) on the response. Four volume fractions (Vf = 0, 0.5, 1 and 1.5%) of polyolefin fibers and three bar sizes (db = 16, 20 and 25 mm) with the corresponding (c/db = 2.31, 1.75 and 1.30) were considered to evaluate the bond strength. The test results demonstrated that the polyolefin fibers noticeably enhanced the bond strength and ductility of spliced tension bars. Experimental results were compared with those obtained from two theoretical methods including ACI Committee 318 design provisions. The results showed that the equation proposed by the ACI Committee overestimates the bond strength.

Mechanical characterization of high-strength carbon-epoxy composite laminates

High-strength carbon/epoxy composites (HSCEC) are known to exhibit comparably high specific strength and stiffness than high-strength steel alloys. Consequently, they have a range of applications in the automotive, aerospace, and ship-building industries But extensive studies on the mechanical properties of HSCECs, especially at the laminate level, are lacking in the literature. This study characterizes the tensile and compressive properties of HSCEC laminates with various uni-directional (UD) and bi-directional (BD) ply sequences. The ply sequence that best combines specific strength and modulus is identified. The effects of fiber volume fraction on load–displacement behavior are analyzed. An increase in the fiber volume fraction increases the stiffness and strength of the laminate but decreases its failure strain. Overall, this study highlights the sensitivity of the specific modulus, specific strength, and percentage elongation of the composite laminates to the stacking sequence and fiber volume fraction.

Investigating the lap shear adhesion of coir and glass-fibre reinforced epoxy bonding to mild steel with varying volume fractions

Bonding synthetic fibres to metals to improve strength, durability, and corrosion resistance is a prevalent practise in the automotive, marine, and aerospace industries. Lap shear adhesion, a measurement of the bonding strength between composites and metallic substrates, is essential for structural integrity. The emergence of natural fibre composites as sustainable alternatives to synthetic composites makes it essential to investigate their lap shear behaviour and the effect of fibre volume fraction on composite properties. This research investigates the adhesion behaviour of coir and glass fibre epoxy composites to mild steel. Coir fibres, which are known for their resilience and tenacity, were treated with an alkaline solution to improve their adhesion to the resin. Samples of lap shear adhesion were prepared in accordance with ASTM specifications, and tests were conducted using a tensile machine. Increasing the volume fraction of coir or glass fibres decreased the bond strength, as demonstrated by the results. Due to the fibres’ greater tensile strength and rigidity, glass fibre composites exhibited superior strength. However, under tensile loading conditions, coir fibres exhibited superior adhesion to mild steel surfaces. SEM micrographs confirmed that coir composites exhibit shear failure while glass composites exhibit fibre pull-out behaviour. This study concludes by highlighting the engineering potential of coir fibres, considering their natural properties and cost-effectiveness. It is necessary to further optimise the fiber-matrix interface and comprehend the mechanical behaviour of coir composites in order to maximise their effectiveness. To assure the long-term durability of composite-metal joints, surface preparation, adhesive type, application procedure, and environmental conditions must also be considered. At a content percentage of 10%, glass fibres exhibited 100% higher shear strength compared to coir fibres in epoxy composites. Conversely, coir fibres at 10% content demonstrated approximately 75% greater shear strength than the values obtained with 40% glass fibres. The failure mechanisms observed are delamination or fibre fracture in the bonding area under tensile and shear loading. Increasing the fibre volume fraction reduces bond strength. Factors such as limited space for the matrix, tension concentrations, and the mechanical properties of the fibres contribute to weakened bonds. Glass fibres have better strength and rigidity than coir fibres, affecting load transfer and adhesion. Interfacial bonding is crucial, and maintaining it becomes more difficult with higher fibre volume fractions, resulting in weakened bonds.

Effect of tension on liner buckling and performance of a type-4 cylinder for storage of compressed gases with experimental validation

Composite pressure vessels are extensively used for on-board storage of compressed gases for their light weight. The burst pressure and weight of the cylinder play a vital role in determining their safety and storage efficiency. These cylinders can be tailor-made for its strength, thickness, and weight by optimizing the winding parameters of the composite. The mechanical properties mainly depend on its fiber volume fraction, which is critically affected by the applied winding tension. This study aims to analyze the effects of winding tension and fiber volume fraction on performance of the composite. Plastic liners are weaker structures for winding the cylinder at high tensions and tend to deform at critical buckling load. Finite element analysis is used to predict the critical buckling pressure of the liner, the theoretical burst pressure, and the weight of the vessel. Actual prototype is manufactured and tested to validate the theoretical results. The validated design model is used to study the effect of fiber volume fraction on burst pressure and weight of the vessel. A property performance relationship matrix between the applied tension, compaction pressure on liner body, burst pressure and weight performance is established for which the critical buckling pressure is set as a safety limit.

Mechanical Properties and Crack Resistance of Basalt Fiber Self-Compacting High Strength Concrete: An Experimental Study.

Pure self-compacting concrete has many disadvantages, such as early shrinkage and cracking. The addition of fibers can effectively improve the properties of resistance to tension and cracking of self-compacting concrete, thereby the effect of improving its strength and toughness can be achieved. Basalt fiber is a "new green industrial material" that has unique advantages, such as high crack resistance and being lightweight compared with other fiber materials. In order to study the mechanical properties and crack resistance of basalt fiber self-compacting high-strength concrete intensively, the self-compacting high-strength concrete of C50 was designed and obtained using the absolute volume method with multiple proportions. Orthogonal experimental methods were used to study the influence of the water binder ratio, fiber volume fraction, fiber length, and fly ash content on the mechanical properties of the basalt fiber self-compacting high-strength concrete. Meanwhile, the efficiency coefficient method was used to determine the best experiment plan (water binder ratio 0.3, fiber volume ratio 0.2%, fiber length 12 mm, fly ash content 30%), and the effect of fiber volume fraction and fiber length on the crack resistance of the self-compacting high-performance concrete was investigated using improved plate confinement experiments. The results show that (1) the water binder ratio had the greatest impact on the compressive strength of basalt fiber self-compacting high-strength concrete, and as the fiber volume fraction increased, the splitting tensile strength and flexural strength both increased; (2) there was an optimal value for the effect of the fiber length on the mechanical properties; (3) with the increase in fiber volume fraction, the total crack area of the fiber self-compacting high-strength concrete significantly decreased. When the fiber length increased, the maximum crack width first decreased and then slowly increased. The best crack resistance effect was achieved when the fiber volume fraction was 0.3% and the fiber length was 12 mm. Therefore, basalt fiber self-compacting high-strength concrete can be widely used in engineering fields, such as national defense construction, transportation, and building structure reinforcement and repair, due to its excellent mechanical and crack resistance properties.

Study on durability of transverse shear properties for novel carbon/glass hybrid fiber‐reinforced polymer bars in simulated concrete environments

AbstractDurability on the transverse shear properties of hybrid fiber‐reinforced polymer (HFRP) bar may control the cross‐sectional load‐bearing capacity and failure mode of the HFRP bar reinforced concrete members due to its strength degradation with time. Herein, the degradation of novel carbon/glass (C/G)‐HFRP bars were accelerated in simulated concrete environments at 60°C to investigate the effects of fiber volume fraction and distribution pattern, matrix resin volume fraction, exposure environment, and period on their transverse shear properties. The results displayed that the transverse shear strength of the samples reduced by 15%, 20%, and 8% after exposure to the simulated ordinary concrete, seawater sea‐sand concrete environments, and tap water for 6 months, respectively. The inward diffusion of water molecules and free hydroxyl ions caused the hydrolysis of matrix resin, etching of glass fiber and debonding of fiber/matrix interface, which were the incentives of the degradation of C/G‐HFRP bars. The increase of matrix resin volume fraction and the application of a waterproof coating were recommended to alleviate the degradation of fibrous composites in concrete environments. Finally, two prediction models were proposed to determine the transverse shear strength of HFRP bar before and after exposure to different harsh environments, respectively. The comparisons indicated that the predicted values were coincided with the experimental results.

The Effect of Fiber Volume Fraction on Fiber Distribution in Steel Fiber Reinforced Self-Compacting Concrete

This paper investigates the effect of fiber volume fraction on fiber distribution in steel fiber reinforced self-compacting concrete (SFRSCC) through experiments and numerical simulations. Three types of SFRSCC beam specimens with different fiber volume fractions (0.3%, 0.6%, and 0.9%) were cut to expose the steel fibers. The number and the orientation angle of the steel fibers on the beam sections were determined by image analysis techniques. Fiber density, fiber segregation coefficient, fiber dispersion coefficient and fiber orientation coefficient were applied to evaluate fiber distribution on the beam sections. Based on the experimental data, numerical models simulating the pouring process of fresh SFRSCC were established to analyze the overall fiber distribution in the specimens. The results show that the distribution state of the fibers on the beam sections is not random and uniform, which is correlated to the fiber volume fraction. Due to the variable rheological properties, a greater fiber volume fraction causes better fiber uniformity, lower fiber segregation and worse fiber alignment on the beam sections. Meanwhile, the numerical results show that the distribution law of fibers along the length direction of the specimens is almost independent of the fiber volume fraction. In addition, increasing the fiber volume fraction results in the increase of the average angle of the fiber orientation in the specimens. The results can provide a reference for optimizing the fiber distribution in the concrete matrix.

Effects of fiber volume fraction, fiber length, water-binder ratio, and nanoclay addition on the 3D printability of strain-hardening cementitious composites (SHCC)

Strain-Hardening Cementitious Composites (SHCC) exhibit superior mechanical performance and show potential in 3D printing applications. However, the formation of fiber agglomerates causes significant challenges during pumping and 3D printing. This study explores the 3D printability of SHCC, using a progressive cavity pump. Various situations are found: Some SHCC mixtures could be 3D printed smoothly with a continuous and non-fractured filament; Some show fractured filaments; Some cause the pump automatically stopped. For these failed extrusion cases, fiber agglomerates are found in the nozzle resulting in fractured filaments, or in the pump screw resulting in automatic cessation of the pump. Effects of fiber volume fraction, fiber length, water-binder ratio, and nanoclay addition on the 3D printability of SHCC are explored. Analysis based on the contact percolation packing fraction of flexible fibers is performed to explore the formation of fiber agglomerates and its impact on 3D printability. The significance of fiber deflection is also highlighted.

Bending behavior of strain hardening cementitious composites based on the combined fiber-interface constitutive model

Strain-hardening cementitious composites (SHCC) are a class of fiber-reinforced cementitious composites characterized by strain hardening behavior accompanied by multiple cracking, which is designed by tailoring matrix, fiber, and fiber/matrix interface based on the micromechanics theory. At present, there are several numerical simulation methods to study the multiple cracking behavior, such as discrete crack model, unity finite element method, 3D smeared crack model, multiscale constitutive models, and lattice model. However, it is difficult to provide a good balance between accuracy and computational efficiency due to the vast number of fiber and the complex relationship between fibers, matrix, and interface. This paper developed a combined fiber-interface constitutive model based on the single fiber pull-out theory, and established a combined unit. A three-dimensional two-phase finite element model was established, which had been proved to be effective on simulating the cracking behavior of SHCC. Furthermore, the effects of fiber volume fraction and matrix cracking strength on the four-point bending properties of SHCC were investigated. Further study showed that there was a critical matrix cracking strength for a specified fiber and matrix. This value can optimize the design of SHCC to achieve high strength and high toughness performance.

The Effect of Fiber Volume Fraction on the Bending Strength of Fiber-Reinforced Composites of Oil Palm Empty Fruit Bunches

In this modern era, the palm oil industry is growing, so the waste is also increasing. If the waste from the palm oil industry is not processed, it will pollute the environment. One way to process palm oil waste is to turn the empty palm fruit bunches (OPEFB) fibers into composite reinforcement. Various natural fibers can be applied to become composite reinforcement, so it is necessary to study the character of OPEFB fibers for composite reinforcement. This study will look at the effect of various volume fractions on the bending strength of the composite. The volume fraction consists of 20%, 30%, and 40% fiber. The composite is then tested for bending to determine the bending strength of the composite. The results of the tests showed that the highest bending strength value was the 30% volume fractional variation with 47.70 MPa. The 40% volume fraction variation has the lowest bending strength value of 29.53 MPa.

A constitutive model for sheared dense fiber suspensions

We propose a constitutive model to predict the viscosity of fiber suspensions, which undergoes shear thinning, at various volume fractions, aspect ratios, and shear stresses/rates. We calibrate the model using the data from direct numerical simulation and prove the accuracy by predicting experimental measurements from the literature. We use a friction coefficient decreasing with the normal load between the fibers to quantitatively reproduce the experimentally observed shear thinning in fiber suspensions. In this model, the effective normal contact force, which is directly proportional to the bulk shear stress, determines the effective friction coefficient. A rise in the shear stress reduces the effective friction coefficient in the suspension. As a result, the jamming volume fraction increases with the shear stress, resulting in a shear thinning in the suspension viscosity. Moreover, we extend the model to quantify the effects of fiber volume fraction and aspect ratio in the suspension. We calibrate this model using the data from numerical simulations for the rate-controlled shear flow. Once calibrated, we show that the model can be used to predict the relative viscosity for different volume fractions, shear stresses, and aspect ratios. The model predictions are in excellent agreement with the available experimental measurements from the literature. The findings of this study can potentially be used to tune the fiber size and volume fraction for designing the suspension rheology in various applications.