High Fiber Volume Fraction Research Articles

Minimum potential method appropriate to generate 2D RVEs of composites with high fiber volume fraction

This work proposes a novel method, entitled minimum potential method, to generate Representative Volume Elements (RVEs) of unidirectional fibers composites with high fiber volume fractions (FVFs, generally ≥70.0%). In the proposed method, a given VF of random and periodic fibers are initially created within the matrix and the fiber overlap is allowed, and then the fiber overlap is gradually removed by adjusting the fiber centroids based on the principle of the minimum overall potential. In the process of fiber overlap removal, the fiber periodicity and the fibers completely or partly contained in the matrix are preserved. The overall potential of the fibers consists of fiber overlap potential, fiber position potential and fiber periodicity potential, and is minimized using the gradient descent method. The numerical implementation of the proposed method is detailed, and the RVEs of the composites with various FVFs are generated. Through the probability distribution function of the nearest neighbor distance, the cumulative probability distribution function of the nearest neighbor orientation angle, the second-order intensity and pair correlation functions, the fiber distribution in the generated RVEs is analyzed, and the results indicate a completely random distribution of the fibers in the generated RVEs. Comparing with the available experimental test, the literature and the Double-Inclusion model, the proposed method to generate RVEs of the composites with high FVFs is validated.

Fatigue behavior of unidirectional fiber‐reinforced pultruded composites with high volume fiber fraction

AbstractPultrusion is a high‐volume manufacturing process for fiber‐reinforced polymer (FRP) composites ensuring high strength and quality products. However, research studies are very limited on the fatigue behavior of these products, especially with unidirectional fiber alignment. This study investigates the fatigue behavior of the unidirectional pultruded glass FRP (GFRP) composites with high fiber volume fraction ( ). Tension–tension fatigue loading was applied with different levels of applied stress, frequency, and gripping condition until failure. Results showed that the high composites have significantly low fatigue life cycle. Moreover, increasing the frequency showed better fatigue resistance, while the tabs geometry has insignificant effect on the fatigue behavior of the dog‐bone shaped specimens. Comparison with available literature showed that GFRP composites with high have lower fatigue performance than those with low . A fatigue capacity reduction factor is also proposed for unidirectional GFRP composites as a function of the .

The impact of the fiber volume fraction on the fatigue performance of glass fiber composites

The dependency of the fatigue resistance on the fiber volume fraction of a non-crimp glass fiber fabric reinforced polyester polymer matrix composite is investigated, in the range of 55% to 60% fiber volume. The experimental investigation cover tension–tension, tension–compression, and compression-compression cyclic loading cases. Both an overall and local fiber volume fraction are considered. It is observed that the high fiber volume fraction cases also have higher porosity densities. The tension–tension fatigue loading is found to be most dependent on the fiber volume fraction, while the compression-compression load case is found to have the least dependency.

Punching shear behavior of RC slabs incorporating macro-synthetic fibers

The effect of macro synthetic fibers on punching shear behavior of reinforced concrete slabs was investigated. Twenty-four square reinforced concrete slabs (1500 mm × 1500 mm) were prepared, instrumented, and tested under monotonic, displacement controlled, center-point load in a simply-supported configuration. The main test parameters were the fiber volume fraction (0.5% and 1%), slab thickness (100 mm and 150 mm), and the flexural reinforcement ratio (0.9% and 1.5%). Test measurements included applied load, slab deflection, strains in the steel reinforcement and in the concrete. The development of the cracks for the duration of the test was also monitored and recorded. The test results showed that the punching shear strength, deflection capacity, and energy absorption of the FRC slabs were significantly improved by the presence of macro synthetic fibers. This improvement was associated by a more defined punching shear area, higher cracking density, higher strain in the concrete and a lower strain in the reinforcement steel. Furthermore, the level of improvement was found to be more pronounced in the FRC slabs with lower thickness, lower reinforcement ratio and higher fiber volume fraction.

Mechanical and durability behaviour of fiber reinforced concrete

Fiber Reinforced Concrete (FRC) is broadly used in the construction of large buildings, industrial floors, and pavements due to the presence of exceptional mechanical and durable properties, having modest production cost. The impact of different types of fiber and environmental conditions on the strength and durability of ordinary concrete, such as steel fiber, polypropylene(PP) fiber, and natural palm tree fiber, varies. A variety of conventional material tests were performed to analyze the compressive strength and flexural properties. The experimental results showed that fiber stomping may take place at higher fiber volume fractions, resulting in mixing and casting issues. Based on the mechanical properties and anti-dry-shrinkage cracking resistance of FRC, the suitable fiber length and volume fractions were determined. In 28 days of water curing, adding small amounts of PP fiber can significantly increase compressive strength, flexural strength, and durability. However, in 6 months of wet-dry and heat-cool cycles, steel fiber performed better than PP fiber. The study also found that early shrinking of cracks decreases with an increase in fiber volume fraction, and no cracks are observed when a volume of 0.20% is used. These results can be used as a testimonial for the material proportion design of concrete.

Greedy-based approach for generating anisotropic random fiber distributions of unidirectional composites and transverse mechanical properties prediction

A novel adaptive greedy-based generation (GBG) algorithm is proposed to generate 2D random distribution of fibers for unidirectional composites. Inspired by greedy algorithm, the “fitness function” is introduced to better overcome the jamming limit of the traditional hard‐core method than most published algorithms and generate representative volume element (RVE) with high fiber volume fraction adaptively. The good agreement of statistical analysis with experiments suggests that the generated anisotropic RVEs is statistically equivalent to real composites. The influence of anisotropy on mechanical properties and progressive failure process is further revealed based on finite element method (FEM) using a progressive damage model. The results show that the predicted transverse elastic and strength properties are both anisotropic, which is not consistent with the traditional transverse isotropic hypothesis. The proposed algorithm can generate RVEs with high fiber volume fraction (up to 80%) and provide anisotropic RVEs statistically equivalent to real composites, and thus can serve as a promising method to guide the design and analysis of composites.

Study on Curing Deformation of Composite Thin Shells Prepared by M-CRTM with Adjustable Injection Gap.

A composite thin shell with a high fiber volume fraction prepared by resin transfer molding (RTM) may have void defects, which create deformations in the final curing and lead to the final product being unable to meet the actual assembly requirements. Taking a helmet shell as an example, a multi-directional compression RTM (M-CRTM) method with an adjustable injection gap is proposed according to the shape of the thin shell. This method can increase the injection gap to reduce the fiber volume fraction during the injection process, making it easier for the resin to penetrate the reinforcement and for air bubbles to exit the mold. X-ray CT detection shows that the porosity of the helmet shell prepared by the newly developed technology is 36.6% lower than that of the RTM-molded sample. The void's distribution is more uniform, and its size is decreased, as is the number of voids, especially large voids. The results show that the maximum curing deformation of the M-CRTM-molded helmet shell is reduced by 13.7% compared to the RTM molded sample. This paper then further studies the deformation types of the shell and analyzes the causes of such results, which plays an important role in promoting the application of composite thin shells.

A novel method for creation of complex microstructure cells through artificial molecular dynamics simulations

Composites have a spectrum of mechanical behavior resulting from uncertainty and variation in the microstructure shape and position. With microstructural simulation of fiber architectures, complex numerical algorithms are needed to enforce boundary constraints such as fiber-to-fiber overlap or periodic boundary conditions. Variations are not typically modeled because randomization of unique aggregate shapes can be challenging and current methods for doing so do not achieve high fiber volume fraction (FVF) when packing; however, this can cause inaccurate predictions in simulations. To address this challenge, a novel approach is developed using Molecular Dynamics (MD), achieving high FVFs up to 85% with rapid speed, easy user implementation, and a potential for capturing non-uniform fiber geometry. Two types of packing are presented to demonstrate the scope of possibilities with this approach: a post randomization molecular dynamics (PRMD) method for uniform fibers, and a mixed aggregate randomization using varying radii circles. Comparisons between periodic hexagonal, randomized, and variable radii packing fiber microstructures are performed to determine the significance of randomization and non-uniform aggregate shape for mechanical property homogenization and damage prediction in a unidirectional laminate. It was found that homogenization between the three microstructures do not vary from randomization; however, using the molecular dynamics approach randomizing fiber position and aggregate shape resulted in significant differences in predicting the transverse damage initiation, reducing the error by approximately 25% from the periodic method.

Unit-cell geometry and mechanical properties of three-dimensional seven-directional braided composites

Three theoretical microstructural models were constructed based on manufacturing three-dimensional seven-directional (3D7d) braided preforms, and their relationships with braiding angles, fiber volume fractions, and yarn filling factor were investigated. The influences of braiding parameters, loading directions, and braiding structure on the performances of 3D7d braided composites were predicted in combination with a bridging model. The results concluded that the longitudinal modulus and tensile strength decreased with increasing braiding angles, while the transverse modulus and strength were opposite, and the performances of composites were better at higher fiber volume fractions. Compared with 3D4d braided composites, the transverse strength of 3D7d braided composites improved significantly. Furthermore, the three microstructural models were damaged in the order of interior, surface, and corner unit cell models during tensile loading. Especially, the fifth and seventh yarns within unit cell models were damaged firstly under longitudinal and transverse loads, respectively. This method adopted in this work provides a basis for predicting the mechanical properties of 3D7d braided composites.

On the dispersion and experimental investigation on transverse tensile low-cycle-fatigue behaviour of GFRP nanocomposites filled with CNTs and GNPs

Improvements in the thermo-mechanical properties of nanocomposites (NCs), particularly containing nanoparticles (NPs) in the resin largely depends upon the dispersion state of nanoparticles in the matrix phase. A 3-phased GF-NC-Epoxy composite prepared by such method witnesses a final reduction in the volume fraction of nanoparticles due to overall reduction in the matrix volume fraction. This work explores an effective dispersion method based on rheological behaviour of 2-phased NCs and compares the efficacy of the same in dispersion of 0.5 wt% carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and their mixture in the ratio of 1:1 (GPNTs). The NPs possess close densities and specific surface area (SSA) of SSACNT = 330 m2/g; SSAGNP = 300 m2/g; ρCNT=0.28g/cm3;andρGNP=0.3g/cm3. The prepared GFRP laminates were tested for their static and dynamic (low cycle fatigue (LCF)) flexure properties and it was observed that the effectiveness of nanoparticles depends upon their final volume fraction in the laminates. A laminate containing higher fiber volume fraction (vf) witnessed large improvement in the static strength post addition of NPs due to improved toughness, but they often witness early failure under fatigue loading owing to limited toughening due to lesser volume of NPs in the matrix phase. It was also observed that once the samples witnessed a crack in the midplane, it requires only few cycling to fail abruptly.

Numerical modeling of steel fiber reinforced concrete spallation exposed to medium loading rate

Properties of unreinforced concrete and cement-based matrix are well understood. One of the issues with the cement-based matrix is its inherently brittle failure when exposed to loading. As such, steel fibers were proposed to enhance the ductility of cement-based and concrete materials. Ever since, Fiber-Reinforced Concrete (FRC) has become a commonly used building material in many construction activities such as bridges, airport pavements, shotcrete, and many others. According to previous research, the addition of steel fibers, typically from 20 to 50 kg/m3 into the conventional concrete, can significantly enhance many of the desired engineering properties of hardened concrete such as flexural strength, tensile strength, micro-cracks as well as splitting. This research presents a study aimed to numerically investigate the influence of steel fibers on the dynamic behavior of Plain Concrete (PC) exposed the tensile loading at medium strain-rate. The influence of steel fibers is investigated using different fiber volume fractions ranging from 0.0 to 4.5%. The Modified Split-Hopkinson-Bar (MSHB) apparatus is employed to investigate the dynamic tensile behavior of PC and Steel Fiber-Reinforced Concrete (SFRC). Validation of the finite element model and constitutive material behavior is carried out with the comparison of computed and measured experimental pull-back velocities of the specimen’s free end. The results showed that impact properties of steel fibers exhibit significant improvement in the toughness and the dynamic tensile strength of concrete and higher fiber volume fraction is more effective in enhancing the mechanical properties of SFRC composite.

Modeling and characterizations of mechanical behaviors of short carbon fiber and short glass fiber reinforced polyetherimide composites

As the major manufacturing methods for short fiber reinforced polymer (SFRP) composites, extrusion compounding and injection molding techniques usually lead to complex fiber length and orientation distributions in final composites for mechanical computation analysis. It is still a challenging task about how to accurately predict the comprehensive mechanical behaviors (tensile properties, damage evolutions and failure modes) of SFRPs from complicated microstructures. This work builds a new finite element model (FEM) based on the classical random sequential adsorption algorithm with genetic algorithm (GA) for high-efficiency geometrical construction for short carbon fiber and short glass fiber reinforced polyetherimide (SCF/PEI and SGF/PEI) composites. Fiber length and orientation measurements, single fiber filament and pure PEI tensile tests are carried out to support model establishment. It is found that the longer initial length would accompany with the longer final average length and the higher fiber volume fraction would bring about shorter average final length. Short carbon fibers with larger aspect ratios tend to be more preferentially aligned along mold flow direction than short glass fibers. The predicted tensile properties, damage evolutions and failure modes are in good agreement with experimental results. Finally, the effects of fiber volume fractions, orientations and lengths on the strength and modulus of SCF/PEI and SGF/PEI composites are quantitatively explored, respectively. Our proposed model can provide an efficient evaluation of the mesoscopic structure-property relationship of SFRP composites.

Micromechanical analysis of high fibre volume fraction polymeric laminates using micrograph-based representative volume element models

This work develops RVE-based finite element (FE) models to understand how the microstructure of Ultra-High-Molecular-Weight Polyethylene (UHMWPE) composites affects the overall mechanical behaviour of the laminate. The models represent a [0/90] configuration with a random fibre packing sequence through the thickness of each ply, as well as a variation in the cross-sectional shape of the fibres, both obtained from laminate cross section micrograph images. The uncertainty of interface properties and its effects on the overall mechanical response is also investigated. The response of the fibre is assumed to be viscoelastic-plastic and transversely isotropic and the three-dimensional constitutive behaviour is implemented through a user-defined subroutine in the LS-DYNA explicit FE code. Constituent properties are calibrated using experimental results on UHMWPE single fibres and a generic thermoplastic polyurethane resin material. The numerical results generated by the RVE models are validated against experimental results found in the open literature. Special focus was given to the in-plane shear and out-of-plane compression response of UHMWPE laminates. Our results can be used as inputs in a homogenised continuum level model, to express the effect of uncertainties which propagate from the microstructure to the macro-scale response.

Mechanical properties and failure behavior of 3D printed thermoplastic composites using continuous basalt fiber under high-volume fraction

Continuous basalt fiber (CBF) is an outstanding inorganic fiber produced from nature, which has a wide range of applications in the field of armor protection of national defense military. However, the mechanical response and failure mechanism of 3D printed CBF reinforced components are still not well understood. Here, the 3D printing thermoplastic composites with high volume fraction CBF have been successfully prepared by fused deposition modelling (FDM) method. The effects of fiber printing direction and polymer matrix type on the tensile and flexural properties of the 3D printed composites have been explored, and the detailed failure morphology has been characterized using scanning electron microscopy and optical microscopy. It was found that under high fiber volume fraction, 3D printed CBF reinforced polyamides (PA) composites have the best ability to maintain material integrity of the composites, followed by acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS). Besides, the results from rule of mixtures can accurately predict the longitudinal Young’s modulus of the 3D printed specimens, but there exists a large discrepancy for the prediction of the tensile strength. The microstructure analysis shows that the failure modes of 3D printed composites mainly include fiber debonding, fiber pull-out, stress whitening and matrix cracking.

Analysis and prediction of woven fabric design impact on fabric/polymer composite drilling energy

Damage, generated during drilling processes, will affect the material integrity and further delamination through the fiber-reinforced composite cross-section. Drilling is necessary for the assembly processes of composite parts. This article deals with the effect of the weave parameters on the drilling mechanism. The mechanism of the yarn shearing ring drilling was investigated, and the quality of the drilled hole was carefully examined for different drilling conditions. Set up for measuring the power consumption during the drilling of different samples as well as the value of the thrust force was constructed. In the drilling of fabric-reinforced polymer composite, the torque, thrust force, and delamination factor are depending directly on fabric design parameters. It was shown that both, drilling power and drilling thrust force, are proportional to the total specific fabric stiffness. Delamination caused by drilling thrust is one of the most problematic defects after drilling laminate composite. A drilling Index was developed and could be used to evaluate the effect of the fabric design of laminate on its composite drilling performance. It was revealed that significantly higher drilling power is needed for the plain weave fabric design than for the other fabric designs of the same unit repeat as well as for the laminates of high fiber volume fraction and high total flexural rigidity. Analysis of the delamination factor and the drilling power showed a high correlation with total fabric flexural rigidity.

Effects of Fiber Volume Fraction and Length on the Mechanical Properties of Milled Glass Fiber/Polyurea Composites.

Composites of polyurea (PU) reinforced with milled glass fiber (MGf) were fabricated. The volume fraction and length of the milled glass fiber were varied to study their effects on the morphological and mechanical properties of the MGf/PU composites. The morphological attributes were characterized with scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The SEM investigations revealed a uniform distribution and arbitrary orientation of milled glass fiber in the polyurea matrix. Moreover, it seems that the composites with longer fiber exhibit better interfacial bonding. It was found from the FTIR studies that the incorporation of milled glass fiber into polyurea leads to more phase mixing and decreases the hydrogen bonding of the polyurea matrix, while having a negligible effect on the H-bond strength. The compression tests at different strain rates (0.001, 0.01, 0.1, 1, 2000 and 3000 s−1) and dynamic mechanical properties over the temperature range from −30 to 100 °C at 1 Hz were performed. Experimental results show that the compressive behavior of MGf/PU composites is nonlinear and strain-rate-dependent. Both elastic modulus and flow stress at any given strain increased with strain rate. The composites with higher fiber volume fraction and longer fiber length are more sensitive to strain rate. Furthermore, the elastic modulus, stress at 65% strain and energy absorption capability were studied, taking into account both the effect of fiber volume fraction and mean fiber length. It is noted that an increase in fiber volume fraction and fiber length leads to an increase in elastic modulus, stress at 65% strain and absorbed energy up to ~103%, 83.0% and 137.5%, respectively. The storage and loss moduli of the composites also increase with fiber volume fraction and fiber length. It can be concluded that the addition of milled glass fiber into polyurea not only improves the stiffness of the composites but also increases their energy dissipative capability.

3D printing of continuous carbon fibre reinforced powder-based epoxy composites

This paper presents an experimental study on 3D printing of continuous carbon fibre reinforced thermoset epoxy composites. Powder-based solid epoxy was electrostatically flocked on the 1K continuous carbon fibre tow and then melted to fabricate composite filaments. The produced filament was printed using a modified extrusion-based printer which melted and deposited the filament following designed printing paths, to form multilayer preforms with complex geometries. After vacuum bagging and oven curing, high tensile strength (1372.4 MPa) and modulus (98.2 GPa) were obtained in the fibre direction due to the good wettability of epoxy and the consequent high fibre volume fraction (56%). The tensile tests of open-hole composites were also conducted, in which the sample with designed stress-lines fibre paths was seen to improve the ultimate strength by 95% compared with the mechanically-drilled sample. Other case studies, such as a spanner and a lattice structure, further demonstrated the design freedom of produced filaments for complex geometries.

3D printing of continuous carbon fiber reinforced polyphenylene sulfide: Exploring printability and importance of fiber volume fraction

Additive manufacturing (AM) of thermoplastic polymer composites is rapidly advancing in the aerospace industry. Here, fused deposition modeling (FDM) of continuous carbon fiber reinforced polyphenylene sulfide (CCF/PPS) was explored and involved experimental filaments with nominal fiber volume fractions (V f ) ranging from 30% to 50%. The printability was evaluated using a design of experiments to quantify the contribution of process parameters to the printed filament quality, which considered microstructure, surface texture and both the thermal and mechanical properties. Results showed that nozzle height, nozzle temperature, printing speed, and flow rate were most influential parameters to the printing process; the relative importance of the printing parameters depended on the V f . The filament with 50% V f was successfully printed despite its high fiber volume fraction and achieved an average ultimate tensile strength of 1930 ± 150 MPa, which sets a new benchmark in strength for composites developed by AM. Nevertheless, there are challenges to achieving that strength in printed components. • Fused filament fabrication of an experimental continuous carbon fiber reinforced polyphenylene sulfide. • High volume fraction of fibers achieves tensile strength approaching 2GPa. • Parametric dependence in printed material quality depends on fiber volume fraction.

Effects of fibers on the mechanical properties of UHPC: A review

Ultra-high performance concrete (UHPC) developed rapidly in research and commercial use during the recent decade. Significant progress has been achieved in its material science and technology, including why and how to add discontinuous fiber reinforcement in it. This paper reviews the researches on understanding the effects of various fibers on the mechanical properties of UHPC, focus on the straight steel fibers but involving also deformed steel fibers, non-steel fibers as well as hybrid fibers. It also discusses the research methodology, prediction of mechanical properties by fiber factors, and the classification of UHPC mechanical properties related to this topic. It shows that (1) the experimental research is the main methodology for investigating the effect of the fibers on the mechanical properties of UHPC; the tensile performance of UHPC should be studied by uniaxial tensile tests and its representative indicators should include tensile strength, initial cracking strength, and peak tensile strain; (2) fiber plays an essential role in the reinforcement of the tensile strength, compressive strength, modulus of elasticity, and other material properties of UHPC, but in weakening the flowability of fresh UHPC. The positive and negative effects of fibers on the mechanical properties of UHPC should be considered, and the technology should be developed to maintain the flowability when high volume fraction of fibers is added in the UHPC; (3) the parameters of steel fibers affecting the mechanical properties of UHPC include volume fraction, size, shape, orientation and distribution, average bonding strength and minimum tensile strength, etc., which are mainly studied independently in the existing research. The studies on the combined effect of these parameters are limited but worthy of further investigation; (4) hybrid fibers could efficiently produce reinforcement effects for UHPC. It has great practical and research significance to conduct in-depth studies though the theoretical analysis and quantitative prediction are complex.

Finite element modelling and experimentation of plain weave glass/epoxy composites under high strain-rate compression loading for estimation of Johnson-Cook model parameters

Split Hopkinson pressure bar (SHPB) is a widely used experimental technique for testing materials at a high strain-rate. SHPB testing of fiber-reinforced polymer (FRP) composite samples have become common in recent decades. Specimen geometry is one of the essential parameters that can ease sample fabrication and help in-situ analysis when altered as per convenience. Further, developing a computationally accurate model would reduce the need for multiple experimental iterations, thus saving cost and time. As part of the current study, high strain-rate tests using a compressive SHPB setup were conducted on glass/epoxy (GE) laminated composite samples of both square prismatic and cylindrical shape along the through-thickness direction experimentally. Negligible differences were observed due to the change in specimen geometry. Further, we know that the woven fabric consists of yarns, which are a bundle of fibers. The strain-rate dependency of the epoxy's material property is well known, but very limited information is available about the strain-rate dependency of yarn's properties. The effect of strain-rate dependency of the yarn was analysed numerically on Abaqus software using a square prismatic shaped yarn-level finite element composite model. The homogenised properties of the yarn were taken to be reflective of a high fiber volume fraction composite. The bulk epoxy's and yarn's material property were defined using the Johnson-Cook (JC) constitutive model, and the failure mechanism was defined using the JC damage model. One of the primary reasons for using this model is its availability and ease of implementation in almost every finite element analysis (FEA) simulation software. Three cases were analysed numerically, first keeping both yarn and bulk matrix property strain-rate dependent, second keeping the strain-rate dependency only in the bulk matrix, and in third case both yarn and matrix were kept strain-rate independent. It was observed that completely strain-rate dependent model showed comparable peak stress and strain values with the experimental result than other models.