Variation Of Fiber Volume Fraction Research Articles

Utilization of Palm Fiber King as a Strengthening Material on Biocomposite

Royal palm (Roystonea regia) is still utilized in traditional way. In this study, royal palm fiber is employed as a reinforcing material in composites. The fiber is divided into two groups of fibers, which are continuous and discontinuous, with a length of fibers of 20 and 5 cm, respectively. Continuous fibers are arranged in parallel, while discontinuous fibers are sown in random orientation. The variations in fiber volume fraction were 15, 25, 50, and 75%. Tensile tests were performed to determine composite strength. The test results show that composite tensile strength values with continuous fibers are higher than those of discontinuous fibers. In addition, the increase in fiber volume fraction is directly proportional to the tensile strength of the specimen. These results indicate that the royal palm fiber has the potential to be used in composite applications.Keywords: royal palm fiber, biocomposite, tensile strength

Elastic properties of unidirectional fiber-reinforced composites using asymptotic homogenization techniques

The objective of this work is to use an asymptotic homogenization numerical model to obtain elastic properties of unidirectional fiber-reinforced composites. Square and perfect hexagonal unit cells are employed, and the influence of the fiber volume fraction over the homogenized elastic properties is studied. The effectiveness of the predictions is assessed by comparisons to experimental properties, and also another micromechanical model based on a representative volume element. The composites E-Glass 21xK43 Gevetex (glass fiber)/LY556/HT907/DY063 (epoxy matrix) and AS4 (carbon fiber)/3501-6 (epoxy matrix) were studied and good agreement between experimental and numerical predictions was found. Discrepancies between experimental and numerical data are explained in terms of simplifications considered in the homogenization model. An adjustment of properties here performed, based on varying fiber volume fractions, showed to be effective to physically represent the studied fiber composites in a micromechanical stress model based on asymptotic homogenization, developed to estimate failure envelopes of such materials.

Physical properties of lyocell-reinforced polypropylene composites from intermingled fibre with varying fibre volume fractions

Polypropylene (PP)-cellulose fibre blends exhibit substantial potential for the production of high-performance textile fibre–reinforced composites. The production of reinforced parts from PP-cellulose composites through thermal shaping of intermingled fibre blends is a strategy to form parts which exhibit superior mechanical properties. In this study, the use of intermingled fibre slivers with different ratios of lyocell fibres (CLY) and PP fibres as raw materials for thermally formed composites was investigated. Such a concept will maximize the interface between the reinforcement fibres and polymer matrix. The cellulose fibres remain oriented along the direction in which the drawing process was performed, which forms the basis for tailored fibre placement in technical production. Because of good surface contact between the cellulose fibre surface and PP matrix, no special coupling agents were required to improve the interfacial adhesion between the two different polymers. The share of CLY and PP fibres in the composite varied from 50% w/w CLY content, up to 70% w/w CLY. Besides analysis of the mechanical properties, such as tensile strength and E-modulus, attention was directed towards moisture sorption of the composites. The rate of sorption and amount of water bound in the composite were found to be dependent on the cellulose fibre content. Composites with a higher CLY content exhibited a more rapid and higher moisture uptake. In water saturated state, the ultimate tensile strength of composites reduced from 160 MPa to 90 MPa, which is an indicator for a reduced adhesion between the CLY surface and PP matrix. The results indicate the potential of the intermingled fibre concept blend for the efficient manufacturing of composite parts.

Behavior of mortar beams with randomly distributed superelastic shape memory alloy fibers

The addition of fibers to cementitious composites can provide improved ductility, energy dissipation, and resistance to cracking. However, it is also important to minimize residual deformations and provide crack-closing capabilities when the material is subjected to cyclic loading. In this study, the behavior of mortar mixtures with randomly distributed superelastic shape memory alloy fibers was investigated. Superelastic shape memory alloys are metallic alloys that possess unique characteristics such as the ability to undergo large deformations, excellent re-centering ability, and good energy dissipation capacity. To study the impact of shape memory alloys as a viable alternative to conventional fiber-reinforced cementitious composites, shape memory alloy fiber–reinforced mortar beam specimens with varying fiber volume fractions were prepared and tested under cyclic flexural loading. Digital image correlation method was used to measure full-field deformations and monitor the damage evolution on the surface of the specimens. Test results were analyzed in terms of flexural strength capacity, mid-span deflection, crack width, fiber distribution, and re-centering and crack recovery ratios for each specimen. Results indicate that the addition of shape memory alloy fibers to mortar composites can enhance flexural strength and ductility while providing re-centering and crack recovery capabilities at large deformation levels.

Simulation of the Influence of Embedded Inserts on the RTM Filling Behavior Considering Local Fiber Structure

Resin Transfer Molding (RTM) enables an intrinsic manufacturing of fiber reinforced composite parts containing integrated metallic inserts. The inserts are embedded into the fiber layers in the preforming stage of the process and therefore influence the following mold filling. The fiber structure around the embedded insert is strongly influenced by the insert resulting in high local variations of fiber volume fraction which changes the local permeability. This leads to an inhomogenic flow front and can even result in dry spots of the cured part. To predict the formation of air bubbles, a two-phase mold filling simulation is used under consideration of local fiber volume fraction. Local fiber structure is determined using CT-scans of manufactured parts with different orientations of the insert in relation to the preform and to the filling direction. The mold filling simulations allow the evaluation of different filling strategies and show a strong influence of the insert on the local flow front propagation.

Utjecaj obloženih E-staklenih vlakana na svojstva čvrstoće betona

Test results obtained by studying the influence of epoxy coated E-glass fibre composites on the compressive and splitting tensile strengths of concrete are reported in the paper. Three grades of concrete and varying fibre volume fractions (0.5 %, 1 %, 1.5 % and 2 %) were used as test variables. It was observed that the maximum compressive strength was attained for the fibre volume fraction of 1.5%, whereas the splitting tensile strength was found to increase with an increase in the fibre volume fraction. Based on the test results, a mathematical model was developed using regression analysis.

Application of steel fibre reinforced cementitious composites in high velocity impact resistance

The application of fibre composites in the construction of protective structures for impact and blasts is an active area of research. Important mechanical properties like compressive strength, tensile strength, flexural toughness, acoustic impedance, mass density, ultrasonic pulse velocity, are required to determine the high velocity impact (HVI) resistance of the cementitious composite target panels. However, the above mechanical properties of steel fibre reinforced cementitious composites (SFRCC) for varying fibre volume fraction are difficult to find in existing literature. This paper presents results of an extensive experimental study, conducted to characterize the SFRCC for varied fiber volume fractions between 0 and 12 %. Hooked end steel fibres having an aspect ratio about 66 (fibre length 30 mm diameter 0.45 mm) are used in the preparation of control specimens. Important engineering properties like, compressive, tensile, and flexural strengths, toughness and acoustic impedances are determined through the laboratory tests. A total of 250 numbers standard cylinder, cube, prism and dog-bone specimens are prepared for the characterization of steel fibre reinforced cementitious composite. The significance of the present study in impact resistance applications is also demonstrated through the HVI tests on SFRCC panels. This study highlights various aspects related to judicious selection of materials in layered cementitious composite targets.

Characterisation and modelling of thermal expansion coefficient of woven carbon/epoxy composite and its application to the determination of spring-in

Properties of resin and composite, especially anisotropic coefficients of thermal expansion, are very crucial to precisely determine residual stress generated in a composite part. No comprehensive study is available in the literature to determine these properties for woven composites and then its application to model residual stress in woven carbon epoxy composite parts. In the present article, experimental results on thermal coefficients of RTM6 epoxy resin as well carbon/epoxy woven composites obtained using different experimental techniques are compared with homogenised coefficients of thermal expansion results. Evolution of spring-in angle of L-shaped carbon/epoxy woven composite (during and after cure) with three different thicknesses is modelled by simultaneously solving the thermal-kinetics and thermal-chemical-mechanics coupling by using finite element code COMSOL Multiphysics. Objective was to quantify the contribution of curing and cooling to the formation of residual stress. Anisotropic properties of composite, during and after cure, required for numerical simulation are obtained using an analytical method. Variation in properties with degree of cure and thermal gradients induced in the part during fabrication are considered while modelling. Modelled properties of cured composites were compared with experimental values and were found in agreement. The spring-in angle values obtained by numerical simulation are compared with the results of the analytical model as well as experiments. Effect of variation of fibre volume fraction and presence of thermal gradients on spring-in was studied as well.

Micromechanical damage analysis in laminated composites with randomly distributed fibers

Damage mechanisms in uni-directional fiber-reinforced plastics have been studied at the micro-scale by developing three-dimensional-repeating unit cells with randomly distributed fibers. Three damage mechanisms have been considered, viz., matrix damage, fiber failure and fiber-matrix interface debonding. The development of these damage modes and their effect on the overall stress–strain response of the micro-structure due to varying fiber volume fractions, loading conditions (longitudinal, transverse and combined transverse tension and shear), spatial distribution of fibers and fiber strength distributions (deterministic and Weibull) are of interest. A numerical framework has been developed that allows for conducting such studies for the chosen parameters. Microscopic images of real micro-structure of uni-directional fiber-reinforced plastics have been used to develop the random micro-structure for the three-dimensional-repeating unit cell. In the longitudinal loading scenario, fibers with Weibull strength distribution are closer to reality. While the three-dimensional-repeating unit cell under longitudinal loading fails in predominantly fiber failure mode, debonding and matrix damage play a major role in determining the average response of the micro-structure under transverse and combined transverse and shear loading.

KARAKTERSTIK SERAPAN SUARA KOMPOSIT POLYESTER BERPENGUAT SERAT TAPIS KELAPA

The purpose of this study is to investigate of sound absorption of coconut filter fiber composites. The research material made with coconut filter fiber as reinforcement and matrix resin unsaturated polyester (UPRs) type Yukalac BQTN 157 with 1% hardener types MEKPO (Methyl Ethyl Ketone Peroxide) and fiber treatment by 0,5% KMnO4. Production methods is poltrusion and the variations of fiber volume fraction are 20, 25 and 30% and fiber length are 5, 10 and 15 mm. Testing of sound absorption frequency are 250, 500, 1000, 2000 and 4000 Hz. The results of research show that the highest value of sound absorption coefficient is on the composites with composition of 10 mm fiber length and 30% fiber volume fraction, that is 0.550828. The values are included in the class “Sound Absorption Coefficient Class D (Extremely absorbing)” with the range 0.40 – 0.60 based on ISO standard 11654:1997.

Modelling of Laser Welding Process on Thermoplastic Composites

Thermoplastics composites for structural applications are under growing development from the aerospace (carbon fibers with PEI, PPS or PEEK matrices mainly) to the automotive industry (glass and carbon fibers with PP, PA). The plastic deformation they can provide and the assembly facilities through welding techniques are well appreciated. Among the available welding technics, laser offers the possibility to assemble materials in a precise and localized manner and can be easily automated. However, due to the presence of continuous fibers at a high fiber volume fraction, propagation of the laser energy through the composite that present local variation of fiber volume fraction is not as straight forward as in a homogeneous material. Modelling of the laser welding of a thermoplastic/continuous glass fiber is considered here. The study takes into account the microstructure of the composite in order to evaluate changes in local energy absorption and diffusion directly linked with the thickness. Modelling of the welding process is developed from the representation of the moving laser beam. The beam propagation through the composite thickness is considered thanks to the ray tracing method. The proposed method is able to optimise the welding process in function of the microstructure and the material properties of the welded parts.

Uncorrelated volume element for stochastic modeling of microstructures based on local fiber volume fraction variation

Abstract One source of microstructural variability in fiber reinforced polymers is variability in fiber volume fraction. Despite large scatter in fiber volume fraction, an average value is usually reported without any consideration regarding the variability. Significant variation in fiber volume fraction across the sample reveals that homogeneity throughout the sample is a poor assumption and the commonly employed representative volume element is a poor representation of real microstructures. In this work, the distributions of fiber volume fraction at different length scales are investigated. The variation in distributions suggests that a length scale-dependent distribution must be selected in probabilistic analysis. A cross-correlation between fiber volume fractions of nearest neighbors was computed and an uncorrelated volume element (UVE) is introduced for the length scale at which fiber volume fractions become uncorrelated. The concept of a UVE enables random attribution of properties in stochastic modeling.

Stochastic analysis of functional failure pressures in glass fiber reinforced polyester pipes

• Stochastic analysis of Functional Failure (FF) pressures in GRP pipes is conducted. • Both fiber volume fraction and winding angles are chosen as random parameters. • FF pressures are more significantly affected by fiber volume fraction variations. • Statistical analysis show that most probably FF pressure exceeds its mean value. The main objective of this study is to investigate the functional failure of Glass fiber Reinforced Polyester (GRP) pipes subjected to hydrostatic internal pressure implementing stochastic approach. In this regard, a progressive damage modeling is developed to evaluate the pressure at which weepage takes place throughout the pipe wall thickness. The functional failure implies on a certain pressure that the fluid finds a path through the pipe wall thickness as a consequence of weepage phenomenon. Fiber volume fraction and winding angles in cross plies are considered as the random parameters representing the most important uncertain parameters of filament winding production process. Sufficient numbers of samples are generated using Monte-Carlo technique on the basis of defined convergence criterion. The influence of random behavior of these parameters on the both first-ply-failure and functional failure of GRP pipes are analyzed in an integrated procedure. The results demonstrate that the effect of fiber volume fraction variation on the functional failure pressure is more crucial than that of winding angle variation. Finally, statistical analysis of obtained results is presented on obtained results from stochastic analysis in the form of Weibull probability density function.

Viscoelastic modeling and experimental characterization of thermo-electromechanical response of 1–3 piezocomposites

The viscoelastic behaviour of 1–3 piezocomposites with different volume fractions and bulk piezoceramics is studied under thermal environment subjected to electrical loading. Experiments are conducted to measure the temperature dependent effective properties based on IEEE standards and time dependent thermo-electromechanical response of 1–3 piezocomposites and piezoceramic subjected to high cyclic electrical loading under elevated thermal environment. The temperature dependent effective properties are predicted using the proposed numerical model based on unit cell approach and implemented into the viscoelastic model to predict the time dependent thermo-electro-elastic effective properties. The predicted effective properties are incorporated in a finite element based 3-D micromechanical model to predict the time dependent thermo-electro-mechanical performance behaviour of 1–3 piezocomposites. Comparison between the experiments and simulations shows that this model can reproduce the characteristics of time dependent non-linear electromechanical response under thermal environment. It is observed that the variation in fiber volume fraction and elevated operating temperature has a significant influence on the response of the 1–3 piezocomposites.

Effects of thickness and fiber volume fraction variations on strain field inhomogeneity

In this study, variations in thickness and fiber volume fraction are investigated as causes of elastic strain inhomogeneity in composite laminates under an applied transverse load. Standard carbon/epoxy tensile specimens were fabricated from unidirectional pre-impregnated material using two different manufacturing techniques that produced two different levels of surface roughness. Fiber volume fraction variation was computed by analyzing optical micrographs of the samples. During loading and unloading of the samples two-dimensional surface strain fields were measured on the specimen using digital image correlation. It was shown that in both cases the strain in the specimen is not uniform, as is generally assumed. Using finite element simulations the effects of fiber volume fraction variation and thickness variation were modeled individually and in combination. The simulations agree well with the experimental results and suggest that thickness variations are the dominant mechanisms involved in this elastic strain inhomogeneity.

KARAKTERISTIK SIFAT TARIK DAN MODE PATAHAN KOMPOSIT POLYESTER BERPENGUAT SERAT TAPIS KELAPA

The purpose of this study is to investigate the mechanical properties i.e. tensile strength of composites coconut filter fiber. In the future this material can be used to replace the wood, bamboo and gipsun which are high price and lower water resistance.The research material made with coconut filter fiber as reinforcement and matrix resin unsaturated polyester (UPRs) type Yukalac BQTN 157, with 1% hardener types MEKPO (Methyl Ethyl Ketone Peroxide) and fiber treatment by 0.5% KMnO4. Production methods are poltrusion and the variations of fiber volume fraction are 20, 25 and 30% and fiber length are 5, 10 and 15 mm. Testing of mechanical properties is tensile test (ASTM D3039-76) The results of research show that the longer of fiber and the bigger of fiber volume fraction, the higher of tensile strength are obtained. The fracture mode are overload, debonding, pullout and crack deflection

Micromechanical modeling and experimental characterization of 1-3 piezocomposites subjected to electromechanical loads

An experimental and theoretical study is carried out to compare the performance behavior of 1-3 piezocomposites with different volume fractions and bulk piezoceramics. Experiments are conducted to measure the electric displacement and strain on piezocomposites and ceramics under high cyclic electrical loading superimposed with mechanical prestress. Elastic, piezoelectric and dielectric constants are measured using IEEE (weak-field) methods for 1-3 piezocomposites with different volume fractions. A numerical model is developed to calculate the effective properties and the results are compared with experimental measurements. To study the overall behavior of piezocomposites, a micromechanically motivated model is developed based on thermodynamic principles and embedded into an electromechanically coupled finite element formulation. The predicted effective properties are incorporated in the proposed model and the dielectric hysteresis (electric displacement versus electric field) as well as butterfly curves (strain versus electric field) are simulated. Comparison between the experiments and simulations show that this model can reproduce the characteristics of non-linear response. The Figures of Merit (FoM) obtained for various compressive stress and varying fiber volume fraction, compared with different regions in the cyclic electric field, which will be helpful in optimizing the devices for underwater and biomedical applications.

Effect of Deformation Delayed of the Concrete on the Seismic Response of Shear Walls Strengthened by Composites with a Sinusoidal Distribution of Fibers

The present paper deals with the effect of deformation delayed creep and shrinkage of the concrete on the seismic response of shear walls reinforced concrete strengthened with composite materials having a sinusoidal distribution of fibers. The lateral stiffness of shear walls RC, adhesives and composite material taking into account the phenomenon of creep and shrinkage of concrete described by the Eurocode 2, and widthwise varying fiber volume fraction of the composite plate has been determined by a finite element model. Large earthquakes recorded in Algeria (El-Asnam and Boumerdes) have been tested to demonstrate the accuracy of the proposed method. Numerical results obtained are discussed and the factors influencing the seismic response of reinforced concrete shear walls strengthened taking account the effects of the delay mechanism creep and shrinkage of concrete are highlighted. Prospects are being studied

Consistent Finite Element mesh generation for meso-scale modeling of textile composites with preformed and compacted reinforcements

A new automated method to generate smooth Finite Element meshes for the meso-scale representation of textile composites unit cells with preformed and compacted reinforcements is presented. The reinforcement geometry is obtained from textile geometry preprocessors or by modeling of the preforming step. It is then transformed into a geometric model of the entire composite unit cell, taking into account the real yarn shape after preforming and compaction, the contact interactions between the yarns, as well as the resulting local variations of fiber volume fraction. A consistent mesh of the complete cell, conformal between the parts, is ensured, without the need for inserting artificial matrix layers between the yarns. The methodology is illustrated by mechanical modeling of the representative unit cell of a multi-layer composite with a compacted and nested woven reinforcement.

Temperature-dependent ferroelectric switching of 1–3 type piezocomposites: an experimental and theoretical study

An investigation on the temperature-dependent behavior of 1–3 piezocomposites for different fiber volume fractions and bulk piezoceramics is carried out. Experiments are conducted on 1–3 piezocomposites at room and elevated temperatures under a high cyclic electric field to understand the behavior of these materials. Temperature-dependent effective properties of piezocomposites are measured using resonance technique. A simple analytical model based on equivalent layered approach is proposed for the determination of the effective properties of 1–3 piezocomposites at elevated temperature. A uniaxial constitutive model has been developed based on a thermodynamic approach, to predict the nonlinear behavior of 1–3 piezocomposites under thermo-electrical loading conditions. Volume fractions of three distinct uniaxial variants are used as internal variables to describe the microscopic state of the material. A nonlinear hardening parameter based on a Gaussian function is used to describe the grain boundary effects. The predicted effective properties are used in the proposed uniaxial model and the classical dielectric hysteresis (electric displacement vs. electric field) as well as butterfly curves (strain vs. electric field) are simulated and compared with experimental data. It is observed that the variation in fiber volume fraction and temperature has a strong influence on the response of 1–3 piezocomposites.