Different Volume Fractions Of Fibers Research Articles

Flammability and moisture absorption behavior of sisal-polyester composites

The risk of fire and water is inevitable so the performance of composites in building constructions should be at par with the code requirements. This paper researches on the fire and water resistance of untreated sisal fiber composites using polyester resin as matrix for different volume fractions of fiber viz. 5%, 10%, 15%, 20%, 25%, 30% and for two different thicknesses namely 3mm and 5mm. The panels of size 30cm*30cm were fabricated by compression molding technique. The investigation on fire resistance was done as per flammability test mentioned in ASTM D 635-03 standards. In this test, the rate of burning was found out in mm/min. The burning rate and the corresponding mass loss rates were found to decrease as the volume fraction of fibers increased. The moisture test was done as per ASTM D 570-98 standards. The moisture absorbed which was expressed in percentage was found to increase as the volume fraction of fibers increased.

Micromechanical modeling on cyclic plastic behavior of unidirectional fiber reinforced aluminum matrix composites

This work investigates the cyclic plastic behavior of continuous fiber-reinforced aluminum matrix composites (CFAMCs) with different volume fractions of fiber up to a maximum value of 63.61% using micromechanical approach of modeling. Shakedown, ratcheting limit and load-bearing capacity have been studied. The FEM models, based on two dimensional micromechanical representative volume element (RVE) with a square packing geometry, were subjected to constant macro stress under off-axis loading condition and thermal cycling conditions. A number of direct numerical methods, under the Linear Matching Method (LMM) framework, are adopted for the determination of limit load, reverse plasticity limit and ratchet limit of AMCs. The typical micromechanical model adopted in all analysis consists of continuous fibers with circular cross section, embedded in an aluminum matrix. Two most common reinforcing materials alumina and silicon carbide are investigated. Various factors that affect shakedown and ratcheting behaviors of composites are analyzed and discussed, including effects of fiber volume fraction and temperature on the AMC's low cycle fatigue life.

IMPACT RESISTANCE OF STEEL FIBER REINFORCED CONCRETE

Synopsis/ ABSTRACT The present experimental investigation is to study the impact resistance of Fiber Reinforced Concrete with inclusion of steel fibers. The concrete composites comprises of steel fibers in different percentages. The hooked end type steel fibers varied from 0 to 2.5% at an interval of 0.5% by weight of cement. A simple economical and practical drop weight impact testing machine was used to determine the impact resistance for Steel Fiber Reinforced concrete [SFRC]. Impact test were carried out on SFRC with aspect ratio (l/d) as 60. The specimens were tested at 7 days and 28 days strength for concrete grade category like M20, M30 and M40. The specimens for impact studies were tested by drop weight Impact test method which was recommended by ACI-544 committee. The addition of steel fibers to concrete has improved the impact resistance considerably. The test results showed the variation of impact energy strength with different volume fraction of fibers.

Effect of Fiber Geometry and Representative Volume Element on Elastic and Thermal Properties of Unidirectional Fiber-Reinforced Composites

The aim of present work is focused on the evaluation of elastic and thermal properties of unidirectional fiber-reinforced polymer composites with different volume fractions of fiber up to 0.7 using micromechanical approach. Two ways for calculating the material properties, that is, analytical and numerical approaches, were presented. In numerical approach, finite element analysis was used to evaluate the elastic modulus and thermal conductivity of composite from the constituent material properties. The finite element model based on three-dimensional micromechanical representative volume element (RVE) with a square and hexagonal packing geometry was implemented by using finite element code ANSYS. Circular cross section of fiber and square cross section of fiber were considered to develop RVE. The periodic boundary conditions are applied to the RVE to calculate elastic modulus of composite. The steady state heat transfer simulations were performed in thermal analysis to calculate thermal conductivity of composite. In analytical approach, the elastic modulus is calculated by rule of mixture, Halpin-Tsai model, and periodic microstructure. Thermal conductivity is calculated analytically by using rule of mixture, the Chawla model, and the Hashin model. The material properties obtained using finite element techniques were compared with different analytical methods and good agreement was achieved. The results are affected by a number of parameters such as volume fraction of the fibers, geometry of fiber, and RVE.

Mechanical Properties of Luffa Fiber and Ground nut Reinforced Epoxy Polymer Hybrid Composites

This paper presents the study of the tensile, compressive, flexural, impact energy and water absorption characteristics of the luffa fiber and Ground nut reinforced epoxy polymer hybrid composites. Luffa fiber and Ground nut reinforced epoxy resin matrix composites have been developed by hand lay-up technique with luffa fiber treated conditions and Ground nut with different volume fraction of fibers as in 1:1 ratio (10%, 20%, 30%, 40% and 50%). Effects of volume fraction on the Tensile, Compressive, Flexural, Impact strength were studied. SEM analysis on the composite materials was performed. Tensile strength varies from 10.35MPa to 19.31MPa, compressive strength varies from 26.66MPa to 52.22MPa, flexural strength varies from 35.75MPa to 58.95MPa and impact energy varies from 0.6 Joules to 1.3 Joules, as a function of fiber volume fraction. The optimum mechanical properties were obtained at 40% of fiber volume fraction of treated fiber composites. Fractures surface of the composite shows the pull out and de-bonding of fiber is occurred.

Dynamic compressive behaviour of spiral steel fibre reinforced concrete in split Hopkinson pressure bar tests

It has been well demonstrated that adding fibres into concrete increases the impact loading resistance capacity of the concrete material. Recent studies proved that using spiral-shaped steel fibres further increases the post-failure, energy absorption and crack stopping capacities of concrete as compared to other conventional steel fibres because spiral-shaped fibre better bonds in the concrete matrix and has larger deformation ability. This research further investigates the dynamic compressive properties of spiral fibre reinforced concrete (SFRC) by conducting high rate impact tests using split Hopkinson pressure bar (SHPB). SFRC specimens with different volume fractions of spiral fibres ranging from zero to 1.5% are prepared and tested. The concrete matrix for all SFRC specimens is mixed to obtain a compressive strength of 35MPa. The influences of different volume fractions of fibres on strength, Young’s modulus, stress–strain relationand energy absorption of SFRC specimens under quasi-static and dynamic loadings are studied. In dynamic compression tests, the strain rate achieved ranges from 50s−1 to 200s−1. The failure processes and failure modes of SFRC specimens with different fibre volume fractions are captured by the high speed camera during the tests and compared. Dynamic stress–strain curves under different strain rates are derived. The energy absorption capacities of the tested specimens are obtained and compared. Rate effects on the compressive strength and Young’s modulus are also discussed. The corresponding empirical DIF (dynamic increase factor) relations for spiral SFRC are proposed.

Experimental Investigation on Mix Designed HSC HSFRC Specimens Perfomed with Volcanic Aggregate

The selection of mix proportion is the process of choosing suitable ingredients of concrete and determine their quantities with the object of producing as economically as possible concrete of notably strength. The current paper deals with the mix design of both an HSC and HSFRC constituted by volcanic aggregates from the quarries of Eastern Sicily in Italy. The mix design was carried out on eight different concrete mixtures by using the theoretical model developed by Feret – De Larrard’s and it is capable of simulating the experimental compressive strength. The HSFRC mixtures consider different volume fractions of fibers equal to 0% (HRC), 0.5% and 2% (HSFRC). Straight Polyvinylalcohol (PVA) and hooked-end steel fibers (ACC) were the two types of fibers employed in the study. Compression and tensile tests were carried out on specimens performed according to UNI codes in order to validate the mixture proportion method adopted. The HSFRC (0.5%) mixtures did not show great differences in mechanical performance by any variation of the fiber type (steel or PVA). The mechanical properties obtained by experimental tests give back a very good accordance with the theoretical prediction of the mix design procedure adopted, and with the data reported in the literature in terms of toughness.

Evaluation of Longitudinal and Transversal Young’s Moduli for Unidirectional Composite Material with Long Fibers

This work represents a comparative study of available analytical micromechanical models used to evaluate the elastic properties of unidirectional (UD) composite material with long fibers (where the ratio Length/Diameter of the fibers is considered to be infinite). The objective of this work is to find the appropriate model, to be used with different volume fractions of fibers, to determine the micromechanical elastic properties. This study is carried out due to the importance of using the suitable micromechanical model, when modeling bi-dimensional and tridimensional composite materials. The models are divided into two different categories: rheological, and inclusion models. The UD composite material represents a transversely isotropic material composed of two phases: the reinforcement phase and the matrix phase. Isotropic fibers (e.g. glass fibers) or anisotropic fibers (e.g. carbon fibers) represent the reinforcement phase while an isotropic material (e.g. epoxy) represents the matrix phase. In this study only longitudinal and transversal Young’s moduli are discussed. Analytical and Finite element modeling is made for a carbon fiber/epoxy UD composite. The obtained analytical results are compared to those obtained numerically and to the available experimental data. The analytical results are evaluated for different values of fiber volume fraction Vf ranging from 0 to 1.

A three-dimensional micromechanical model to predict the viscoelastic behavior of woven composites

Polymer matrix based cloth composites are increasingly used in engineering applications. For such composites, significant viscoelastic behavior can be observed for dynamic load conditions. The viscoelastic effect is primarily due to the polymeric matrix used as most of the fibers used in structural applications are elastic. Matrix does not show a major contribution in the axial properties of composites, thus in the traditional modeling its viscoelastic nature is often ignored. However, the effective out of plane properties are influenced by the matrix material and exhibit significant damping characteristics. Therefore, a complete three-dimensional (3-D) model considering the viscoelastic nature of matrix is needed for better understanding of cloth composites. An analytical 3-D micromechanical model based on classical laminate theory (CLT) is verified, in this paper for the prediction of effective elastic and viscoelastic properties of a cloth composite. The method is shown to be accurate. This model is extended to the viscoelastic regime with the use of Laplace transform and correspondence principle. Prony series coefficients for composite cloth are obtained for different volume fractions of fibers in yarn. It is observed from the hysteresis plots that dissipation in out of plane normal and shear modes is significantly higher than the normal directions.

Dry sliding wear behavior of aluminum based hybrid composites with graphite nanofiber–alumina fiber

The wear behavior of aluminum based hybrid composites reinforced with graphite nanofiber (GNF) and alumina short fiber (Al 2O 3sf) in different volume fraction of fibers (10%, 15% and 20%) was studied under dry sliding conditions. The Taguchi approach to experimental design was used to identify those testing parameters that have the largest effects on wear loss and coefficient of friction of the composites. Sliding distance was found to be the prominent parameter affecting wear loss; applied load affected coefficient of friction most significantly. The results of Taguchi analysis indicate that wear loss increases with increasing load and sliding distance, but it is reduced with increasing sliding speed. Coefficient of friction decreases with increasing applied load and sliding speed whereas it increases with increasing sliding distance. The composites with 10 vol.% and 15 vol.% of fiber had the lowest wear loss and friction because of the mixture effect of GNFs and Al 2O 3sf. However, due to the effect of agglomerated GNFs, there was an increase in wear loss and friction at 20 vol.%.

Sunnhemp Fiber-reinforced Waste Polyethylene Bag Composites

The present article expounds the development of sunnhemp fiber-reinforced waste polyethylene bag composites. No surface modifications of fibers were made. Sunnhemp fibers of 25.4 mm in length with waste polyethylene bags were stacked and composite materials were fabricated using hot compression molding technique. These composites were prepared at different fiber volume fraction (Vf) varying from 0.10 to 0.50. Mechanical properties at different volume fractions of fibers were investigated. The tensile strength, tensile modulus, flexural strength, and flexural modulus of composites containing upto 0.30 Vf were found to increase linearly with Vf and the results showed good agreement with the rule of mixtures. However, beyond 0.30 Vf there was a significant deterioration in the mechanical properties. The work of fracture determined by Izod impact test shows increased impact strength with increased fiber volume fraction up to 0.20 and then a decrease thereafter. The result of this study suggests that sunnhemp fibers have potential as reinforcing material in waste polyethylene bags to produce inexpensive thermoplastic composite materials with a high toughness for various applications like door panels, furniture, packaging, etc. Thus environmental pollution due to waste polyethylene bags can be minimized.

Mechanical Behavior of Polyethylene Fibers Reinforced Resol/VAC-EHA

Polyethylene fibers reinforced Resol/VAC-EHA composites have been prepared in the laboratory at different volume fraction of fibers for the evaluation of mechanical properties. Resol solution was blended with vinyl acetate-2-ethylhexyl acrylate (VAc-EHA) resin in an aqueous medium with varying volume fraction of polyethylene fibers. It has also been observed that reinforcement of the polyethylene fiber in Resol/VAC-EHA matrix shows improvement in ductility, tensile strength and Young's modulus. But damping property decreases as soon as percentage of the polyethylene fiber increases. In order to study the static and dynamic response of polyethylene fiber reinforced Resol/VAC-EHA composite plate at uniformly distributed load and fluctuating uniformly distributed load, a multi-quadric radial basis function (MQRBF) method is developed. MQRBF is applied for spatial discretization and a Newmark implicit scheme is used for temporal discretization. The discretization of the differential equations generates a greater number of algebraic equations than the unknown coefficients. To overcome this ill-conditioning, the multiple linear regression analysis, based on the least square error norm, is employed to obtain the coefficients. Simple supported and clamped boundary conditions are considered. Numerical results are compared with those obtained by other analytical methods.

Mechanical Behavior of Unidirectional Glass Fibers Reinforced Resol/VAC‐EHA Composites at Different Volume Fraction of Fibers

Glass fibers reinforced Resol/VAC‐EHA Composites were fabricated at different volume fraction of fibers to determine the mechanical behavior. Resol solution was blended with vinyl acetate‐2‐ethylhexyl acrylate (VAc‐EHA) resin in an aqueous medium with varying volume fraction of glass fibers. The role of fiber/matrix interactions in glass fibers reinforced composites were investigated to predict the stiffness and damping properties and their different mechanical behavior was compared with pure Resol and Resol/VAC‐EHA blend. In order to study the static and dynamic response of Resol, Resol/VAC‐EHA blend, and glass fibers reinforced composites, a multiquadric radial basis function (MQRBF) method was developed. MQRBF was applied for spatial discretization and a Newmark implicit scheme was used for temporal discretization. The discretization of the differential equations generates a larger number of algebraic equations than the unknown coefficients. To overcome this ill conditioning, the multiple linear regression analysis, which is based on the least square error norm, was employed to obtain the coefficients. Simple supported and clamped boundary conditions were considered. Numerical results were compared with those obtained by other analytical methods.

Measurement and prediction of thermal conductivity for hemp fiber reinforced composites

AbstractThe thermal conductivity of hemp fiber reinforced polymer composites were studied from the steady state temperature drop across samples exposed to a known heat flux. The transverse and in‐plane thermal conductivities for oriented and randomly oriented composites for different volume fractions of fiber were investigated. Experimental results showed that the orientation of fibers has a significant effect on the thermal conductivity of composites. To validate the experimental results, the heating tests for the thermal conductivity measurements were simulated by a finite element model using the thermal conductivity values obtained from the experiments. Predicted temperatures show close agreement with measured temperatures. Moreover, the experimental results of thermal conductivities of composites at different directions were compared with two theoretical models and illustrated good agreement between the obtained results and models. POLYM. ENG. SCI. 47:977–983, 2007. © 2007 Society of Plastics Engineers

Mean field modelling of the plastic behaviour of co-continuous dual-phase alloys with strong morphological anisotropy

This work addresses the plastic flow properties of a composite material in which the reinforcing phase is continuous and cannot be suitably represented by isolated ellipsoidal inclusions. The dual-phase metal under consideration is composed of a network of Inconel-601 fibres infiltrated by pure aluminium. Hence, both phases exhibit elastic–plastic behaviour and are continuous in the three dimensions of space. The fibre network presents a large morphological anisotropy that is reflected in the mechanical response of the composite. The modelling is based on Eshelby’s equivalent inclusion theory. Strain partitioning between the phases is computed incrementally based on tangent operators derived from the isotropic response of individual phases. Assessment of the model relies on extensive experimental data. Uniaxial tensile tests, involving measurement of the Lankford coefficient, have been performed at various temperatures on samples containing different volume fractions of fibres. Measurement of the phase stresses by neutron diffraction supplements the information provided by the macroscopic stress–strain curves. It is demonstrated that predictions are valid only when the micro–macro averaging scheme accounts for the co-continuous character of the constitutive phases.

Probability of fatigue failure of steel fibrous concrete

The paper presents a study on the fatigue strength of steel fibre reinforced concrete (SFRC) at various stress levels. To obtain the fatigue lives of SFRC at various stress levels beam specimens of size 500 mm × 100 mm × 100 mm were tested under four-point flexural fatigue loading. Static flexural tests were also carried out to determine the static flexural strength of SFRC prior to fatigue testing. The specimen incorporated three volume fractions, namely 0·5, 1·0 and 1·5% of corrugated steel fibres of size 0·6 mm × 2·0 mm × 30 mm. All the fatigue tests were conducted on a 100 kN closed-loop universal testing machine. Fatigue life data thus obtained were analysed in an attempt to determine the relationship for SFRC between stress level S, number of cycles to failure N and probability of failure Pf for SFRC. It was found that this relationship can be represented reasonably well graphically by a family of S–N–Pf curves for SFRC containing different volume fractions of fibres. The experimental coefficients of the equation were determined from the fatigue test data to represent the S–N–Pf relationships analytically.

Probability of fatigue failure of steel fibrous concrete

The paper presents a study on the fatigue strength of steel fibre reinforced concrete (SFRC) at various stress levels. To obtain the fatigue lives of SFRC at various stress levels beam specimens of size 500 mm × 100 mm × 100 mm were tested under four-point flexural fatigue loading. Static flexural tests were also carried out to determine the static flexural strength of SFRC prior to fatigue testing. The specimen incorporated three volume fractions, namely 0·5, 1·0 and 1·5% of corrugated steel fibres of size 0·6 mm × 2·0 mm × 30 mm. All the fatigue tests were conducted on a 100 kN closed-loop universal testing machine. Fatigue life data thus obtained were analysed in an attempt to determine the relationship for SFRC between stress level S, number of cycles to failure N and probability of failure Pf for SFRC. It was found that this relationship can be represented reasonably well graphically by a family of S–N–Pf curves for SFRC containing different volume fractions of fibres. The experimental coefficients of the equation were determined from the fatigue test data to represent the S–N–Pf relationships analytically.

The influence of short-term water storage on the flexural properties of unidirectional glass fiber-reinforced composites

Objective: The aim of this study was to determine flexural properties of unidirectional E-glass fiber-reinforced composite (FRC) with polymer matrices of different water sorption properties. Methods: Rhombic polymer and FRC test specimens made of three commercially available diacrylate resin (Sinfony Activator, Triad Gel, 3M Scotchbond Adhesive) and different volume fractions of fibers were tested with three-point bending test according to ISO 10477 after storing in water for 30 days. Water sorption of specimens was also measured. Results: Flexural strength of specimens with 45 vol% fraction E-glass fibers varied from 759 to 916 MPa in dry conditions. Water-stored specimens showed flexural strengths of 420–607 MPa. ANOVA analysis revealed that the fiber-volume fraction and the water sorption of the polymer matrix had a significant effect ( p<0.001) on the flexural properties. Dehydration of specimens recovered the mechanical properties. Decrease of flexural properties after water immersion was considered to be mainly caused by the plasticizing effect of water and the decrease depended on water sorption. Significance: Use of polymers with low-water sorption seems to be beneficial in order to optimize the flexural properties of FRC.

Analytical methods for prediction of tensile properties of plain knitted fabric reinforced composites

This paper describes analytical models for predicting the elastic and tensile strength properties of knitted fabric reinforced composites. Owing to the looped yarn architecture, knitted fabric composites possess fiber and resin-rich regions. Initially, a geometric model has been identified for estimating the orientation of yarn in the knitted fabric. Using the unit cell approach, a 'cross-over model' has been proposed for expressing the cross-over of curved yarns of knitted fabric. Using laminated plate theory, the effective elastic properties of the yarns in the cross-over model have been estimated. Elastic properties of the composite were determined by combining the effective elastic properties of the curved yarns and the resin-rich regions. Tensile strength properties have been predicted by estimating the fracture strength of yarns bridging the fracture plane. Tensile properties of knitted fabric composites with different volume fraction of fibers were predicted. The analytical procedures have been validated by comparing one set of experimental results with the predictions. The applicability and limitation of these models have been discussed.

Characterization and modeling of the tensile properties of plain weft-knit fabric-reinforced composites

This paper describes analytical models for predicting tensile properties of knitted fabric-reinforced composites. Initially, tensile properties of plain weft-knit glass-fiber fabric-reinforced epoxy composites were determined experimentally in the wale and course directions. Elastic properties were predicted by using a ‘cross-over model’ and laminated plate theory. The analytical model expresses the crossing over of looped yarns of knitted fabric, and fiber- and resin-rich regions of composite. Elastic properties of the composite were determined by combining the effective elastic properties of looped yarns and resin-rich regions. Study of tensile failure mechanisms indicated that ultimate failure of a knitted-fabric composite occurs upon the fracture of yarns bridging the fracture plane. Tensile strengths were predicted by estimating the fracture strength of bridging yarns. Tensile properties of knitted-fabric composites with different volume fractions of fibers were predicted. Analytical procedures have been validated by comparing predictions with the experimental results. The applicability and limitation of these models have been discussed.