Coated Fiber Composites Research Articles

Experimental study on the combustion characteristics of carbon fiber composite materials coated in different coatings

The special environment in which the aircraft operates in terms of flight and safety assurance has special requirements for coating performance. Based on the combustion characteristics of four kinds of high-performance aviation coatings coated with carbon fiber composites, for parameters such as average ignition time and heat release rate of the composite, the results show that the carbon fiber composite has the longest average ignition time, Minimum heat release rate, while the 2-ethyl-4-Mylimidazole cured epoxy coated fiber composite had the shortest average ignition time. The maximum heat release rate was observed.

Analytical solutions for coated circular inhomogeneity with non-uniform axisymmetric eigenstrain distribution

In this paper, a general model for coated circular inhomogeneous inclusion problems is proposed and studied, where non-uniform axisymmetric eigenstrains are independently distributed within the circular zone and annular zone (coating layer). The main difficulties are from the dissimilarity of three-phase materials, the non-uniform axisymmetric eigenstrain distribution, and the presence of intermediate annularity, which are hardly treated within the classical Eshelby inclusion mechanics. By employing the equivalent eigenstrain principle, these challenges can be completely tackled, and a general explicitly analytical solution is obtained. From this solution, a couple of solutions for typical inclusion problems are readily degenerated, which have been derived with great efforts in literature. With the general model and its solution, the analytical solution for the coated hollow-cored inhomogeneous inclusion problem with non-uniform axisymmetric eigenstrain is provided, and an eigenstrain-based nano-inclusion model is subsequently proposed. The applications of coated circular inhomogeneity with eigenstrains can be found in coated fiber composites, thermoelastic problems, and micro- & nano-mechanics.

Investigation of interfacial and mechanical properties of alumina-coated steel fiber reinforced geopolymer composites

In this study, alumina coated steel reinforced geopolymer composites were successfully fabricated and their interfacial and mechanical properties were investigated. The fiber–matrix interface characteristics were assessed using single-fiber push-out and water contact angle experiments as well as SEM-EDS analysis. Finally, the role of alumina coating on the compressive, flexural and toughness of the geopolymer composites was investigated. The morphological studies revealed that alumina coating on steel can chemically bonded and microstructurally integrated with the surrounding matrix. The push-out test showed that the interfacial shear strength was increased approximately 150% in composites produced with alumina coated steel fiber, suggesting an enhancement of stress transfer across the fiber/matrix interface. The results showed that the composites containing alumina coated steel fibers possess significantly higher mechanical properties in comparison with the uncoated specimens under all tested conditions. A comparison of the mechanical properties of composites at 0.75 vol%, showed that the flexural and compressive strength of alumina coated fiber composites were improved by ~ 17% and ~ 14%, respectively. The calculated toughness and load–deflection curves were indicated an improvement up to ~ 94%. It was also found that deflection hardening behavior is more developed in composite containing alumina coated fibers. These results were considered as an effectiveness of alumina coated steel fibers on reinforcing of metakaolin-based geopolymer composites.

Synthesis and novel development of electroless Ni-P coating on bamboo fibre

This work aims to develop a natural fibre reinforced by epoxy composite with improved mechanical properties using the technique of compression moulding. The use of electroless Ni-P coating process made a new approach to natural fibre substrates. Increase the coating thickness of electroless Ni-P coating on the bamboo fibre substrate by varying fibre length. The amplitude of the coating thickness is between 1.24 and 8.52 µm for 10, 20, 30 and 60 min. This new moderation of fibre will lead to better mechanical properties by coating electroless Ni-P on bamboo fibre. In this study, a scanning electron microscope identified the surface characteristics and cross-sectional area images of redesigned coated bamboo fibres. Electroless Ni-P coated bamboo fibres reinforced on the epoxy polymer matrix. This composite material enhances the bonding of the interfacial between the electroless Ni-P coated bamboo fibre and the matrix material. The samples were made from compression moulding and subjected to mechanical properties such as tensile, flexural and impact test. The sample is prepared by 5, 10, 20, 30 and 40 mm varying fibre length as 14% weight Ni-P coating bamboo fibre and 86% polymer matrix weight. The better tensile, flexural and impact strength of 48.9 MN/m2, 70.7 MN/m2 and 60.2 kJ/m2 were observed in coated fibre composites. The result shows that the Ni-P coated bamboo fibre plays a significant role in enhancing mechanical properties.

Polylactic acid/Lignocellulosic residue composites compatibilized through a starch coating

AbstractThe use of natural fiber residues as reinforcement in biodegradable composites has been performed; however, the incompatible interface limits the applications. In this work, the use of starch coating as a natural coupling agent was studied in three different natural residues: sugarcane bagasse, maçaranduba, and pinus wastes, aiming biodegradable composites. The coating in bagasse showed low efficiency, with low thickness and failures, due to residue intrinsic higher surface area; while the wood residues showed shorter fibers with uniform starch deposition. These results affected the compatibility between filler and matrix; while the bagasse composite showed voids and decrease in the mechanical properties; however, the maçaranduba and pinus showed an increase in the stiffness and strength. All the coated fiber composites showed stable thermal properties and an increase in the crystallinity in the coated samples. The addition of the natural filler resulted in a high water absorption with coated samples absorbing six times more water than neat PLA and without stabilization in a short time. This characteristic may favor the initial abiotic hydrolysis in the biodegradation, showing that the material could be an option to produce short‐life packaging in dry environments.

The optimisation of fabrication process for various chemically treated kenaf fibres in epoxy matrix composites

The fabrication process is crucial since it determines the overall performance of the bio-composites. This study draws from the drawbacks of the natural fibre reinforced composites that are high voids content, low in surface interaction as well as low-stress distribution property especially using a simple mould-press process. The study explores the correlation between various fabrication processes of thermoset matrix towards the composites density, voids content, tensile and morphological properties. The study was carried out by mould pressed only 10 percent (%) filled composites by varying its curing temperatures, moulds type, fibres size and fibres chemical treatments afflicted. The results showed that 50 ˚C of curing temperature, in plunger mould-type, using 0.25 mm mesh size fibre are the optimised parameters. The coated 1:6 composite showing the optimum properties since it improves 6.5% density, 99.95% voids content, 38.1% water uptake and 33.2-50.6% of tensile properties. The suitable processing parameters and high coating penetration might contribute to the total improvement of the coated fibre composites properties. Since it influences the fibres compact-ability that leads to low voids formation as analysed on its fractured surfaces. In summary, a better understanding of the materials characteristic and fabrication processes are needed to obtain the optimum bio-composites performance.

Simultaneous improvement of interfacial strength and toughness between carbon fiber and epoxy by introducing amino functionalized ZrO2 on fiber surface

Amino-functionalized ZrO2 was prepared and incorporated on carbon fiber surface by a simple dip-coating approach to simultaneously strengthen and toughen the interphase of carbon fiber/epoxy composite. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetry confirmed the successful functionalization of ZrO2 by (3-Aminopropyl) triethoxysilane (APTES-ZrO2). Scanning electron microscopy and atomic force microscope demonstrated that uniform coating with well dispersed particles on fiber surface was achieved at 1.0wt% addition of APTES-ZrO2 particles. Under this condition, the interfacial shear strength (IFSS) and fracture toughness (Gic) revealed respective 41.3% and 257.6% augments, compared with epoxy-only coated fiber composite. The enhanced IFSS is attributed to the improved chemical bonds between fiber and resin. While the increase in Gic can be ascribed to the intermittent distribution of strong/weak bonding zones and the mobility of APTES-ZrO2 particles in the interphase region. This work affords a simple, scalable and cost effective approach to simultaneously increase the interfacial strength and toughness of composites, which has always been sought after for structural materials.

An analytical method for predicting the effective transverse thermal conductivity of nano coated fiber composites

A four-phase concentric cylinder model with interface effect is proposed. Based on the model and surface/interface theory, a generalized self-consistent method is developed for predicting the effective transverse thermal conductivity of nano coated fiber composites. An analytical solution is obtained for effective thermal conductivity by applying complex elastic theory. Comparisons with the finite element analysis (FEA) and other available theoretical methods show the efficiency and the accuracy of the present method. Numerical results show the dependence of the effective thermal conductivity of the nano composites when the size of fiber and coating are on the order of nanometer. The effects of the interface thermal constant and the coating thermal conductivity on the effective thermal conductivity are discussed. The present solutions are useful to the theoretical research and engineering applications of the nano coated fiber composites.

Effective properties of coated fiber composites with piezoelectric and piezomagnetic phases

The finite element method is proposed to analyze coated fiber composites with piezoelectric and piezomagnetic phases. The computational homogenization technique is applied for fiber composites with magnetoelectroelastic properties to determine effective material parameters. The evolution of the magnetoelectroelastic fields at the macroscopic level is resolved through the incorporation of the microstructural response. The microstructural analyses are performed on the representative volume element, where essential physical geometrical information about the microstructural components is included. Circular cross section of fibers is considered in numerical analyses. A thin coating layer is considered on the surface of the piezoelectric fiber which is embedded in the piezomagnetic matrix. Influence of the coating layer on the effective material properties is analyzed.

A four-phase confocal elliptical cylinder model for predicting the effective thermal conductivity of coated fibre composites

A four-phase confocal elliptical cylinder model is proposed from which a generalised self-consistent method is developed for predicting the thermal conductivity of coated fibre reinforced composites. The method can account for the influence of the fibre section shape ratio on conductivity, and the physical reasonableness of the model is demonstrated by using the fibre distribution function. An exact solution is obtained for thermal conductivity by applying conformal mapping and Laurent series expansion techniques of the analytic function. The solution to the three-phase confocal elliptical model, which simulates composites with idealised fibre–matrix interfaces, is arrived at as the degenerated case. A comparison with other available micromechanics methods, Hashin and Shtrikman's bounds and experimental data shows that the present method provides convergent and reasonable results for a full range of variations in fibre section shapes and for a complete spectrum of the fibre volume fraction. Numerical results show the dependence of the effective conductivities of composites on the aspect ratio of coated fibres and demonstrate that a coating is effective in enhancing the thermal transport property of a composite. The present solutions are helpful to analysis and design of composites.

Numerical simulation of the densification processing of titanium-matrix coated fiber composites

The densification behavior of Ti–6Al–4V composites reinforced by SiC fibers under vacuum hot pressing (VHP) is studied by using finite element method (FEM). The effect of fiber packing geometry, fiber volume fraction and consolidation parameters (temperature and time) on densification behavior are analyzed emphatically during the consolidation process. The results indicate, compared with the square fiber array, the hexagonal fiber array is of great of benefit to the matrix flow into void and can remarkably decrease the matrix stress during densification. For both square and hexagonal fiber array, fiber volume fraction has a significant effect on the densification. The high fiber volume fraction would cause low consolidation rate. The optimal temperature and time parameters of Ti–6Al–4V matrix-coated fibers composites for vacuum hot pressing must exceed 750 °C and 0.2 h, respectively.

Influence of mechanical working on properties of aluminium base short steel fiber reinforced composites

In the present investigation aluminium base short plain steel fiber, copper and nickel coated steel fiber reinforced composites were prepared by vortex method. These were subsequently given deformation upto 40% by hot rolling. Microstructure of deformed sample showed random orientation of fibers. Breakdown of fibers due to the hot rolling was also predominant. Density of composites increased with increase in % of deformation due to reduced porosity. The hardness and strength improvement observed is attributed to decrease in porosity and increase in the number of fibers due to fiber breakage. In case of copper-coated fiber reinforced composite some additional mechanism is observed to operate. After 40% rolling, porosity level of 5-wt% copper coated fiber composites was decreased from 3.9% to 0.7%. Hardness of as cast Al-5FeCu composite was 38.2 BHN, which increased to 45.8 BHN on 40% reduction. UTS (Ultimate tensile strength) of 5-wt% copper coated steel fiber composites increased from 124 MPa to 145 MPa on 40% deformation along with an improvement of percentage of elongation from 9.2 to 11.6. The simultaneous increase in UTS and percentage of elongation indicate that reduction in porosity is the main factor-giving rise to improvement of the properties. Fracture surface investigation showed that cracks are initiated at the fiber matrix interface, propagated through the interface and linked up with other cracks or fiber/matrix interface leading to failure. In case of as cast composites micro-porosity played a vital role in failure which is noted from SEM fractographs.

Effect of C coating on the interfacial microstructure and properties of SiC fiber-reinforced Ti matrix composites

C coating of the SiC fiber critically influences the interfacial microstructure and properties of titanium matrix composites, and thus affects the overall composite properties. In this work, the interfacial microstructure and debond strength of SiC(C)/Ti–6Al–4V and SiC/Ti–6Al–4V composites was studied by comparison. The C coating prevented direct fiber–matrix interaction, and the interfacial reaction product for SiC(C)/Ti–6Al–4V composite was only TiC, comprising fine particles adjacent to the C coating and coarse particles adjacent to the matrix. At the interface of SiC/Ti–6Al–4V composite, a narrow layer of fine TiC particles was adjacent to the fiber, and a broad mixture layer of TiC and Ti 5Si 3 particles was adjacent to the matrix; the particle size increases gradually from the fiber to the matrix. C coating offered a weak interfacial bonding between the fiber and matrix, and the interfacial debond strength for SiC(C)/Ti–6Al–4V and SiC/Ti–6Al–4V composites was 118.2 ± 4.24 and 230 ± 6.28 MPa, respectively. Interfacial debonding occurred between the C coating and the reaction layer for the coated fiber composite, but between the fiber and the interface reaction layer for the naked fiber composite.

A model for the consolidation of hexagonal array matrix coated fibre composites

Physically based constitutive equations for the consolidation of matrix coated fibres (MCFs) arranged in hexagonal arrays are presented in this paper. The constitutive equations have firstly been developed using a variational method for a unit cell representing hexagonal array packing of the coated fibres under symmetric in-plane compressive load. The resulting constitutive equations have subsequently been generalized to multiaxial stress states and implemented into finite element software within a finite deformation framework to enable simulations of practical manufacturing processes. The model has been validated by comparing predicted results with those obtained from independently developed explicit micromechanical finite element models. The ability of the model to predict the observed behaviour has been tested by comparing the results of simulations with those of experiments. The model predictions compare well with the measured results. In addition the results of simulations suggest that the densification curves for square and hexagonal array packing effectively provide the lower and upper bounds, respectively, for practical consolidation behaviour of MCFs under uniaxial constrained compression.

Generalised constitutive equations for densification of metal matrix coated fibre composites

The present paper completes a study of constitutive equations for the consolidation processing of continuous fibre reinforced metal matrix composite materials. It builds on an earlier paper in which physically based constitutive equations were derived for the case of symmetrical, isostatic loading. In the present paper, constitutive equations are developed for in plane, general stress states. The total deformation of the consolidating composite is expressed as the sum of a conventional deviatoric creep term, together with a dilatational term, which was derived using a variational method previously published. The equations contain only two material parameters, which are the conventional creep coefficient and exponent for the fibre coating material (in this case, Ti-6Al-4V). The resulting equations have been implemented into finite element software enabling the simulation of practical consolidation processes. The model has been verified by comparing predicted results with those obtained from independent micromechanical models. A number of experimental tests have been carried out, and the model is used to predict the rates of densification for a range of experimental pressure and temperature histories. Good comparisons have been achieved.

Young's Modulus of Coated Inclusion Composites by the Generalized Mechanics-of-Materials (GMM) Approach

A micromechanical model of the Young's modulus for three special cases of composites - continuous unidirectional fiber composites, particulate composites and periodically bilaminate composites - has been developed within the framework of the mechanic-of-materials approach. Parallel-series (PS) and series-parallel (SP) schemes were adopted based upon opposing combination sequence of the parallel model (direct rule-of-mixture) and the series model (inverse rule-of-mixture). By expressing the inclusion's geometrical characteristics in terms of reinforcement volume fraction and interphase volume, a set of reinforcement parameters for the inclusion and its interphase are extracted. Based on reinforcement parameters for the special cases, those of more general cases, which are intermediates of the special cases, are obtained by curve-fitting approximation. Young's modulus of simple cases such as coated fiber composites in longitudinal direction and coated lamina composites are shown to be approximate to the parallel and series models respectively. Cases such as coated fiber composites in transverse direction and coated particulate composites are compared with other results and observed to be highly and moderately conservative by the PS and SP techniques respectively.

Simple model for consolidation of metal matrix coated SiC fibre composites

A simple approach to modelling the consolidation of matrix coated fibre composites is presented. It employs an existing porous material constitutive model for monolithic materials. It is argued that in the consolidation of metal coated SiC fibres, the deformation primarily occurs in an outer layer of the fibre coating, and the internal core remains undeformed, largely because of the generally hydrostatic compressive loading, and because of the incompressible nature of the material in creep. The consolidation process is therefore not vastly different to that occurs for monolithic metal fibres, and similar equations can therefore be used for the composite consolidation. The constitutive equations have been implemented into general purpose non-linear finite element software within a large deformation formulation by means of two different user subroutines, one providing a general implementation, and the other a cpu time efficient approach. The manufacture and testing of SiC continuous fibre, Ti-6Al-4V metal matrix composite specimens is described and the results of the tests compared with the model calculations, showing that good agreement can be achieved with a simple model. The dependence of volume fraction of fibres and temperature can be introduced empirically through the specification of just two material constants. The model is therefore useful in the development of consolidation processes.

Thin interphase/imperfect interface in elasticity with application to coated fiber composites

The imperfect interface conditions which are equivalent to the effect of a thin elastic interphase are derived by a Taylor expansion method in terms of interface displacement and traction jumps. Plane and cylindrical interfaces are analyzed as special cases. The effective elastic moduli of a unidirectional coated fiber composite are obtained on the basis of the derived imperfect interface conditions. High accuracy of the method is demonstrated by comparison of solutions of several problems in terms of the imperfect interface conditions or explicit presence of interphase as a third phase. The problems considered are transverse shear of a coated infinite fiber in infinite matrix and effective transverse bulk and shear moduli and effective axial shear modulus of a coated fiber composite. Unlike previous elastic imperfect interface conditions in the literature, the present ones are valid for the entire range of interphase stiffness, from very small to very large.

Analytical modeling of damping at micromechanical level in polymer composites reinforced with coated fibers

Theoretical models using theory of elasticity, finite-element, and mechanics-of-materials formulations for characterizing the damping loss factor of composites with coated fiber reinforcement are described. The theoretical models are validated through comparison with experimental damping results conducted on composites having coated fibers as reinforcement. Explicit micromechanics equations are presented in order to define the damping and stiffness of unidirectional coated fiber composites under longitudinal normal (LN), transverse normal (TN), transverse shear (TS) and longitudinal shear (LS) loading conditions. Since shear deformation is essential for viscoelastic damping in polymers, and large shear strains are generated near the fiber/matrix interface in composites, it is shown that the use of a viscoelastic polymer coating on the fibers is an effective way of improving damping in such composites. A strain-energy approach was implemented with both a closed-form theory-of-elasticity solution and finite-element numerical simulations in order to carry out the analysis.

A dual homogenization and finite-element study on the in-plane local and global behavior of a nonlinear coated fiber composite

In order to uncover the influence of localized deformation in the soft interphase layer on the global elastoplastic behavior of a fiber-reinforced composite, a dual homogenization and finite-element study is presented in this paper. The homogenization approach makes use of the concept of secant moduli and an energy-based effective stress which is evaluated by a field fluctuation method. In the finite-element analysis NASTRAN was used, with the triangular elements carefully constructed in the unit cell to deliver the local stress and strain fields of the constituent phases. These dual investigations are complementary in that the homogenization theory could readily provide the overall stress–strain curves of the composite whereas the finite-element analysis could give the local stress fields which are important to the onset of damage or crack initiation. The results of finite-element method (FEM) could also be used to assess the accuracy of the homogenization theory. Detailed comparisons between the two have indicated that the homogenization theory is sufficiently accurate. The propagation of plastic zone in both ductile phases are also vividly demonstrated. In addition, the soft interphase is found to be a region of high strain concentration, rendering the entire system with a lower elastoplastic strength as compared to an ordinary 2-phase composite.