Thermal Conductivity Of Unidirectional Composites Research Articles

Identification and evaluation of optimal fiber shape for transverse thermal conductivity of unidirectional composites

Identification and evaluation of optimal fiber shape for transverse thermal conductivity of unidirectional composites

Thermal conductivity of unidirectional composites consisting of randomly dispersed glass fibers and temperature-dependent polyethylene matrix

Abstract This extensive study investigated the influence of microstructure on the effective transverse thermal conductivity of unidirectional glass fiber reinforced composites, in which the fibers are randomly dispersed and the thermal conductivity of polyethylene matrix is a function of test temperature. The microstructure is characterized by parameters such as the number of fibers, fiber volume fraction, fiber size, fiber arrangement and thermal property contrast. Firstly, a simple algorithm is developed to automatically generate closest-to-real random array of fibers in unit cell to reconstruct the composite microstructure. Then, the established two-dimensional random two-component composite unit cell is solved using finite element simulation and the obtained effective thermal conductivities are compared with the theoretical predictions and the experimental results. Subsequently, the effects of microstructure parameters and test temperature are investigated, respectively. It is found that the finite element predicted properties are in very good agreement with the experimental predictions, while they are always lower than the analytically predicted properties. These results can find applications in the design of composite materials taking into account the fiber distribution morphology.

Effect of fibre shape on transverse thermal conductivity of unidirectional composites

The determination of thermal conductivities of a composite lamina is of paramount importance in the effective design and application of composite materials. The thermal conductivity of a lamina along the fibre direction can be easily estimated from the Rule of Mixtures but, the thermal conductivity in the transverse direction which depends on many factors need to be determined effectively. The transverse thermal conductivities of continuous fibre reinforced composite lamina are computed by numerical method using finite element analysis. Different fibre concentrations, fibre shapes and different fibre-matrix combinations are examined. A Regular array of square pattern of fibres is considered. The finite element model is validated with the available experimental results and theoretical models for a circular fibre and then extended to other shapes of fibres. Two-dimensional finite element model is adopted for the analysis, due to the restriction of heat flow only in transverse direction and the fibres are assumed to be continuous and perfectly bonded to the matrix. Analysis is carried out for a wide range of fibre-matrix combinations and up to the maximum fibre concentration in the composite. The analysis is extended for circular, square, elliptical and rhombus shaped fibres. From the results it is observed that there is a significant variation in the transverse thermal conductivity due to the shape of fibre, concentration ratios and fibre matrix combinations. This variation in thermal conductivity of a composite lamina results into a broader choice for the selection of composite materials in thermal applications.

Thermophysical and fire properties of vakka natural fiber reinforced polyester composites

Partially biodegradable green composites have been made by incorporating vakka fibers as reinforcement in the polyester matrix. The influence of fiber content and temperature on thermal conductivity, specific heat and thermal diffusivity of composites was investigated. The transverse thermal conductivity of unidirectional composites was investigated experimentally by a guarded heat flow meter method. It was observed that the thermal conductivity of composite decreased with increase in fiber content and at maximum volume fraction of fiber, thermal conductivity of the composites was found to be 0.179 W/m · K. Moreover, the experimental results of thermal conductivity as a function of volume fraction were compared with theoretical model. Thermal conductivity and specific heat capacity of the composite increased with temperature. The lowest thermal diffusivity of 0.55 × 10−7 m2/s for the composite was achieved at a temperature of 120℃. Fire behavior of vakka fiber composite and virgin polyester was investigated using cone calorimeter. The composite ignite earlier and emit lower values of heat release rate and peak heat release rate, when compared to neat polyester resin. Theoretical models were used to predict time to flashover and ignition temperature using cone calorimeter test results as input data.

Mechanical, thermophysical and fire properties of sansevieria fiber-reinforced polyester composites

The objective of present work is to introduce sansevieria natural fiber as reinforcement in the preparation of partially biodegradable green composites. The effect of fiber content on mechanical properties of composite was investigated and found that tensile strength and impact strength at maximum fiber content were 2.55 and 4.2 times to that of pure resin, respectively. Transverse thermal conductivity of unidirectional composites was investigated experimentally by a guarded heat flow meter method. The thermal conductivity of composite decreased with increase in fiber content and the quite opposite trend was observed with respect to temperature. In addition, the experimental results of thermal conductivity at different volume fractions were compared with theoretical model. The response of specific heat capacity of the composite with temperature as measured by differential scanning calorimeter was discussed. Lowest thermal diffusivity of composite was observed at 90°C and its value is 0.9948E−07m2s−1.Fire behavior of composite was studied using the oxygen consumption cone calorimeter technique. The addition of sansevieria fiber has effectively reduced the heat release rate (HRR) and peak heat release rate (PHRR) of the matrix by 10.4%, and 25.7%, respectively. But the composite ignite earlier, release more amount of carbon dioxide yield and total smoke during combustion, when compared to neat polyester resin.

Thermal and mechanical properties of waste grass broom fiber-reinforced polyester composites

The main focus of this study is to utilize waste grass broom natural fibers as reinforcement and polyester resin as matrix for making partially biodegradable green composites. Thermal conductivity, specific heat capacity and thermal diffusivity of composites were investigated as a function of fiber content and temperature. The waste grass broom fiber has a tensile strength of 297.58MPa, modulus of 18.28GPa, and an effective density of 864kg/m3. The volume fraction of fibers in the composites was varied from 0.163 to 0.358. Thermal conductivity of unidirectional composites was investigated experimentally by a guarded heat flow meter method. The results show that the thermal conductivity of composite decreased with increase in fiber content and the quite opposite trend was observed with respect to temperature. Moreover, the experimental results of thermal conductivity at different volume fractions were compared with two theoretical models. The specific heat capacity of the composite as measured by differential scanning calorimeter showed similar trend as that of the thermal conductivity. The variation in thermal diffusivity with respect to volume fraction of fiber and temperature was not so significant.The tensile strength and tensile modulus of the composites showed a maximum improvement of 222% and 173%, respectively over pure matrix. The work of fracture of the composites with maximum volume fraction of fibers was found to be 296Jm−1.

Effect of physicochemical structure of natural fiber on transverse thermal conductivity of unidirectional abaca/bamboo fiber composites

To study the effect of the microstructure of natural fiber on the transverse thermal conductivity of unidirectional composite, abaca and bamboo fibers were unidirectionally aligned to fabricate epoxy composites by a resin transfer molding (RTM) technique. The transverse thermal conductivity of these two types of composites was measured in a steady-state platform. X-ray diffractometer and scanning electron microscopy were applied to analyze the microstructure and morphology of both fibers and composites. The results indicated that the transverse thermal conductivity showed two types of tendencies with fiber content increasing: increasing for bamboo fiber composites, and decreasing for abaca fiber composites. The microstructure and theoretical analysis suggest that the lumen structure plays a great role rather than crystal structures and chemical compounds on the transverse thermal conductivity of unidirectional composites, which is useful for further development and design of natural fiber reinforced composites with better thermal insulation property for people’s daily life.

Application of MFS for determination of effective thermal conductivity of unidirectional composites with linearly temperature dependent conductivity of constituents

In this paper the problem of the effective conductivity in composite material is considered. It is assumed that the thermal conductivity coefficients of both the matrix and fibres materials are temperature-dependent. It yields the temperature-dependency of the effective thermal conductivity. To determine the effective thermal conductivity a unit-cell approach is used, i.e. heat flow in repeated element, which consists of one fibre in the matrix, is considered. It leads to 2-D nonlinear boundary value problems in matrix and fibre regions. In the paper, it is proposed to solve the given nonlinear boundary value problem by Picard iteration. For every iteration step, the linear boundary value problem with two uncoupled linear partially differential equations and coupled boundary conditions is solved. The method of fundamental solution, supported by radial basis functions approximation, is implemented to obtain the required solutions. The numerical experiment has been performed. The results of the experiment and some conclusions are included as well.

Study on Optimization of Transverse Thermal Conductivities of Unidirectional Composites

Abstract Two models, E-S and R-S unit cell models, are presented based on the thermal-electrical analogy technique. The analytical expressions for transverse thermal conductivities of unidirectional composites are derived. The dimensionless effective transverse thermal conductivities ke+ are expressed as a function of the ratio (β) of thermal conductivities of filler to matrix, filler volume fraction vf and the geometry ratio ρ=a/b of the filler. The optimization of transverse thermal conductivities of unidirectional composites is then analyzed under different filler volume fractions vf, thermal conductivity ratios β and different geometric architectures. The present analysis allows for a fairly precise evaluation of configuration performance and comparisons of different arrangements. The results show that if a composite is designed for insulation material, we should choose ρ<1, and if a composite is designed for heat dissipating purpose, we should choose ρ>1.

Effect of Cylindrically Orthotropic Carbon Fibers with Transversely Isotropic Core on Effective Thermal Conductivity of Unidirectional Composites

Carbon fibers can be considered cylindrically orthotropic. Depending on the arrangement of basal planes, predominant configurations are circumferential and radial, but in the core of the fiber, the alignment is undetectable, and consequently it is considered as transversely isotropic. In composites reinforced with these types of fibers, the effective thermal conductivity transverse to the fiber direction will be affected by the core and by the thermal resistance between the fiber and the matrix. The analytical models available are not adequate because they assume that the fiber is totally homogeneous. In this paper, a model of finite elements is presented, which allows combination of the effects of core with the cylindrical orthotropic of the fiber and the thermal contact resistance between the fiber and the matrix. The effective conductivity of composites with orthotropic and inhomogeneous fibers are compared to those with orthotropic and homogeneous fibers. This allows evaluation of the effect for the different morphology of the fibers. The model reveals a significant effect for radially orthotropic fibers (pitch-based). The model also contributes to a better understanding of the heat flux paths in cylindrically orthotropic and inhomogeneous fibers. Finally, this numerical simulation can be of interest first, in the microstructural studies focused on the relationship between the transverse thermal conductivity of carbon fibers and some microstructural parameters, and secondly, in the studies designed to estimate the interfacial contact resistance.

Dependence of the Transverse Thermal Conductivity of Unidirectional Composites on Fiber Shape

The model for the traverse thermal conductivity of unidirectional composite materials published by Springer and Tsai, which yields good results when compared to experimental results, is generalized to include fibers having elliptical cross sections. It is shown that the thermal conductivity of the unidirectional composite normal to the filaments depends strongly on fiber shape.

Some Investigations of Effective Thermal Conductivity of Unidirectional Fiber-Reinforced Composites

The effective thermal conductivity of a unidirectional composite was determined. Inner structure of the composite was approximated by symmetric, rectangular arrangement of fibers. The composite thermal con ductivity was calculated with the use of different theoretical methods and compared to experimental data obtained from a model of the composite and the composite itself. Good agreement was found between theory and experiment. Temperature fields in the composite were also calculated. The results of the effective thermal conductivity occurred to be lower than the analogical values obtained by Adams and Doner. It was found that for isotropic composite having up to 50% fiber volume fraction, Hashin and Rosen's formula for "random arrangement" of fibers could be successfully used. Two pairs of bounds on the composite thermal conductivity were studied. Each of them was found to be narrower for different range of fiber volume fraction.