Overall Properties Of Composites Research Articles

Investigation on the improvement of microwave dielectric properties of plasma-prepared fluoropolymer-coated CaTiO3-filled PTFE composites

High-performance polymer matrix composites preparation has been urgently hampered by poor interfacial adhesion between two phases. In this article, a thorough analysis of the microstructure and overall properties of composites made of polytetrafluoroethylene filled with fluorocarbon polymer film-coated CaTiO3 was conducted. The similar fluorocarbon molecular structure of CaTiO3 surface and PTFE provides a bridge between the two, significantly improving and promoting the microstructure and interface adhesion of the composite. The comprehensive properties of modified composites are obviously superior to those of untreated composites. Composites filled with 30 wt% CaTiO3 have an excellent dielectric constant at 5.53, acceptable dielectric loss at 0.0047, an outstanding heat resistance index of 281.1°C, and relatively low hygroscopicity of 0.10%. At the same time, the mechanical properties are maintained at a high application level, which makes them promising for microwave devices.

Analytical solution for doubly-periodic harmonic problems with circular inhomogeneities and superconducting or membrane-type interfaces

A novel analytical solution for two-dimensional harmonic problems involving doubly-periodic arrays of circular inhomogeneities with superconducting or membrane type interfaces is derived. The complex potential inside each inhomogeneity is sought in the form of power series, while its counterpart inside the matrix is represented by the series in terms of Weierstrass ζ-function and its derivatives. Compliance with the interface conditions results in an infinite system of linear algebraic equations for unknown series coefficients. A rigorous theoretical study of the system properties is performed. The solution is used for evaluating the local fields and overall properties of composites. For the case of square and hexagonal unit cells, accurate formulas for the effective properties are provided. Numerical examples are presented and comparison with the results reported in the literature is performed.

Study on structural and functional properties of porous SiO2 core‐shell construction/polyethylene nanocomposites with enhanced interfacial interaction

AbstractThe addition of inorganic particles can endow polymer matrices with different new features, thereby realizing an optimization to the structural and functional properties of composite. The overall properties of composites are greatly influenced by both fillers dispersion and fillers‐polymer interfacial interaction. However, to simultaneously improve these mentioned two issues is still a critical challenge in the field of polymer‐based nanocomposite. Herein, a typical core‐shell structured mesoporous silica‐coated silica (SiO2@mSiO2) construction was successfully synthesized by using a bi‐phase method. The SiO2@mSiO2 filled polyethylene (PE) nanocomposite was fabricated through a precisely controlled melt‐mixing approach. Benefiting from the additional mesoporous SiO2 shell, both the dispersion of SiO2@mSiO2 and the SiO2@mSiO2‐PE matrix interfacial interaction are improved. Moreover, the stress–strain behavior, temperature‐dependent mechanical property, thermal stability, and electrical insulating property of SiO2@mSiO2/PE composite were studied in detail. It is found that SiO2@mSiO2 core‐shell nanoparticles are capable of not only making a balance between the strength and toughness of the PE‐based composite, but also improving the thermal stability of the composite. In addition, the SiO2@mSiO2/PE composite exhibited an enhanced breakdown strength (256.4 MV·m−1) when filled with as small as 1 wt% SiO2@mSiO2, which is 108% higher than neat PE. All these optimized features are attributed to the well‐designed core‐shell structure. These experimental results provide a promising way to design and fabricate future advanced composite with excellent structural and functional properties in the future.

Homogenization of Composites with Extended General interfaces: Comprehensive Review and Unified Modeling

Abstract Interphase regions that form in heterogeneous materials through various underlying mechanisms such as poor mechanical or chemical adherence, roughness, and coating, play a crucial role in the response of the medium. A well- established strategy to capture a finite-thickness interphase behavior is to replace it with a zero-thickness interface model characterized by its own displacement and/or traction jumps, resulting in different interface models. The contributions to date dealing with interfaces commonly assume that the interface is located in the middle of its corresponding interphase. We revisit this assumption and introduce a universal interface model, wherein a unifying approach to the homogenization of heterogeneous materials embedding interfaces between their constituents is developed. The proposed novel interface model is universal in the sense that it can recover any of the classical interface models. Next, via incorporating this universal interface model into homogenization, we develop bounds and estimates for the overall moduli of fiber-reinforced and particle-reinforced composites as functions of the interface position and properties. Furthermore, we elaborate on the computational implications of this interface model. Finally, we carry out a comprehensive numerical study to highlight the influence of interface position, stiffness ratio and interface parameters on the overall properties of composites, where an excellent agreement between the analytical and computational results is observed. The developed interface-enhanced homogenization framework also successfully captures size effects, which are immediately relevant to emerging applications of nano-composites due their pronounced interface effects at small scales.

Thermoelastic bounds and self-consistent estimation for the overall properties of composites

In the present work, static thermoelastic bounds for a composite with spheroidal isotropic inclusions embedded in an isotropic matrix are calculated. Using the Green’s function derived for the thermoelastic case by Valdiviezo-Mijangos, et al., (2009) and the variational formulation for anisotropic composites developed by Willis (1992), thermoelastic bounds are explicitly obtained. In the case of the thermal expansion coefficient, the results are also compared with experimental data as well as with the Rosen-Hashin bounds. A good agreement among the bounds, the self-consistent method and the experimental data is shown.

Manufacturing and Characterization of Green Composites with Partially Biobased Epoxy Resin and Flaxseed Flour Wastes

In the present work, green-composites from a partially biobased epoxy resin (BioEP) reinforced with lignocellulosic particles, obtained from flax industry by-products or wastes, have been manufactured by casting. In this study, the flaxseed has been crushed by two different mechanical milling processes to achieve different particle sizes, namely coarse size (CFF), and fine size (FFF) particle flaxseed flour, with a particle size ranging between 100–220 µm and 40–140 µm respectively. Subsequently, different loadings of each particle size (10, 20, 30, and 40 wt%) were mixed with the BioEP resin and poured into a mold and subjected to a curing cycle to obtain solid samples for mechanical, thermal, water absorption, and morphological characterization. The main aim of this research was to study the effect of the particle size and its content on the overall properties of composites with BioEP. The results show that the best mechanical properties were obtained for composites with a low reinforcement content (10 wt%) and with the finest particle size (FFF) due to a better dispersion into the matrix, and a better polymer-particle interaction too. This also resulted in a lower water absorption capacity due to the presence of fewer voids in the developed composites. Therefore, this study shows the feasibility of using flax wastes from the seeds as a filler in highly environmentally friendly composites with a wood-like appearance with potential use in furniture or automotive sectors.

Prediction of Mechanical Properties of Graphene Oxide Reinforced Aluminum Composites

Estimating the effect of graphene oxide (GO) reinforcement on overall properties of aluminum (Al) matrix composites experimentally is time-consuming and involves high manufacturing costs and sophisticated characterizations. An attempt was made in this paper to predict the mechanical properties of GO/Al composites by using a micromechanical finite element approach. The materials used for prediction included monolayer and multilayer GO layers distributed uniformly on the spherical Al matrix particles. The estimation was done by assuming that a representative volumetric element (RVE) represents the composite structure, and reinforcement and matrix were modeled as continuum. The load transfer between the GO reinforcement and Al was modeled using joint elements that connect the two materials. The numerical results from the finite element model were compared with Voigt model and experimental results from the GO/Al composites produced at optimized process parameters. A good agreement of numerical results with the theoretical models was noted. The load-bearing capacity of the Al matrix increased with the addition of GO layers, however, Young’s modulus of the GO/Al composites decreased with an increase in the number of layers from monolayer to 5 layers. The numerical results presented in this paper have demonstrated the applicability of the current approach for predicting the overall properties of composites.

Development of WC-Inconel composites using selective laser melting

In the present study, selective laser melting (SLM) was used to successfully fabricate Inconel 718–tungsten carbide (WC) composites. The processing parameter optimization results reveal that nearly non-porous composites (99.54%) were achieved with the laser power of 220W, scanning speed of 850mms−1, and the hatch spacing of 150μm. The microstructural characterization unveils that elongated grain structure in the heat flow direction was observed in the case of pure IN718 while WC particles served as obstacles to hinder the grain growth in the composites. The formation of in situ intermediate layer and the strong interfacial bonding between WC super-hard particles and the matrix acted as load bearing and significantly contribute to the overall properties of composites. Mechanical tests indicate significant improvements of microhardness and tensile strengths, although a drop in strength was observed when the amount of WC reached 15wt.%. In addition, the thermal experiment shows that the composites are dimensionally stable at higher temperature compared to their monolithic counterpart. The findings suggest that the developed IN718-WC composites can be utilized in many critical engineering applications in nuclear sector.

Fabrication and Evaluation of Mechanical Properties of Carbon/Epoxy Square Tube Using Pressure Bag Molding and Compared with Autoclave Method

The present article concentrates on the fabrication of square tube by utilizing high strength carbon fabric epoxy resin prepreg through low cost pressure bag molding technique. In this process vacuum bag which was used has excellent expansion and high thermal stability. The manufactured carbon-epoxy prepreg square tube was evaluated on the basis of fiber volume fraction and mechanical properties such as longitudinal, transverse direction tensile strength. Further, carbon epoxy prepreg composite was manufactured by autoclave technique and compared the mechanical properties fabricated with pressure bag molding as square tube products can be obtained majorly by this technique. The results concluded that, the overall properties of composites manufactured by both the process are almost the same especially tensile strength. However, the specimens manufactured by pressure bag molding process have voids compared to the specimens manufactured by autoclave technique due to vacuum. Nonetheless, pressure bag molding technique can be satisfactorily considered to replace the autoclave technique molding technique and can eventually be applied to manufacture various industrial products such as yacht mast, bicycle frame, tennis racket etc. with low cost.

Processing and characterization of natural rubber/stearic acid-tetra-needle-like zinc oxide whiskers medical antibacterial composites

The Tetra-Needle-like zinc oxide whiskers (T-ZnOw) were modified by stearic acid, and Natural rubber/Stearic acid-T-ZnOw medical antibacterial composites were prepared by blending the Stearic acid-T-ZnOw with natural rubber latex. The morphology, mechanical properties, thermal stability, antibacterial property and water absorption of composites were investigated. The results show that the incorpation of Stearic acid-T-ZnOw into rubber matrix leads to a significantly betterment in the over-all properties of composites when the Stearic acid-T-ZnOw loading is less than 6%. The Stearic acid-T-ZnOw act as a skeleton in the rubber matrix, with its tetra-needles tightly inserting into rubber matrix. It plays an important role in improving the performance of natural rubber. When in nitrogen atmosphere loading of 5 wt%, all the performance of composite achieve optimum results. The Natural rubber/Stearic acid-T-ZnOw has great prospects in producing medical products with greens environmental protection and high performance.

Bounds for the overall properties of composites with time-dependent constitutive law

Abstract This paper deals with the search, via variational methods, of bounds on the overall mechanical properties of composite materials, with the constitutive laws of the constituents governed by linear operators, generally non-symmetric with respect to the chosen bilinear form. For these types of problems, by virtue of a symmetrization technique derived by Tonti (1984), we provide a minimum formulation, then used to derive bounds for the overall properties of composites having a linear time-dependent constitutive law. Some of the examples already known in the literature prove to be special cases of the theory proposed here, such as the results derived by Cherkaev and Gibiansky (1994) and Milton (1990), those obtained by Rafalski (1969a, 1969b) and Reiss and Haug (1978), and those provided by Carini and Mattei (2015).

A Study On the effect of Surface treatment on the Physical and Mechanical properties of date-palm stem liber embedded epoxy composites

Natural fiber reinforced polymer composites are being used frequently for variety of engineering applications due to many of their advantages like ease of availability, low density, low production cost and good mechanical properties but natural fibers are more or less hydrophilic in nature. Therefore, an investigation has been carried out to make better utilization of a class of natural fiber that is date palm stem fiber, for making a wide range of products. Attempts have been made in this research work to study the effect of fiber loading on the physical, mechanical and water absorption behaviour of treated and untreated short fiber based epoxy composites. Composites of various compositions of different amounts of fiber loading are fabricated by simple hand lay-up technique. It has been observed that there is a significant effect of surface treatment of fibers on the overall properties of composites. Further enhancement of properties with lower water absorption rate was attained with glass fiber-epoxy based hybrid composites.

Eigenstrain and Fourier series for evaluation of elastic local fields and effective properties of periodic composites

The elastic stress and strain fields and effective elasticity of periodic composite materials are determined by imposing a periodic eigenstrain on a homogeneous solid, which is constrained to be equivalent to the heterogeneous composite material through the imposition of a consistency condition. To this end, the variables of the problem are represented by Fourier series and the consistency condition is written in the Fourier space providing the system of equations to solve. The proposed method can be considered versatile as it allows determining stress and strain fields in micro-scale and overall properties of composites with different kinds of inclusions and defects. In the present work, the method is applied to multi-phase composites containing long fibers with circular transverse section. Numerical solutions provided by the proposed method are compared with finite element results for both unit cell containing a single fiber and unit cell with multiple fibers of different sizes.

Homogenization of fibrous piezoelectric composites with general imperfect interfaces under anti-plane mechanical and in-plane electrical loadings

The present paper aims mainly to estimate the size-dependent effective properties of fibrous piezoelectric composites with general imperfect interfaces. The interface model used states that the displacement, traction, electric potential, and normal electric displacement all suffer jumps across an interface. In addition, it can degenerate into the well-known special ones by employing appropriate high-contrast interfacial parameters. To achieve our objective, an auxiliary inhomogeneity problem of a circular fiber embedded in an infinite cylindrical reference phase via general imperfect interface under anti-plane mechanical and in-plane electrical boundary conditions is analytically solved. This solution allows us to apply the well-known micromechanical schemes such as the dilute, Mori–Tanaka to obtain the closed-form expressions for the size-dependent overall properties of composites under consideration. Some numerical examples are provided for illustrating the features of the obtained general results.

Development of slate fiber reinforced high density polyethylene composites for injection molding

During the last decade the use of fiber reinforced composite materials has consolidated as an attracting alternative to traditional materials due to an excellent balance between mechanical properties and lightweight. One drawback related to the use of inorganic fibers such as those derived from siliceous materials is the relative low compatibility with conventional organic polymer matrices. Surface treatments with coupling agents and the use of copolymers allow increasing fiber–matrix interactions which has a positive effect on overall properties of composites. In this research work we report the use of slate fiber treated with different coupling agents as reinforcement for high density polyethylene from sugarcane. A silane (propyltrimethoxy silane; PTMS) and a graft copolymer (polyethylene-graft-maleic anhydride; PE-g-MA) were used to improve fiber–matrix interactions on HDPE-slate fiber. The effect of the different compatibilizing systems and slate fiber content were evaluated by scanning electron microscopy (SEM), dynamic thermomechanical analysis (DTMA) as well as mechanical properties (tensile, flexural and impact). The results show that the use of silane coupling agents leads to higher fiber–matrix interactions which has a positive effect on overall mechanical properties. Interesting results are obtained for composites containing 30wt.% slate fiber previously treated with propyltrimethoxy silane (PTMS) with an increase in tensile and flexural strength of about 16% and 18% respectively.

Bounds on the overall properties of composites with ellipsoidal inclusions

A new model is put forward to bound the effective elastic moduli of composites with ellipsoidal inclusions. In the present paper, transition layer for each ellipsoidal inclusion is introduced to make the trial displacement field for the upper bound and the trial stress field for the lower bound satisfy the continuous interface conditions which are absolutely necessary for the application of variational principles. According to the principles of minimum potential energy and minimum complementary energy, the upper and lower bounds on the effective elastic moduli of composites with ellipsoidal inclusions are rigorously derived. The effects of the distribution and geometric parameters of ellipsoidal inclusions on the bounds of the effective elastic moduli are analyzed in details. The present upper and lower bounds are still finite when the bulk and shear moduli of ellipsoidal inclusions tend to infinity and zero, respectively. It should be mentioned that the present method is simple and needs not calculate the complex integrals of multi-point correlation functions. Meanwhile, the present paper provides an entirely different way to bound the effective elastic moduli of composites with ellipsoidal inclusions, which can be developed to obtain a series of bounds by taking different trial displacement and stress fields.

Exact effective relations for dynamics of a laminated body

Milton and Willis [Milton, G.W., Willis, J.R., 2007. On modifications of Newton’s second law and linear continuum elastodynamics. Proc. R. Soc. A 463, 855–880] have recently discussed the general form of constitutive relations that should apply for the description of the dynamics of media with microstructure below the scale of measurement, and concluded that these relations should have the form, somewhat generalized, of effective relations for composites implied by a formulation of Willis [Willis, J.R., 1981. Variational and related methods for the overall properties of composites. In: Yih, C.S. (Ed.), Advances in Applied Mechanics, vol. 21. Academic Press, New York, pp. l–78; Willis, J.R., 1981. Variational principles for dynamic problems for inhomogeneous elastic media, Wave Motion 3, 1–11]. Whereas for a general composite (treated as a random medium), these relations can only be found at some level of approximation, they can be found exactly for a laminate with periodic microstructure, restricted to one-dimensional propagation normal to the lamination, for which Floquet theory is available. Such a medium becomes random if it is randomly translated: the exact position of any one interface is then not known, and ensemble averages may correspondingly be calculated. Example calculations demonstrate, completely explicitly, that “effective modulus” and “effective density” are operators, non-local in space and time; furthermore, if the medium does not display symmetry under reflection, mean stress is coupled not only to mean strain but also to mean velocity, and mean momentum density is likewise coupled not only to mean velocity but also to mean strain. A precisely similar structure applies to the propagation of electromagnetic waves: the effective medium is non-local and bi-anisotropic. The same structure is preserved under a generalized formulation, applicable to cases where only some component of the microstructure is observable.

Eigenstrain formulation of boundary integral equations for modeling particle-reinforced composites

A novel computational model is presented using the eigenstrain formulation of the boundary integral equations for modeling the particle-reinforced composites. The model and the solution procedure are both resulted intimately from the concepts of the equivalent inclusion of Eshelby with eigenstrains to be determined in an iterative way for each inhomogeneity embedded in the matrix. The eigenstrains of inhomogeneity are determined with the aid of the Eshelby tensors, which can be readily obtained beforehand through either analytical or numerical means. The solution scale of the inhomogeneity problem with the present model is greatly reduced since the unknowns appear only on the boundary of the solution domain. The overall elastic properties are solved using the newly developed boundary point method for particle-reinforced inhomogeneous materials over a representative volume element with the present model. The effects of a variety of factors related to inhomogeneities on the overall properties of composites as well as on the convergence behaviors of the algorithm are studied numerically including the properties and shapes and orientations and distributions and the total number of particles, showing the validity and the effectiveness of the proposed computational model.

Microstructurally-based homogenization of electromagnetic properties of periodic media

A general method for homogenization of the electromagnetic properties of a heterogeneous periodic medium is developed, based on its microstructure. This method is inspired by micromechanics (Nemat-Nasser and Hori, 1999). Contrary to other conventional techniques, commonly used in electromagnetism to calculate the overall properties of composites, this microstructurally-based method does not require an explicit numerical solution of the Maxwell equations. We define the macroscopic field quantities as volume averages of the spatially variable fields, taken over a representative volume element (RVE), consisting of a unit cell of the periodic medium (Hill, 1963; Willis, 1981; Hashin, 1983; Nemat-Nasser, 1986). The boundary conditions are based on the Bloch representation of wave propagation in the heterogeneous media. Instead of explicitly solving the Maxwell equations, these equations are directly used in the averaging scheme. This distinguishes our method from others, where usually a known point-wise solution is used to obtain the average field quantities. The resulting constitutive relations therefore may be used to directly estimate the response of any heterogeneous periodic assembly of material constituents of given geometry and properties. To cite this article: A.V. Amirkhizi, S. Nemat-Nasser, C. R. Mecanique 336 (2008).

A Method to Evaluate the Elastic Properties of Ceramics-Enhanced Composites Undertaking Interfacial Delamination

A micromechanical approach is developed to investigate the behavior of composite materials, which undergo interfacial delamination. The main objective of this approach is to build a bridge between the intricate theories and the engineering applications. On the basis of the spring-layer model, which is useful to treat the interfacial debonding and sliding, the present paper proposes a convenient method to assess the effects of delamination on the overall properties of composites. By applying the Equivalent Inclusion Method (EIM), two fundamental tensors are derived in the present model, the modified Eshelby tensor, and the compliance tensor (or stiffness tensor) of the weakened inclusions. Both of them are the fundamental tensors for constructing the overall constitutive law of composite materials. By simply substituting these tensors into an existing constitutive model, for instance, the Mori-Tanaka model, one can easily evaluate the effects of interfacial delamination on the overall properties of composite materials. Therefore, the present method offers a pretty convenient tool. Some numerical results are carried out in order to demonstrate the performance of this model.