Theory Of Composite Materials Research Articles

A Model for Estimation The Shear Strength of The Frozen Soil Based on The Theory of Composite Materials

1 GAO Ling-xia, LI Shun-qun, CHAI Shou-xi, 4 Qin Likun 1, First author State Key Laboratory of Frozen Soil Engineering, Lanzhou, China, 730000; School of Civil and Architecture Engineering, Dalian Nationalities University, Dalian, 116600, gaolingxia2006@126.com *2, Corresponding Author State Key Laboratory of Frozen Soil Engineering, Lanzhou, 730000; Department of Civil Engineering, Tianjin Institute of Urban Construction, Tianjin, China, 300384; Tianjin Key Laboratory of Soft Soil Characteristics and Engineering Environment, Tianjin, china, 300384,lishunqun@sina.com 3 Department of Civil Engineering, Tianjin Institute of Urban Construction, Tianjin, China, 300384, chaishouxi@163.com 4 School of Civil and Architecture Engineering, Dalian Nationalities University, Dalian, 116600, qinlk89@163.com

Effective microwave magnetic response of two-component metaferrite

The complex effective relative permeability of a two-component ferrite-like metamaterial was studied for the two cases of electromagnetic wave propagation with respect to direction of dc magnetic bias field, namely, parallel and transverse. The metamaterial of interest is the host dielectric with periodically embedded ferric cylindrical or spherical inclusions. The inclusions are saturated with the biasing magnetic field and the magnetic losses are taken into account. The analysis was performed utilizing the Microwave Effective Medium Theory for two-component artificial composite materials with saturated losslessferricinclusions (1). Computations revealed thatlowvalues ofrefractiveindexaswellasnegativevalues ofpermeability can be achieved.

Meso-element equivalent method for the simulation of macro mechanical properties of concrete

A meso-element equivalent method is proposed to investigate the macro mechanical properties of concrete. The randomly distributed aggregates with different sizes and shapes are built by using the Monte Carlo simulation approach, and they are discretized into a finite number of identical elements with a characteristic element size. Each meso-element formed is then processed to be a homogeneous and isotropic unit based on homogenization theory of composite materials. There are two key issues emphasized in the present research, they are the equivalence of the mechanical behaviors of the aggregated concrete material and the determination of the mesh-element size, respectively. The classical Voigt parallel approach is applied to establish the equivalent mechanical behaviors of the meso-elements containing the two-phase medium composed of aggregates and mortar matrix. Since the macroscopic nonlinearity of concrete material is essentially attributed to the inherent heterogeneities, the non-homogeneity of concrete is described by the dispersion coefficient of the effective elastic moduli of concrete meso-elements. And the characteristic element size is introduced and determined by means of a statistical analysis of the aggregate sizes and taken as an appropriate mesh size of concrete specimens. The proposed approach reflects the fact that the concrete nonlinearity originates from the inherent heterogeneity. Several two-dimensional samples of concrete specimens are carried out to verify the feasibility and the accuracy of the proposed meso-element equivalent method. Furthermore, the damage process and the deformation of a three-dimensional four-point bending concrete beam are studied. The numerical results show the high efficiency and accuracy of the proposed method. Compared with other meso-mechanical methods, the advantage of the present meso-element equivalent method is that the degrees of freedom of the concrete specimens reduce significantly, making the computational efficiency improved drastically, especially for three-dimensional problems, while the accuracy of the numerical results is acceptable.

On modeling shape memory polymers as thermoelastic two-phase composite materials

A model has been proposed recently, which describes the experimentally observed mechanical behavior of some shape memory polymers. It considers a purely thermoelastic behavior, without strain rate effects, and assumes essentially that the polymer can be considered as a two-phase composite, with glassy and rubbery phases having volume fractions that depend on temperature only. Since a uniform stress hypothesis was used in the original formulation, with an inconsistency when thermal expansion was considered, this model is revisited here by taking advantage of many results that have been established in the theory of composite materials. It is shown, especially, that a uniform strain hypothesis is more appropriate than assuming a uniform stress.

Analysis and design procedures for the flexural behavior of glass fiber-reinforced polymer composite poles

Earlier research progress on using fiber-reinforced polymer (FRP) composite poles for transmission lines revealed that the use of these poles is economically viable and industrially reliable. While this promising alternative technique is coming to be widely accepted in practice and evolving to become the future of the construction in transmission lines, the development of appropriate design guidelines that deal with detailed analysis of such poles has lagged behind. Design approaches for conventional steel/wood poles were influential in providing safety and robustness to these poles. However, little advanced approaches focused on the design of fiber-reinforced polymer poles. This is the focus of the present paper. The available design procedures of fiber-reinforced polymer poles are based on the allowable stress design theory of composite material under various states of stress. However, various experimental results show that cracking and early failure of fiber-reinforced polymer poles are normally controlled by the relative location of the opening from the base of the pole. Most of the design guidelines ignore such effect and accounts only for the effect of these holes by considering their influence on the abrupt reduction in the cross-sectional area of the poles. These guidelines do not give a specific attention to the impact of the opening on the generated stress concentrations in their vicinity. Furthermore, local buckling at a nearby area of the opening generally dominates the mode of failure of such poles that requires more attention to the relative locations of the openings. A new design approach is introduced to accurately evaluate the design equations for the flexural behavior of fiber-reinforced polymer -composite poles. The accuracy of both the developed design procedures and that of existing design approaches are verified by comparison with documented test results of an early experimental program of the authors.

Inorganic Composite Material Based on Fly Ash, Red Residue from Bauxite Ore for Road Building Projects in Vietnam

The paper present solidifying technology based on geopolymer theory of inorganic composite materials from bauxite, red residue from bauxite ore, fly ash and activators for road building projects in Vietnam. This study describes physical properties and chemical compositions of bauxite, red residue, fly ash and the effects of bauxite-red residue-fly ash-activator mixes on the geotechnical properties of inorganic composite materials. Mixture design and testing procedures for inorganic composite materials. New inorganic composite materials have high durability and ability to water resistance. The presentation also show microstructure analysis of inorganic composite materials based on bauxite residue, fly ash and activators by X-ray diffraction, Infrared spectroscopy (IR), transmission electron microscopy (TEM) display high density, and modified microstructure of inorganic composite materials. Construction method of road using inorganic composite materials is also presented.

Research on Strengthening Mechanism of Bamboo Fiber Concrete under Splitting Tensile Load

Bamboo fiber concrete is a type of architectural material. Because of its fast growth and environmental protection, bamboo fiber concrete attracts much attention from researchers and industries. However, research on bamboo fiber concrete is not enough which greatly affects its applications in engineering. Based on the splitting tensile test of bamboo fiber concrete, the formulas of splitting tensile strength are presented using composite material theory and fiber spacing theory respectively. A comparison of the theoretical values of splitting tensile strength with those of test is made. It is found that the formula deduced from composite material theory leads to severe errors because of its unrealistic hypothesis. Therefore the composite material theory is inappropriate to explain the strengthening mechanism of bamboo fiber concrete. On the other hand, fiber spacing theory not only has higher accuracy but also reflects the effect of fiber content and length-radius-ratio on the splitting tensile strength of concrete. So the fiber spacing theory is adapted to study the strengthening mechanism of bamboo fiber to concrete.

DEFORMATION ABILITY OF SINGLE POINT INCREMENTAL FORMING FOR THEMO-PLASTIC COMPOSITE MATERIALS

The studies of theory and simulation for composite materials have not yet built model for analyzing the effects of temperature’s influence on the deformation ability of these materials. The article focused on studying the relationship between temperatures and deformation ability of composite sheets in SPIF method, building and analyzing simulation model, determining the limited deformation angle according to the temperatures and building the chart of limited forming for the polypropylene (PP) glass fiber type E mat composite material.

A Theoretical Analysis of the Fracture Behavior of a Multi-Layered Thin Film Structure under Residual Tensile Stress

In this work, the fracture behavior of a multi-layered thin film structure under residual tensile stress is investigated theoretically. Using composite material theory and a modified shear-lag model, the analytical solutions for the distribution laws of the tensile stress developed in the first-layer thin film and the shear stress developed along the interface can be obtained. In addition, the crack density of the first-layer thin film can be derived from the residual stress and the mechanical and geometric parameters of the cracked system. This result also yields a measurement of the residual stress from the crack density and the mechanical and geometric parameters of the system. Finally, a numerical example is presented to show how the crack density varies versus the residual stress.

Electromechanical stability of electro-active silicone filled with high permittivity particlesundergoing large deformation

In this paper, an expression for the permittivity of electro-active silicone undergoing largedeformation with high permittivity particles filled uniformly has been proposed.Two expressions are proposed for the permittivity, one based on experimentaltests and the other based on the theory of composite material. By applying thethermodynamic model incorporating linear dielectric permittivity and nonlinearhyperelastic performance, the mechanical performance and electromechanicalstability of the coupling system constituted by silicone filled with PMN–PT havebeen studied. The results show that the critical electric field decreases, namelythe stability performance of the system declines when the content of PMN–PTc(v) increases and the electrostrictive coefficients increase. The results are beneficial for us tounderstand deeply the influence of the filled particle on the stability performance of siliconeand to guide the design and manufacture of actuators and sensors based on dielectricelastomers.

Boundary layers in fibrous composite materials

Many studies in the theory of composite materials are based on the homogenization approach, which consists of the substitution of the original heterogeneous medium by a homogeneous one with certain effective properties. Though this procedure works well for the entire composite solid, it cannot be applied in the vicinity of the outer boundary. The transmission of an external load applied at the boundary to the inner domain of the material occurs by a redistribution of stresses between the constitutive components (inclusions and matrix) and involves strong singularities in the local stress field, which may result in microscopic failure of the composite structure. In the present paper, we propose an approximate analytical procedure, allowing determination of the stress–strain field in the vicinity of the outer boundaries of fibre-reinforced composite materials. It is also shown that controlled decrease in bonding between the components leads to a more uniform redistribution of local stresses, which can essentially reduce the risk of failure.

The effective stiffness of a nanoporous rod

279 Many nanomaterials have abnormal physical prop� erties, which differ considerably from the properties of bulk materials. One of the explanations for these dif� ferences consists in the presence of surface effects, the role of which can be extremely large for nanodimen� sional structures in comparison with those in classical mechanics [1]. The purpose of this work is analysis of the influence of surface effects on the elastic characteristics of nan� oporous materials. Two models are considered. The first one is based on taking into account the surface stresses [1–4]. The surface stresses τ are the generali� zation of the surface tension known in the theory of capillarity for the case of solids. As is shown in [1, 5], taking into account surface stresses results in increas� ing stiffness of nanoporous materials. This phenome� non is similar to increasing flexural stiffness of nano� plates in comparison with the plates of macroscopic sizes [6, 7]. The second model uses the approach of the theory of composite materials [8–10]. In this approach, the surface effects are taken into account due to the surface layer of finite thickness with elastic moduli differing from those of the basic material (the matrix). Here the increase or decrease in the rod stiff� ness depends on the relation between the elastic mod� uli of the surface layer and the matrix. The effective stiffness can both decrease and increase with decreas� ing pore radius. On the basis of these two approaches, we proposed a complex model combining both the presence of surface stresses and the surface layer with the properties that differ from those of the matrix. PROBLEM FORMULATION We consider the problem on the tension–compres� sion of a linear elastic rectilinear rod. Let the rod have a circular cross section of radius R. We consider that n cylindrical pores with identical radii r (Fig. 1) are located in parallel to the rod axis. We designate the area occupied with pores in the rod cross section as S = πnr 2 . We assume also that the rod cross section is symmetric so that it is not subjected to bending under tension. A regularly distributed load, which is stati� cally equivalent to forces P, acts on the rod end faces. We designate the Young’s modulus of the rod mate� rial as E. For a large number (n � 1) of pores, the rod can be considered as a homogeneous cylinder made of transversally isotropic material. We designate the cor� responding effective longitudinal Young’s modulus

Self-Consistent Micromechanics Models of an Asphalt Mixture

An asphalt mixture is a composite material consisting of three components: asphalt binder, aggregate, and air. The mechanical properties of asphalt mixtures are mostly evaluated from empirical approaches that are usually limited to measurement conditions. This paper takes a mechanistic approach by using micromechanics theory for composite materials to develop self-consistent micromechanics models for an asphalt mixture. The mixture analysis method described in this paper is applied to measured properties of an asphalt concrete mixture that is commonly used in Texas. These models are programmed in MATLAB using the system identification method and are applied to the analysis of the frequency-dependent magnitudes of the viscoelastic properties of an asphalt mixture at different aging periods. The inverse micromechanics model takes as input the volumetric composition of the mixture and the measured frequency-dependent bulk and shear properties of the asphalt mixture and the binder and extracts from them the bulk and shear properties of the aggregate. The forward micromechanics model takes as input the frequency-dependent bulk and shear properties of the aggregate and binder and produces the frequency-dependent properties of the asphalt mixture. It has been demonstrated that the inverse and forward micromechanics models are in fact the inverse of each other and that the inferred aggregate properties are realistic. These models provide a technique to catalog the properties of aggregates and use them in a computerized determination of the combinations of binders, aggregates, and air to produce the desired properties of asphalt mixtures.

The Modulus of Fibroblast-Populated Collagen Gels is not Determined by Final Collagen and Cell Concentration: Experiments and an Inclusion-Based Model

The fibroblast-populated collagen lattice is an attractive model tissue for in vitro studies of cell behavior and as the basis for bioartificial tissues. In spite of its simplicity-containing only collagen and cells-the system is surprisingly difficult to describe mechanically because of the ability of the cells to remodel the matrix, including compaction at short times and synthesis and/or degradation (and cell proliferation) at longer times. The objectives of this work were to measure the equilibrium modulus of fibroblast-populated gels with different collagen and cell concentrations, and to use that characterization as the basis for a theoretical model that could be used to predict gel mechanics based on conditions. Although many observations were as expected (e.g., the gel compacts more when there are more cells in it, and the gel is stiffer when there is more collagen in it), an unexpected result arose: the final modulus of the gel was not dependent solely on the final composition. Even if it compacted more than a gel that was originally at a high collagen concentration, a gel that started at a low collagen concentration remained less stiff than the higher-concentration gel. In light of these results and experimental studies by others, we propose a model in which the gel compaction is not homogeneous but consists instead of extreme densification near the cells in an otherwise unchanged matrix. By treating the dense regions as spherical inclusions, we used classical composite material theory to develop an expression for the modulus of a compacted gel based on the initial collagen density and the final inclusion (i.e., cell) density. The new model fit the data for moderately compacted gels well but broke down, as expected, for larger volume fractions at which the underlying model assumptions did not apply.

Poroelastic Evaluation of Fluid Movement Through the Lacunocanalicular System

A poroelastic lacunocanalicular model was developed for the quantification of physiologically relevant parameters related to bone fluid flow. The canalicular and lacunar microstructures were explicitly represented by a dual-continuum poroelastic model. Effective material properties were calculated using the theory of composite materials. Porosity and permeability values were determined using capillaric and spherical-shell models for the canalicular and lacunar microstructures, respectively. Pore fluid pressure and fluid shear stress were calculated in response to simulated mechanical loading applied over a range of frequencies. Species transport was simulated with convective and diffusive flow, and osteocyte consumption of nutrients was incorporated. With the calculated parameter values, realistic pore fluid pressure and fluid shear stress responses were predicted and shown to be consistent with previous experimental and theoretical studies. Stress-induced fluid flow was highlighted as a potent means of species transport, and the importance of high-magnitude low-frequency loading on osteocyte nutrition was demonstrated. This new model can serve as the foundation for future hierarchical modeling efforts that may provide insight into the underlying mechanisms of mechanotransduction and functional adaptation of bone.

Dynamic stability analysis of an elastic composite material having a negative-stiffness phase

The rigorous classical bounds of elastic composite materials theory provide limits on the achievable composite stiffnesses in terms of the properties and arrangements of the composite's constituents. These bounds result from the assumption, presumably made for stability reasons, that each constituent material must have positive-definite elastic moduli. If this assumption is relaxed, recently published elasticity analyses and experimental measurements show these bounds can be greatly exceeded, resulting in new materials of enormous potential. The key question is whether a composite material having a non-positive-definite constituent can be stable overall in the practically useful situation of applied traction boundary conditions. Drugan [2007. Elastic composite materials having a negative-stiffness phase can be stable. Phys. Rev. Lett. 98 (5), article no. 055502] first proved the answer is yes, by applying the energy criterion of elastic stability to the basic two- and three-dimensional composites consisting of a cylinder or sphere having non-positive-definite (but strongly elliptic) moduli with a thin positive-definite coating and proving overall stability provided the coating is sufficiently stiff. Here, we perform a complete and direct dynamic stability analysis of the plane strain fundamental elastic composite consisting of a circular cylinder of non-positive-definite material firmly bonded to a positive-definite concentric coating, for the full range of coating thicknesses (i.e., volume fractions). We determine quantitatively the full permissible range of inclusion and coating moduli, as a function of coating thickness, for which the overall composite is stable under dead traction boundary conditions. Among the results, we show that in the thin-coating case, the present dynamic stability analysis leads to precisely the same analytical stability requirements as those derived via the energy criterion by Drugan [2007. Elastic composite materials having a negative-stiffness phase can be stable. Phys. Rev. Lett. 98 (5), article no. 055502], and we derive new analytical stability requirements that are valid for a wider range of coating thickness. At the other extreme, we show that in the case of very thick coatings (corresponding to the dilute case of a matrix-inclusion composite), even an inclusion with merely strongly elliptic moduli can be stabilized by a positive-definite matrix satisfying weak requirements, for which we derive analytical expressions. Overall, our results show that surprisingly weak restrictions on the moduli and thickness of the positive-definite coating are sufficient to stabilize a non-positive-definite inclusion, even one whose moduli are merely strongly elliptic. These results legitimize expanding the search for novel materials with extreme properties to those incorporating a non-positive-definite constituent, and they provide quantitative restrictions on the constituent materials’ moduli and volume fractions, for the geometry examined here, that ensure overall stability of such composite materials.

Effective thermoelastic properties of discrete-fiber reinforced materials with transversally-isotropic components

In the present paper, we will illustrate the application of the method of conditional moments by constructing the algorithm for determination of the effective elastic properties of composites from the given elastic constants of the components and geometrical parameters of inclusions. A special case of two-component matrix composite with randomly distributed unidirectional spheroidal inclusions is considered. To this end it is assumed that the components of the composite show transversally isotropic symmetry of thermoelastic properties and that the axes of symmetry of the thermoelastic properties of the matrix and inclusions coincide with the coordinate axis x3. As a numerical example a composite based on carbon inclusions and epoxide matrix is investigated. The dependencies of Young's moduli, Poisson's ratios and shear modulus from the concentration of inclusions and for certain values which characterize the shape of inclusions are analyzed. The results are compared and discussed in context with other theoretical predictions and experimental data. The problem of finding the macroscopic properties of composites from those of its constituents is both practi- cally and theoretically important and currently attracts much attention. The corresponding theory for compos- ites with isotropic components is rather well developed, including different approaches to the problem with varying degrees of mathematical precision and physical relevance. An important direction in the theory of composite materials is the investigation of overall properties of randomly inhomogeneous media. The main three methods for studying randomly inhomogeneous media are based on perturbation theory, ad hoc assumptions to truncate a hierarchy, and variational principles. Pertur- bation theory works well for media whose properties vary only slightly from point to point. If composites are strongly heterogeneous the necessity of using other approximations is inevitable in practice. Thus exact esti- mates were determined for the effective properties of ad hoc models of composites by various authors; rigorous variational bounds were given for the properties of random composites, and precise definitions and explicit "homogenization" formulae were first proposed for properties of periodic composites and then developed for stochastic one's ("stochastic homogenization" theory). A comparative analysis of different approaches, but by

Ultrasound aided extrusion process for preparation of polyolefin–clay nanocomposites

AbstractA continuous ultrasound assisted process using a single screw compounding extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites. High‐density polyethylene and isotactic polypropylene were compared. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology, and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. Similarities and differences of obtained nanocomposites are discussed based on their properties and structural characteristics. The modified Halpin‐Tsai theory of composite materials has been employed in order to predict the effect of incomplete exfoliation of clay platelets on the Young's modulus of the nanocomposites. A good agreement between experimental and theoretical data has been observed when reduction of the reinforcement efficiency of clay had been incorporated through the reduced aspect ratio of elementary clay platelets. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Effect of porosity on the elastic properties of porcelainized stoneware tiles by a multi-layered model

Porcelainized stoneware represents a leading product in the world market of ceramic tiles, thanks to its relevant bending strength (with respect to other classes of tiles) and extremely low water absorption: these properties derive from its really low content of residual porosity. Nevertheless, an accurate investigation of the cross section of a porcelainized stoneware tile reveals a non-uniform distribution of the residual pores through the thickness, which results in a spatial gradient of properties. Porcelainized stoneware, therefore, may be looked at as a functionally graded material. In the present research, commercial porcelainized stonewares were analysed in order to define the effect of the residual porosity and its spatial distribution on the mechanical properties of tiles. Polished cross sections of porcelainized stoneware tiles were investigated by optical and scanning electron microscopy in order to define the content and distribution of residual pores as a function of distance from the working surface. For each porcelainized stoneware, the local elastic properties of the ceramic matrix were measured by a depth-sensing Vickers micro-indentation technique, then the so-obtained microstructural images and elastic properties were used to model the stoneware tile mechanical properties. In particular, the cross section of each tile was described as a multi-layered system, each layer of which was considered as a composite material formed by a ceramic matrix and residual pores. The elastic properties of each layer were predicted by applying analytical equations derived from the theory of composite materials and, as a new approach, by performing microstructure-based finite element simulations. In order to validate the proposed multi-layered model and identify the most reliable predictive technique, the numerical results were compared with experimental data obtained by a resonance-based method.

Constitutive modeling of solid propellant materials with evolving microstructural damage

Solid propellants are composite materials with complex microstructure. In a generic form, the material consists of polymeric binder, crystal oxidizer (e.g., ammonium perchlorate), and fuel particles (e.g., aluminum). Severe stressing and extreme temperatures induce damage which is manifested in particle cracking, dewetting along particle/polymer interfaces, void nucleation and growth. Damage complicates the overall constitutive response of a solid propellant over and above the complexities associated with the differing constitutive properties of the particle and binder phases. Using rigorous homogenization theory for composite materials, we propose a general 3-D nonlinear macroscopic constitutive law that models microstructural damage evolution upon straining through continuous void formation and growth. The law addresses the viscous deformation rate within the framework of additive decomposition of the deformation rate and the concept of back stress is used to improve the model performance in stress relaxation. No restriction is placed on the magnitude of the strains. Experimental data from the standard relaxation and uniaxial tension tests are used to calibrate the model parameters in the case of a high elongation solid propellant. It is emphasized that the model parameters are descriptors of individual phase constitutive response and criticality conditions for particle decohesion which can systematically be determined through experiment. The model is used to predict the response of the material under more complex loading paths and to investigate the effect of crack tip damage on the mechanical behavior of a compact tension fracture specimen.