Multiphase Composite Materials Research Articles

Compositional Design of Multiphase Composite Ceramic Tool Material Based on the Thermal Shock Resistance and Its Application

Thermal shock resistance is one of the primary properties for the ceramic cutting tool materials with perspectives in high speed machining. An optimum model for the compositional design of the composite ceramic tool materials is built based on the thermal shock resistance. The thermal stress fracture resistance factor R is used to characterize the thermal shock resistance of the ceramic material. Results show that the developed (W,Ti)C/SiC/Al2O3 multiphase ceramic tool material can be expected to achieve the highest thermal shock resistance when the volume fraction of (W,Ti)C and SiC is about 15.8% and 24.8%, respectively. Thermal fracture resistance of the (W,Ti)C/SiC/Al2O3 ceramic tool material is approximately 81-88% higher than that of the pure alumina ceramic when machining the hardened carbon steel, which coincides well with the theoretical prediction from the optimum model. It suggests that the method used here is feasible for the development of ceramic tool materials with designed thermal shock resistance.

Preparation and performance of an advanced multiphase composite ceramic material

According to the optimum composition achieved from the material design, an advanced 15 vol.% SiC and 15 vol.% Ti(C,N) containing alumina-based multiphase ceramic material with good comprehensive mechanical properties has been fabricated with hot pressing technique. Only under suitable hot pressing conditions and material compositions can better microstructures and mechanical properties be achieved. The optimum hot pressing parameters for the SiC/Ti(C,N)/Al 2O 3 material are as follows: the hot pressing temperature is 1780 °C, the time duration equals to 60 min and the pressure remains 35 MPa. The content of each dispersed SiC and Ti(C,N) phase has significant effects not only on the mechanical properties but on the engineering performances of the ceramic materials. Good wear resistance is found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel. Failure mechanisms are mainly the abrasive wear and the adhesive wear. The developed SiC/Ti(C,N)/Al 2O 3 multiphase ceramic material will be well used as the structural parts with the requirement of high wear resistance such as cutting tools.

Investigation into Waste Tire Rubber-Filled Concrete

Over the years, there has been mounting interest in the use of recycled tire rubbers in highway construction. Tire rubber-filled concrete, a rubberized Portland cement concrete with a portion of aggregates replaced by tire rubber particles, represents an alternative of using recycled tire rubbers. It is found that rubberized concrete has very high toughness. However, its strength decreases significantly as the rubber content increases. This limits its application to secondary structural components only. Very little progress has been made in increasing the strength of rubberized concrete due to the lack of understanding of the toughing mechanism. In this study, rubberized concrete was treated as a multiphase particulate-filled composite material. A modified three-layer built-in composite model was proposed based on a previous study on ordinary concrete. Finite element analysis was conducted on the developed composite model. Cylindrical rubberized concrete samples and ordinary concrete samples were prepared and tested to provide basic physical/mechanical properties in the analysis. The effect of various design parameters on the composite strength was evaluated. The finite element analysis validated the test results.

Layered versus multiphase magneto-electro-elastic composites

Several researchers have focused on developing material properties for homogeneous magneto-electro-elastic multiphase composite materials. The candidate materials for this study are piezoelectric BaTiO 3 barium titanate as the embedded material with magnetostrictive CoFe 2O 4 cobalt iron oxide as the matrix material. The materials are evaluated in terms of modeling the physical problem of the free vibration an infinite plate. Multiphase material properties vary depending upon the ratio of fiber material to matrix material. Actual electromagnetic materials are modeled as layered materials with the ratio of constituent materials being controlled by varying the number and thickness of layers of each material. Frequencies of vibration are compared for the layered materials versus the multiphase materials as a measure of the accurateness of the derived material constants. Multiphase material predictions for frequency agree quite well with layered materials for the problem that is studied.

Mechanical properties of multiphase materials and rocks: a phenomenological approach using generalized means

Difficulties associated with specifying details of microstructure and distributions of internal stress and strain within multiphase rocks prompt the development of semi-empirical models to connect the effective properties of composites to the properties of their components. We apply here generalized means to describe the elastic moduli ( E, K and G) and flow strength of an isotropic multiphase composite material in terms of its component properties, volume fractions and microstructures. The microstructures are expressed by a scaling parameter J, which is mainly controlled by the shape and distribution (continuity and connectivity) of the phases. The case J=1 yields the arithmetic mean or Voigt average and the case J=−1 yields the harmonic mean or Reuss average. The geometrical mean occurs as J approaches zero. The means with J=−0.5 or J=0.5 provides good agreement with the experimental data of Young's modulus for the two-phase composites in which strong or weak inclusions are shaped like spheres isolated in a continuous host medium. For most composite materials in which the inclusions are of somewhat arbitrary geometry, the means with J=−0.25 and J=0.25 do well at predicting the measured values of Young's modulus for those with weak-phase continuous (the volume fraction of strong phase f s≤0.5) and strong-phase continuous ( f s≥0.7) structures, respectively. In the intermediate range (0.5≤ f s≤0.7), J is expected to vary progressively from −0.5 to 0.5 or from −0.25 to 0.25 due to the transition in microstructure. Thus the generalized means offer a promising, phenomenological approach for the prediction of elastic and rheological properties of multiphase materials and rocks, especially for those consisting of more than two unlike phases. As an example, the approach is applied to interpret the sharpness of the 410-km seismic discontinuity as a corollary of the transition from an olivine- to a wadsleyite-dominant structure.

Generalized means as an approach for predicting Young’s moduli of multiphase materials

Difficulties associated with specifying details of microstructure and distributions of internal stress and strain within multiphase materials prompt the development of semi-empirical models to connect the effective properties of composites to the properties of the components. We propose here the generalized means as an approach for predicting the Young’s modulus ( E) of an isotropic multiphase composite material in terms of its component properties, volume fractions, and microstructures. The microstructures are expressed by a scaling parameter J, which is mainly controlled by the phase geometry, continuity, and connectivity. The case J=1 yields the arithmetic mean or Voigt average and the case J=−1 yields the harmonic mean or Reuss average. The geometrical mean occurs as J approaches 0. The means with J=−0.25 and J=0.25 provide a quite good agreement with the experimental data of Young’s modulus for a wide variety of two-phase composites with weak-phase continuous ( V s≤0.5) and strong-phase continuous ( V s≥0.7) structures, respectively. In the intermediate range (0.5≤ V s≤0.7), J is expected to vary progressively from −0.25 to 0.25 due to the transition in microstructure. For porous materials (e.g., glass foams) with non-interconnecting spherical pores, J=∼0.5. Thus the generalized means offers a promising approach for the prediction of elastic properties of multiphase materials if the microstructural exponent J has been determined.

Critical resistance for multi-phase composite materials

The effect of interfacial resistance on the effective conductivity of a multi-phase composite material was studied. The composite under study is composed of a matrix surrounding different types of circular cylinders arranged in rectangular order. It was assumed that the interfacial resistance is concentrated on the surface of the cylinders. For any direction of calculating the effective conductivity of the system, a condition was found in which the effect of cylinders of one type can be neglected. This condition may be estimated by R⩽ k−1, where R and k are the non-dimensional interfacial resistance and the relative conductivity of the neglected cylinders, respectively. The case R= k−1 applies when the same relation exists between the interfacial resistance and conductivity of all types of cylinders.

Computer simulation of the temperature field in the hot pressing process of multi-phase composite ceramic material

Models of the heat transfer in the hot pressing process of ceramic materials have been built theoretically. Then, with the example of Al 2O 3/SiC/(W, Ti)C multi-phase composite ceramic material, designs of the hot pressing technology are made through the study of the temperature field in the ceramic blanks by means of computer simulation. It is shown that the heating and cooling rate and the existence of voids before sintering have great effects on the temperature field in the ceramic blanks. Under the experimental conditions, it is found suitable for the heating and cooling rates to be 0.5–0.75 and 0.33 °C/s, respectively, through comprehensive consideration of the requirements of both the material properties and the manufacturing efficiency. From the view of the temperature field, the ceramic blanks should be cold-pressed first before hot pressing. Thus, the initial relative density of the blanks can be increased and the temperature difference can be reduced. As a result, the physical and mechanical properties of the ceramic material will be improved further.

On predicting elastic moduli and natural frequencies of multi-phase composites with randomly distributed short fibers

This study presents a formulation to determine the overall stiffness of an n-phase short fiber composite to include the inclusions' aspect ratio ranging from less than one to greater than one. The Mori-Tanaka theory is initially employed to investigate the overall stress-strain relation of a multi-phase short-fiber-reinforced composite material, particularly whether or not the fibers and the matrix are isotropic, cubic, or transversely isotropic material. The effective stiffness tensor of a multi-phase composite is then denoted as a function of the matrix's elastic moduli, the n-phases' inclusions' elastic moduli, the n-phases' inclusions' Eshelby tensor, and the n-phases' inclusions' volume fractions. Utilizing the equivalent inclusion method allows us to model inclusions of n-phases that consist of fictitious eigenstrains. In addition, the corresponding Eshelby tensors' values for ellipsoidal inclusion embedded in the isotropic matrix with the variation of aspect ratio are presented. Numerical results of the proposed formulation in solving a two-phase composite closely correspond to the Halpin-Tsai Equation. Results presented herein provide valuable information on the appropriate manufacturing requirements of multi-phase composite materials or the design and optimization of multi-phase composite structures.

On micromechanics approximation for the effective thermoelastic moduli of multi-phase composite materials

It has been shown that for multi-phase composite materials, the Mori–Tanaka and self-consistent approaches may give non-symmetric effective moduli, may violate some exact connections between the effective moduli, may violate the Hashin–Shtrikman variational bounds, and may exhibit incorrect behavior at the unitary (100%) reinforcement concentration limit. An effective-medium-field micromechanics approximation using normalized concentration factors is proposed and is shown to overcome these difficulties. Such a normalization is necessary to satisfy the consistency relationship.

A hygro-thermo-mechanical constitutive model for multiphase composite materials

The paper describes a hygro-thermo-mechanical constitutive model appropriate for numerical simulation of multiphase composite material behaviour. The theory is based on the mixture of the basic substances of the composite and allows to evaluate the inter-dependent behaviour between the different compounding constitutive models. The initial anisotropy of each compounding can be taken into account by means of a mapped isotropic plastic formulation. This is a generalization of classic isotropic plasticity theory applied to orthotropic or anisotropic materials. The basic assumption is the existence of a stress and strain real anisotropic spaces and the respective fictitious isotropic spaces where a mapped fictitious problem is solved. Those spaces are related by means of two fourth order transformation tensor. The combination of mixing theory and the mapped isotropic plastic approach provides a powerful constitutive framework for the numerical treatment of bulk-fiber composite materials.

A plastic damage constitutive model for composite materials

In this paper a generalized elasto-plastic damage model for the analysis of multiphase frictional composite materials is presented. Details of the derivation of the secant and tangent constitutive equations are given. Mixing theory is used to insert the basic constitutive expressions for each substance on the multiphase composite solid. Details of the numerical implementation of the model into a general non-linear finite element solution scheme are presented. Some examples of linear and non-linear behaviour of composites are given.

Calculation of deformative and thermal properties of multiphase composite materials filled with composite or hollow spherical inclusions by the effective medium method

A theoretical investigation was carried out to examine the possibilities of a structural approach to prediction of elastic constants, creep functions, and thermal properties of multiphase polymer composite materials filled with composite or hollow spherical Inclusions of several types. The problem of determining effective properties of the composite was solved by generalizing the effective medium method, a variant of the self-consistent method, for the case of a four-phase kernel-shell-matrix-equivalent homogeneous medium model. Exact analytical expressions for the bulk modulus thermal expansion coefficient, thermal conductivity coefficient, and specific heat were obtained. The solution for the shear modulus is given in the form of a nonlinear equation whose coefficients are the solution of a system of 12 linear equations.

The effect of interphase on overall average mechanical properties and local stress fields of multi-phase medium materials

Using the self-consistent model, a self-consistent finite element method (SCFEM) is presented for the prediction of overall mechanical properties of multi-phase composite materials with an interphase. Numerical results are presented for typical composite materials with different volume fractions and interphase thicknesses. The results show that interphase thickness affects the overall average transverse shear modulus and bulk modulus considerably, but influences the longitudinal Young's modulus only slightly. The paper is also concerned with the evaluation of local stress fields in the interphase region.

Effect of imperfect interphase on overall average mechanical properties and local stress fields of multiphase composite materials

The effect of an imperfect interphase on the overall average transverse mechanical properties of multiphase composite materials is investigated using a generalized self-consistent iterative method, which is developed on the basis of earlier work by the present authors. Numerical results are presented for typical composite materials with different volume fractions and characteristics of imperfect interphase. The numerical evaluation has shown that the extent and thickness of the imperfect interphase may have a significant effect on the overall average transverse plane strain bulk and shear moduli. The paper is also concerned with the evaluation of local stress fields in the imperfect interphase region.

An improved model for simulating impedance spectroscopy

A numerical method for simulating the frequency-dependent impedance response of multi-phase composite materials has been developed. The algorithm takes as input 1) a digital image of a microstructure, in two or three dimensions, of any specified composite material, and 2) the frequency-dependent electrical properties of the individual phases of the composite. An impedance spectrum of any frequency range can then be computed using a conjugate gradient algorithm operating on a finite difference solution scheme of Laplace's equation. Examples are given of the impedance of analytically solvable microstructures, to validate the algorithm, and of a random system, to test the usefulness of two different effective medium theories.

Effect of imperfect interphase on overall average mechanical properties and local stress fields of multiphase composite materials

The effect of an imperfect interphase on the overall average transverse mechanical properties of multiphase composite materials is investigated using a generalized self-consistent iterative method, which is developed on the basis of earlier work by the present authors. Numerical results are presented for typical composite materials with different volume fractions and characteristics of imperfect interphase. The numerical evaluation has shown that the extent and thickness of the imperfect interphase may have a significant effect on the overall average transverse plane strain bulk and shear moduli. The paper is also concerned with the evaluation of local stress fields in the imperfect interphase region.

Chemically Bonded Ceramics as an Alternative to High Temperature Composite Processing

ABSTRACTProcessing of multi-phase ceramic composite materials using chemically bonded ceramics as a binding agent appears to be a promising route for fabricating complex-shaped structures. In a zirconia-calcium aluminate ceramic matrix composite, the hydraulic property of fine, monocalcium aluminate (CaAl2O4) powders was used to prepare strong prefired bodies.The changes in the physical characteristics of the composite during the conversion from a chemically bonded compact into a sintered composite were studied using thermogravimetric analyses (TGA), X-ray diffraction and scanning electron microscopy. The density and the hardness of the chemically bonded and sintered composite were measured.

Finite Element Analysis of Multiphase Viscoelastic Solids

The properties of composite solids containing multiple, viscoelastic phases are studied numerically. The dynamic correspondence principle of viscoelasticity is utilized in a finite element model to solve boundary value problems for obtaining global complex moduli of the composite. This numerical procedure accounts for the coupled interactive deformation of the phases and thus the resultant accuracy is limited only by that of finite element analyses in general. The example composite considered in this study contains cylindrical viscoelastic inclusions embedded in a viscoelastic matrix. This investigation focuses on the global composite moduli and their relationship to the individual phase properties as a function of volume fraction. A given phase material is shown to have differing effects on the composite properties, depending on whether it is the continuous or the included phase: In general, the composite moduli are dominated by the matrix material. Comparison is made with two simple analytical models for global effective moduli of composites. “Upper Bounds” reproduce the behavior over the whole frequency range when the matrix is the “stiffer” of the two solids while the “lower bond” associates with the converse arrangement, also over the whole frequency range. The nature of time-temperature behavior of multiphase composite materials is examined in a companion paper.

Mori-Tanaka Estimates of the Overall Elastic Moduli of Certain Composite Materials

Simple, explicit formulae are derived for estimates of the effective elastic moduli of several multiphase composite materials with the Mori-Tanaka method. Specific results are given for composites reinforced by aligned or randomly oriented, transversely isotropic fibers or platelets, and for fibrous systems reinforced by aligned, cylindrically orthotropic fibers.