Effective Moduli of Two-Layered Spherical Inclusions Reinforced Composites

A model is proposed to evaluate the,effective modufi of a composite reinforced by two-layered spherical inclusions.This model is based on the localisation problem of a two- layered spherical inclusion embedded in an infinite matrix.The interations of the reinforced phases are taken into account by using the average matrix stress concept.When the external layer vanishes,the proposed model reduces to the classical Mori-Tanaka's model for spherical inclusions.Theoretical results for the composite of polyester matrix filled by hollow glass spheres and voids show excellent agreement with experimental results.

Influence of spherical inclusions on effective thermoelectric properties of thermoelectric composite materials

A homogenization theory is developed to predict the influence of spherical inclusions on the effective thermoelectric properties of thermoelectric composite materials based on the general principles of thermodynamics and Mori-Tanaka method.The closed-form solutions of effective Seebeck coefficient,electric conductivity,heat conductivity,and figure of merit for such thermoelectric materials are obtained by solving the nonlinear coupled transport equations of electricity and heat.It is found that the effective figure of merit of thermoelectric material containing spherical inclusions can be higher than that of each constituent in the absence of size effect and interface effect.Some interesting examples of actual thermoelectric composites with spherical inclusions,such as insulated cavities,inclusions subjected to conductive electric and heat exchange and thermoelectric inclusions,are considered,and the numerical results lead to the conclusion that considerable enhancement of the effective figure of merit is achievable by introducing inclusions.In this paper,we provide a theoretical foundation for analytically and computationally treating the thermoelectric composites with more complicated inclusion structures,and thus pointing out a new route to their design and optimization.

Elastic Properties of Particulate Composites with Imperfect Interface

An effective analytical approach is developed for the problem of pardculate composites containing spherical inclusion with imperfect interface between the matrix and spherical inclusions. In this paper, a general interface model for a variety of interfaced defects has been presented, in which both displacement discontinuity across the interface and the elastic moduli varing with radius outside of the inclusion are considered, The imperfect interface conditions are appropriate in the case of thin coatings on the inclusion. Furthermore, in the case of thin elastic interphase, the displacement field and the stress field in the inclusion and matrix are exactly solved for the boundary problem of hydrostatic compression of an infinite spherical symmetrical body by Frobenius series , and the expression of the normal interface parameter, Dr, is derived. In addition, it has been proved that two previous results derived in some literatures by considering the interface to be a thin interphase with displacement jump or with some variance in its moduli can be reverted from the present formula, respectively. Numerical results are given to demonstrate the significance of the general imperfect interface effects.

Formation Mechanism of Inclusion Defects in Large Forged Pieces

Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects.For upset forging,the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece.The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally.The results show how,during upsetting,the morphology of MnS plastic inclusions varies from spherical to ellipsoidal,until finally becoming flat in shape.The larger the inclusion is,the larger the degree of deformation of the inclusion is,and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws.Strain significantly concentrates in the matrix near a hard inclusion.When the hard inclusion reaches a certain size,conical fractures form on both sides of the inclusion.To pass inclusion-flaw inspection and close hole defects to the extent possible,the flat-anvil upsetting is recommended.Finally,the inclusiondeformation state obtained by finite element simulation is verified experimentally.

BOUNDARY INTEGRAL EQUATIONS FOR ISOTROPIC LINEAR ELASTICITY

This articles first investigates boundary integral operators for the three-dimensional isotropic linear elasticity of a biphasic model with piecewise constant Lam´e coefficients in the form of a bounded domain of arbitrary shape surrounded by a background material.In the simple case of a spherical inclusion,the vector spherical harmonics consist of eigenfunctions of the single and double layer boundary operators and we provide their spectra.Further,in the case of many spherical inclusions with isotropic materials,each with its own set of Lam´e parameters,we propose an integral equation and a subsequent Galerkin discretization using the vector spherical harmonics and apply the discretization to several numerical test cases.