The micromechanics involved in increased crack growth resistance, KR, due to the addition of TiBz particulate in a SIC matrix was analyzed both experimentally and theoretically. The fractography evidence, in which, the advancing crack was attracted to adjacent particulates, was attributed to the tensile region surrounding a particulate. Countering this effect is the compressive thermal residual stress, which results in the toughening of the composite, in the matrix. This thermal residual stress field in a particulate-reinforced ceramic-matrix composite is induced by the mismatch in the coefficients of thermal expansion of the matrix and the particulate when the composite is cooled from the processing to room temperature. The increase in K R of the composite over the monolithic matrix, which was measured by using a hybrid experimental-numerical analysis, was 77%, and compared well with the analytically predicted increase of 52%. The increase in K R predicted by the crack deflection model was 14%. Dependence of K R on the volume fraction of particulates, &, and of voids, fv, is also discussed. [

This paper examines the effective thermal conductivity of a misoriented short fiber composite. The analysis is based on the equivalent inclusion method for steady-state heat conduction in composite which we have recently proposed. The present approach is unique in that it takes into account the interaction among fibers at different orientations. Closed form solutions are given for the thermal conductivity of a misoriented short fiber composite. Then, numerical results are presented to demonstrate the effects of volume fraction, fiber aspect ratio, and distribution function of fiber orientation on the thermal conductivity.

Enlarging the molecular size of zinc phthalocyanine (Pc) dyes three dimensionally with 2,6-diphenylphenoxy substituents significantly reduced the aggregation of the dyes on a TiO(2) surface. As a result, the incident photon-to-current conversion efficiency was improved not only in the Q band but over the whole absorption range, achieving 4.6% energy conversion efficiency under one-sun conditions. Electron lifetime measurements indicated that these Pc dyes do not enhance charge recombination, encouraging further development of Pc.

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A theoretical approach is forwarded to predict the electromechanical properties of porous piezoelectric ceramics. The analysis is able to account for the effects of porosity shape and concentration and is applicable to piezoelectric ceramics of arbitrary material symmetry. By coupling the exact solution for a single ellipsoidal pore embedded in an infinite piezoelectric matrix with an effective medium approximation, the theory considers, in an approximate manner, interaction effects at finite porosity concentrations. The theoretical estimates are developed using a matrix formulation which enables all elastic, dielectric, and piezoelectric moduli of the porous solid to be readily computed. Numerical results are presented to illustrate the effects of the shape and concentration of the porosity on the effective electroelastic moduli and transducer parameters of practical importance. Particular attention is devoted to assessing the sensitivity of the effective electromechanical properties to the accuracy of the input data. Finally, theoretical estimates are shown to be in good agreement with existing experimental results for porous piezoelectric ceramics with various microstructural geometries.