Effects of dispersed microvoids on thermal expansion behavior of compositematerials

In our earlier papers [T. Takei, H. Hatta, M. Taya, Mater. Sci. Eng. A131 ( 1991) 133; T. Takei, H. Hatta, M. Taya, Mater. Sci. Eng. A131 (1991) 145], we found that the coefficients of thermal expansion (CTEs) of particulate c omposites are lowered by dispersed microvoids in the matrix. In order to pr ove this void dispersion effect by an analytical model and to utilize this effect for wide control of composite CTE, an analytical parametric study is conducted in this paper. It is found in this study that the combination of fiber type reinforcement with high elastic modulus and low CTE and disk-sh aped voids was identified to remarkably lower the composite CTE. This CTE c ontrol technique is based on the mechanism that microvoids in the matrix ar e compressed by compressive stress field developed around reinforcement whe n the composite is subjected to temperature rise. In order to confirm exper imentally this void dispersion effect on CTEs, three types of composite mat erials with dispersed voids in their matrices were fabricated, particulate, short fiber, continuous fiber (3D) reinforced composites, and CTEs of thes e composites were measured. It was concluded from comparison between the pr edictions and experimentally observed CTEs that the CTE reduction by the vo id dispersion actually occurs and this effect is analytically predictable u p to some limit volume fraction, which depends on a composite type. (C) 200 0 Elsevier Science S.A. All rights reserved.