Negative thermal expansion from disc, cylindrical, and needle shaped inclusions

Abstract

The concept of reducing the thermal expansion of composites by exploiting the thinning that is observed when a conventional material is mechanically stretched (the Poisson's effect) is explored through finite elements (FE) simulations with the scope of assessing the potential of such systems to exhibit negative thermal expansion (NTE). It is shown that systems made from hard highly expanding needle, cylindrical or coin shaped inclusions embedded within a soft matrix with a high positive Poisson's ratio having low coefficients of thermal expansion may exhibit NTE under certain conditions. In the case of the coin-shaped inclusions, the NTE is maximum in the direction orthogonal to the surface of the coins and in the case of systems with needle-shaped inclusions, the NTE is maximum in the direction orthogonal to the length of the needles.