Macroscopic elastic properties of randomly packed balloons

Abstract

Macroscopic elastic properties of sintered, randomly packed balloons are estimated for various degrees of sintering and for a wide range of balloon wall thickness. Macroscopic elastic moduli are little affected by a balloon's inner/outer, diameter ratio for thicker balloons, while those of thinner balloons are very sensitive to the ratio. The elastic moduli rapidly decline with decreasing wall thickness. They are larger in the direction of gravity than in the horizontal one, corresponding to gravity-affected packing structures. Specific elastic moduli have a peak against porosity. Poisson's ratios are negative in some cases of very thin balloon walls and very low sintering degree. Comparison of the present random packing with the regular simple cubic packing reveals that there is a significant difference between them in their elastic properties and their structures of anisotropy, although both have almost the same coordination number.