Influence of wavy imperfections in cell walls on elastic stiffness of cellular solids

The stiffness of open and closed cell low density cellular solids, or solid foams, is affected by "imperfections" such as non-uniform cell size (multi-dispersity), non-uniform cell wall thickness, wavy distortions of cell walls, etc. Metal foams generally have lower relative stiffnesses than, for example, expanded PVC based polymer foams, and a comparison of the morphologies suggests that the main difference between these cellular solids is wavy distortions of the cell walls of the metal foams. The influence of wavy distortions on stiffness is modeled in this paper. The concepts are introduced through application to open cell materials, for which closed form solutions are obtained, primarily to illustrate the phenomenon. Closed cell materials are analysed subsequently, and results that are considered to be in good agreement with experimental observations are obtained. (C) 1997 Elsevier Science Ltd. All rights reserved.