Models for the compressibility of layered polymeric sponges

The characteristic sigmoid compressive stress‐strain relationships of sponges and their layered arrays are described by two kinds of mathematical models having three experimentally determined parameters. Since sponge compression is not accompanied by a significant cross‐sectional area expansion, it was assumed that the stress in a multilayered array is the same in each layer. This enables prediction of the array's stress‐strain relationship from the parameters of the individual layers and their known thickness. The applicability of the method is demonstrated with experimental data of two kinds of double‐layered arrays of polyurethane sponges. It is shown that the arrays' compressive behavior can be satisfactorily predicted irrespective of the mathematical form of the model and whether the strain is expressed as engineering strain or Hencky's.