The plastic flow characteristics of cellular materials containing a large proportion of voids are discussed. A very low Poisson's ratio and a tendency toward orderly cellular collapse are identified as important characteristics of such materials.
Compression studies reveal the appearance of slightly inclined Luder's-like bands and upper and lower yield points resembling those observed in mild steel. A simple cellular collapse mechanism is shown to be consistent with all observed behavior.
The yield criterion for a cellular material is found to be the maximum compressive stress when experiments are performed on foamed polystyrene under a variety of loading conditions.
The deformation properties of cellular materials are also investigated for conditions of localized loading. The ratio of hardness to compressive flow stress that is normally close to three for ordinary metals is found to be close to one for a cellular material having a very low Poisson's ratio. The ratio of hardness to flow stress is shown to vary from one to three as the plastic Poisson's ratio goes from 0 to 12.