A numerical study of large deformations of low-density elastomeric open-cell foams

A numerical study is presented of the mechanical properties of low-density open-cell polymer foams subjected to large deformations. The foams are modelled as three-dimensional frameworks of slender struts. Regular as well as random foams are analyzed, where the latter are generated using the Voronoi technique. The macroscopic mechanical properties are determined for various types of struts properties through unit-cell analyses containing many foam cells per unit-cell. The computations make use of standard Finite Element (FE) techniques. Bending of the struts dominates the mechanical foam response at low strains. Axial deformation of the struts becomes the dominant mechanism at larger tensile strains. Strut buckling becomes the main mechanism at larger compressive strains, and causes a significant decrease in load carrying capacity of the foam. The large strain mechanical behavior of foams is found to be dependent on the weakest cross-section of the foam appearing in the random foam structure, the so-called "minimum effective cross-section". The minimum effective cross-section determines the tangential foam modulus at large tensile strains. Regular foam structures have a uniform unit-cell cross-section and, as a result, a higher minimum effective cross-section than regular foam structures and, therefore, a higher tangent modulus in the large strain range.