Stress-Strain Relationships of Open-Cell Foams

Open-cell foams provide cushioning and precise positioning in medical applications. To design cushions and supporting surfaces with these types of foams, a thorough understanding of the foam material properties, such as the elastic tangent modulus, is needed. While these foam materials do not have the same type of stress-strain relationship as more traditional engineering materials, this relationship can be determined. Four types of foam material were tested according to the ASTM D-3574-91, “Standard Methods of Testing Flexible Cellular Materials-Slab, Bonded and Molded Urethane Foams”. The variation in stiffness among the materials was approximately an order of magnitude. The stress-strain relationships for all of the materials began with a linear region at small strains followed by a non-linear region at higher strains. The polyurethane materials also contained a linear transitional region which exhibited a reduced stiffness. The effect of applying a liquid proof coating to the foam was also investigated.