Stiffness predictions for closed-cell PVC foams

Light-weight polymeric foams are frequently used in composite sandwich construction in which foam core material properties could significantly influence the overall performance of the sandwich structure. Foam mechanical properties usually depend on a number of factors, including foam density, cell microstructure, and properties of foam–matrix polymer. Although the properties of foam–matrix polymer are determined mainly by the properties of the foam base (parent) polymer, they are also affected by other factors such as foam processing conditions. With the large number of material and microstructure parameters that influence foam properties, modeling mechanical behavior of polymeric foams could be quite involved, especially if foam behavior is anisotropic. This paper describes an effort to predict static elastic stiffness of closed-cell PVC foams. PVC foams are modeled as transversely isotropic materials with properties in the foam rise direction different from those in the planar (plane of isotropy) directions. An engineering approach, based on fibrous composites, is developed to predict in-plane and out-of-plane stiffness of PVC foams. The validity of the engineering model for the PVC foam stiffness is first demonstrated through comparison with test results on DIAB H80 foam obtained from a systematic in-house test program. Comparison of the predictions with the stiffness properties reported by a PVC foam manufacturer for various other density foams is also carried out. Good agreements are obtained for the cases studied. Comparison of stiffness predictions obtained in the paper with predictions from other published models of isotropic foam behavior is presented.