Stiffness and Strength Models for Rigid PVC Structural Foams

Abstract

Light-weight polymeric foams are frequently used as core materials in composite sandwich construction in which the core material properties will influence the overall performance of the sandwich structure. Foam core mechanical properties usually depend on a number of factors, including foam density, cell microstructure, and properties of the polymer matrix. Although properties of the foam matrix polymer are mainly determined by the 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 the foam properties, detailed modeling the mechanical behavior of polymeric foams could be quite involved, especially if the foam behavior is anisotropic. This paper describes an effort to model the elastic stiffness and strength of rigid PVC closed-cell foams. The rigid PVC foam is modeled as a transversely isotropic material with properties in the foam rise direction different from those in the planar (plane of isotropy) directions. An approximate theory is developed to predict in-plane and out-of-plane stiffnesses of PVC foams. Strength equations are also developed for predicting tensile, compressive, and shear properties of PVC foams. The validity of the stiffness and strength predictions for PVC foams is first demonstrated with the test results on DIAB H80 foam obtained from a systematic in-house test program. Comparison between stiffness and strength predictions with the material property data provided by the foam manufacturer for other density PVC foams are also carried out. Reasonable agreements are obtained which support the applicability and effectiveness of the proposed stiffness and strength models for assessing properties of PVC foams. Comparison of property predictions obtained in this paper with those from published models on mechanical properties is also discussed.