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Anisotropy and variability in polyurethane foams: experiments and modeling

Authors:  B. Kraus, R. Das, B. Banerjee

Abstract:

Modern foam-filled composite products have the advantage of low weight while providing improved shock absorption, acoustic, and thermal properties.  Recent investigations of foam-filled thin metal open sections have shown that these composites also have excellent structural properties.  However, when optimizing new foam-filled products for structural applications, the material behaviour of each constituent material has to be known before simulations can be performed and potential failure predicted.  This paper presents the results of mechanical characterization tests of a low density polyurethane (PU) foam and describes a new anisotropic plasticity model that can be used for large deformation simulations of foams and foam-filled composites.  Uniaxial tension and compression, triaxial compression, simple shear, and fracture toughness tests on the PU foam are described.  These tests indicate that the foam is strongly anisotropic, exhibits a significant amount of variation between samples, and that a non-associated flow rule is needed for predictive simulations.  The new piriform (pear-shaped) anisotropic yield surface is convex, has excellent smoothness properties, is able to predict the observed behavior of the foam, and reduces to an ellipsoidal form for some choices of parameters.  The yield function has the potential to be applied to a large variety of foams as well as soils, rocks, bone, and concrete.

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Elastic Anisotropy:

Piriform yield surface:

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