FAILURE OF POLYURETHANE FOAMS UNDER PLANE STRESS CONDITIONS

摘要

Trough this work the mechanical response of rigid polyurethane (PUR) foams has been successfully measured for a variety of plane stress loadings using a standard uniaxial universal testing machine equipped with special grips and a home-made video-extensometer. Specimen configurations included uniaxial tension and compression, restricted (biaxial) tension and compression, and simple shear. PUR foams behave in a brittle way with isotropic behaviour. SEM examination confirms that PUR failure is governed by cell wall bending, cell face stretching and brittle fracture under tensile loading, while cell wall bending and buckling followed by brittle crushing are dominant under compressive loads. Failure stresses dependence on foam's relative density was taken into account and a universal failure surface was obtained. Universal failure locus followed a theoretical criterion for brittle crushing of closed-cell foams capped by a theoretical elastic buckling criterion under compressive loadings.