Plastic deformation modes in rigid polyurethane foam under static loading

Abstract

The mechanical response of rigid polyurethane foam to compression in the rise and transverse directions was examined experimentally. Compression in the rise direction yields a three-stage stress-strain response-an initial linear elastic response leading to yield, a protracted post-yield plateau and a final sharp rise in compressive stress. Other prominent features accompanying this are strain-softening and deformation localisation. Compression in the transverse direction however, gives rise to a monotonously increasing stress-strain curve and always produces uniformly distributed deformation. This difference in deformation is attributed to anisotropy in the internal cellular structure that arises from the fabrication process. To describe deformation localisation in the foam rise direction, a simple theoretical analysis employing the concept of deformation bands is proposed. This analysis involves the parameters of deformation band thickness, band front propagation velocity, strain and strain rate within the band front, and is shown to correlate well with experiments. © 2001 Elsevier Science Ltd. All rights reserved.