Plastic deformation modes in rigid polyurethane foam under static loading

The mechanical response of rigid polyurethane foam to compression in the ri se and transverse directions was examined experimentally. Compression in th e rise direction yields a three-stage stress-strain response-an initial lin ear elastic response leading to yield, a protracted post-yield plateau and a final sharp rise in compressive stress. Other prominent features accompan ying 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 de formation localisation in the foam rise direction, a simple theoretical ana lysis employing the concept of deformation bands is proposed. This analysis involves the parameters of deformation band thickness, band front propagat ion velocity, strain and strain rate within the band front, and is shown to correlate well with experiments. (C) 2001 Elsevier Science Ltd. All rights reserved.