Creep compression behaviour of a polyurethane foam from cryogenic temperatures: size effect and long-term prediction

Abstract

The objective of this work was to predict the long term behavior of Polyurethane foam (PU) at very low-temperature, by applying the time-temperature superposition principle (TTSP). The experimental background of the TTSP was based on a Dynamical Mechanical Analysis technique. Two issues arise from this experimental approach: the relevance of the temperature range to apply the TTSP, and the possible size-effect associated to the small DMA samples. Firstly, on the studied temperature range (-170°C; +180°C) many transitions have been observed, particularly from -20°C. Thus to apply the TTSP, it would be necessary to limit the temperature range (between temperature of molecular transitions, i.e. from -20°C up to 80°C). At very low temperatures, DMA spectra did not evidence any viscoelastic domain. However a deformation has been measured during creep tests in the same temperature range. So it would be necessary to determine which micro-mechanism is responsible for the observed deformation. Secondly, it was important to determine if the volume of DMA sample was representative. Several techniques have shown that a representative volume would be reached between 8 and 12mm3.