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

A.G Denay,A Roy,S Castagnet,G Alise

doi:10.1051/epjconf/20100625006

Abstract

The objective of this work was to predict the long term behavior of Polyurethane foam (PU) at very lowtemperature, by applying the timetemperature 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 sizeeffect associated to the small DM A samples. Firstly, on the studied temperature range (�170°C; +180°C) many transitions hbeen 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 micromechanism 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 12mm 3 .

Highlights

Polyurethane (PU) foams are widely used for impact applications [1] as well as for thermal insulation [2], as addressed in the present study for storage and transport by methane carrier of liquid natural gas (LNG at-170°C)
Taking into account the very low strain range involved in the application, it seemed reasonable to base the experimental background of the temperature superposition principle (TTSP) on a Dynamical Mechanical Analysis (DMA) technique, interesting for the ease of implementation of tests, and for the saving time
To predict long term behavior at low temperature, the TTSP can be used with a modification of range temperature, because no viscoelastic phenomena have been observed at low temperatures

Summary

Introduction

Polyurethane (PU) foams are widely used for impact applications [1] as well as for thermal insulation [2], as addressed in the present study for storage and transport by methane carrier of liquid natural gas (LNG at-170°C). Among other aims of the study, the present contribution deals with the prediction of long term creep properties of PU foams at very low temperatures, and more precisely with the relevance of the time-temperature superposition principle (TTSP) widely used for polymeric bulk materials to predict creep behavior over very long times. Due to the cellular microstructure of the material, it must be highlighted if deformation micro-mechanisms correspond to structure effects of cell calls or to very local and elementary mechanisms, close to that activated in the bulk and short scale enough to obey a TTSP. Taking into account the very low strain range involved in the application, it seemed reasonable to base the experimental background of the TTSP on a Dynamical Mechanical Analysis (DMA) technique, interesting for the ease of implementation of tests, and for the saving time

Objectives

Results

Conclusion