Modelling the creep of open-cell polymer foams

The high-strain creep of open-cell low-density polymer foams is analysed us ing linear viscoelasticity theory. The microstructure is represented by the Kelvin foam, a regular lattice of tetrakaidecahedral cells. Compressive cr eep curves are predicted from the measured stress relaxation modulus of a p olyurethane (PU) and the foam density. Geometric non-linearity develops as some cell edges become S-shaped, causing the creep rate to increase. The lo w-strain creep response can be predicted accurately. The response for strai ns between 10 and 50% is qualitatively correct, but the Kelvin foam, if it maintains its initial symmetry when compressed in the [001] lattice directi on, has less geometric non-linearity than the irregular PU foam. A buckling mode is proposed which would cause increased geometric non-linearity. Poly mer nonlinearity also contributes to the medium strain creep response of so me low-density PU foams. (C) 1999 Elsevier Science Ltd. All rights reserved .