In this paper, the effects of long-term storage in compressed cold
hibernated elastic memory (CHEM) polyurethane foam, a kind of shape memory
polymer, are investigated experimentally. The foams were pre-strained at a
high temperature, which was above the glass transition temperature, to 80%
and 93.4%, respectively, and then cooled back to room temperature. After
various periods of cold hibernation (up to two months), they were heated up at
fixed length or against different constant loads. It is found that: (1) the
maximum stress that the foam could exert at fixed length depends heavily on
the amount of pre-strain; (2) expansion rates of 380 and 1273% from the
hibernated size against a 1 N load (pre-strained by 80 and 93.4%,
respectively) are achievable. However, upon further increases in load, the
expansion is reduced dramatically. It appears that the tested CHEM
polyurethane foam retains its shape memory properties even after being stored
in a compacted state for a long period. Complete strain recovery is attainable
for a hibernation period of up to two months.
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