Thermal properties of an open cell epoxy shape memory polymer foam
The thermal properties of an epoxy SMF (shape memory polymer foam) are measured and reported for an 18% dense foam, and it was found that the thermal diffusivity increased by an order of magnitude in going from fully expanded to fully compressed, while the thermal conductivity increased by almost as much. Under these same conditions the specific heat increased by less than 50% on average, while the density increased by a factor of about 3.5. Overall the properties are like those of a thermal insulating material, as would be expected. Next, a simple transient thermal analysis is carried out for using this material with an electric resistance heating element as the skin of a morphing aircraft wing. At steady state for a 9.5 mm thick SMF skin the ratio of the maximum to minimum temperature within the material is found to be 21 for the compressed foam and 69 for the expanded foam, which is excessive for practical applications. A dense network of electric resistance heating elements embedded within the material would be required. The analytical results given here emphasize the need to develop volumetric material heating systems if shape memory polymers are to be used extensively for morphing aircraft applications.
