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Quasi-static compression tests have been performed on polyurethane foam specimens. The modulus of the foam exhibited a power-law dependence with respect to density of the form: E* ϰ (*) n , where n ϭ 1.7. The modulus data are described well by a simple geometric model (based on the work of Gibson and Ashby) for a closed-cell foam in which the stiffness of the foam is governed by the flexure of the cell struts and cell walls. The compressive strength of the foam is also found to follow a power-law behavior with respect to foam density. In this instance, Euler buckling is used to explain the density dependence. The modulus of the foam was modified by addition of gas-atomized, spherical, aluminum powder. Additions of 30 and 50 wt % Al measurably increased the foam modulus, but without a change in the density dependence. However, there was no observable increase in modulus with 5 and 10 wt % additions of the metal powder. Strength was also increased at high loading fractions of powder. The increase in modulus and strength could be predicted by combining the Gibson-Ashby model, referred to above, with a well-known model describing the effect on modulus of a rigid dispersoid in a compliant matrix.

The synthesis of a polythiophene-based conductive polymer gel is described. Preliminary measurements of the electrochemically driven extension and force response of this gel are reported when driven under the action of an applied square-wave potential. Over each square wave interval (i.e., one oxidation pulse followed by one reduction pulse), the axial change in dimension was found to be approximately 2%. Some hysteresis was noted in that the cylindrical specimens did not return to their original axial dimension. The axial pressure generated by the expansion of the gel against a fixed surface was also measured and found to be on the order of 15 kPa -4 -

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The shape-memory polymer performance of urethane foams compressed under a variety of conditions was characterized. The foams were water-blown thermosets with a closed-cell structure and ranged in density from about 0.25 to 0.75 g/cm 3 . Compressive deformations were carried out over a range of strain levels, temperatures, and lateral constraints. Recovery stresses measured between fixed platens were as high as 4 MPa. Recovery strains, measured against loads up to 0.13 MPa, demonstrated the effects of various parameters. The results suggest that compression near the foam glass-transition temperature provided optimal performance. Foams with densities of about 0.5 g/cc and compressed 50% provided a useful balance (time, strain, and load) in the recovery performance.

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The room temperature mechanical properties of a closed-cell, polyurethane encapsulant foam have been measured as a function of foam density. Tests were performed on both unfilled and filler reinforced specimens. Over the range of densities examined, the modulus of the unloaded foam could be described by a power-law relationship with respect to density. This power-law relationship could be explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model found in the literature. The collapse stress of the foam was also found to exhibit a power-law relationship with respect to density. Additions of an aluminum powder filler increased the modulus relative to the unfilled foam.

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