Cyclic and monotonic behavior of epoxy shape memory polymer foam

Shape memory polymer (SMP) foams have low density, high compressibility, and shape memory properties that give them a wide range of potential applications. However, their thermo-mechanical and structural behavior is not well understood. We investigated epoxy SMP foam with a relative density near 20% with an observed glass transition temperature of 90°C. The foam was deformed under both tension and compression at temperatures ranging from 25°C to 125°C. Tensile strain to failure as a function of temperatures was used to determine that the optimum deformation temperature is 80°C. Large strain cyclic testing confirmed that deformation at 80°C maximized macroscopic strain recovery. Compression tests were performed to examine the compressibility of the material as a function of temperature and shape recovery tests showed a recovery dependence on packaging temperature. Micro-computed tomography scans of the foam at various compressed states were used to understand foam deformation mechanisms. The microCT studies revealed the bending, buckling, and collapse of cells with increasing compression, consistent with results from published numerical simulations. MicroCT scans have also been coupled with cyclic testing to determine the structural effect of imparted permanent macroscopic strain.