Thermo-mechanical behavior of adaptive polymer foam
Adaptive (shape memory) polymer foams have potential aerospace applications, but their thermo-mechanical behavior under deformation conditions is not well understood. We examined epoxy adaptive foams with an average relative density near 20% by deforming them under conditions of varying stress, strain, and temperature. The glass transition temperature of the foam was measured to be 90°C, while compression and tensile tests were performed at temperatures between 25°C and 125°C Tensile strain to failure was measured to probe the foam's maximum recovery limits in temperature and strain space. Compression tests were performed to examine material compressibility as a function of temperature; these foams were compacted up to 80% and still experienced full strain recovery over multiple cycles. Both tensile strain to failure and cyclic compression recovery tests revealed that deforming at 80°C minimizes damage and maximizes macroscopic strain recovery. Deformation temperatures above or below this optimal value lead to lower failure strains in tension and the accumulation of permanent strains in cyclic compression. 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 published numerical simulations.
