Shape memory polymer foams have significant potential in biomedical and aerospace applications, but their thermo-mechanical behavior under relevant deformation conditions is not well understood. In this paper we examine the thermo-mechanical behavior of epoxy shape memory polymer foams with an average relative density of nearly 20%. These foams are deformed under conditions of varying stress, strain, and temperature. The glass transition temperature of the foam was measured to be approximately 90 °C and compression and tensile tests were performed at temperatures ranging from 25 to 125 °C. Various shape recovery tests were used to measure recovery properties under different thermo-mechanical conditions. Tensile strain to failure was measured as a function of temperature to probe the maximum recovery limits of the foam in both temperature and strain space. Compression tests were performed to examine compressibility of the material as a function of temperature; these foams can be compacted as much as 80% and still experience full strain recovery over multiple cycles. Furthermore, both tensile strain to failure tests and cyclic compression recovery tests revealed that deforming at a temperature of 80 °C maximizes macroscopic strain recovery. Deformation temperatures above or below this optimal value lead to lower failure strains in tension and the accumulation of non-recoverable strains in cyclic compression. Micro-computed tomography (micro-CT) scans of the foam at various compressed states were used to understand foam deformation mechanisms. The micro-CT studies revealed the bending, buckling, and collapse of cells with increasing compression, consistent with results from published numerical simulations.

This paper deals with the elastodynamic finite integration technique for axisymmetric wave propagation in a homogeneous and heterogeneous cylindrical medium ͑CEFIT͒. This special variant of a finite difference time domain ͑FDTD͒ scheme offers a suitable method to calculate real three-dimensional problems in a two-dimensional staggered grid. In order to test the accuracy of the numerical CEFIT code, problems for which analytical solutions are available are presented. These solutions involve wave propagation in an elastic plate, the scattering of a plane longitudinal wave by a spherical obstacle, and ultrasound generation by a thermoelastic laser source. For the latter problem experimental results are included. The CEFIT code also allows the treatment of more complicated problems. Further possible applications are the investigation of elastic waves generated in an acoustic microscope, the simulation of impact-echo measurements in multi-layer systems, axisymmetric wave propagation in arbitrary bodies of revolution, the calculation of elastic wave fields of longitudinal wave transducers with a circular aperture, and the investigation of multi-layer models for particulates.

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