Simulation of the microstructural evolution of a polymer crosslinked templated silica aerogel under high-strain-rate compression

Surfactant-templated mesoporous silica aerogels (or nanofoams) with their entire skeletal framework nanoencapsulated conformally by a thin polyurea layer are emerging as materials with high specific strength and high energy absorption. In this paper a modified split Hopkinson pressure bar was used to investigate their mechanical behavior under dynamic compression at high strain rates. The evolution of the mesoporous structure under such dynamic impact conditions was simulated using the Material Point Method (MPM). The material point model was generated from X-ray micro-computed tomography whereas each voxel was converted to a material point corresponding to the local skeletal density of the material. Simulation results agree well with the experimental data, indicating that the MPM can effectively model the compression of complex mesoporous structures. Simulations indicate a nearly uniform deformation at all three stages of compression: the elastic region, compaction and the final densification due to the low ratio of pore size to wall thickness and random distribution of the pores. Simulations have also indentified the function of the conformal polymer coating as a reinforcing factor, showing that different porosities, obtained by varying the skeletal wall thickness, affect the local stress distribution. Eventually, simulations confirm that the stress-strain behavior of aerogels under compression follows a power-law relationship with the initial bulk density, consistent with experimental results.