Rate-sensitive strain localization and impact response of carbon nanotube foams with microscale heterogeneous bands

We describe the deformation mechanisms and the bulk dynamic response of vertically aligned carbon nanotube (VACNT) foams comprised of bands of different densities. The densities of the bands are controlled during synthesis by varying the flow-rate of gas feedstock in discrete steps. We show that the impact response of VACNT foams can be distinctively tailored by introducing heterogeneous bands. For example, we demonstrate that this approach can be used to maintain the stress plateau at low stresses over a broad range of strains and to disrupt the expected progressive deformation of the sample. These are desirable characteristics for impact and energy absorption applications. The banded VACNT foams exhibit different deformation mechanisms in dynamics compared to those in quasistatic compression, as observed through in-situ high-speed microscopy.