Anomalous impact and strain responses in helical carbon nanotube foams
We describe the quasistatic and dynamic response of helical carbon nanotube (HCNT) foams in compression. Similarly to other CNT foams, HCNT foams exhibit preconditioning effects in response to cyclic loading; however, their fundamental deformation mechanisms are unique. In quasistatic compression, HCNT foams exhibit strain localization and collective structural buckling, nucleating at different weak sections throughout their thickness. In dynamic compression, they undergo progressive crushing, governed by the intrinsic density gradient along the thickness of the sample. HCNT micro-bundles often undergo brittle fracture that originates from nanoscale defects. Regardless of this microstructural damage, bulk HCNT foams exhibit super-compressibility and recover more than 90% of large compressive strains (up to 80%). When subjected to striker impacts, HCNT foams mitigate impact stresses more effectively compared to other CNT foams comprised of non-helical CNTs ([similar]50% improvement). The unique mechanical properties we revealed demonstrate that the HCNT foams are ideally suited for applications in packaging, impact protection, and vibration mitigation.
© 2015 The Royal Society of Chemistry. Received 27th February 2015. Accepted 16th March 2015. We acknowledge Fabian Gramm (ScopeM, ETH Zurich) for assistance in TEM imaging and Jan Rys (ETH Zurich) for assistance in SEM imaging. We acknowledge financial support from the Institute for Collaborative Biotechnologies (ICB) under the contract W911NF-09-D-0001 with the Army Research Office (ARO). A portion of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. X-ray characterization was performed at beamline 7.3.3 at the Advanced Light Source, which is supported by the Director, Office of Science, and Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract no. DE-AC02-05CH11231.
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