Waviness reduces effective modulus of carbon nanotube forests by several orders of magnitude

Abstract

Waviness is invariably present in vertically-aligned Carbon Nanotubes (CNTs) regardless of how controlled the fabrication process is. This study, using experiments and models, shows that such inherent waviness is the main mechanism by which the effective modulus of CNTs is reduced by several orders of magnitude. At this time, most studies have shown that the compliant mechanical response of the CNT forests under compressive loading is due to bending and buckling of CNTs as well as the variation of CNT density throughout the forest height. Subjecting CNT forests to tensile loads as well as to compressive loads, it is shown here that the high compliance of CNT forests is due to the inherent waviness of individual CNTs, and not necessarily due to bending and buckling of CNTs. The experimental findings are also supported through analytical models and numerical models that show that the CNT wavy geometry causes the CNTs to have 4–5 orders of magnitude greater compliance than a straight CNT.