Visualizing Strain Evolution and Coordinated Buckling within CNT Arrays by In Situ Digital Image Correlation

Spatial mapping of strain fields within compressed carbon nanotube (CNT) array columns is achieved using digital image correlation (DIC) analysis of in situ scanning electron microscopy (SEM) image sequences. Full-field displacement and strain maps are generated based upon the motion of the constituent CNTs, which serve as a traceable high-contrast speckle pattern for DIC analysis. The deformation modes and CNT array buckling characteristics vary systematically as a function of column aspect ratio, including bending, crushing, and bottom-up buckle accumulation behaviors. In spite of disparate appearing deformation modes, strain maps indicate that CNT array buckling consistently initiates at 5% local principal strain (?2) for all columns. The ability to quantitatively assess the deformation modes and buckling behavior of CNT arrays at the nanoscale will enable their improved design for high-strain electrical contacts, compliant thermal interfaces, force sensors, energy-absorbing foams, or other applications.