Large-Displacement Indentation Testing of Vertically Aligned Carbon Nanotube Arrays

Mechanical properties and deformation of the vertically aligned carbon nanotube arrays (VA-CNTs) has been examined with large-displacement indentation tests inside a scanning electronic microscope (SEM). The in-situ indentation allows for establishment of the load-depth responses and real-time observations of the deformation processes. Under a cylindrical, flat indenter, the VA-CNTs exhibit elastic deformation at small displacement and then plastic deformation at large displacement. The critical indentation pressure (P_m), a measure of collapsing stress of the CNT arrays, is obtained. The magnitude of P_m is approximately equal to the collapsing stress of the carbon nanotube arrays obtained under uniaxial compression.