On the rate dependence of mechanical properties of aligned carbon nanotube arrays

Aligned carbon nanotube arrays are a new form of carbon nanomaterials that have received great interest due to their superior structure and properties. The present work comprehensively examines the rate-dependent mechanical deformation of the vertically aligned carbon nanotube arrays (VA-CNTs) by the use of indentation tests. The small-displacement, elastic property of the VA-CNTs was measured by a spherical indenter. The effective indentation strain rate was varied by adjusting the indenter unloading rate. The instantaneous modulus of the VA-CNTs has been calculated and is found to increase linearly with indentation strain rate. The large-displacement, plastic property of the VA-CNTs was measured by a cylindrical, flat-ended indenter. At large indentation depths, the stress-strain curve of the VA-CNTs reveals distinct plastic deformation. The indentation strain rate was varied by directly changing the indenter velocity. The yield strength (sigma (y)) of the VA-CNTs also increases linearly with respect to indentation strain rate.