Carbon nanotube caps as springs: Molecular dynamics simulations

We present a detailed investigation of the spring behavior of carbon nanotube caps. We show that the caps act as harmonic springs, responding linearly to axial forces for appreciable displacements. Interestingly, we find the spring constant to be essentially independent of diameter and number of layers, but the maximum harmonic displacement increases with tube diameter and especially with number of layers. This spring effect is significant when the tubes are sufficiently short so that buckling does not occur before cap compression.