Carbon nanotube films change Poisson's ratios from negative to positive

In this paper, a discovery is reported that carbon nanotube (CNT) films can change in-plane Poisson's ratios from negative to positive during a uniaxial tensile loading. First, in situ experimental investigations of the deformation fields about the CNT films fabricated using vertically aligned CNT arrays are performed by digital speckle correlation method, the novel phenomenon for changing Poisson's ratio from negative to positive during the stretching process is discovered. Furthermore, the physical mechanisms for changing the Poisson's ratio from negative to positive are explained based on the interactions among CNTs. Finally, a potential engineering application for designing intelligent connector is proposed based on the intriguing Poisson's ratio of CNT films. (C) 2010 American Institute of Physics. [doi:10.1063/1.3479393]