Coupling influences of nonlocal stress and strain gradients on dynamic pull-in of functionally graded nanotubes reinforced nano-actuator with damping effects

The paper reports a result of investigation on the dynamic pull-in instability of functionally graded carbon nanotubes (FGCNTs) reinforced nano-actuator considering damping behavior. Here, the nonlocal stress gradient and strain gradient theories are jointly utilized to capture the size effects of nanoscale structures. The material properties of FGCNTs reinforced nano-actuator are temperature-dependent, and the influences of geometrical nonlinearity and intermolecular forces such as van der Waals interaction and Casimir force are also considered. The results indicate that the fundamental frequency decreases with the increase of initial amplitude and electrostatic voltage until drops to zero when the dynamic pull-in occurs. It is shown that the frequencies of nano-actuator decline with the increment of nonlocal stress gradient parameter whereas increasing the strain gradient parameters enlarges the frequencies. In addition, it is observed from the time history and phase portrait that the dynamic pull-in voltage of system with damping behavior is larger than that without damping system, since the dissipative effect of damping requires more energy injected into the system. (C) 2016 Elsevier B.V. All rights reserved.