Finite-Element Contact Modeling of Rough Surfaces Applied to Au-Coated Carbon Nanotube Composites

Multiwalled carbon nanotubes (CNTs) have been used to improve the lifetime of the electrical contact of microelectromechanical system (MEMS) switches. The surface, usually gold-coated, demonstrates a complex structure. Due to the lateral gaps between the nanotubes, the sputtered gold penetrates into the top part of the CNT to a limited thickness and is supported by the rest of the CNT. The surface also presents a much higher roughness than metal surfaces. Based on the nanoindentation test, a finite-element smooth-contact model has been developed, and it was shown that the surface was best modeled as a bilayered structure. In this paper, roughness is considered in contact modeling. It is shown that roughness plays an important role in the contact behavior, and that the material properties, such as Young's modulus and hardness estimated from the nanoindentation tests, need to be reevaluated. It is also shown with finite element method (FEM) that the force-displacement behavior of the composite depends on the location of the indentation test.