Size dependent pull-in behavior of functionally graded sandwich nanobridges using higher order shear deformation theory

In this study the behavior of beam-type micro/nano electromechanical systems (MEMSs/NEMSs) made of functionally graded sandwich materials subjected to electrostatic actuation effect and intermolecular Casimir forces is investigated. Euler-Bernoulli, Timoshenko and higher order shear deformation (Reddy) beam theories are used to model the system. The modified couple stress theory is used to investigate size dependency in such systems. The three cases of softcore, hardcore, and functionally graded core are considered for the sandwich structure. The principle of minimum potential energy and variational approach are used to derive the governing nonlinear equations and boundary conditions of the system. Considering the nonlinearity of equations in the two force and geometric cases, the efficient generalized differential quadrature method is used to discretize the equations and boundary conditions, and the discretized equations are solved numerically afterwards. In the end, shear deformation effect and size effect on the system behavior are examined.