Abstract
It is well recognized that size dependency of materials characteristics, i.e. size-effect, often plays a significant role in the performance of nano-structures. Herein, strain gradient continuum theory is employed to investigate the size dependent pull-in instability of beam-type nano-electromechanical systems (NEMS). Two most common types of NEMS i.e. nano-bridge and nano-cantilever are considered. Effects of electrostatic field and dispersion forces i.e. Casimir and van der Waals (vdW) attractions have been considered in the nonlinear governing equations of the systems. Two different solution methods including numerical and Rayleigh-Ritz have been employed to solve the constitutive differential equations of the system. Effect of dispersion forces, the size dependency and the importance of coupling between them on the instability performance are discussed.
Highlights
Micro/nano-electromechanical systems (MEMS/NEMS) are increasingly used in various engineering and science branches i.e. mechanics, chemistry, optics, biology, electronics, etc
Koochi et al / Size dependent pull-in instability of beam-type NEMS 1807 with decreasing the dimensions to sub-micron, the nano-scale phenomena should be considered in theoretical models
In strain gradient theory in spite of whatever was stated in classic mechanic, equations contain a parameter which introduced as length scale parameter that has statistical nature and indicates that material behavior is depending on material dimensions in micrometer scale
Summary
Micro/nano-electromechanical systems (MEMS/NEMS) are increasingly used in various engineering and science branches i.e. mechanics, chemistry, optics, biology, electronics, etc. The plastic intrinsic material length scale of 4μm for copper and 5μm for nickel were determined (Wang et al, 2003) All these experiments imply that when the characteristic size (thickness, diameter, etc.) of a micro/nano element is in the order of its intrinsic thematerial length scales (typically sub-micron), the material elastic constants highly depend on the element dimensions. One of the first works in this field has been conducted by Wang et al (2011a) who modeled the sizedependent instability of clamped structure using strain gradient elasticity theory They have not considered the effect of nano-scale attractions such as Casimir and vdW force in their models. The Rayleigh–Ritz method is applied to solve the nonlinear governing equation as well as numerical solution
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