Carbon nanotube-reinforced composites as structural materials for microactuators in microelectromechanical systems

Abstract

Nanocomposites are a promising new class of structural materials for the mechanical components of microelectromechanical systems (MEMS). This paper presents a detailed theoretical investigation of the utility of carbon nanotube-reinforced composites for designing actuators with low stiffness and high natural frequencies of vibration. The actuators are modelled as beams of solid rectangular cross-section consisting of an isotropic matrix reinforced with transversely isotropic carbon nanotubes. Three different types of nanotube reinforcements are considered: single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and arrays of SWNTs. The effects of nanotube aspect ratio, dispersion, alignment and volume fraction on the elastic modulus and longitudinal wave velocity are analysed by recourse to the Eshelby–Mori–Tanaka theory. The calculated bounds on Young’s modulus and wave velocity capture the trend of the experimental results reported in the literature. Polymer–matrix nanocomposites reinforced with aligned, dispersed SWNTs are identified as excellent candidates for microactuators and microresonators, with properties rivalling those of monolithic metallic and ceramic structures used in the current generation of MEMS. A qualitative comparison between the state-of-the-art in nanocomposite manufacturing technology and the predicted upper bound on Young’s modulus and longitudinal wave velocity highlights the enormous improvements needed in materials processing and micromachining to harness the full potential of carbon nanotube-reinforced composites for microactuator applications. These results have immediate and significant implications for the use of nanotube composites in MEMS.

Micromechanics modeling for the stiffness and strength properties of glass fibers/CNTs/epoxy composites

“…The tensor S, given by Eshelby [11], is called Eshelby's tensor whose elements are functions of the aspect ratio of an ellipsoidal inclusion and the Poisson's ratio of the matrix [13]. The terms enclosed with angle brackets in eqn (2) represent the average (or expectation) value of the term over all orientations.…”

“…The Mori-Tanaka model [10] and Halpin-Tsai equations [11] are popular methods for estimating the mechanical properties of fiber reinforced composites and are used widely to predict the mechanical properties of nanocomposites [12][13][14][15][16]. Using the Eshelby-Mori-Tanaka method, Ashrafi et al [13] showed that CNTs are able to enhance the axial Young's modulus and longitudinal wave velocity of nanocomposite beams. Odegard et al [14] and Ashrafie and Hubert [15] linked the atomistic simulations of nanostructured materials to continuum models of the corresponding bulk material to determine the properties of SWNT/polymer composites.…”

Synthesis and characterization of carbon nanotube-reinforced epoxy: Correlation between viscosity and elastic modulus

“…However, a significant increase of 24% was measured in the elastic modulus for the specimen reinforced with 1% of plasmaproduced, carboxyl-functionalized SWCNT. This increase can be placed in context by noting that the predictions of the Mori-Tanaka calculation for random composites [17] (which assumes perfect bonding between reinforcement and matrix) is 30% for this specimen. Fig.…”

“…The last column in this table shows the change in the elastic modulus of the nanocomposite using the neat epoxy as the baseline. The measured change (in percentage) is compared with the change computed using the Mori-Tanaka method [17], assuming that the reinforcing agents are arrays of SWCNT with perfectly-random orientation within the matrix. The predicted change for specimens with low loading of SWCNT (in the range of 0.125-0.25%) is only 3.75%, which is below the resolution of this technique.…”

Formation and mechanical characterisation of SU8 composite films reinforced with horizontally aligned and high volume fraction CNTs

“…However, to maximize the effectiveness of the reinforcement and hence the relevant properties of the composites, CNT alignment [6], dispersion [7] and volume fraction [8] have always been the major challenges in the field. Recently, a strong interest has emerged to exploit CNT reinforced composites for applications in the area of MEMS [9][10][11]. It was reported [9] that, CNT reinforced polymer composites can exhibit mechanical properties rivalling those of monolithic materials used in the current generation of MEMS (e.g.…”