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While comprehensive researches have been conducted on modeling the electromechanical stability of wide-enough beam-plate nano-switches, few researchers have focused on modeling the electromechanical instability of narrow-width nano-switches. For such systems, considering the coupled effects of surface stresses and size dependency of material characteristics is crucial as well as applying appropriate force models. In this paper, Gurtin-Murdoch surface theory incorporating with strain gradient elasticity is employed to study the pull-in instability of narrow-width beam-type nanoswitch with small width to height ratio. The model accounts for the force corrections, i.e. the impact of finite dimensions on the fringing field, Casimir attraction and van der Waals force. Furthermore, a modified gas damping model has been incorporated in the governing equation. The nonlinear governing equation was solved using analytical Rayleigh-Ritz method. The influences of the above-mentioned corrections on the static and dynamic pull-in parameters, phase planes and stability threshold of the switch are demonstrated. The modified model is compared with conventional parallel beam-plate models in the literature.

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Toughening of epoxy with different types of modifiers produces a bimodal blend that might show better fracture resistance in comparison with single-modified ones. In this research, bimodal epoxy formulations including mixtures of glass microsphere and silica nanoparticles are explored for possible synergistic toughening. The influence of composition on the glass transition temperature (T g ), tensile characteristics, and fracture toughness (K IC ) is investigated. Interestingly, a synergism in fracture toughness is observed when mixtures of modifiers were incorporated. For the fixed overall modifier content, K IC is higher when the volume fraction of glass microsphere is lesser than the volume fraction of nanosilica. Fractographs reveal that glass microsphere increases the toughness of epoxy matrix by crack pinning/bridging mechanisms. On the other hand, nanosilica enhances the toughness by increase in plastic deformation via shear banding/particle debonding. Interestingly, the origin of synergistic toughness in bimodal epoxies is the interaction between the glass microsphere and crack-tip damage zone which provides comprehensive stable crack deflection within the nanosilica-toughened epoxy. This mechanism results in a mixed-mode crack growth that reduces the strain energy release rate in bimodal formulations.