Browsing by Subject "Snap-through"

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Open Access
An experimental approach to nanomechanical buckling and snap-through phenomenon
(2019-08) Hatipoğlu, Utku
Buckling has received little attention as a valuable resource for engineering applications since it is regarded as a type of failure in civil and mechanical engineering. Nevertheless, buckling has a great potential in nanoelectromechanical systems(NEMS) field as a bistable process that has rich and complex dynamics. Here, we explore post buckling dynamics of a nano-beam experimentally by employing various probing techniques. By employing an all-electronic architecture, we precisely control the buckling amount as well as buckling direction of the nano-beam which eventually gives us the ability to control a two-level mechanical system with high precision and speed. A full control over the potential energy landscape of the system is demonstrated with different techniques such as Scanning Electron Microscopy operated in three different modes and microwave coupling method. During proof of concept experiments, left and right buckling, large deflection buckling, nonvolatility – which is an indication of pure bistable states – and snap-through phenomenon is demonstrated. Further steps of the study focused on the snap-through phenomenon that is the interstate transitions of the buckling beam after bifurcation. During these experiments, more involved relations are investigated such as mechanical bias and effect of plastic deformation as well as the effect of actuation scheme on interstate jumps. Moreover, to obtain a better grasp of post-buckling dynamics, quantitative measurements are carried out which reveal the reaction speed of the system and time scale of interstate jumps. Lastly, oscillatory snap-through motion is observed in some special conditions that can be beneficial to understand noise dynamics of the system and it has a potential to contribute energy harvesting applications.
Open Access
Pre- and post-buckling analysis of nanobeams
(2019-02) Vardar, Onur
Interest in nanobeams is increasing as their application areas widen and new properties are discovered. These structures exhibit size dependent intrinsic properties that are absent in macroscale. This requires employment of new material models as bulk models by themself are not sufficient to describe the physics unless one considers the domain as a composite material, which is undesirable. In this work it was confirmed that incorporation of surface elasticity results in a good match with experiments. Moreover it was shown that due to lack of out-of-plane shear support of surfaces and curves, Euler beam assumptions fail for numerical implementations when the beam size reduces. This phenomenon was shown to be a severe drawback for curved energetic domains with a still noticable effect for surface energies. A geometrically nonlinear buckling model is proposed based on linear elastic material model. It is implemented in an ordinary differential equations solver and the solutions were confirmed to meet the finite element method (FEM) results to a very high degree. The theory is integrated with surface layers in which its accuracy was confirmed when compared with FEM results.