A numerical study of squeeze-film damping in MEMS-based structures including rarefaction effects

In a variety of MEMS applications, the thin film of fluid responsible of squeeze-film dampingresults to be rarefied and, thus, not suitable to be modeled though the classical Navier-Stokes equation. Thesimplest way to consider fluid rarefaction is the introduction of a slight modification into its ordinaryformulation, by substituting the standard fluid viscosity with an effective viscosity term. In the present paper,some squeeze-film damping problems of both parallel and torsion plates at decreasing pressure are studied bynumerical solving a full 3D Navier-Stokes equation, where the effective viscosity is computed according toproper expressions already included in the literature. Furthermore, the same expressions for the effectiveviscosity are implemented within known analytical models, still derived from the Navier-Stokes equation. In allthe considered cases, the numerical results are shown to be very promising, providing comparable or evenbetter agreement with the experimental data than the corresponding analytical results, even at low air pressure.Thus, unlike what is usually agreed in the literature, the effective viscosity approach can be efficiently applied atlow pressure regimes, especially when this is combined with a finite element analysis (FE

analysis of crack trapping in 3d printed bio inspired structural interfaces

Abstract Specific features of biological materials, such as microstructure, heterogeneities or hybrid compositions, already inspired the fabrication of several architected materials. More recently, special emphasis has been placed on the development of damage tolerant interfaces by introducing tailored surface heterogeneities. However, thanks to the current developments in the area of additive manufacturing, the mating substrates can be now fashioned into complex shapes to confer the desired joint behavior. By taking inspiration from the base plate of the Balanus Amphitrite, we recently employed 3D printing to fabricate bio-inspired structural interfaces and adhesive bonded Double Cantilever Beam (DCB) fracture specimens. The results of DCB tests have shown a remarkable increase in the total dissipated energy with respect to baseline samples. In this work we supplement our previous study by performing finite element simulations in order to ascertain the variation of the driving force as a function of crack advance. The obtained results, which are analyzed in conjunction with high resolution imaging of the crack propagation process, allow to further elucidate the mechanics of debonding. It is shown that the sub-surface channels can modulate the driving force available for crack growth, introducing a crack trapping ability which depends on the specific geometry of the interfacial region

analysis of debonding in bio inspired interfaces obtained by additive manufacturing

Abstract The present work is focused on the analysis of fracture in adhesive bonded Double Cantilever Beam (DCB) specimens with 3D printed nylon substrates. The substrates were obtained using selective laser sintering of polyamide powder and embed sub-surface channels with circular and square cross-section. The proposed strategy allows to mimic the crack trapping effect already observed in a multitude of biological materials, that is originated by the spatial modulation of the driving force available for crack growth. Mechanical tests have shown that the channels induce load fluctuations in the global load-displacement response. A significant increase in the total dissipated energy was observed with respect to bulk samples, i.e. no channels. The observed fluctuations in the global response were associated to the sequential storage and sudden release of elastic energy. Indeed, the spatial modulation of the stiffness around the interfacial region ultimately affects the crack driving force

A numerical study of squeeze-film damping in MEMS-based structures including rarefaction effects

In a variety of MEMS applications, the thin film of fluid responsible of squeeze-film damping results to be rarefied and, thus, not suitable to be modeled though the classical Navier-Stokes equation. The simplest way to consider fluid rarefaction is the introduction of a slight modification into its ordinary formulation, by substituting the standard fluid viscosity with an effective viscosity term. In the present paper, some squeeze-film damping problems of both parallel and torsion plates at decreasing pressure are studied by numerical solving a full 3D Navier-Stokes equation, where the effective viscosity is computed according to proper expressions already included in the literature. Furthermore, the same expressions for the effective viscosity are implemented within known analytical models, still derived from the Navier-Stokes equation. In all the considered cases, the numerical results are shown to be very promising, providing comparable or even better agreement with the experimental data than the corresponding analytical results, even at low air pressure. Thus, unlike what is usually agreed in the literature, the effective viscosity approach can be efficiently applied at low pressure regimes, especially when this is combined with a finite element analysis (FE