ABSTRACT
This paper presents a 3D finite element model to investigate intergranular fatigue damage of microelectromechanical systems (MEMS) devices and to account for the effects of topological randomness of material microstructure on fatigue lives. The topology of MEMS material grain structures is modelled using randomly generated 3D Voronoi tessellations. Continuum Damage Mechanics is used to model progressive material degradation due to fatigue. A new 3D micro-grain debonding procedure is developed to consider both intergranular crack initiation and propagation stages. The fatigue damage model is then used to investigate the effects of microstructure randomness on the variability in fatigue life of cantilever MEMS devices. Three different types of randomness are considered: (1) topological disorder due to random shapes and sizes of the material grains, (2) variation in material properties considering a normally (Gaussian) distributed elastic modulus and (3) material defects or internal voids. The stress–life results obtained are in good agreement with experimental data. The progression of damage and the overall crack pattern obtained from the microcantilever beam model are consistent with empirical observations.
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