FEM modelling and experimental characterization of microbeams in presence of residual stress

Abstract

Out-of-plane bending tests are here used to experimentally validate some numerical models of microbeams actuated by the electric field. Out-of-plane bending microcantilevers and clamped–clamped microbeams often suffer the presence of residual strain and stress, respectively, which affect their static and dynamic behaviour and pull-in voltage. In case of microcantilever an accurate modelling has to include the effect of an initial curvature due to microfabrication process, while in double clamped microbeams constraints may impose a pre-loading caused by a tensile stress. So-called geometrical nonlinearity sometimes occurs, when microcantilever exhibits large displacement, or because of the mechanical coupling between axial and flexural behaviours in double clamped microbeams. Modelling this kind of nonlinearity is an additional goal of this study. Experiments demonstrated a good agreement with results of FEM approaches proposed. In the case of microbridges numerical models are used to identify the residual stress. A reverse analysis is implemented, the axial pre-stress is calculated by means of the measured pull-in voltage.