Mircea Gh. Munteanu

Static Behavior Prediction of Microelectrostatic Actuators by Discrete Geometric Approaches

The analysis of a microelectrostatic actuator is presented, formulated by means of the so-called Discrete Geometric Approach applied to the solution of the electrostatic-elastostatic coupled problem. Numerical results computed by means of the proposed approach are compared to those coming from assessed approaches like the finite-element method (FEM) (for both the structural and the electric domains) and FEM/boundary element method (BEM) (FEM for the structure, BEM for the electric domain). A preliminary experimental validation is finally added.

A harmonic one-dimensional element for non-linear thermo-mechanical analysis of axisymmetric structures under asymmetric loads: The case of hot strip rolling:

This work presents a one-dimensional harmonic finite element for the transient elasto-plastic analysis of axisymmetric structures loaded by non-axisymmetric thermal and mechanical loads. The one-dimensional element exploits a semi-analytical approach, based on Fourier series decomposition of the applied loads. The initial stress method is used for the non-linear solution of elasto-plastic analysis. As a case study, the proposed one-dimensional harmonic element is applied for modelling a two-dimensional circle under thermal and mechanical loadings rotating over its surface, which is used as an approximation of a work roll in hot strip rolling. With the one-dimensional harmonic element, the cyclic thermo-mechanical behaviour of the work roll can be simulated by considering localized plasticity caused by thermo-mechanical loads representative of strip and back-up roll. Compared to two-dimensional models already used in the literature, the one-dimensional element allows a significant reduction in the computational time to be achieved; it follows that the whole transient thermo-mechanical response can be simulated, thus permitting a more complete evaluation of the stress–strain response that is necessary for fatigue life assessment.

Validation of compact models of microcantilever actuators for RF-MEMS application

Microcantilever specimens for in-plane and out-of-plane bending tests are here analyzed. Experimental validation of 2D and 3D numerical models is performed. Main features of in-plane and out-of-plane layouts are then discussed. Effectiveness of plane models to predict pull-in in presence of geometric nonlinearity due to a large tip displacement and initial curvature of microbeam is investigated. The paper is aimed to discuss the capability of 2D models to be used as compact tools to substitute some model order reduction techniques, which appear unsuitable in presence of both electromechanical and geometric nonlinearities.

RF-MEMS beam components: FEM modelling and experimental identification of pull-in in presence of residual stress

In this paper an experimental validation of numerical approaches aimed to predict the coupled behaviour of microbeams for out-of-plane bending tests is performed. This work completes a previous investigation concerning in plane microbeams bending.

Flexural stiffness of leaf springs for compliant micromechanisms

Von Kármán equations have been used to evaluate the flexural behaviour of rectangular leaf springs with constant thickness. A closed form solution is obtained, showing that flexural stiffness varies continuously from that obtained by considering a beam model to the value given by the linear plate theory. This behaviour depends on section geometry, Poissons ratio, and main curvature. A new characterizing parameter, whose relation with flexural stiffness allows a typical non-linear behaviour to be emphasized, is introduced in this work. In particular, for a given geometry and material, the flexural stiffness increases with the deflection and consequently with the load.

Shaft design: A semi-analytical finite element approach

ABSTRACT This work deals with the practical use of semi-analytical finite elements in the machine design. The case of mechanical shafts is considered. The most usual loading condition characterized by the presence of axial, torsional, bending, and shear loads can be modeled by over imposing an axi-symmetric, an axi-antisymmetric and a harmonic load, corresponding to the first three terms of the Fourier series expansion, if semi-analytical plane finite element is used. A practical case is presented and the advantages, with respect to the three-dimensional approach in terms of computational time and accuracy for stress and displacement evaluation, is put in evidence.

Role of the Structural Nonlinearity in Enhancing the Performance of a Vibration Energy Harvester Based on the Electrets Materials

Films of the electrets material are currently proposed to design compact vibration energy harvesters. They are used to cover the surface of electrodes of some capacitive devices based on a deformable microbeam clamped at both its ends. The performance of those energy harvesters is often predicted in the literature by neglecting the effect of the geometric nonlinearity due to a mechanical coupling occurring between the axial and flexural behaviors of the clamped-clamped microbeam. This nonlinearity is herein investigated, by resorting to a distributed model of the electromechanical coupling applied to the vibration energy harvester. The analysis is performed by means of the finite element method. The performance of energy conversion is then analyzed and some new configurations of the vibration energy harvester are proposed.

Continuum Microstructures Loaded Electrostatically

Electrostatic actuated flexible structure are frequently encountered in microsystems. The behaviour of these devices is characterized by electromechanical coupling, due to the mutual interaction between the electrostatic field and the deflection of the structure. A common case, frequently analyzed in the literature, is that of cantilever beam loaded electrostatically; in this case different analytical approaches based on a strong simplification of the elctromechanical model are available. If a more accurate analysis has to be performed, methods based on numerical techniques have to be preferred. In this case possible approaches are: lumped models, methods based on a Newton’s non-linear solution scheme, sequential field coupling algorithms.

Optimizated Design of Notch Shapes for Microfabricated Compliant Mechanisms

In this work a procedure for the optimal design of flexural hinges to be microfabricated with a lithographic process is proposed. The structural optimization problem is approached by coupling a parametric finite element model to an optimization algorithm. A computer code was developed to generate the mesh at each optimization step accordingly to the values of the design parameters provided by an optimization toolbox. The objective function is the maximum displacement of the mechanism, which must be maximized. The solution is constrained by strength and kinematic requirements. The notch shape is described by spline functions according to an original procedure developed by the authors. Different cases were proposed showing that the procedure is always convergent.