Francesco De Bona

Meshing approach in non-linear FEM analysis of microstructures under electrostatic loads

The aim of this work is that of analyzing how the discretization of a coupled electro-mechanical system has to be approached to have accurate results from a Finite Element Method (FEM) simulation. Main aspect concerns the definition of the finite element mesh at the interface between the two domains. From this point of view a hybrid approach is proposed, where a fixed mesh is used for the mechanical structure and for the electrostatic area, whereas a morphing approach is followed for the volume that surrounds the most deformable part of the structure. Other aspects related to the electrical domain discretization, as open boundary modelling, pole positioning of infinite mapped element dimension of the electrostatic area were also considered. Numerical tests were carried out in the simple case of a cantilever, following an explicit coupled solution based on an iterative scheme elaborated in ANSYSTM parametric design language (APDL).

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.

Thermo-mechanical analysis of a fire door for naval applications

In this work, the thermo-mechanical response of fire doors for naval application is considered. In order to evaluate their behaviour, fire doors must undergo a standardized fire test. A realistic simulation of the heating process can be useful during the design phase in order to reduce the number of prototypes to be constructed and tested. In this work, a finite element model is developed with the aim of capturing the qualitative behaviour of the fire door and its supporting frame. Two different types of thermal analysis are considered: (1) transient analysis and (2) steady-state analysis. A non-linear mechanical analysis predicts the displacement field that occurs at the end of the heating phase. The adopted model is validated through a comparison with experimental measurements obtained during standard fire tests, confirming that the proposed approach can be a valid tool for the prediction of the thermo-mechanical performance of a naval fire door.

Design of Compliant Micromechanisms

A broad overview of the topics related to the mechanical design of compliant micromechanisms is presented. Design methodologies to be used in the design of devices based on leaf springs, flexural notches and continuum structures with distributed compliance are given, and a critical presentation of the peculiarities of these solutions is provided. The extensive bibliographical list is given as means to extend further the study to details of each of the treated topics.

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.

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.

Microstructures Under Electrostatic Loads: Discrete System Modelling

Due to a scaling effect, electrostatic forces, usually negligible at macro-scale, become relevant at micro-scale. It follows that electrostatic actuation is used very often for microsystems. The evaluation of the mechanical behavior of microstructures under electrostatic forces requires a new approach based on a so-called coupled field analysis; in fact, due to electrostatic forces structure exhibits a deformation that generally influences the electrical field and therefore again the electrostatic forces themselves. The case of a single degree of freedom electromechanical system was first considered; as generally the case of continuum structure is developed by referring to a FEM discretisation, the more general case of a multi degrees of freedom system was then considered.