1,721,149 research outputs found
Computational analysis of the collapse behaviour of thin-walled polygonal steel beams
Full text linkThe present paper is focused on the development of an accurate computational method, based on the Finite Element (FE) approximation, for predicting the collapse behavior of thin-walled polygonal steel beams subject to bending. The numerical model has been created using the software ABAQUS, and has been validated with experimental data obtained from the literature, concerning rectangular hollow section (RHS) in the four-point-bending situation. The model has been improved by means of a thorough study of material hardening, imperfections and residual stresses. The computational results of the analyses have been compared with the design procedures provided by Eurocode 3 (effective cross-section method and reduced stress method), in order to check their suitability
Flutter analysis of piezoelectric beams in MEMS
Full text linkMicro-electro-mechanical systems (MEMS) represent a huge class of devices characterized by the smart coupling between electronics and mechanics, in order to obtain microscopic sensors and actuators. The use of piezoelectric materials in MEMS is steadily increasing, considering both the “direct effect”, e.g. in energy harvesters, and the “indirect effect”, for the cases of resonators, micropumps and other actuators. This paper is devoted to the study of piezoelectric laminate beams in the presence of aeroelastic effects due to the interaction of the structure with a fluid flow, as it may happen if the MEMS is embedded in a fluidic system. More specifically, the analytical conditions for the onset of flutter instability are studied, with the purpose of providing a sound basis for further studies focused on energy harvesting from fluid flows
Thermoelastic damping in layered micromechanical resonators
No full textThe effect of coatings and superficial oxide on the behavior of micro resonators deserves attention in view of its impact on real-life devices. To this purpose, in this work we focus on the thermoelastic damping in layered thin resonating beams. Including the effect of thermally imperfect interfaces, the quality factor is analytically computed. The results obtained are discussed
and compared with available data
Statistical approach to damage diagnosis of concrete dams by radar monitoring: formulation and a pseudo-experimental test
No full textThis paper deals with the investigation of a diagnostic procedure especially suited for large concrete dams. The main features of such methodology are as follows: static excitation of the dam; displacement monitoring by radar device; identification of the unknown Young moduli in pre-defined homogeneous zones through a batch least square method. The uncertainty of the identified parameters is assessed by means of a thorough statistical processing. The numerical validation of the proposed method is carried out on the basis of pseudo-experimental data. The most important results, summarized in the paper together with some computational remarks, are critically examined
Nonlocal thermoelastic damping in microelectromechanical resonators
No full textThe evaluation of loss mechanisms in microscale mechanical resonators is addressed. Among various dissipation causes,
thermoelastic loss is considered as a fundamental dissipation mechanism in microbeam resonators packed in a near-vacuum environment.
However, the standard thermoelastic analysis is unable to interpret the size effect experimentally evidenced in resonators when the dimensions become very small, below several microns. In this paper we propose an enhanced nonlocal thermoelastic model, based on a thermodynamical formulation, which incorporates internal characteristic material lengths. Analytical results obtained with this nonlocal theory are compared with experimental results reported in the literature. It is shown how nonlocality can better interpret the observed behavior, at least in a certain range of resonators dimensions
MEMS energy harvesters based on aeroelastic phenomena
No full textThis paper deals with the study of some of the classical aeroelastic phenomena in the fluid-structure interaction of piezolaminated beams at the microscale, with the aim of evaluating a possible application in the field of energy harvesting. The performances of this kind of structure are critically assessed by considering the theoretical estimate of electric power generation on the basis of realistic microfluidic flows
Modelling of spontaneous adhesion phenomena in micro-electro-mechanical systems
No full textAn innovative approach for the numerical study of spontaneous adhesion (or stiction) phenomena in Micro-Electro-Mechanical Systems (MEMS) is proposed, based on the use of 3D Finite Element (FE) models. Stiction is a major reliability problem in MEMS which can completely destroy the normal mobility of parts which have the task e.g. to sense the external acceleration in micro-accelerometers or the rotation velocity in micro-gyroscopes. Capillary and van der Waals forces are first selected as the most important sources of stiction; subsequently, these forces are modelled in a simplified way in view of their introduction in a FE model. As a second important ingredient in the proposed modelling approach for spontaneous adhesion, rough surfaces are numerically generated by making use of suitably adapted algorithms originally developed for tribology studies. A complete 3D FE model for two rough surfaces which come at very short distances is thus built and various results showing the modelling capabilities are shown. A comparison with experimental results recently appeared in the literature is proposed
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