Dipartimento di Ingegneria Meccanica, Energetica e Gestionale - Tesi di Dottorato

Permanent URI for this collectionhttp://localhost:4000/handle/10955/100

Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Ingegneria Meccanica, Energetica e Gestionale dell'Università della Calabria.

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Author: search.filters.author.Rizzuti, SergioEnd date: 2023

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Now showing 1 - 10 of 22
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    Metodi e tool per l'ottimizzazione della calibrazione e della validazione dei sistemi di controllo motore
    (2012-09-29) Guzzo, Alessandra; Rizzuti, Sergio; Bova, Sergio; Riegel, Alessandro
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    Integrazione di tecniche ottiche e acustiche di imaging 3D in ambiente subacqueo
    (2015-12-16) Lagudi, Antonio; Pagnotta, Leonardo; Rizzuti, Sergio; Bruno, Fabio
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    Progettazione e prototipazione di dispositivi meccatronici per la gestione sostenibile dell'ecosistema marino
    (2015-12-16) Spadafora, Francesco; Pagnotta, Leonardo; Rizzuti, Sergio; Muzzupappa, Maurizio
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    Progettazione end-effector per chirurgia laparoscopica
    (2010-11-28) Perrelli, Michele; Danieli, Guido; Rizzuti, Sergio
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    Design and application of a novel microelectromechanical system for in situ SEM/TEM displacement controlled tensile testing of nanostructures
    (2012-11-30) Pantano, Maria; Pagnotta, Leonardo; Espinosa, Horacio; Rizzuti, Sergio
    Since the 1920s, different methodologies have been developed especially for mechanical characterization of material samples with characteristic length on the order of micro/nanometers. In the present manuscript, the main of such methodologies are presented and compared, in order to provide guidelines for mechanical characterization at the micro/nanoscale, and to identify the most versatile and effective among them. These are based on complete and miniaturized tensile testing stages, developed on proper microelectromechanical systems (MEMS). Because of their small size (they lie onto silicon wafers with area smaller than 1mm2 and thickness of only few micrometers), such testing devices are particularly suitable to handle micro/nanosized components, and can fit inside the tight chamber of scanning/ transmission electron microscopes (SEM/TEM), for real-time imaging of sample deformation. However, the effectiveness of the tests they allow to perform can be compromised by some disturbing phenomena, like onset of instability, as reported in a certain kind of tensile testing devices. In particular, these devices become unstable as soon as the sample under investigation shows stress relaxation, after some strain has been applied. Nevertheless, it is very important to be able to detect such singularities, since they may allow a deeper comprehen sion of materials’ behavior. In the present work, the above mentioned instability issue is overcome through the design of a novel device for in situ SEM/TEM tensile testing of nanostructures under true displacement control. Like other stages, also the one presented herein consists of two main components: an actuator and a sensor, which are separated by a small gap for positioning of the specimen. Actuation is performed by a thermal actuator, which pulls the end of the sample attached to it. The other end of the sample is instead connected to a displacement sensor, which moves from its equilibrium position, as a consequence of the force transmitted to it by the specimen. However, the main novelty of the present design is the introduction of a feedback control loop. In particular, a controller, implemented within a software routine, receives as input the sensor output, and computes the voltage to be applied to an electrostatic actuator, in order to generate a rebalance force of electrostatic nature, thus bringing the sensor back to equilibrium. In this way, the end ofand this boundary condition removes any potential source of instability. The MEMS sensing and actuating structures were designed by the means of both analytical and numerical approaches, in order to provide sufficiently high deformation (up to about 50% strain) and forces (up to 100μN) to break a variety of material samples. Fabrication was carried out by an external foundry on the basis of the masks drawings, reported in the present manuscript. In order to guarantee a correct functioning of the device, a proper experimental apparatus was developed. This allowed electrical connection of all of the actuating and sensing parts with external instrumentation, including current pre-amplifiers, power supplies, a lock-in amplifier, and a data acquisition card, which was used as interface between the controller and the MEMS device. The effectiveness of the present experimental apparatus was proven through an application on silver nanowires, with about 70 nm diameter and 3-4 μm gage length. The corresponding results, in terms of Young modulus, fracture and yield strength, showed good agreement with data already available in the literature, obtained for samples with comparable size. Also the device ability to detect singularities in the sample characteristic was demonstrated, as emerges from a load drop recorded after yielding of a nanowire. As a conclusion, the present experimental apparatus can be considered for future in situ SEM/TEM tensile tests on other material samples, as well as for electromechanical tests, since the specimen results to be electrically isolated from the remaining of the device. Thus, very interesting properties, like piezoresistivity and piezoelectricity, could be evaluated.
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    Studio di modelli di calcolo della luminanza del cielo e confronto con dati sperimentali
    (2012-11-15) Mele, Marilena; Rizzuti, Sergio; Marinelli, Valerio
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    Innovative methodologies for multi-view 3D reconstruction of cultural heritage
    (2012-11-15) Gallo, Alessandro; Rizzuti, Sergio; Bruno, Fabio
    This dissertation focuses on the use of multi-view 3D reconstruction techniques in the field of cultural heritage. To name just a few applications, a digital 3D acquisition can be used for documentation purposes in the event of destruction or damage of an artefact, or for the creation of museums and virtual tourism, education, structural studies, restoration, etc... All these applications require high precision and accuracy to reproduce the details, but there are other important characteristics such as low cost, ease of use, the level of knowledge needed to operate the systems, which have also to be taken into account. At the present time, the interest is growing around the use of images for the digital documentation of cultural heritage, because it is possible to obtain a 3D model by the means of common photographic equipment. In this work, we have investigated multi-view 3D reconstruction techniques in two specific fields that have not been treated in literature: the 3D reconstruction of small objects (from few mm to few cm) and the survey of submerged archaeological finds. As for the 3D reconstruction of small objects, a new methodology based on multi-view and image fusion techniques has been developed. The used approach solves the problems related to the use of macro lenses in photogrammetry, such as the very small depth of field and the loss of quality due to diffraction. Since image matching algorithms cannot work on blurred areas, each image of the sequence is obtained by merging pictures acquired at different focus planes. The methodology has been applied on different case studies, and the results have shown that it is possible to reconstruct small complex objects with a resolution of 20 microns and an accuracy of 10 microns. For which concerns the underwater imaging, a preliminary comparative study between active and passive techniques in turbid water has been conducted. The experimental setup consists in a 3D scanner designed for underwater survey, composed by two cameras and a projector. An analysis on the influence of the colour channel has been conducted, showing how it is possible to obtain a cleaner reconstruction by using the green channel only. The results have shown a denser point cloud when using the passive technique, characterized by missing areas since the technique is more sensible to turbidity. By contrast, the reconstruction conducted with the active technique have shown more stable results as the turbidity increases, but a greater noise. A multi-view passive technique has been experimented for the survey of a submerged structure located at a depth of 5 meters, on a seabed characterized by poor visibility conditions and the presence of marine flora and fauna. We performed an analysis of the performances of a multi-view technique commonly used in air in the first instance, highlighting the limits of the current techniques in underwater environment. In such conditions, in fact, it has not been possible to obtain a complete reconstruction of the scene. The second stage of the process was the testing of image enhancement algorithms in order to improve matching performances in poor visibility conditions. In particular, a variational analysis of the factors that influence the quality of the 3D reconstruction, such as the image resolution and the colour channel, has been performed. For this purpose, the data related to the parameters of interest, such as the number of features extracted or the number of oriented cameras, have been evaluated. The statistical analysis has allowed to find the best combination of factors for a complete and accurate 3D reconstruction of the submerged scenario.
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