Browsing by Author "Rizzuti, Sergio"

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Analisi tecnico-sperimentale delle metodologie transitori di identificazione dei parametri caratteistici dei collettori solari termici a liquido
(2008) Cucumo, Silvio; Rizzuti, Sergio; Marinelli, Valerio
Definizione di un modello di sintesi per l’analisi del comportamento dinamico dei veicoli
(2014-04-07) Malito, Giorgio; Rizzuti, Sergio; Gatti, Gianluca
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.
Development of static and dynamic techniques for the elastic characterization of isotropic and composite material
(2008-11-21) Stigliano, Giambattista; Rizzuti, Sergio; Pagnotta, Leonardo
Flow-altering countermeasures against local scour at bridge piers
(2014-06-09) Tafarojnoruz, Ali; Gaudio, Roberto; Rizzuti, Sergio
The ability to protect bridge piers and abutments against scour is critical to bridge safety. Excessive pier scour can cause high maintenance costs or even bridge collapse resulting in the interruption of traffic and possibly death. Up to now, various types of countermeasures have been recommended to reduce scouring around pier foundations. The countermeasures against pier scour can be broadly classified into two categories: (1) flow-altering and (2) bed-armouring countermeasures. This thesis focuses on the first category of countermeasures. Based on a comprehensive review of the up-to-date studies on various types of flow-altering countermeasures, these can be classified into four main groups based on their shapes and performances: (1) openings through piers, (2) pier attachments, (3) bed attachments and (4) other devices. After evaluation and considering all the countermeasures, a few countermeasures were recommended for further investigations. Among them, five countermeasures were selected for analysis in the present thesis. They are transverse sacrificial piles, collar, threading, pier slot and bed-sill. The first part of the experiments, were performed in clear-water scour condition, near threshold condition of sediment movement. In this part, countermeasures were tested individually. Afterwards, countermeasures that showed appropriate efficiency in scour depth reduction were combined one by one. Results of this part showed that a collar, pier slot and sacrificial piles may show efficiency of about 30% in scour depth reduction; however, threading cannot be assumed as a reliable pier scour countermeasure. Results show that the blockage ratio of sacrificial piles is an important parameter, since by increasing the number of piles from three to five, the efficiency reduces. In this part also optimum size and location of a pier slot were criticised and best configuration based on previous and present studies was proposed. In fact, the best configuration can be suggested as a pier slot half as long as the flow depth plus maximum scour depth. In this case, the pier slot near the water surface may not significantly increase the efficiency. A combination of sacrificial piles with a collar and sacrificial piles with a slot showed that they cannot reduce the scour depth significantly with respect to each individual countermeasure. In particular, a combination of a collar and sacrificial piles increases the rate of scouring with respect to a single collar. At the end of this part, a combination of a bed-sill and cut-collar was selected as the best configuration. Two forms of this countermeasure were proposed for further studies. In the first proposed countermeasure, the use of a sill as wide as the channel width was recommended. This form, although reliable to prevent souring at the upstream part of the bed-sill, may not be applicable for some practical purposes. Therefore, in another attempt, a shorter bed-sill was also proposed, protected with two side-walls, in order to reduce the risk of scour intrusion in front of the bed-sill. These two proposed countermeasures showed efficiencies of 68.5% and 64.5% in scour depth reduction, however owing to the use of a border around the collar rim, the scour did not reach the pier body. In next part, the later form of proposed countermeasure that consists of a shorter bed-sill and seems to be more practical, was evaluated in unsteady flow tests with the peak flow intensity slightly greater than the threshold for the inception of sediment movement. In this section of the thesis, circular and round nose and tail rectangular piers were tested in both configurations of single and two in-line piers. The results of unsteady flow tests also show that the proposed combined countermeasure can protect pier foundation during a flood event. Specifically, it seems that the proposed countermeasure is more effective when it is applied to round nose and tail rectangular piers than circular ones
Fundamental aspects in metal cutting modelling
(2014-04-07) Rizzuti, Stefania; Rizzuti, Sergio; Filice, Luigino
Identation-Based fracture characterization of brittle materials
(2008-11-21) Leonardi, Alessandro; Rizzuti, Sergio; Furgiuele, Franco; Wood, Robert J.K.; Syngellakis, Stavros
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.
Integrazione di tecniche ottiche e acustiche di imaging 3D in ambiente subacqueo
(2015-12-16) Lagudi, Antonio; Pagnotta, Leonardo; Rizzuti, Sergio; Bruno, Fabio
Interazione Uomo Macchina nella Progettazione Industriale: l’utilizzo della Realtà Virtuale come Strumento di Progettazione
(2008-11-21) Pasquino, Germana; Rizzuti, Sergio; Luchi, Maria Laura
Inventory and warehouse management in production systems and supply chain based on advanced modeling & simulation
(2014-04-07) Curcio, Duilio; Rizzuti, Sergio; Mirabelli, Giovanni
Mechanisrns and modeling of white and dark layersı formation in hard machining of AISI 52100 steels
(2011) Caruso, Serafino; Rizzuti, Sergio; Umbrello, Domenico
Methodologies to enhance performances in sheet metal forming processes
(2009-11-16) Manco, Giuseppe Leonardo; Rizzuti, Sergio; Filice, Luigino
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
Modellazione numerica di un sistema integrato digestore anaerobico-celle a combustione ad ossidi solidi con reforming indiretto interno
(2012-11-15) Corigliano, Orlando; Rizzuti, Sergio; Petronilla, Fragiacomo
Progettazione e prototipazione di dispositivi meccatronici per la gestione sostenibile dell'ecosistema marino
(2015-12-16) Spadafora, Francesco; Pagnotta, Leonardo; Rizzuti, Sergio; Muzzupappa, Maurizio
Progettazione end-effector per chirurgia laparoscopica
(2010-11-28) Perrelli, Michele; Danieli, Guido; Rizzuti, Sergio
Studio di modelli di calcolo della luminanza del cielo e confronto con dati sperimentali
(2012-11-15) Mele, Marilena; Rizzuti, Sergio; Marinelli, Valerio
Synthesis and characterization of helically coiled carbon nanotubes
(2011-11-23) Csató, Anita; Rizzuti, Sergio; Nagy, Jànos B.
Although coiled carbon nanofibers can be synthesized on large scale, the selective synthesis of coiled carbon nanotubes is still a challenge for the scientific community. In the present work we aimed to produce helically coiled CNTs (HCNTs) in at least 10% of the product, taking in consideration previous works. Alumina-, sepiolite and silica supported Co-; Fe-; Co-Fe and Co-Pr catalysts were prepared and tested in CNT synthesis reactions applying different conditions. Sepiolite and alumina supported catalysts showed low activity in the synthesis of HCNTs. The helices were maximum 1-2% of all the synthesized CNTs. A more detailed study was carried out with silica supported catalysts. The catalysts were prepared with the ion-adsorption-precipitation (IAP) method. A preliminary study was carried out to observe the behavior of different silica supported catalysts. Co-; Fe-; Co-Fe and Co-Pr catalysts were prepared with different metal loadings. Special attention was dedicated to the Co-Pr catalysts that showed higher activity in the HCNT production. The 2.5%Co-2.5%Pr; 4%Co-1%Pr and the 1%Co-4%Pr catalysts were chosen for a more detailed study. The effect of the temperature, the carbon source flow and the carrier gas flow variation was tested in the synthesis of helically coiled carbon nanotubes. The most favorable reaction conditions for the HCNT synthesis in our conditions are presented in table 1. Catalyst Reaction temperature (°C) C2H2 flow (ml/min) N2 flow %HCNTs 2.5%Co-2.5%Pr 700 30 300 15 4%Co-1%Pr 650 30 300 14-15 4%Co-1%Pr 700 30 600 14-15 1%Co-4%Pr 700 30 300 15-17 1%Co-4%Pr 700 30 600 14-15 Table 1.: Most favorable reaction conditions for HCNT formation over 5%Co-Pr catalysts with different metal ratios The synthesis products contain approximately 15% helically coiled MWCNTs. This gives the possibility to apply the synthesized HCNTs in nanocomposite materials, and exploit the peculiar properties of these structures. However, the purification process of the samples should be optimized. The characteristics, such as coil diameter and coil pitch, of the helices produced on 5%Co- Pr/SiO2 catalysts were analyzed. The morphology of these helices vary from wavy coils, Sshaped tubes, to tight helices and loose telephone-cord-like nanotubes. Their coil diameter varies from 25 nm to 270 nm but the most frequent values are present in the range of 25-50 nm. The coil pitch varies from 20 nm to 300 nm. The most frequent coil pitch values ae between 20-130 nm. Occasionally, helical tubes with coil pitch higher than 300 nm were found in the samples. In most of the samples S-shaped elongated coils are prevalent, however, tight coils are typical for the synthesis using 1%Co-4%Pr and the 4%Co-1%Pr catalysts applying different nitrogen flows. The aim of this work to obtain more than 10% of helically coiled carbon nanotubes in the synthesized product was achieved, however further study is needed to understand the formation of the helices and the role of the different reaction parameters
Un approccio analitico basato sui grafi per lo studio funzionale di prodotti industriali
(2009-11-16) Lofranco, Francesco; Rizzuti, Sergio