Studio sperimentale del comportamento a fatica di calcestruzzi rinforzati con fibre sintetiche

La presente tesi di Laurea Magistrale ha lo scopo di studiare sperimentalmente il comportamento a fatica dei calcestruzzi rinforzati con fibre macro-sintetiche (Macro Synthetic Fiber Reinforced Concrete, MSFRC). Sono condotte prove cicliche di flessione su tre punti al fine di caratterizzare il comportamento dei calcestruzzi fibrorinforzati in regime fessurato nel caso di fatica ad alto numero di cicli (High Cycle Fatigue, HCF). Oltre a prove di fatica sono condotte anche prove monotone a flessione al fine di ottenere la caratterizzazione meccanica del materiale determinandone i principali parametri di frattura; i risultati di tali prove sono utili anche a definire la procedura di prova definitiva da adottare durante i test di fatica. Le testimonianze presenti in letteratura sul comportamento a fatica degli FRC rinforzati con fibre sintetiche sono molto limitate, specialmente nel caso di fatica ad alto numero di cicli; inoltre le prove cicliche, a differenza delle prove monotone, non sono prove standardizzate e quindi definite dalla normativa. Nel corso della presente campagna sperimentale si cercherà quindi di definire una procedura per poter eseguire in maniera stabile le prove di flessione, monotone e di fatica, su campioni prismatici di calcestruzzo fibrorinforzato. L’idea alla base della campagna sperimentale oggetto di questa tesi è quella di riprodurre, mediante prove di fatica, le usuali condizioni di esercizio a cui sono sottoposte, durante la loro vita utile, strutture come pavimentazioni stradali o industriali; infatti il traffico stradale o il transito di macchinari possono indurre su strutture del genere dei carichi ripetuti nel tempo tali da provocarne il collasso per fatica. La presente tesi è articolata in otto capitoli nei quali verranno evidenziate le principali proprietà, sia meccaniche che fisiche, del materiale composito oggetto dello studio, saranno definite le procedure dei test eseguiti e verranno discussi i risultati derivanti da essi.

Measurement of LSP-induced residual stresses and fatigue life on thin-walled aluminium alloys specimens

This thesis work encloses activities carried out in the Laser Center of the Polytechnic University of Madrid and the laboratories of the University of Bologna in Forlì. This thesis focuses on the superficial mechanical treatment for metallic materials called Laser Shock Peening (LSP). This process is a surface enhancement treatment which induces a significant layer of beneficial compressive residual stresses underneath the surface of metal components in order to improve the detrimental effects of the crack growth behavior rate in it. The innovation aspect of this work is the LSP application to specimens with extremely low thickness. In particular, after a bibliographic study and comparison with the main treatments used for the same purposes, this work analyzes the physics of the operation of a laser, its interaction with the surface of the material and the generation of the surface residual stresses which are fundamentals to obtain the LSP benefits. In particular this thesis work regards the application of this treatment to some Al2024-T351 specimens with low thickness. Among the improvements that can be obtained performing this operation, the most important in the aeronautic field is the fatigue life improvement of the treated components. As demonstrated in this work, a well-done LSP treatment can slow down the progress of the defects in the material that could lead to sudden failure of the structure. A part of this thesis is the simulation of this phenomenon using the program AFGROW, with which have been analyzed different geometric configurations of the treatment, verifying which was better for large panels of typical aeronautical interest. The core of the LSP process are the residual stresses that are induced on the material by the interaction with the laser light, these can be simulated with the finite elements but it is essential to verify and measure them experimentally. In the thesis are introduced the main methods for the detection of those stresses, they can be mechanical or by diffraction. In particular, will be described the principles and the detailed realization method of the Hole Drilling measure and an introduction of the X-ray Diffraction; then will be presented the results I obtained with both techniques. In addition to these two measurement techniques will also be introduced Neutron Diffraction method. The last part refers to the experimental tests of the fatigue life of the specimens, with a detailed description of the apparatus and the procedure used from the initial specimen preparation to the fatigue test with the press. Then the obtained results are exposed and discussed.

Design of an indirectly fired gas turbine integrated with an organic rankine cycle unit for combined heat and power production

In the last years, the European countries have paid increasing attention to renewable sources and greenhouse emissions. The Council of the European Union and the European Parliament have established ambitious targets for the next years. In this scenario, biomass plays a prominent role since its life cycle produces a zero net carbon dioxide emission. Additionally, biomass can ensure plant operation continuity thanks to its availability and storage ability. Several conventional systems running on biomass are available at the moment. Most of them are performant either in the large-scale or in the small power range. The absence of an efficient system on the small-middle scale inspired this thesis project. The object is an innovative plant based on a wet indirectly fired gas turbine (WIFGT) integrated with an organic Rankine cycle (ORC) unit for combined heat and power production. The WIFGT is a performant system in the small-middle power range; the ORC cycle is capable of giving value to low-temperature heat sources. Their integration is investigated in this thesis with the aim of carrying out a preliminary design of the components. The targeted plant output is around 200 kW in order not to need a wide cultivation area and to avoid biomass shipping. Existing in-house simulation tools are used: They are adapted to this purpose. Firstly the WIFGT + ORC model is built; Zero-dimensional models of heat exchangers, compressor, turbines, furnace, dryer and pump are used. Different fluids are selected but toluene and benzene turn out to be the most suitable. In the indirectly fired gas turbine a pressure ratio around 4 leads to the highest efficiency. From the thermodynamic analysis the system shows an electric efficiency of 38%, outdoing other conventional plants in the same power range. The combined plant is designed to recover thermal energy: Water is used as coolant in the condenser. It is heated from 60°C up to 90°C, ensuring the possibility of space heating. Mono-dimensional models are used to design the heat exchange equipment. Different types of heat exchangers are chosen depending on the working temperature. A finned-plate heat exchanger is selected for the WIFGT heat transfer equipment due to the high temperature, oxidizing and corrosive environment. A once-through boiler with finned tubes is chosen to vaporize the organic fluid in the ORC. A plate heat exchanger is chosen for the condenser and recuperator. A quasi-monodimensional model for single-stage axial turbine is implemented to design both the WIFGT and the ORC turbine. The system simulation after the components design shows an electric efficiency around 34% with a decrease by 10% compared to the zero-dimensional analysis. The work exhibits the system potentiality compared to the existing plants from both technical and economic point of view.

Controllo ultra-low power di un modulatore back-scattering per applicazioni di localizzazione in sistemi RFID

In questa tesi viene elaborata un'applicazione ultra-low power (ULP) basata su microcontrollore, per implementare la procedura di controllo di diversi circuiti di un tag RFID. Il tag preso in considerazione è pensato per lavorare in assenza di batteria, da cui la necessita' di ridurre i consumi di potenza. La sua attivazione deve essere inoltre comandata attraverso un'architettura Wake up Radio (WuR), in cui un segnale di controllo radio indirizza e attiva il circuito. Nello specifico, la rete di decodifica dell'indirizzo è stata realizzata mediante il modulo di comunicazione seriale del microcontrollore. Nel Capitolo 1 verrà introdotto il tema dell'Energy Harvesting. Nel Capitolo 2 verrà illustrata l'architettura del sistema nel suo complesso. Nel Capitolo 3 verrà spiegato dettagliatamente il funzionamento del microcontrollore scelto. Il Capitolo 4 sarà dedicato al firmware implementato per svolgere le operazioni fondamentali imputate al micro per i compiti di controllo. Verrà inoltre introdotto il codice VHDL sviluppato per emulare l'output del modulo WuR mediante un FPGA della famiglia Cyclone II. Nel Capitolo 5 verrà presentata una stima dei consumi del microcontrollore in funzione dei parametri di configurazione del sistema. Verrà inoltre effettuato un confronto con un altro microcontrollore che in alcune condizioni potrebbe rappresentare iun'alternativa valida di progetto. Nei Capitoli 6 e 7 saranno descritti possibili sviluppi futuri e conclusioni del progetto. Le specifiche di progetto rilevanti della tesi sono: 1. minimo consumo energetico possibile del microcontrollore ULP 2. elevata rapidità di risposta per la ricezione dei tag, per garantire la ricezione di un numero maggiore possibile di indirizzi (almeno 20 letture al secondo), in un range di tempo limitato 3. generazione di un segnale PWM a 100KHz di frequenza di commutazione con duty cycle 50% su cui basare una modulazione in back-scattering.

Light coloured and draining wearing courses for low-impact urban pavements

Urban health and well-being are becoming current issues of modern cities due to local climate change and environmental noise. The Urban Heat Island and the Urban Noise Island have a direct impact on the economic, social, and environmental aspects of urban life, negatively affecting the well-being of worldwide citizens. The present research is focused on the study of innovative materials employed in the production of wearing course mixtures aiming to mitigate these phenomena. In particular, a synthetic transparent binder substituting bitumen and recycled aggregates produced from construction and demolition waste. Four mixtures were analysed. Among them, Mix 1 and Mix 2 are conventional wearing courses. The first is exclusively made of natural aggregates, while the second is constituted of 45 % of recycled aggregates (RA). Mix 3 and Mix 4 are draining wearing courses and, in this case, Mix 4 was produced by using 55 % of RA. Laboratory tests were required to fully characterize all the produced samples, allowing a proper comparison of results. Overall, all the mixtures studied provide prominent results suggesting potential applications of these innovative wearing courses in cycle lanes, historical centres, plazas, and parking lots. Among the conventional mixtures, Mix 2 is the most likely to assure the best performance in terms of road safety, efficiency, and durability while as far as the draining mixtures are concerned, Mix 4 is preferable due to its high content of recycled aggregates.

Towards the sustainable production of methyl methacrylate: A comparative analysis of industrial chemical production processes using life cycle assessment methodology

Increasing environmental awareness has been a significant driving force for innovations and process improvements in different sectors and the field of chemistry is not an outlier. Innovating around industrial chemical processes in line with current environmental responsibilities is however no mean feat. One of such hard to overhaul process is the production of methyl methacrylate (MMA) commonly produced via the acetone cyanohydrin (ACH) process developed back in the 1930s. Different alternatives to the ACH process have emerged over the years and the Alpha Lucite process has been particularly promising with a combined plant capacity of 370,000 metric tonnes in Singapore and Saudi Arabia. This study applied Life Cycle Assessment methodology to conduct a comparative analysis between the ACH and Lucite processes with the aim of ascertaining the effect of applying principles of green chemistry as a process improvement tool on overall environmental impacts. A further comparison was made between the Lucite process and a lab-scale process that is further improvement on the former, also based on green chemistry principles. Results showed that the Lucite process has higher impacts on resource scarcity and ecosystem health whereas the ACH process has higher impacts on human health. On the other hand, compared to the Lucite process the lab-scale process has higher impacts in both the ecosystem and human health categories with lower impacts only in the resource scarcity category. It was observed that the benefits of process improvements with green chemistry principles might not be apparent in some categories due to some limitations of the methodology. Process contribution analysis was also performed and it revealed that the contribution of energy is significant, therefore a sensitivity analysis with different energy scenarios was performed. An uncertainty analysis using Monte Carlo analysis was also performed to validate the consistency of the results in each of the comparisons.

Constraints on the duty cycle of the remnant radio galaxy NGC 6086 in the galaxy group Abell 2162

Galaxy clusters and groups are the most massive bounded structures and the knots of the large-scale structure of the Universe. These structures reside in dark matter haloes, hosting tens to hundreds of galaxies and they are filled with hot and rarefied gas. Radio Galaxies are a peculiar class of galaxies with a luminosity in the radio band up to 10^46 erg/s between 10 MHz and 100 GHz. These galaxies are a subclass of AGN in which there is accretion on the Super Massive Black Hole. The accretion generates jets of relativistic particles and magnetic fields which lose energy through synchrotron radiation, best observable at radio frequencies. The study of the spectral ageing of the AGN plasma is fundamental to understand its evolution, interaction with the environment and to constrain the AGN duty cycle. n this thesis, we have investigated the duty cycle of the nearby remnant radio galaxy NGC 6086, located in the centre of the galaxy group Abell 2162. We have made major steps forward thanks to the new high-sensitivity interferometers in the low-frequency radio band. We have detected for the first time three filaments of emission and a second couple of lobes. We have performed an integrated and resolved analysis on the previously known inner lobes, the new filaments and the older outer lobes. We have performed an age estimate of the two pairs of lobes to give constraints on the duty cycle of the source and an estimate of its active time.