Additive Manufacturing by LPBF and WAAM of metals: correlation between production process, microstructure and mechanical properties

In the most recent years, Additive Manufacturing (AM) has drawn the attention of both academic research and industry, as it might deeply change and improve several industrial sectors. From the material point of view, AM results in a peculiar microstructure that strictly depends on the conditions of the additive process and directly affects mechanical properties. The present PhD research project aimed at investigating the process-microstructure-properties relationship of additively manufactured metal components. Two technologies belonging to the AM family were considered: Laser-based Powder Bed Fusion (LPBF) and Wire-and-Arc Additive Manufacturing (WAAM). The experimental activity was carried out on different metals of industrial interest: a CoCrMo biomedical alloy and an AlSi7Mg0.6 alloy processed by LPBF, an AlMg4.5Mn alloy and an AISI 304L austenitic stainless steel processed by WAAM. In case of LPBF, great attention was paid to the influence that feedstock material and process parameters exert on hardness, morphological and microstructural features of the produced samples. The analyses, targeted at minimizing microstructural defects, lead to process optimization. For heat-treatable LPBF alloys, innovative post-process heat treatments, tailored on the peculiar hierarchical microstructure induced by LPBF, were developed and deeply investigated. Main mechanical properties of as-built and heat-treated alloys were assessed and they were well-correlated to the specific LPBF microstructure. Results showed that, if properly optimized, samples exhibit a good trade-off between strength and ductility yet in the as-built condition. However, tailored heat treatments succeeded in improving the overall performance of the LPBF alloys. Characterization of WAAM alloys, instead, evidenced the microstructural and mechanical anisotropy typical of AM metals. Experiments revealed also an outstanding anisotropy in the elastic modulus of the austenitic stainless-steel that, along with other mechanical properties, was explained on the basis of microstructural analyses.

Dry grinding technology for automotive gears manufacturing: process modeling and optimization

The following thesis focused on the dry grinding process modelling and optimization for automotive gears production. A FEM model was implemented with the aim at predicting process temperatures and preventing grinding thermal defects on the material surface. In particular, the model was conceived to facilitate the choice of the grinding parameters during the design and the execution of the dry-hard finishing process developed and patented by the company Samputensili Machine Tools (EMAG Group) on automotive gears. The proposed model allows to analyse the influence of the technological parameters, comprising the grinding wheel specifications. Automotive gears finished by dry-hard finishing process are supposed to reach the same quality target of the gears finished through the conventional wet grinding process with the advantage of reducing production costs and environmental pollution. But, the grinding process allows very high values of specific pressure and heat absorbed by the material, therefore, removing the lubricant increases the risk of thermal defects occurrence. An incorrect design of the process parameters set could cause grinding burns, which affect the mechanical performance of the ground component inevitably. Therefore, a modelling phase of the process could allow to enhance the mechanical characteristics of the components and avoid waste during production. A hierarchical FEM model was implemented to predict dry grinding temperatures and was represented by the interconnection of a microscopic and a macroscopic approach. A microscopic single grain grinding model was linked to a macroscopic thermal model to predict the dry grinding process temperatures and so to forecast the thermal cycle effect caused by the process parameters and the grinding wheel specification choice. Good agreement between the model and the experiments was achieved making the dry-hard finishing an efficient and reliable technology to implement in the gears automotive industry.

Models and methods for power monolithic microwave integrated circuits

Computer aided design of Monolithic Microwave Integrated Circuits (MMICs) depends critically on active device models that are accurate, computationally efficient, and easily extracted from measurements or device simulators. Empirical models of active electron devices, which are based on actual device measurements, do not provide a detailed description of the electron device physics. However they are numerically efficient and quite accurate. These characteristics make them very suitable for MMIC design in the framework of commercially available CAD tools. In the empirical model formulation it is very important to separate linear memory effects (parasitic effects) from the nonlinear effects (intrinsic effects). Thus an empirical active device model is generally described by an extrinsic linear part which accounts for the parasitic passive structures connecting the nonlinear intrinsic electron device to the external world. An important task circuit designers deal with is evaluating the ultimate potential of a device for specific applications. In fact once the technology has been selected, the designer would choose the best device for the particular application and the best device for the different blocks composing the overall MMIC. Thus in order to accurately reproducing the behaviour of different-in-size devices, good scalability properties of the model are necessarily required. Another important aspect of empirical modelling of electron devices is the mathematical (or equivalent circuit) description of the nonlinearities inherently associated with the intrinsic device. Once the model has been defined, the proper measurements for the characterization of the device are performed in order to identify the model. Hence, the correct measurement of the device nonlinear characteristics (in the device characterization phase) and their reconstruction (in the identification or even simulation phase) are two of the more important aspects of empirical modelling. This thesis presents an original contribution to nonlinear electron device empirical modelling treating the issues of model scalability and reconstruction of the device nonlinear characteristics. The scalability of an empirical model strictly depends on the scalability of the linear extrinsic parasitic network, which should possibly maintain the link between technological process parameters and the corresponding device electrical response. Since lumped parasitic networks, together with simple linear scaling rules, cannot provide accurate scalable models, either complicate technology-dependent scaling rules or computationally inefficient distributed models are available in literature. This thesis shows how the above mentioned problems can be avoided through the use of commercially available electromagnetic (EM) simulators. They enable the actual device geometry and material stratification, as well as losses in the dielectrics and electrodes, to be taken into account for any given device structure and size, providing an accurate description of the parasitic effects which occur in the device passive structure. It is shown how the electron device behaviour can be described as an equivalent two-port intrinsic nonlinear block connected to a linear distributed four-port passive parasitic network, which is identified by means of the EM simulation of the device layout, allowing for better frequency extrapolation and scalability properties than conventional empirical models. Concerning the issue of the reconstruction of the nonlinear electron device characteristics, a data approximation algorithm has been developed for the exploitation in the framework of empirical table look-up nonlinear models. Such an approach is based on the strong analogy between timedomain signal reconstruction from a set of samples and the continuous approximation of device nonlinear characteristics on the basis of a finite grid of measurements. According to this criterion, nonlinear empirical device modelling can be carried out by using, in the sampled voltage domain, typical methods of the time-domain sampling theory.

Enabling Blocks for Integrated CMOS UWB Transceivers

The last decades have seen an unrivaled growth and diffusion of mobile telecommunications. Several standards have been developed to this purposes, from GSM mobile phone communications to WLAN IEEE 802.11, providing different services for the the transmission of signals ranging from voice to high data rate digital communications and Digital Video Broadcasting (DVB). In this wide research and market field, this thesis focuses on Ultra Wideband (UWB) communications, an emerging technology for providing very high data rate transmissions over very short distances. In particular the presented research deals with the circuit design of enabling blocks for MB-OFDM UWB CMOS single-chip transceivers, namely the frequency synthesizer and the transmission mixer and power amplifier. First we discuss three different models for the simulation of chargepump phase-locked loops, namely the continuous time s-domain and discrete time z-domain approximations and the exact semi-analytical time-domain model. The limitations of the two approximated models are analyzed in terms of error in the computed settling time as a function of loop parameters, deriving practical conditions under which the different models are reliable for fast settling PLLs up to fourth order. Besides, a phase noise analysis method based upon the time-domain model is introduced and compared to the results obtained by means of the s-domain model. We compare the three models over the simulation of a fast switching PLL to be integrated in a frequency synthesizer for WiMedia MB-OFDM UWB systems. In the second part, the theoretical analysis is applied to the design of a 60mW 3.4 to 9.2GHz 12 Bands frequency synthesizer for MB-OFDM UWB based on two wide-band PLLs. The design is presented and discussed up to layout level. A test chip has been implemented in TSMC CMOS 90nm technology, measured data is provided. The functionality of the circuit is proved and specifications are met with state-of-the-art area occupation and power consumption. The last part of the thesis deals with the design of a transmission mixer and a power amplifier for MB-OFDM UWB band group 1. The design has been carried on up to layout level in ST Microlectronics 65nm CMOS technology. Main characteristics of the systems are the wideband behavior (1.6 GHz of bandwidth) and the constant behavior over process parameters, temperature and supply voltage thanks to the design of dedicated adaptive biasing circuits.

Porous Polymeric Bioresorbable Scaffolds for Tissue Engineering

Tissue engineering is a discipline that aims at regenerating damaged biological tissues by using a cell-construct engineered in vitro made of cells grown into a porous 3D scaffold. The role of the scaffold is to guide cell growth and differentiation by acting as a bioresorbable temporary substrate that will be eventually replaced by new tissue produced by cells. As a matter or fact, the obtainment of a successful engineered tissue requires a multidisciplinary approach that must integrate the basic principles of biology, engineering and material science. The present Ph.D. thesis aimed at developing and characterizing innovative polymeric bioresorbable scaffolds made of hydrolysable polyesters. The potentialities of both commercial polyesters (i.e. poly-e-caprolactone, polylactide and some lactide copolymers) and of non-commercial polyesters (i.e. poly-w-pentadecalactone and some of its copolymers) were explored and discussed. Two techniques were employed to fabricate scaffolds: supercritical carbon dioxide (scCO2) foaming and electrospinning (ES). The former is a powerful technology that enables to produce 3D microporous foams by avoiding the use of solvents that can be toxic to mammalian cells. The scCO2 process, which is commonly applied to amorphous polymers, was successfully modified to foam a highly crystalline poly(w-pentadecalactone-co-e-caprolactone) copolymer and the effect of process parameters on scaffold morphology and thermo-mechanical properties was investigated. In the course of the present research activity, sub-micrometric fibrous non-woven meshes were produced using ES technology. Electrospun materials are considered highly promising scaffolds because they resemble the 3D organization of native extra cellular matrix. A careful control of process parameters allowed to fabricate defect-free fibres with diameters ranging from hundreds of nanometers to several microns, having either smooth or porous surface. Moreover, versatility of ES technology enabled to produce electrospun scaffolds from different polyesters as well as “composite” non-woven meshes by concomitantly electrospinning different fibres in terms of both fibre morphology and polymer material. The 3D-architecture of the electrospun scaffolds fabricated in this research was controlled in terms of mutual fibre orientation by properly modifying the instrumental apparatus. This aspect is particularly interesting since the micro/nano-architecture of the scaffold is known to affect cell behaviour. Since last generation scaffolds are expected to induce specific cell response, the present research activity also explored the possibility to produce electrospun scaffolds bioactive towards cells. Bio-functionalized substrates were obtained by loading polymer fibres with growth factors (i.e. biomolecules that elicit specific cell behaviour) and it was demonstrated that, despite the high voltages applied during electrospinning, the growth factor retains its biological activity once released from the fibres upon contact with cell culture medium. A second fuctionalization approach aiming, at a final stage, at controlling cell adhesion on electrospun scaffolds, consisted in covering fibre surface with highly hydrophilic polymer brushes of glycerol monomethacrylate synthesized by Atom Transfer Radical Polymerization. Future investigations are going to exploit the hydroxyl groups of the polymer brushes for functionalizing the fibre surface with desired biomolecules. Electrospun scaffolds were employed in cell culture experiments performed in collaboration with biochemical laboratories aimed at evaluating the biocompatibility of new electrospun polymers and at investigating the effect of fibre orientation on cell behaviour. Moreover, at a preliminary stage, electrospun scaffolds were also cultured with tumour mammalian cells for developing in vitro tumour models aimed at better understanding the role of natural ECM on tumour malignity in vivo.

Studio del processo CVI/CVD per lo sviluppo di compositi ceramici rinforzati a fibra lunga

The most relevant thermo-mechanical properties of SiC or C based CFCCs are high strength, high toughness, low weight, high reliability, thermal shock and fatigue resistance. Thanks to these special characteristics, the CFCCs are the best candidates to substitute metals and monolithic ceramics, traditionally employed to realize components in energy, aeronautic and nuclear fields. Among the commonly techniques for the CFCCs production, CVI still represents the most significant one. Its main advantages are the versatility, the high quality deposits and the fact that it is conducted under mild temperature conditions. On the other hand, this technique is quite complex, therefore the set up of all process parameters needs long development time. The main purpose of the present study was to analyze the parameters controlling the CVD and CVI processes. Specifically, deposition and infiltration of SiC and Py-C tests were conducted on non-porous and porous substrates. The experiments were performed with a pilot size Isothermal/Isobaric CVI plant, designed and developed by ENEA. To guarantee the control of the process parameters, a previously optimization of the plant was needed. Changing temperature, pressure, flow rates and methane/hydrogen ratio, the Py-C deposition rate value, for an optimal fibre/matrix interphase thickness, was determined. It was also underlined the hydrogen inhibiting effect over the Py-C deposition rate. Regarding SiC morphologies, a difference between the inner and outer substrate surfaces was observed, as a consequence of a flow rate non-uniformity. In the case of the Cf/C composites development, the key parameter of the CVI process was the gas residence time. In fact, the hydrogen inhibiting effect was evident only with high value of residence time. Furthermore, lower the residence time more homogeneous the Py-C deposition rate was obtained along the reaction chamber axis. Finally, a CVD and CVI theoretical modelling was performed.

Ricerca sulle Caratteristiche di Filtrabilità della Birra e Ottimizzazione del Processo di Filtrazione

Il presente lavoro ha avuto lo scopo di identificare le caratteristiche di filtrabilità della birra attraverso lo svolgimento di prove tecnologiche di filtrazione in scala di laboratorio e su scala pilota, utilizzando diverse tipologie di sistemi filtranti e sperimentando diversi materiali di membrana. La fase preliminare della caratterizzazione della filtrabilità della birra è stata condotta presso i laboratori del Campden-BRI – The Brewing Research International, Inghilterra, mentre le prove tecnologiche su scala pilota si sono svolte presso il CERB – Centro di Eccellenza per la Ricerca sulla Birra. Le prove di filtrazione e le analisi sui campioni hanno permesso di verificare le performance delle diverse membrane utilizzate in risposta alla variazione dei principali parametri del processo di filtrazione tangenziale. Sono stati analizzati diversi parametri di qualità della birra filtrata attraverso il monitoraggio del processo e lo svolgimento di prove analitiche sul prodotto volte ad evidenziare gli effetti delle differenti tecnologie adottate. Per quanto riguarda le prove di laboratorio per la caratterizzazione della filtrabilità della birra, l’analisi della PCS (Photon Correlation Spectroscopy) è stata utilizzata per verificare l’influenza di diversi trattamenti enzimatici sulla efficienza del processo di filtrazione e la loro influenza sulla stabilità colloidale della birra filtrata. Dai risultati ottenuti è emerso che il PCS è un valido strumento per determinare la distribuzione in classi di diametro e il diametro medio effettivo delle particelle solide in sospensione nella birra e può essere utilizzato sia per predire la stabilità della birra filtrata, sia per monitorare il processo di filtrazione in tempo reale.

Analisi sperimentale dell'influenza dei parametri di processo sulla resistenza di contatto tra polimero e stampo durante la formatura

Con gli strumenti informatici disponibili oggi per le industrie, in particolar modo coi software CAE, le possibile simulare in maniera più che soddisfacente i fenomeni fisici presenti in natura. Anche il raffreddamento di un manufatto in polimero può venire simulato, a patto che si conoscano tutti i dati dei materiali e delle condizioni al contorno. Per quanto riguarda i dati dei materiali, i produttori di polimeri sono molto spesso in grado di fornirli, mentre le condizioni al contorno devono essere padroneggiate dal detentore della tecnologia. Nella pratica, tale conoscenza è al più incompleta, quindi si fanno ipotesi per colmare le lacune. Una tra le ipotesi più forti fatte è quella di una perfetta conduzione all'interfaccia tra due corpi. Questo è un vincolo troppo forte, se paragonato alla precisione di tutti gli altri dati necessari alla simulazione, e quindi si è deciso di eseguire una campagna sperimentale per stimare la resistenza al passaggio flusso termico all'interfaccia polimero-stampo ovvero determinare la conduttanza termica di contatto. L'attività svolta in questa tesi di dottorato ha come scopo quello di fornire un contributo significativo allo sviluppo e al miglioramento dell'efficienza termica degli stampi di formatura dei polimeri termoplastici con tecnologia a compressione.

Vanillin production from ferulic acid with Pseudomonas fluorescens BF13-1p4

Bioconversion of ferulic acid to vanillin represents an attractive opportunity for replacing synthetic vanillin with a bio-based product, that can be label “natural”, according to current food regulations. Ferulic acid is an abundant phenolic compound in cereals processing by-products, such as wheat bran, where it is linked to the cell wall constituents. In this work, the possibility of producing vanillin from ferulic acid released enzymatically from wheat bran was investigated by using resting cells of Pseudomonas fluorescens strain BF13-1p4 carrying an insertional inactivation of vdh gene and ech and fcs BF13 genes on a low copy number plasmid. Process parameters were optimized both for the biomass production phase and the bioconversion phase using food-grade ferulic acid as substrate and the approach of changing one variable while fixing the others at a certain level followed by the response surface methodology (RSM). Under optimized conditions, vanillin up to 8.46 mM (1.4 g/L) was achieved, whereas highest productivity was 0.53 mmoles vanillin L-1 h-1). Cocktails of a number of commercial enzyme (amylases, xylanases, proteases, feruloyl esterases) combined with bran pre-treatment with steam explosion and instant controlled pressure drop technology were then tested for the release of ferulic acid from wheat bran. The highest ferulic acid release was limited to 15-20 % of the ferulic acid occurring in bran, depending on the treatment conditions. Ferulic acid 1 mM in enzymatic hydrolyzates could be bioconverted into vanillin with molar yield (55.1%) and selectivity (68%) comparable to those obtained with food-grade ferulic acid after purification from reducing sugars with a non polar adsorption resin. Further improvement of ferulic acid recovery from wheat bran is however required to make more attractive the production of natural vanillin from this by-product.

Integrated analysis and design of optimization and up-scaling of inductively coupled plasma synthesis of nanoparticles

This study is focused on radio-frequency inductively coupled thermal plasma (ICP) synthesis of nanoparticles, combining experimental and modelling approaches towards process optimization and industrial scale-up, in the framework of the FP7-NMP SIMBA European project (Scaling-up of ICP technology for continuous production of Metallic nanopowders for Battery Applications). First the state of the art of nanoparticle production through conventional and plasma routes is summarized, then results for the characterization of the plasma source and on the investigation of the nanoparticle synthesis phenomenon, aiming at highlighting fundamental process parameters while adopting a design oriented modelling approach, are presented. In particular, an energy balance of the torch and of the reaction chamber, employing a calorimetric method, is presented, while results for three- and two-dimensional modelling of an ICP system are compared with calorimetric and enthalpy probe measurements to validate the temperature field predicted by the model and used to characterize the ICP system under powder-free conditions. Moreover, results from the modeling of critical phases of ICP synthesis process, such as precursor evaporation, vapour conversion in nanoparticles and nanoparticle growth, are presented, with the aim of providing useful insights both for the design and optimization of the process and on the underlying physical phenomena. Indeed, precursor evaporation, one of the phases holding the highest impact on industrial feasibility of the process, is discussed; by employing models to describe particle trajectories and thermal histories, adapted from the ones originally developed for other plasma technologies or applications, such as DC non-transferred arc torches and powder spherodization, the evaporation of micro-sized Si solid precursor in a laboratory scale ICP system is investigated. Finally, a discussion on the role of thermo-fluid dynamic fields on nano-particle formation is presented, as well as a study on the effect of the reaction chamber geometry on produced nanoparticle characteristics and process yield.

Polymeric membranes for CO2 separation: effect of aging, humidity and facilitated transport

Polymeric membranes represent a promising technology for gas separation processes, thanks to low costs, reduced energy consumption and limited waste production. The present thesis aims at studying the transport properties of two membrane materials, suitable for CO2 purification applications. In the first part, a polyimide, Matrimid 5218, has been throughout investigated, with particular reference to the effect of thermal treatment, aging and the presence of water vapor in the gas transport process. Permeability measurements showed that thermal history affects relevantly the diffusion of gas molecules across the membrane, influencing also the stability of the separation performances. Subsequently, the effect of water on Matrimid transport properties has been characterized for a wide set of incondensable penetrants. A monotonous reduction of permeability took place at increasing the water concentration within the polymer matrix, affecting the investigated gaseous species to the same extent, despite the different thermodynamic and kinetic features. In this view, a novel empirical model, based on the Free Volume Theory, has been proposed to qualitatively describe the phenomenon. Moreover, according to the accurate representation of the experimental data, the suggested approach has been combined with a more rigorous thermodynamic tool (NELF Model), allowing an exhaustive description of water influence on the single parameters contributing to the gas permeation across the membrane. In the second part, the study has focused on the synthesis and characterization of facilitated transport membranes, able to achieving outstanding separation performances thanks to the chemical enhancement of CO2 permeability. In particular, the transport properties have been investigated for high pressure CO2 separation applications and specific solutions have been proposed to solve stability issues, frequently arising under such severe conditions. Finally, the effect of different process parameters have been investigated, aiming at the identification of the optimal conditions capable to maximize the separation performance.

Caratterizzazione e simulazione di processi di colata in sabbia di ghise sferoidali

L’oggetto principale delle attività di tesi è la caratterizzazione numerico-sperimentale di processi di colata in sabbia di ghisa sferoidale. Inizialmente è stata effettuata un’approfondita indagine bibliografica per comprendere appieno le problematiche relative all’influenza dei parametri del processo fusorio (composizione chimica, trattamento del bagno, velocità di raffreddamento) sulle proprietà microstrutturali e meccaniche di getti ottenuti e per valutare lo stato dell’arte degli strumenti numerici di simulazione delle dinamiche di solidificazione e di previsione delle microstrutture. Sono state definite, realizzate ed impiegate attrezzature sperimentali di colata per la caratterizzazione di leghe rivolte alla misura ed alla differenziazione delle condizioni di processo, in particolare le velocità di raffreddamento, ed atte a validare strumenti di simulazione numerica e modelli previsionali. Inoltre sono stati progettati ed impiegati diversi sistemi per l’acquisizione ed analisi delle temperature all’interno di getti anche di grandi dimensioni. Lo studio, mediante analisi metallografica, di campioni di materiale ottenuto in condizioni differenziate ha confermato l’effetto dei parametri di processo considerati sulle proprietà microstrutturali quali dimensioni dei noduli di grafite e contenuto di ferrite e perlite. In getti di grandi dimensioni si è riscontrata anche una forte influenza dei fenomeni di macrosegregazione e convezione della lega su microstrutture e difettologie dei getti. Le attività si sono concentrate principalmente nella simulazione numerica FEM dei processi fusori studiati e nell’impiego di modelli empirico-analitici per la previsione delle microstrutture. I dati misurati di temperature di processo e di microstrutture sono stati impiegati per la validazione ed ottimizzazione degli strumenti numerici previsionali impiegati su un ampio intervallo di condizioni di processo. L’impiego di strumenti affidabili di simulazione del processo fusorio, attraverso l’implementazione di correlazioni sperimentali microstrutture-proprietà meccaniche, permette la valutazione di proprietà e difettologie dei getti, fornendo un valido aiuto nell’ottimizzazione del prodotto finito e del relativo processo produttivo.

Studio e ottimizzazione del processo di fabbricazione additiva (SLM) per applicazioni in ambito biomedicale: produzione di protesi e strutture reticolari

Il progetto di dottorato che verrà presentato in questa tesi è focalizzato sullo sviluppo di un metodo sperimentale per la produzione di protesi personalizzate utilizzando il processo di fabbricazione additiva di Selective Laser Melting (SLM). L’obiettivo è quello di definire una condizione di processo ottimizzata per applicazioni in ambito chirurgico che possa essere generalizzabile, ovvero che ne garantisca la riproducibilità al variare dell’anatomia del paziente e che rappresenti la base per estendere il metodo ad altre componenti protesiche. Il lavoro si è sviluppato lungo due linee principali, la cui convergenza ha permesso di realizzare prototipi di protesi complete utilizzando un solo processo: da una parte la produzione di componenti a massima densità per il raggiungimento di elevate resistenze meccaniche, buona resistenza ad usura e corrosione e controllo di tensioni residue e deformazione delle parti stampate. Dall’altra si sono studiate strutture reticolari a geometria e porosità controllata per favorire l’osteointegrazione della componente protesica post impianto. In questo studio sono stati messe a confronto le possibili combinazioni tra parametri di processo e sono state individuate le correlazioni con le proprietà finali dei componenti stampati. Partendo da queste relazioni si sono sviluppate le strategie tecnologiche per la progettazione e la produzione dei componenti. I test sperimentali svolti e i risultati ottenuti hanno dimostrato la fattibilità dell’utilizzo del processo SLM per la produzione di protesi personalizzate e sono stati fabbricati i primi prototipi funzionali. La fabbricazione di protesi personalizzate richiede, però, anche la progettazione e la produzione di strumentario chirurgico ad hoc. Per questo motivo, parallelamente allo studio della lega di Cromo Cobalto, sono stati eseguiti i test anche su campioni in INOX 316L. Anche in questo caso è stato possibile individuare una finestra operativa di processo che garantisse proprietà meccaniche comparabili, e in alcuni casi superiori, a quelle ottenute con processi convenzionali.

Metal additive manufacturing of soft magnetic material for electric machines

This research work concerns the application of additive manufacturing (AM) technologies in new electric mobility sectors. The unmatched freedom that AM offers can potentially change the way electric motors are designed and manufactured. The thesis investigates the possibility of creating optimized electric machines that exploit AM technologies, with potential in various industrial sectors, including automotive and aerospace. In particular, we will evaluate how the design of electric motors can be improved by producing the rotor core using Laser Powder Bed Fusion (LPBF) and how the resulting design choices affect component performance. First, the metallurgical and soft magnetic properties of the pure iron and silicon iron alloy parts (Fe-3% wt.Si) produced by LPBF will be defined and discussed, considering the process parameters and the type of heat treatment. This research shows that using LPBF, both pure iron and iron silicon, the parts have mechanical and magnetic properties different from the laminated ones. Hence, FEM-based modeling will be employed to design the rotor core of an SYN RM machine to minimize torque ripple while maintaining structural integrity. Finally, we suggest that further research should extend the field of applicability to other electrical devices.

Application of Pulsed Electric Fields for the Modulation of Chemico-Physical Properties of Different Foods

Pulsed electric field technology is one of the most attractive new non-thermal technology thanks to its lower energy consumption and short treatment times. It consists of an electric treatment of short duration (from several ns to several ms) with electric field strengths from 0.1 to 80 kV/cm that lead to an increase in the permeability of the cell membrane. In this PhD thesis, PEF technology was investigated with the aim of improving mass transfer in plant and animal foods by using it alone or in combination with conventional food processes. Different methods of evaluating electroporation for optimizing PEF processing parameters were investigated. In this respect, the degree of membrane permeabilization in plant and animal food matrices was investigated using electrical impedance spectroscopy, current-voltage measurements and magnetic resonance imaging. The research findings provided useful insights and calls for critical choice of electroporation assessment methods for the selection of adequate PEF treatment conditions. It was outlined that the effect of electroporation is highly dependent on the properties of the food matrix and secondary phenomena occurring in the cell structure undergoing PEF treatment, such as the water re-distribution in the tissue due to the exchange of fluids between intra- and extra-cellular environments. This study also confirmed the great potential of combining PEF technology with conventional food processes, with the main purpose of improving the quality of the food material and accelerating the kinetics of mass transfers, in both plant and animal tissues. Consistent reduction of acrylamide formation in potato crisps was achieved by monitoring key PEF process parameters and subsequent manufacturing steps. Kiwifruit snacks showed a significant reduction in drying kinetics when pre-treated with PEF, while their quality was well maintained. Finally, the research results showed that PEF pre-treatments can shorten the brine process as well as the rehydration kinetics of fish muscles.