Lo scopo di questa tesi di dottorato di ricerca consiste nel fornire la giusta collocazione della manutenzione fra le discipline dell'ingegneria, raccogliendo e formalizzando le metodologie di analisi di affidabilità e di pianificazione degli interventi all'interno di un unico processo di progettazione e di controllo. In linea di principio, un processo di analisi dei guasti e di programmazione della manutenzione deve essere in grado di fornire chiare e sicure risposte ai seguenti interrogativi: Quali sono le funzioni richieste e con quali criteri di prestazioni il sistema è chiamato ad assolverle? Qual'è l'andamento della disponibilità del sistema in funzione del tempo? Quanti guasti e di quale tipo si possono verificare durante la vita del sistema? Quali possono essere le conseguenze che ledono la sicurezza e la protezione ambientale? Quanti pezzi di ricambio sono necessari? Che tipo di interventi di manutenzione preventiva risultano tecnicamente fattibili? A quali scadenze devono essere programmati? A quanto ammonta la previsione del costo di esercizio del sistema? Quante squadre di manutenzione devono essere assegnate al sistema? Come deve essere organizzata la logistica di manutenzione? Con quali tecniche si prevede di riconoscere i guasti e quali procedure devono essere attivate per farvi fronte? E' possibile implementare tecniche di `condition monitoring' delle macchine? Su quali tempi di preavviso sui guasti si può contare? In tal senso, la manutenzione necessita delle tecniche e degli opportuni strumenti che siano in grado di misurarne l'efficacia e l'efficienza. L'efficacia in primo luogo, in quanto l'obiettivo principe consiste nel garantire che il sistema oggetto di studio continui a svolgere le proprie funzioni nei limiti di prestazioni accettabili, secondo le specifiche richieste degli utilizzatori. L'efficienza in secondo luogo, ma non per questo di minore importanza, in quanto perseguendo l'obiettivo di cui sopra, occorre impegnare il minimo di risorse possibili, organizzando con razionalità il supporto logistico del sistema al fine di raggiungere i massimi livelli di rendimento di gestione. La migliore strategia di manutenzione può essere pianificata, a priori, solo se si è in grado di prevedere con la necessaria precisione l'evoluzione del sistema nel suo contesto operativo futuro. E' allora possibile formulare un modello matematico del sistema, studiarne la dinamica ed osservare le reazioni alla simulazione di eventuali stimoli esterni. I metodi ed i modelli noti dell'ingegneria dei sistemi possono essere molto utili per la risoluzione di casi semplici, ma sovente richiedono la formulazione di ipotesi troppo restrittive che aumentano in modo inaccettabile la distanza del modello dalla realtà. Una strada alternativa ed affascinante, che ho percorso con entusiasmo durante questi tre anni di studi e ricerca, consiste nella simulazione numerica della vita del sistema, utilizzando il metodo Monte Carlo per la gestione dei processi stocastici di guasto e per l'esecuzione degli interventi di manutenzione. Ho quindi messo a punto il codice di simulazione RAMSES, perseguendo l'idea di costruire uno strumento di misura dell'efficacia e dell'efficienza di una politica di manutenzione simulata al calcolatore. Nella tesi si presentano i concetti di base dell'ingegneria dei sistemi applicata al caso della manutenzione e si introduce il formalismo della Reliability Centred Maintenance come miglior guida nella pianificazione delle schede di manutenzione. Si introducono le nozioni di base per fornire una struttura solida e corretta alla simulazione numerica dei sistemi riparabili e si presenta il codice RAMSES corredando le informazioni tecniche con i dovuti esempi ed applicazioni pratiche. Si conclude il lavoro, infine, con la presentazione di un modello di massima verosimiglianza particolarmente utile per le analisi dei dati sperimentali di guasto dei componenti.

This work investigates the slamming phenomenon experienced during the water entry of deformable bodies. Wedges are chosen as reference geometry due to their similarity to a generic hull section. Hull slamming is a phenomenon occurring when a ship re-enters the water after having been partially or completely lifted out the water. While the analysis of rigid structures entering the water has been extensively studied in the past and there are analytical solutions capable of correctly predicting the hydrodynamic pressure distribution and the overall impact dynamics, the effect of the structural deformation on the structural force is still a challenging problem to be solved. In fact, in case of water impact of deformable bodies, the dynamic deflection could interact with the fluid flow, changing the hydrodynamic load. This work investigates the hull-slamming problem by experiments and numerical simulations of the water entry of elastic wedges impacting on an initially calm surface. The effect of asymmetry due to horizontal velocity component or initial tilt angle on the impact dynamics is also studied. The objective of this work is to determine an accurate model to predict the overall dynamics of the wedge and its deformations. More than 1200 experiments were conducted by varying wedge structural stiffness, deadrise angle, impact velocity and mass. On interest are the overall impact dynamics and the local structural deformation of the panels composing the wedge. Alongside with the experimental analysis, numerical simulations based on a coupled Smoothed Particle Hydrodynamics (SPH) and FEM method are developed. The experimental results provide evidence of the mutual interaction between hydrodynamic load and structural deformation. It is found a simple criterion for the onset of fluid structure interaction (FSI), giving reliable information on the cases where FSI should been taken into account.

Studio del componente di supporto del cavo utensile per taglio di materiali lapidei. Analisi delle applicazioni di leghe superelastiche e delle modalità di realizzazione del cavo utensile complessivo in relazione a specifiche esigenze poste a livello industriale. / Study of the supporting component of wire-rod cutting tool for stone manufacturing. Analisys of superelastic alloys applications, and study of wire-rod manufacturing modality with reference to industrial specifications.

Fibre-Reinforced-Plastics are composite materials composed by thin fibres with high mechanical properties, made to work together with a cohesive plastic matrix. The huge advantages of fibre reinforced plastics over traditional materials are their high specific mechanical properties i.e. high stiffness and strength to weight ratios. This kind of composite materials is the most disruptive innovation in the structural materials field seen in recent years and the areas of potential application are still many. However, there are few aspects which limit their growth: on the one hand the information available about their properties and long term behaviour is still scarce, especially if compared with traditional materials for which there has been developed an extended database through years of use and research. On the other hand, the technologies of production are still not as developed as the ones available to form plastics, metals and other traditional materials. A third aspect is that the new properties presented by these materials e.g. their anisotropy, difficult the design of components. This thesis will provide several case-studies with advancements regarding the three limitations mentioned. In particular, the long term mechanical properties have been studied through an experimental analysis of the impact of seawater on GFRP. Regarding production methods, the pre-impregnated cured in autoclave process was considered: a rapid tooling method to produce moulds will be presented, and a study about the production of thick components. Also, two liquid composite moulding methods will be presented, with a case-study regarding a large component with sandwich structure that was produced with the Vacuum-Assisted-Resin-Infusion method, and a case-study regarding a thick con-rod beam that was produced with the Resin-Transfer-Moulding process. The final case-study will analyse the loads acting during the use of a particular sportive component, made with FRP layers and a sandwich structure, practical design rules will be provided.

The present work aims for investigate the influence of electrospun Nylon 6,6 nanofibrous mat on the behavior of composite laminates. The main idea is that nanofibrous interleaved into particular ply-to-ply interfaces of a laminate can lead to significant improvements of mechanical properties and delamination/damage resistance. Experimental campaigns were performed to investigate how nanofibers affect both the static and dynamic behavior of the laminate in which they are interleaved. Fracture mechanics tests were initially performed on virgin and 8 different configuration of nanomodified specimens. The purposes of this first step of the work are to understand which geometrical parameters of the nanointerleave influence the behavior of the laminate and, to find the optimal architecture of the nanofibrous mat in order to obtain the best reinforcement. In particular, 3 morphological parameters are investigated: nanofibers diameter, nanofibers orientation and thickness of the reinforce. Two different values for each parameter have been used, and it leads to 8 different configurations of nanoreinforce. Acoustic Emission technique is also used to monitor the tests. Once the optimum configuration has been found, attention is focused on the mechanism of reinforce played by the nanofibers during static and dynamic tests. Low velocity impacts and free decay tests are performed to attest the effect of nanointerlayers and the reinforce mechanism during the dynamic loads. Bump tests are performed before and after the impact on virgin and two different nanomodified laminates configurations. The authors focused their attention on: vibrational behavior, low velocity impact response and post-impact vibration behavior of the nano-interleaved laminates with respect to the response of non-nanomodified ones. Experiments attest that nanofibers significantly strength the delamination resistance of the laminates and increase some mechanical properties. It is demonstrated that the nanofibers are capable to continue to carry on the loads even when the matrix around them is broken.

A major weakness of composite materials is that low-velocity impact, introduced accidentally during manufacture, operation or maintenance of the aircraft, may result in delaminations between the plies. Therefore, the first part of this study is focused on mechanics of curved laminates under impact. For this aim, the effect of preloading on impact response of curved composite laminates is considered. By applying the preload, the stress through the thickness and curvature of the laminates increased. The results showed that all impact parameters are varied significantly. For understanding the contribution rate of preloading and pre-stress on the obtained results another test is designed. The interesting phenomenon is that the preloading can decrease the damaged area when the curvature of the both specimens is the same. Finally the effect of curvature type, concave and convex, is investigated under impact loading. In the second part, a new composition of nanofibrous mats are developed to improve the efficiency of curved laminates under impact loading. Therefore, at first some fracture tests are conducted to consider the effect of Nylon 6,6, PCL, and their mixture on mode I and mode II fracture toughness. For this goal, nanofibers are electrospun and interleaved between mid-plane of laminate composite to conduct mode I and mode II tests. The results shows that efficiency of Nylon 6,6 is better than PCL in mode II, while the effect of PCL on fracture toughness of mode I is more. By mixing these nanofibers the shortage of the individual nanofibers is compensated and so the Nylon 6,6/PCL nanofibers could increased mode I and II fracture toughness. Then all these nanofibers are used between all layers of composite layers to investigate their effect on damaged area. The results showed that PCL could decrease the damaged area about 25% and Nylon 6,6 and mixed nanofibers about 50%.

Instrumented indentation testing is now considered one of the most attractive tools for characterizing engineering materials. A large number of materials properties can be investigated. The present dissertation was aimed at developing a new methodology for inferring the material behaviour of metallic materials from their indentation response.

In this work an artificial driving agent able to adapt its behavior depending on the specific situation and to generate human-like maneuvers was developed. The agent, called co-driver, was designed with a bio-inspired architecture, with an approach that takes advantage of ideas from cognitive science. In fact the decision process is based on the affordance competition hypothesis: the agent generates a representation of all possible actions given what is perceived in the environment and then chooses the optimal maneuver after inhibiting all the dangerous ones. In the first stage of the development process, atomic actions, called motor primitives, were identified. Then the co-driver was implemented with a layered architecture, where these motor primitives were combined in the upper levels in order to obtain more complex behaviors. Thanks to this particular architecture, the development process of the final artificial driver was split in two parts: initially an advanced driver assistance system (ADAS) was implemented and tested, and finally the architecture was extended in order to have an artificial driving agent for automated driving. In the first case the system was successfully tested on public roads and was able to warn the driver in case of dangerous scenarios, such as blind intersections. In the latter case, the co-driver could manage several challenging test cases in urban scenarios, from car following to cut-in scenario and curves. Finally, it was compared with a state-of-art driver model of CarMaker simulation software used by the main car manufacturers. Due to the achieved results, this work can be considered a valid potential solution for automated driving. In fact, the artificial driver was used as starting point for a European project (“Dreams4Cars”) that is currently in progress.

Cellular materials are characterized by a complex interconnected structure of struts or plates and shells which make up the cells edges and faces. Their structure can be advantageously engineered in order to tailor their properties according to the specific application. This aspect makes them particularly attractive for the manufacturing of bone prosthetics since, compared to traditional fully dense implants, although more complex to produce and with less predictable properties, implants with a highly porous structure can be manufactured to match the bone stiffness and at the same time favor bone ingrowth and regeneration. The development of Selective Laser Melting (SLM) made possible to obtain metallic cellular materials with highly complex structures characterized by a wide range of cell morphologies that allow to finely tune the mechanical properties of the implant to the patient needs. Titanium alloys such as Ti-6Al-4V have shown excellent biocompatibility combined with good mechanical properties and have also been successfully used in the manufacturing of lattice structures with minute details via SLM. Nevertheless, there are still several issues to consider. For instance, despite the static mechanical properties of such lattices being addressed by many studies, the fatigue behavior still remains little investigated, even though it is a critical aspect in load-bearing biomedical implants (consider, for example, the periodic nature of human gait in the case of hip implants). In this regard, increasing the fatigue resistance of cellular lattices by finely adjusting the geometry, for instance by adding fillets at the cell-wall joints, is a new interesting opportunity made possible by additive manufacturing technologies. On the other hand, a discrepancy between the as-designed and the as-built geometry in SLM parts is an issue that can be critically important for lattices with pore size and strut thicknesses of a few hundred microns, such as biomedical lattices. Indeed, any geometrical imperfection introduces a degree of uncertainty that can alter the mechanical properties of the as-built lattice. This work represents an attempt in the direction of building a deeper understanding of the effect of the fine geometrical details, such as the fillet radius at the joints and the thickness of the struts, on the elastic constants and on the fatigue resistance of Ti-6Al-4V SLM lattices, with the aim to develop analytical predictive models of the mechanical properties. Moreover, this work also aims at investigating the as-built/as-designed morphological discrepancy in lattices in relation to the their as-designed geometry and its effects on the elastic modulus and the fatigue resistance. In this regard, the purpose is to develop quantitative relationships between the as-designed and the as-built geometry in order to obtain design tools to predict the final morphology of the lattice by taking into account the manufacturing errors. This thesis covers a wide range of topics, therefore, in the interest of a better presentation, the results of the research have been devided into three independent Chapters. Each of them has been provided of an abstract and an Introduction and divided into a Materials and Methods (or Modelling) section, a Results and Discussion section and finally Conclusions and References. Naturally, the chapters are logically connected and coherent with the frame defined by the title of the thesis. Therefore, this thesis is organized into five chapters. In the first Chapter the backrground to the topics discussed in the subsequent chapters is provided and the relevant literature is reviewed, while in the fifth and last Chapter some conclusions are drawn, and future perspectives are discussed. The core of the work is contained in the three central chapters. In Chapter II, analytical models developed to predict the elastic constants and the stress concentration factors (SCF) of 2D lattices with variously arranged square cells and filleted junctions are presented. The effect of stretching and bending actions on the elastic constants of a single cell is identified by devising an analytical model based on classical beam theory and and periodic boundary conditions. Specifically, two spatial arrangements are considered: a honeycomb with regular square cells and a honeycomb with square cells staggered by a prescribed offset of half of the cell wall length. The theoretical beam model is fitted to the results of a 2D Finite Elements (FE) model based on plane elements via an extensive parametric analysis. In this way, semi-analytical formulas are proposed to calculate the stiffness in large domains of the geometric parameters (strut thickness t0 and fillet radius R). A numerical method is also proposed to estimate the SCFs at the cell wall junctions of a 2D regular square cellular lattice. The aim is to obtain a model capable of calculating the values of the SCF as a function of the unit cell geometrical parameters and consequently assess the stress state in the lattice, which is one of the main factors determining fatigue resistance. This was achieved by applying the FE method to the unit cell for wide intervals of t0 and R to calculate the SCF for each couple of the parameters. The values of the SCFs were then fitted with functions. The models developed in this Chapter are then used in the subsequent chapters as a support in the design of 3D regular square lattices and in the interpretation of the mechanical characterization. In Chapter III, the results of the mechanical and morphological characterization of different regular cubic open-cell cellular structures produced via SLM of Ti-6Al-4V alloy, all with the same nominal elastic modulus of 3 GPa that matches that of human trabecular bone, are presented. The fully reversed fatigue strength at 106 cycles and the elastic modulus were measured and an attempt was made to link them to the manufacturing defects (porosity and geometrical inaccuracies). Half of the specimens was subjected to a stress relief thermal treatment while the other half to Hot Isostatic Pressing (HIP), and the effect of the treatments on porosity and on the mechanical properties was assessed. The results of fatigue and quasi-static tests on regular cubic lattices were compared with FE calculations based on the as-designed geometry and on the as-built geometry reconstructed from micro X-ray computed tomography (ÂμCT) scans. It was observed that the fatigue strength and, to a lesser extent, the elastic modulus are correlated with the number and severity of defects and that predictions on the mechanical properties based on the as-designed geometry are not accurate. The fatigue strength seems to be highly dependent on the surface irregularities and on the notches introduced during the manufacturing process. In fully reversed fatigue tests, the high performances of stretching dominated structures compared to bending dominated structures are not found. In fact, with thicker struts, such structures proved to be more resistant, even if bending actions were present. Given the small size of the unit cells (the unit cell size is 1.5 mm and the strut thickness is 0.26 mm) and the limitations in accuracy of the printer, the fillet radii at the junctions were highly irregular and somewhat hard to recognize. In order to investigate the real benefit of filleted junctions on the stress concentration effects at the junctions and to assess the manufacturability of such minute geometrical detail, a new experimental campaign was set up. In Chapter IV, a set of cubic lattice specimens with filleted junctions was designed and produced via SLM. The size of the unit cell is considerably larger than that of the previous specimens, being 8 mm, 6 mm and 4 mm with the rest of the geometrical parameters scaled accordingly. Thus, nine combinations of the geometrical parameters of the unit cell and three orientations with respect to the printing direction are considered. The aim is to investigate the relationship between the as-designed and the as-built geometry and to find the smallest radius which can be accurately reproduced by the printer. Moreover, a compensation strategy of the morphological defects is devised using the mathematical relationships obtained between the as-designed and the as-built strut thickness. This strategy consists in modifying the input CAD to compensate for the deviations introduced by the SLM process.

This work is focused on the development of controllable suspension systems for heavy-duty vehicles, in particular for agricultural tractors. In this field the research activity is not complete, as confirmed by the lack of scientific literature and for the few examples of commercial application for this kind of vehicles present in the market. For off-highway vehicles the load conditions can vary considerably and have an effect on the dynamic behaviour of the vehicle. Moreover, in many cases (such as tractors in agriculture), only the front axle is provided with a suspension. Typical applications of suspensions in off-highway industry include the cabin suspension (known as secondary suspension system) and the front axle suspension (known as primary suspension system). Up to now, the performance improvements have been reached through new solutions developed for the secondary systems, while the primary systems are generally implemented with passive systems, due to economical motivations and their limited energy demand. Obviously, such technical solutions partially satisfy the system requirements. Moreover, during the past few years there has been an increasing demand in power capabilities, loads and driving speeds of heavy duty vehicles. Therefore, off-highway vehicle manufacturers have shown their interest in employing controllable suspension, assumed as a potential way to reach the desired dynamic performances. The main targets of this activity is the study of the dynamical behaviour of agricultural tractors and the design of a cost-effective controllable suspension, capable to adapt the tractor dynamical behaviour, under different operating conditions. This work is part of a collaboration between Dana Corp. and the University of Trento. The main objective consists in the acquisition of competence in relation to the dynamic control of the vehicle. In particular the development of mechatronic systems according to the Model Based Design approach and the rapid prototyping of control algorithms. On this purpose, a simulation and experimental system was developed, for the testing of suspension systems and control algorithms for primary suspension systems. The first part of the thesis investigates the state of the art of the scientific literature of suspension systems for heavy duty vehicles, referring to different technologies and control solutions. In particular, attention was focused on the analysis and experimental characterization of commercial applications for this kind of vehicles present in the market. In the second part of the thesis the design development of a hydro-pneumatic suspension system is presented. The design of the control algorithms is based on the development of different multibody models of the actual tractor, including the pitch motion of the sprung mass, the load transfer effects during braking and forward-reverse maneuvers and the non-linear dynamics of the system. For an advanced analysis, a novel thermo-hydraulic model of the hydraulic system has been implemented. Several damping controls are analyzed for the specific case study. Therefore, the most promising damping strategy is integrated with other control functions, namely a self-leveling control, an original control algorithm for the reduction of the pitch motion, an anti-impact system for the hydraulic actuator and an on-line adaptation scheme, which preserves an optimal damping ratio of the suspension, even against large variations in operating conditions. According to the system requirements, the control is firstly integrated with other functionalities, such as the calibration of the suspension set-points and the procedures for the lock of the suspension. Finally, in accordance to the industrial product development, the control scheme is redefined in a Finite State Machine, useful for the subsequent generation of the ECU (Electronic Control Unit) Embedded Code. The final section of this work presents the development of an industrial prototype of suspension system, composed of a hydraulic suspension unit and a controller (hardware and software units). The prototype is tested by using a suspension bench test and Rapid Prototyping Tools for testing real-time control systems. Conclusions and final remarks and are reported in the last section.