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Metal foams are a relatively new class of materials with many interesting combinations of physical and mechanical properties. Among them, the closed-cells aluminum foams are the most interesting for structural applications in the aerospace industry. There exist different methods to produce metal foams. An innovative manufacturing technique was developed in this study, proving the possibility to produce closed-cells aluminum foams through the cold spray additive manufacturing technology (CS). In particular, two different sets of samples were produced by varying the cold spray process parameters aiming at: i) studying the advantages and the issues of cold spray for manufacturing precursors for metal foams; ii) analyzing the correlation among the CS printing strategy and parameters, the foaming process and the physical and the morphological characteristics of the resulting foams; iii) finally, finding appropriate conditions to form closed-cells aluminum foams via CS.

Cold spray is a novel production technology for creating metallic layers on various materials. Using a pressurized gas travelling at supersonic speeds, the metallic particles are accelerated and impact the target surface obtaining adhesion through mechanical interlocking between the powders and the substrate. This method is especially well suited for coating thermosensitive materials like composites since it only requires a little amount of heat, as the powders remain in a solid state. The quality and comprehension of this manufacturing process can be greatly improved by using machine learning techniques. In order to evaluate the characteristics of the particle's deformation upon collision, the goal of this work is to forecast it using machine learning approaches. The parameters chosen as an input for the model were related to 3 macro-categories: process parameters, powder parameters and substrate parameters. As regards the output parameters, flattening and penetration were chosen as they are the main characteristics of the coating on which homogeneity and adhesion depend. In order to obtain reliable results, a mix of data FEM and experimental data were used to train the neural network. The model was then tested on a dataset of experimental data.

Low Pressure Cold Spray process is a relatively new coating technique which allows to create high quality metallic coatings, on both metallic and non-metallic substrates, without extensive heating of the powders sprayed. Upon impact with a target surface, conversion of kinetic energy to plastic deformation occurs, the solid particles deform and bond together. To date, the complex adhesion mechanisms of the particles are still being discussed and, what is more, the phenomena occurring during the long time deposition processes, the most interesting ones for industrial applications, are not adequately studied and known. The aim of this paper is to contribute to fill this lack of knowledge through the detailed analysis of the phenomena occurring during long time depositions. To this end a full experimental campaign was carried out. Moreover it was also proposed a numerical model focusing on both geometrical features and fluid-dynamic behaviour of converging-diverging de- Laval nozzle system. Micron-sized aluminium powders and compressed air as carrier gas were used in this experimentation. It has been found that the deposition efficiency tends to decrease due to the critical phenomena occur into the spray nozzle during long time depositions. The sprayed particles tend to stick to the walls of the nozzle and, moreover, a shock wave occurs inside the nozzle further promoting the particles stick phenomena, making the system inefficient.

Incremental forming process, in all its variants, results to be ideal when flexibility is required, especially for small-batch and customized production. Two point incremental forming with partial die (TPIF) presents notable advantages compared to single point incremental forming (SPIF) for obtaining components that present both concave and convex zones; on the other hand, these advantages are not so evident in the case of simple geometries. The following study compares the two techniques by geometrical considerations, FEM analyses and experimental evaluations. Cone frusta are obtained starting from aluminum alloy sheets and features like geometric accuracy, forming and setup times, forming forces and deformative states are investigated, in order to highlight differences and similarities between the two techniques. In particular, TPIF allows to obtain geometries very similar to the designed ones, but requires higher setup and forming times.

Cemented carbides present some characteristics that ensure high performances for cutting and wear-resistant tools. The aim of the work is to evaluate the influence of Chromium Carbide and Nickel on the properties (wear and friction) of a cemented carbide constituted by a hard phase of tungsten carbide and a binder phase of cobalt. Different tests were carried out by varying the percentage of Cr3C2 and, for one only case, also Nickel was added. The tests were carried out by a pin-on-disk apparatus and diamond abrasive sheet. The experimental campaign provided tests for different values of load and relative velocity. Friction coefficient was directly evaluated by the apparatus and data on the wear were obtained by measuring the loss of weight of the samples (parallelepipeds with hemispherical head). The tests allowed to determine the percentage of Cr3C2 that ensure an improvement of the aforementioned properties and to highlight the irrelevance of Nickel.

La profilatura a freddo (cold roll forming) è una lavorazione per deformazione plastica che consente di realizzare profilati, di una definita sezione e lunghezza, dalla deformazione plastica di una lamiera. Questa è indotta ad attraversare diverse stazioni di rulli deformatori, disposti sullo stesso asse di avanzamento. I banchi di rulli, assemblati in maniera folle nella singola stazione, inducono la deformazione plastica nella lamiera e quindi portano alla configurazione desiderata. Al fine di controllare i parametri geometrici della lamiera deformata durante la profilatura, è stata simulata in ambiente FE la fase finale del processo messo a punto dalla Imi Sud S.r.l. mediante il codice di calcolo non lineare LS-Dyna 971, che ha permesso di analizzare le grandezze di interesse nei differenti step di avanzamento. I risultati ottenuti numericamente sono stati confrontati con quelli sperimentali mediante la misurazione di 5 campioni ottenuti direttamente dal processo tecnologico.

Dalla crescente consapevolezza ambientale, dalle preoccupazione per la sostenibilità ambientale e dal crescente problema dello spreco globale, negli ultimi decenni è derivata una notevole tendenza verso l'utilizzo di fibre naturali, piuttosto che di fibre tradizionali, come rinforzi nei materiali compositi. Le fibre naturali sono state utilizzate per rinforzare termoplastici per i loro vantaggi relativi al basso costo, alla bassa densità, alla resistenza specifica accettabile, alle buone proprietà di isolamento termico, alla biodegradabilità e alla rinnovabilità. Tra i polimeri biodegradabili, l'acido polilattico (PLA) si è mostrato essere molto interessante per il suo uso come matrice nei compositi in fibra naturale per molteplici ragioni. L'obiettivo di questo lavoro è la valutazione delle proprietà meccaniche di compositi bio canapa/PLA realizzati con tessuti di fibre naturali al variare della percentuale volumetrica di fibra e della tipologia di tessuto utilizzato come rinforzo.

This work is part of scientific studies with the wider aim to produce components for aerospace industrial applications. Particularly, components with complex geometry are manufactured by using innovative technologies. The aim of this paper is to verify the technological feasibility of the manufacturing of components formed using Super Plastic Forming (hereinafter called SPF) process and filled with aluminum foam. The component under investigation is composed of an outer layer of a thin sheet in titanium alloy, formed by SPF technology, and a core in aluminum foam manufactured by the powder compact melting technique. Drop weight impact tests have been carried out with the aim to estimate the improvement of the innovative component in terms of energy absorption compared to the sum of the single constituents. The results have showed significant improvements in the energy absorption capability, proving that the proposed concept is technically promising.

Natural fibres represent an interesting alternative to synthetic ones for many engineering applications of composites, both for their low cost and for environmental sustainability. In particular, hemp fibres highlighted high potential as a reinforcement in composite materials based on polymeric matrix. Laminates of epoxy resin reinforced by hemp fibres were manufactured by adopting low cost technology. In particular, different typologies of composite laminates, starting from unidirectional and bidirectional woven fabrics and loose hemp fibres, were impregnated by infusion process. Successively, the characterization of the laminates was carried out; in particular, permeability values, flexural characteristics, thicknesses and volumetric percentage of reinforcement were evaluated, in order to investigate impregnation, process quality and mechanical properties of the composite materials.

Superplastic forming is a near net shape process used to produce various items with complex geometry. However in many cases, only some portions of the workpiece undergo superplastic deformation. In these cases, instead of choosing expensive starting sheet material with superplastic properties, a low-cost conventional material can be chosen and a grain refinement process can be performed in the selected regions to enhance superplastic properties locally [1]. This process is known as "selective superplastic forming" [R.S. Mishra, M.W. Mahoney, US Patent 6,712,916, 2002]. In some previous works the use of Friction Stir Processing (FSP) was used to obtain locally a microstructure with ultrafine grains in the AZ31 magnesium alloys [2, 3]. In this study a modeling approach was adopted thanks to a commercial FE code and different simulations were conducted in order to correlate the experimental and numerical results for the model optimization [4, 5]. Free bulge forming tests of friction stir processed AZ31 sheets, in conjunction with numerical simulations, were used to evaluate the proposed optimization approach, with the aim to reduce the time and costs in the design of components with complex geometry.

This work is part of scientific studies that have the wider aim of producing components for aerospace industrial applications such as the realization of complex geometry using innovative technologies. The aim of this paper is to verify the technological feasibility of the manufacturing of components formed using Super Plastic Forming (hereinafter called SPF) processes and filled with aluminium foam. The component under investigation is composed by an outer layer in thin sheet of titanium alloy, formed by SPF technology, and a core in aluminium foam manufactured by the powder compact melting technique. Drop weight impact tests have been carried out to the aim to estimate the improvement of the innovative component in terms of energy absorption compared to the sum of the single constituents. The results have showed significant improvements in the energy absorption capability, proving that the proposed concept is technically promising.

The bending behavior of hybrid sandwich panels, with aluminum foam core, and carbon fiber reinforced thermoset resin face sheets, have been investigated. The effect of core and face sheets thickness and span , on 3-point bending test, has been evaluated for the sandwich panels . Core yielding and indentation failure modes, influenced by the core properties, have been identified and analytical models to evaluate the maximum load have been applied. The failure mode map has been constructed, which illustrates the dominant failure mode for practical beam design. In order to simulate the different failure modes, FE analysis has been pointed out.

Nel presente lavoro sono stati studiati giunti FSW di testa in lega innovativa AA 6156, di cui sono state valutate sia le proprietà meccaniche che le tensioni residue indotte dal processo di saldatura stesso. Per lo studio delle tensioni residue è stata utilizzata una tecnica innovativa denominata QNA che si basa sull’interpretazione di immagini termografiche che ritraggono l’oggetto in esame, opportunamente sollecitato, attraverso il software matlab ed in particolare l’utilizzo della trasformata Wavelet.