In this paper an associative-parametric approach is proposed in order to model the mesh of an aeronautical concept starting from a set of high-level structural primitives. This approach allows the designer to carry out the geometric modelling and the automatic mesh generation within one software environment in a fast and interactive way. The structural optimisation process is then simplified, with a relevant man-hours saving. A lower number of data transfers between different software is, moreover, involved with less problems related to the data corruption. To assure orders of continuity higher than C0 between adjacent instances, a suitable mathematical description of the structural primitives has been proposed. This description assures the maintenance of the required continuity constraints when the mesh is modified. Appropriate schemes of dependences are identified to guarantee the automatic propagation of the modifications complying with the continuity constraints.

In this work, a scheme of representation for aircraft structural concepts is identified. Based on this scheme, a parametric-associative geometrical modelling of the aeronautic structure, consisting in a quad-mapped mesh, is proposed. The mesh generation is based on a hierarchical scheme ensuring the one-to-one correspondence between mesh elements belonging to adjacent primitives. The automatic propagation of modifications is efficiently implemented according to well-defined schemes of dependence thanks to which the modifications involve only the concerned instances. This scheme is implemented in an original software, called MeshFEM and developed using C++, Matlab and the VTK library for 3D graphic visualisation.

Purpose: In this paper, an associative-parametric approach is proposed in order to model the mesh of an aeronautical concept starting from a set of high-level structural primitives. To assure orders of continuity higher than C0 between adjacent instances, a suitable mathematical description of the structural primitives has been identified. The maintenance of the continuity constraints must be assured when the mesh is modified. Method: The Bézier curve and the Coons surface patch, with a suitable degree, are used in order to assure orders of continuity higher than C0 in the connection points or edges. Appropriate schemes of dependences are identified to assure the automatic propagation of the modifications complying with the continuity constraints. Result: The approach here proposed allows the designer to carry out the geometric modelling and the automatic mesh generation within one software environment in a fast and interactive way and complying with the geometric continuity constraints and the one-to-one correspondence between the mesh elements. This represents evidently a large advantage since the structural optimization process is simplified, with a relevant man-hours saving. A lower number of data transfers between different software is, moreover, involved with less problems related to the data corruption. Finally low conceptual value operations, due to manual correction activity of the model, are eliminated. Discussion & Conclusion: The methodology here proposed allows the automatic propagation of modifications satisfying the geometric continuity constraints and the one-to-one correspondence between the mesh elements. The approach is implemented into a CAD/CAE tool, called MeshFEM and developed using C++ and Matlab languages and the VTK library for the 3D graphic visualization.

The aim of this work is the development of microstructural numerical models of metallic foams. In particular, attention is focused on closed cell foam made of aluminium alloy. By means of a finite elements code, the material cellular structure was shaped in different ways: firstly the Kelvin cell, with both plane and curved walls; finally an ellipsoidal cell defined by random dimensions, position and orientation has been adopted as base unit. In order to validate the foam numerical models, static tests were performed to obtain the typical stress–strain curves and then compared with the numerical analysis results.

This work considers the possibility to apply the improved hybrid Capacitor Discharge Welding process (CDW), based on projection Welding principles, to aluminium alloy Al 5754. The innovative aspects are the effective possibility to weld aluminium alloys with CD Welding process and establish the mechanical weld characteristics and defects presence as function of the technological parameters. Intrinsic CDW process characteristics need to be investigated on the base of interaction between the technological aspects and the related mechanical properties. The geometrical and technological factors are combined to improve the welding efficiency and reduce defects size. In order to assess the technological parameters, visual and ultrasonic inspection of the most significant welded joints were performed and room temperature tensile and fatigue tests were executed to verify the welding results.

In case of composites, fatigue damage can be analysed by measurements based on compliance variation and dissipation energy, during the fatigue cycling load. Final results are interesting and show the possibility to monitor the damage state with these procedures

This work studies the improved hybrid Capacitor Discharge Welding process (CDW), based on projection welding principles applied to stainless steel AISI 304. The innovative idea is to modify the igniting points geometry on the section to be welded and optimize the weld characteristics in order to guide the local fusion processes more uniformly on the whole area and enhance the weld properties. Eight different profile geometries for the contact surfaces have been realized in order to evaluate the geometry influence on joints quality and according to process parameters influence. The mechanical behavior of the welds has been verified with static characterization at room temperature and fatigue tests for welded samples with the better observed microstructure.

Lo scopo di questo lavoro è quello di identificare le potenzialità e i limiti della tecnica termografica pulsata nell’individuazione e caratterizzazione delle difettosità su GFRP, confrontando i risultati sperimentali con quelli di analisi numeriche agli elementi finiti che riproducono le stesse indagini. A partire dai risultati sperimentali ottenuti, che permettono di determinare caratteristiche calorimetriche del difetto in base alla risposta termica in superficie, viene simulato con modelli numerici appositi agli elementi finiti il comportamento termico del difetto in relazione ai parametri di conducibilità, allo spessore del composito e alla profondità ed estensione del difetto. Il metodo consente di implementare in maniera rapida differenti modelli numerici e caratterizzare numerose tipologie di difetti, stabilendo delle correlazioni iniziali fra posizione dello stesso e risposta termica del modello di partenza.

Quest lavoro descrive lo studio sperimentale svolto per valutare la resistenza a trazione di alcuni giunti in schiuma di alluminio ottenuti mediante diverse tipologie di collegamento, sia mediante bulloni che adesivi a base di resina epossidica. Sono state considerate diverse diverse tipologie di disposizione dei bulloni e per ogni prova è stato ricavato il valore della forza massima necessaria per la rottura del collegamento. Le migliori prestazioni meccaniche si ottengono con il collegamento realizzato mediante due piastre coprigiunto e resina epossidica. Nel caso di collegamenti mediante bulloni, il carico trasmesso aumenta al crescere del numero dei bulloni.

DIC (Digital Image Correlation) based methodology gives full field measure of the displacement using a well defined algorithm for matching the images of loaded and load free component, so that displacement in a plane can be evaluated for a certain number of grid reference points on the analysed surface. In this work, the authors present an application of DIC technique to analyse fatigue damage phenomena in two notched GFRC laminates under tensile load. Damage analysis based on optical DIC technique has been performed to detect the damaged areas on the specimen surface. The damage evolution and failure mechanism has been followed monitoring two parameters: the local hysteresis area of stress-strain cycles, the local stiffness variation.

Nel presente lavoro viene presentato lo studio del comportamento a fatica di provini in laminato composito in fibra di carbonio e resina epossidica uniassiali realizzati con tecnologia RTM. L’obiettivo è quello di valutarne il danneggiamento all’aumentare del numero di cicli di carico. A tale scopo, il processo di danneggiamento è stato studiato sia in termini globali, valutando il decadimento della rigidezza del composito, sia in termini locali, valutando le variazioni delle mappe di temperatura in funzione del numero di cicli.

The residual stresses introduced into a component as a result of the mechanical processes necessary for its manufacture significantly influence of fatigue behaviour. The application of loads themselves can, however, alter the initial residual stress distribution, so it is feasible to believe that the residual stress field of a fatigue-stressed structure develops over its entire lifespan. The aim of this article is to analyse the development that the residual stresses initially present in a welded butt joint undergo following the application of the external cyclic load. Comparisons between two residual stress measurements, conducted on the same joint before and after the application of fatigue cycles, have made it possible to obtain interesting information regarding the development of residua stresses in components subjected to fatigue. In particular, it has been found that unlike what is commonly reported, there are particular conditions where the application of a cyclic load results in an increase in the residual stresses initially present, rather than their relaxation. This phenomenon should be taken into consideration in order to avoid unexpected failure in components subjected to fatigue.

Two different full-field techniques are here used to investigate the heat sources and dissipation sources that compare onto the surface of a composite laminate under fatigue load. The material here studied is a glass fibre reinforced epoxy laminate employed in the field of wind turbine. During fatigue tests, 8-bit (256 grey levels) images and thermal images were acquired and elaborated to relate the hysteresis area and the heat sources, finding the energy of damage in three points of specimens. The data shows a clear intensification of dissipative phenomena just in that region where final failure is then registered.

In this paper a discussion about the determination of the stress state corresponding to the application of four-points bending load on a sandwich panel having a core made of closed cell aluminium foam is reported. An analytical model based on laminated plate classical theory is compared to a more complex FEM model, considering the effect of geometric parameters of panels, like core and plate thickness, and of loading mode, like span length. The results show the difficulties to define a reliable model to calculate stress state in this kind of composite material.

Aluminium foam sandwiches are subjected to four point bending fatigue test considering the effect of geometric parameters of panels, like core and plate thickness, and loading mode, like arm distance. Fatigue strength curves are expressed in terms of different stress amplitude parameters calculated using an analytical model based on laminated plate classical theory and a solid FEM model. Nevertheless the relevant fatigue data scatter, originated by foam intrinsic in-homogeneity, experimental fatigue curves are coherent and allow obtaining unified fatigue curves.

Several studies on Digital Image Correlation technique allowed this methodology to be recognised in the last decade as a welloptimised tool for mechanical experimental measures, but much work is to be done to apply DIC based analyses on advanced applications, such as fatigue damage studies and composite materials failure investigations. DIC based methodology gives direct measure of the displacement field using a well defined formulation of matching the images of loaded and load free component, so that displacement vectors can be evaluated for a certain number of grid reference points on the analysed surface. In this work, the authors present the latest research with this method, and analyse fatigue damage phenomena in GFRC laminates under tensile fatigue load employing notched and notch-free specimens. Damage analysis based on optical DIC technique has been performed to detect the damaged areas on the specimen surface and to follow failure mechanisms during lifetime; the damage evolution in composites was performed monitoring two parameters: the local hysteresis area of stress strain cycles, the local stiffness variation. These parameters are evaluated on a grid by means of DIC strain measurements during the entire fatigue life showing encouraging results.

Complex time dependent damage phenomena are characteristic of Composites under fatigue; this is due to material structural heterogeneity and fibre/matrix interactions. Fatigue life is mainly determined by the progressive damage evolution, difficult to be modeled with numerical tools or mathematical frames. Experimental methods are to be applied to achieve correct information about the evolving fatigue damage and the authors propose a methodology based on Digital and Thermal Image analyses, to measure on notched GFRC specimens the dissipative sources in terms of temperature and deformation based data; starting from previous works, the measurements procedures were improved for these techniques, in order to obtain useful results with notched composites and capable to detect different damage states on specimen surface.

A CDM (continuum damage mechanics) model for damage valuation is here considered and applied to the study of two different typologies of notched and cylindrical specimens. The model presents some parameter and authors determined them in a previous work testing cylindrical and smooth specimens. Firstly fatigue characterization was conducted and the SN curves found. In order to evaluate the capability of CDM model to predict the sequence effect and to simulate a more realistic loading condition, tests with various loading blocks were carried on and in particular high-low, low-high and random blocks were applied to the three specimens considered. Model previsions showed good agreement with results for each geometry considered.

Fatigue behaviour of fastened joints represents a critical issue for aeronautical structure, considering also that a notable amount of data has been collected for static behaviour. In this work, fatigue test of riveted single lap joint made of carbon/epoxy laminates were carried out at different load levels and test frequency. Experimental results showed the importance of monitoring the temperature field in the region between fasteners. Moreover, the evaluation of the residual strength of specimen previously subjected to fatigue load showed a notable improvement of all the mechanical properties.

Il presente lavoro ha come obiettivo principale lo studio del comportamento a creep della superlega per applicazioni aeronautiche Udimet 720Li. E’ stato seguito un piano di prove di creep a due diverse temperature di prova (650 e 700°C), confrontando i risultati ottenuti su provini lisci e su provini con intaglio. E’ stato inoltre implementato un modello numerico per l’analisi agli elementi finiti dell’influenza dell’intaglio sul comportamento a creep del materiale. Questo piano di prove è inserito in un progetto più ampio avviato in collaborazione con Avio S.p.A. di Torino che prevede, tra le altre cose, l’esecuzione di prove di fatica a basso numero di cicli. Il materiale è stato fornito sotto forma di manufatto dalla Avio S.p.A. di Torino.

Superalloys are the most diffused material for aeronautical and aerospace applications, mainly for turbines and compressors production, because of their excellent resistance at high temperature. Among them, polycrystalline superalloys Udimet 720Li and Inconel 718Plus are interesting candidates for turbine disc application, due to their high temperature strength, good corrosion resistance and excellent workability. The aim of the present work is to study the low cycle fatigue (LCF) behaviour of these two nickel-base superalloys for aeronautical applications. The experimental tests plan has been predisposed with two different working temperatures (650 and 700°C). Materials were provided from Avio s.p.a. Torino in the form of manufactured article. This project includes tensile and creep tests, too.

In this work the mechanical behaviour of CFRP laminates having an artificial wrinkle introduced in the critical section has been studied in the Open Hole Tension and Open Hole Compression configuration. The experimental test allowed determining the failure mechanism and the knockdown of the ultimate strength in five different configurations.

In this work, the possibility using two different technologies to repair industrial flat components made of Waspaloy superalloy was investigated. Specimens present a V notch in the central zone of the gage length, which has been refilled by MicroPlasma and Electro Spark Deposition in order to recover the original thickness of the material. These specimens have been used for a complete mechanical characterization, carrying out static, low-cycle fatigue and creep tests. Finally, results have been compared to base material. Static and low-cycle fatigue test have been carried out at Room Temperature and 538°C, while creep test considered the temperature of 704°C. Results of uniaxial tensile tests showed that the two repair process have a different effect on the mechanical properties. While MicroPlasma produced a reduced yield stress and tensile strength but a good performance whit respect to the elongation to failure, Electro Spark Deposition assured a better mechanical strength but a reduced elongation to failure. Low-cycle fatigue properties have been determined carrying out tests at different temperature (Room Temperature and 538°C). Repaired material showed lower fatigue strength and an increase of the data scatter, especially ESD at 538°C. Finally, creep test carried out on a limited number of specimens allowed establishing some changes about the creep rate and time to failure. MP behaviour was more similar to base material, while ESD show the presence of a marked tertiary creep.

Obiettivo del presente lavoro è la caratterizzazione a taglio di schiume di alluminio tramite un sistema di carico biassiale appositamente progettato e lo sviluppo di modelli numerici microstrutturali di schiume soggette a taglio. Sono state considerate due differenti morfologie di cella. Per la loro rilevanza industriale, le tipologie di schiume studiate sono state la schiuma metallica a celle chiuse Alulight e quella a celle aperte M-Pore. Il modello della schiuma a celle chiuse consiste in un cubo costituito da celle ellissoidali le cui dimensioni e posizione sono variabili in maniera casuale uniforme nel volume di riferimento ed entro un range di valori. Il modello per la schiuma a celle aperte è basato sulla tessellatura casuale di Laguerre, che riproduce sia la regolarità macroscopica che la casualità microscopica delle schiume M-Pore. L’adeguatezza dei due modelli è stata valutata mediante il confronto delle curve sperimentali con quelle numeriche.

In this work, the mechanical properties of Waspaloy superalloy have been evaluated in case of welded repaired material and compared to base material. Test program considered flat specimens on base and TIG welded material subjected to static, low-cycle fatigue and creep test at different temperatures. Results of uniaxial tensile tests showed that the presence of welded material in the gage length specimen does not have a relevant influence on yield strength and UTS. However, elongation at failure of TIG material was reduced with respect to the base material. Moreover, low-cycle fatigue properties have been determined carrying out tests at different temperature (room temperature RT, 538°C and 760°C) in both base and TIG welded material. Welded material showed an increase of the data scatter. Fatigue strength was reduced , with respect to the base material. During test, all the hysteresis cycles were recorded in order to evaluate the trend of elastic modulus and hysteresis area against the number of cycles. A clear correlation between hysteresis and fatigue life was found. Finally, creep test carried out on a limited number of specimens allowed establishing some changes about the creep rate and time to failure of base and welded material. TIG welded specimen showed a lower time to reach a fixed strain or failure when a low stress level is applied. In all cases, creep behaviour of welded material is characterized by the absence of the tertiary creep.

Purpose of the job is to perform measurements on two specimens with ND control procedures on composite material with carbon fibers and different thickness, containing artificial defects similar in shape, but with different typology, in order to allow the detection tests to be adapted on large and small defects at certain depths. The analysis was performed using the Thermography Pulsed technique and Phased Array ultrasonic inspection, comparing the detection of artificial defects of different sizes and different typology, identified at different depths as with the real ones. All the important factors that enable the success of a scanning method with ND controls were studied, allowing to evaluate the efficacy of the used techniques and tools in the studied cases.

This paper describes the application of active pulsed Thermography (PT) as Non-Destructive Test (NDT) method for the investigation of CFRP aeronautical components. The analyzed specimens include T-shaped stringers, previously monitored by ultrasonic analysis, and laminated flat panels with internal production defects. Several set-up tests allowed to identify optimal configurations for the defects detection according to specimen geometry and defect location. A custom post-processing algorithm has been developed for more precise defects characterization, elaborating thermographic data; whilst a successive full-field contrast mapping construction allowed to propose a reliable defect distribution map and better definition on larger areas. Detection of defects was studied through proper thermal contrast evaluation, with respect to suitable choice of a sound reference area during the transient cooling phase. Influence of Heating time on the thermal contrast has also been studied and the Thermography ability to detect with accuracy and reliable results real small production defects is verified in this work on typical CFRP aeronautical components.

This work explores the possibility to apply thermographic technique as non destructive test to control glass fiber reinforced polymers having artificial defects. Three symmetrical composite panels reinforced with fiberglass (unidirectional E type fiberglass and epoxy resin) were realized through hand lay‐up and artificial inter‐laminar delaminations of various geometry were introduced at different depths. Several thermal stimulation procedures with different ways to consider the defects in the specimens enable to optimize the thermographic technique, by solving some initial problems related to the experimental set -up and issues. Above all, the minimum requirements for defect which can be revealed trough pulsed thermography have been established, according to present experiences. The importance of geometric and thermo-physic characteristics of the defect related to the material in which it is inserted has been observed, as well as the surface conditions of the observed laminate faces

In this work, a scheme of representation of structural concepts for the aeronautical field is identified. It is based on an original set of 2D and 3D primitives, representing the main structural components of the aeronautical concept. Starting from them, an associative parametric geometrical modelling of the aeronautic structure, consisting in a quad-mapped mesh, is obtained. The automatic propagation of modifications is implemented so that several structural concepts can be efficiently modelled and modified during the very early phases of the design process. The propagation process aims at the automatic regeneration of the whole mesh thanks to a well-defined hierarchy (or relationship of dependences) among the parametrically defined primitives. Based on the above-mentioned considerations, a CAD/CAE tool, called MeshFEM, has been developed using C++ and Matlab languages and the VTK library for the 3D graphic visualization.

Residual stresses, introduced into a component by manufacturing processes, significantly affect the fatigue behaviour of the component. External load application produces an alteration in the initial residual stress distribution, so it is reasonable to suppose that residual stress field into a component subject to a cyclic load presents an evolution during the total life. In this work, the authors analysed the evolution that the residual stress field, pre-existing in a butt-welded joint, suffers following the application of cyclic load. The comparison between two residual stress measurements, carried out on the same joint before and after the cyclic load application, allowed to obtain interesting information about the residual stress evolution. It was found that in particular condition, unlike the general opinion, a cyclic load application produces an increasing in the residual stress level rather then a relaxation. This phenomenon is to take well in account in order to avoid unexpected failure in components subjected to a fatigue load.

In this paper a methodology to analyse the shear behaviour of aluminium foam with closed cells is proposed. A biaxial load device expressly designed and the elaboration with Digital Image Correlation technique of the data acquired during the test with a CCD camera allowed determining the displacement and strain fields. This procedure made possible to evaluate the procedure as suitable or not for conducting a shear characterization for metallic foam. The curves obtained showed an initial elastic outline followed by the yield plateau, a peak load and a rapid load drop.

Many factors are involved in determining the fatigue strength of welded joints. It is, however, very difficult to consider their relative importance. The aim of this paper is to isolate the effect of residual stress from other factors, establishing a relation between the amount of residual stress and fatigue life. A geometrical notch due to the weld bead is removed by milling the upper surface of the welded plates. Moreover, specimens are subjected to four-point bend loading. Before conducting the fatigue test, the magnitude of residual stress for each specimen is experimentally evaluated, and then linked to the number of cycles to failure. This relation is analyzed for three different plate thicknesses and for different stress amplitude levels in the high cycle regime. The results clearly show the significant influence of residual stress on fatigue behaviours when the load level is near the fatigue limit.

Si riportano i dati delle tensioni residue introdotte dalle lavorazioni meccaniche per asportazioni di truciolo su provini a sezione cilindrica realizzati nella superlega Inconel718Plus e se ne studia l’evoluzione a seguito dell’applicazione di cicli ad ampiezza di deformazione costante. Le prove di fatica in controllo di deformazione sono state eseguite a temperatura ambiente e con ampiezze di deformazione comprese tra 0.76% e 1.33%. Le prove sono state interrotte dopo 10 e 100 cicli per consentire la misura delle tensioni residue assiali e circonferenziali mediante diffrattometria a raggi X. I risultati ottenuti hanno permesso di stabilire che l’instaurarsi di fenomeni di rilassamento è fortemente condizionato dall’ampiezza di deformazione applicata. La riduzione di tensioni residue, inoltre, è concentrata nei primissimi cicli, più che essere graduale, a differenza di alcuni modelli proposti in letteratura.

Questo lavoro descrive lo studio sperimentale svolto per valutare la resistenza a trazione di alcuni giunti in schiuma di alluminio ottenuti mediante diverse tipologie di collegamento, sia mediante bulloni che adesivi a base di resina epossidica. Sono state considerate diverse tipologie di disposizione dei bulloni e per ogni prova è stato ricavato il valore della forza massima necessaria per la rottura del collegamento. Le migliori prestazioni meccaniche si ottengono con il collegamento realizzato mediante due piastre coprigiunto e resina epossidica. Nel caso di collegamenti mediante bulloni, il carico trasmesso aumenta al crescere del numero di bulloni.

In questo lavoro sono state valutate le proprietà meccaniche di una superlega di Nickel tipo Waspaloy qualora risulti riparato per saldatura con riferimento al metallo base. Sono state eseguite delle prove sperimentali di trazione a diversi valori di temperatura, su provini in materiale base e, a temperatura ambiente, su provini sottoposti ad una saldatura trasversale tipo TIG. La presenza di materiale saldato risulta quasi ininfluente nel caso delle proprietà statiche, ad eccezione dell’allungamento percentuale a rottura che si riduce, anche se non in maniera drastica. E’ stata effettuata, inoltre, una caratterizzazione a fatica oligociclica della lega a temperatura ambiente, sia in condizioni base che su provini saldati TIG. Il materiale saldato presenta una resistenza a fatica inferiore ma comunque ottima rispetto al metallo base. I dati a fatica sono stati esaminati anche alla luce dell’evoluzione di alcuni parametri di danneggiamento quali il modulo elastico e l’area di isteresi.

Attraverso la diffusione dell'innovazione, la società intende perseguire le migliori condizioni economiche, sociali e professionali, nei settori della formazione, della ricerca e della consulenza nella realizzazione di soluzioni a carattere innovativo di problemi complessi