A novel set up is proposed to measure the energy release rate versus crack propagation speed in viscoelastic materials. The new test is referred to as the square sample tear test. In comparison to other techniques as the pure shear specimen and the pure tensile specimen tests, the square sample geometry guarantees at the same time: (i) a constant flux of elastic energy at the crack tip, (ii) the full development of the annular dissipative region around the crack tip, where the material is in the transion region of the viscoelastic response spectrum. Both conditions allow to precisely control the crack propagation speed and to test the predictions of existing theories. By employing the new set-up we measure the energy release rate as a function of the crack propagation speed. We also measure with a high precision infrared camera the increase of temperature at the crack tip, showing that, notwithstanding the low speed regime considered during the experiments, the viscoelastic dissipation at the crack tip leads to a measurable temperature increase of about 1◦C

Zirconium nitride (ZrN) is a transition metal nitride widely studied to be used in different technological fields, like protective coatings and optoelectronics. High hardness, strong wear resistance, chemical stability and high corrosion resistance make transition metal nitride films suitable for tribological applications. For this kind of applications it is essential to evaluate and to control the film adhesion to the coated tool and its hardness properties. In this work ZrN films were RF-sputtered on WC–wt.10 % Co substrates using different assistance bias voltages (up to 20 V) applied during the film growth. The structural properties of the obtained coatings were analysed using x-ray diffraction (XRD) measurements. It was found that the substrate bias strongly influenced the incorporation of residual oxygen impurities in the films. A structural switch from the (200) to the (111) preferential crystal structure was detected with the increasing bias voltage. In addition, transmission electron microscopy (TEM) analyses showed some twinning features inside the deposited films. The film properties were correlated to the film adhesion, studied by scratch test, and to their wear resistance, carried out by ball-on-disc tribometry. The maximum obtained critical load was about 70 N and the wear rate was about 2.23*10^-6 mm3/Nm. Nanoindentation measurements is in progress in order to correlate them with the structural features and wear resistance properties of the grown films.

he improvement of the adhesion of a coating film to the coated material and of its wear resistance is a fundamental aspect for protective hard coatings. As a consequence, the optimization of the deposition techniques is required to properly tune the film properties.Among the numerous materials for hard coatings, zirconium nitride (ZrN) is extensively studied for use in tribological applications, thanks to its high hardness, strong wear resistance, chemical stability and high corrosion resistance. In this work ZrN films were RF-sputtered on silicon and tungsten carbide substrates, with different assistance bias voltages applied to the substrate during the film deposition. Their adhesion and wear resistance properties were evaluated and correlated to the structural and compositional properties, showing the best responses (higher critical load and scratch hardness, and lower wear rate) when using a low negative bias voltage (− 5 V).

Despite the large number of proposals in the field of fatigue prediction of welded joints, there is no worldwide accepted and unified theory which can be easily applicable to any load condition. Real life components, in fact, differ in geometry and/or type of load from the structural design considered by the Standards, hence a lot of precautionary safety factors are used, leading to an underestimation of the actual fatigue life of joints. Infrared thermography has a great potential in this field. In fact, it enables a full-field stress analysis with an adequate spatial resolution so that the complexity of the stress state at the weld toe and its time evolution are taken into account, emphasising anomalies that may predict structural failure. This paper presents a new method for the evaluation of the fatigue limit, focusing on interesting results derived from the analysis of thermoelastic signal phase evolution. Variations in the value of signal phase indicate a non-elastic behaviour and plastic dissipation in the material.

The work referred to this document was carried out to study the influence of the process parameters on the mechanical properties of aluminum plates (AA 5754-H111) with a thickness of 6 mm, welded by means of Friction Stir Welding. The analysis which were carried out, involved the process parameters such as the welding tool rotation speed and the welding tool travel speed. The process was monitored during each test through thermocouples and infrared cameras. The thermal fields which were detected during the process of FSW have provided important information about the temperatures distributions for each combination of assigned process parameters. The most significant observations concerned the thermal non uniformity recorded along the length of all the welded joints and the asymmetries in terms of the maximum temperatures reached between the two sides of the weld. The most interesting observations showed an asymmetric temperature due to FSW process between the advancing side and the retreating side. In particular it has been observed that higher temperatures are always been recorded along the retreating side compared to advancing side. These results proved that the thermographic techniques could be a very useful tool to monitor the many variables that come into play in the process of FSW. In addition, tests conducted on static mechanical joints previously monitored, showed a non-uniform distribution of the mechanical characteristics also along the welding direction. These evaluations have led to say that, based on the process parameters chosen and the set-up of the equipment employed, the process could not be considered to be "stationary". Considering these results, it has been hypothesized that there was a link between the variation of the thermal properties and the mechanical properties non-uniformity of the same joints, along the welding direction. Finally, through the development of the ANOVA, was demonstrated a significant influence of the used process parameters, on the mechanical characteristics.

Machining of aerospace materials is one of the major challenges of modern manufacturing. Application of nano-multi layered AlTiN/AlN PVD coatings to cemented carbide tooling results in a significant tool life improvement under conditions of cutting hard to machine alloys such as Ni-based Incone l 718 superalloy and Ti-based TiAl6V4 alloy [1]. TiAlN and AlN coatings were prepared using a reactive magnetron sputtering system from TiAl and Al targets. Structural characterization of the coatings using x-ray diffraction (XRD) revealed the B1 NaCl structure of TiAlN with a prominent reflection along the (111) plane and hexagonal wurtizite phase of AlN coatings. Subsequently, nanolayered multilayer coatings of TiAlN/AlN were deposited on silicon and WC-Co substrates at different modulation wavelengths (Λ) with a total thickness of approximately 1.0m. The modulation wavelengths were calculated from the x-ray reflectivity data using modified Bragg’s law. TiAlN/AlN multilayer coatings were textured along (111) for Λ<200 ? Study of thermal stability of the coatings in air indicated that the TiAlN/AlN multilayer coatings were stable up to 900°C in air. TiAlN/AlN multilayer coatings also exhibited improved wear resistance when compared to the substrate.

TiAlN/AlN multilayers are attracting great interest for the possibility to modulate their mechanical and tribological properties through the variation of multilayer design. In this work TiAlN single layer, TiAlN/AlN intermixed-multilayer and nano-multilayer were prepared using a reactive magnetron sputtering system starting from targets of TiAl and Al. The aim is to analyze how the multilayer design affects the thermal and tribological properties of the coatings. The microstructure of as-deposited and annealed films has been studied using X-ray diffraction. The chemical composition has been deduced by XPS analyses. Thermal behavior was assessed by means of differential thermal analysis (DTA) and thermogravimetric analysis (TGA), while mechanical properties have been investigated by wear tests.

L’articolo descrive un lavoro di ricerca, che ITC-CNR, ENEA-UTEE, DES (Diagnostic Engineering Solution) - spin off del Politecnico di Bari e Comune di Bari, stanno portando avanti al fine didefinire un metodo di indagine ottimizzato ed integrato sia per la valutazione dei deficit energetici e di comfort dell’edificio scolastico che per l’individuazione di soluzioni progettuali ad hoc. Il metodo proposto in questa sede si basa su un approccio olistico-sistemico, con validazione sperimentale, che ai metodi tradizionali di indagine strumentale in situ integra un metodo del tipo “post occupancy evaluation” con il coinvolgimento degli utenti e la loro valutazione soggettiva delle condizioni di comfort (scala ASHARAE) durante l’uso effettivo dell’edificio. Gli interventi ipotizzati sono stati del tipo step by step, per l’individuazione di benchmarks di miglioramento minimo, in funzione dell’ottimizzazione delle risorse – scarse - a disposizione.

Il presente lavoro è finalizzato ad esaminare l'influenza dei parametri di processo sulle variazioni delle proprietà meccaniche subite dalla lega di alluminio AA5754-H111, saldata mediante la tecnica di Friction Stir Welding (FSW). Il processo è stato monitorato mediante l’utilizzo di termocamere ad infrarossi, al fine di correlare le informazioni derivanti dai campi termici registrati sul materiale durante la saldatura, con eventuali mutazioni del comportamento meccanico dei giunti saldati. Le indagini termiche hanno consentito di ricavare la distribuzione delle temperature in prossimità di tutti i cordoni di saldatura. Da esse è emersa una rilevante asimmetria termica tra i lembi dei giunti e una distribuzione delle temperature non uniforme dall’inizio alla fine delle saldature. Tali risultati hanno evidenziato come le tecniche termografiche rappresentino un importante strumento di controllo e di analisi delle proprietà meccaniche dei giunti realizzati con il processo di FSW.

The modular device includes a thermal group of excitation, a thermocamera, a capture card, at least one computer and related software for the management and control of the apparatus, at least one feedback controller of the emission levels of the waves used by the thermal group of excitation, one or more laser pointing systems for the identification of the measurement area. The thermal group of excitation is operated by a driver board, analog or digital, through ON / OFF commands and/or square and sine waves. The device is applied, in general, in the field of non-destructive testing (NDT) and, in particular, for the analysis and for the diagnostic of coatings and other details of components and big structures with specific regard to the fields of aviation industry, recreation industry, manufacturing and renewable energy.