1,721,645 research outputs found
Investigation on laser welding of Ti-6Al-4V plates in corner joint
No full textThe article deals with laser beam welding of Ti-6Al-4V plates for aerospace applications. A number of trials are conducted to weld 3-mm-thick plates in corner joint configuration; a specific device for clamping and shielding to prevent oxidation is used. Autogenous welding is investigated, the joint being accessed from the outside, as a butt-welded corner joint. Referring to international standards, the results are first discussed in terms of geometry of the welding bead in the cross-section since titanium alloys are reported to be notch sensitive. Moreover, microstructure and microhardness are investigated. An optimum processing condition is suggested in order to perform laser beam welding with minimal undercut and porosity. © The Author(s) 2017
Freud's clinical writing. An encounter between philology and psychoanalysis
No full textThe authors examine Freud's clinical cases dedicated to Emmy von N. and The Rat Man in a philological perspective. They start with the analysis of the notes taken by Freud during the treatments and then they focus on the way in which the notes were used in the final drafting of the clinical cases. They observe that Freud's clinical writings disregarded the philological adherence of the notes and that the author considered them as a simple trace to be reworked from a formal and also substantial point of view. The lack of coincidences between the notes and the published texts must not be considered as an error or a stretch. It needs to be intended as a legitimate and acceptable variation with the purpose of introducing some significant openings in the meaning and new possible interpretations
IN792 DS superalloy: Optimization of EB welding and post-welding heat treatments
No full textElectron beam (EB) welding has been used to realize the seams on 2 mm thick plates of directionally solidified (DS) IN792 superalloy. A grid of the samples has been prepared by varying the pass speed v from 1 to 2.5 m/min, while the other process parameters (power P = 1 kW, acceleration voltage T = 50 kV, beam current I = 20 mA) were kept constant. Experiments were carried out both at room temperature and with pre-heating at 200 °C or 300 °C. Once found the best process conditions (pre-heating at 300 °C; v = 2.5 m/min) the effect of postwelding heat treatments at 700 and 750 °C for increasing time up to 2 hours has been investigated. © 2017 Trans Tech Publications, Switzerland
Roduction and characterization of steel sandwich structures with aluminum foam core [Realizzazione e caratterizzazione di strutture sandwich di acciaio con core in schiuma di Al]
No full textThe present work describes the results carried out in the manufacture of sandwich panels with stainless steel (SS) AISI 316 skins and an aluminium alloy AISI 10 foam core. Sandwich structures with a core of AI or AI alloys are often realized by ex-situ bonding, i.e. adhesive are employed for joining foam to external sheets. This method is easy to apply, however it entails a strength reduction when temperature increases, which results in serious problems during recycling and high costs. Another approach is the in-situ bonding, which involves the preliminary joining of the skins to the foam precursor to make the composite structure. This composite, once submitted to the foaming heat treatment, achieves the final Foam Sandwich by metallurgical bonding. In this study, a new method to obtain in-situ bonding between the Stainless Steel (SS) skins sheets and the aluminium foam core is described. The first part of this work has focused on the production of sandwich of small size: 20 × 20 mm. The production of the sandwich was done in two steps. The first step is the manufacture of the composite precursor, by both hot and cold pressing. The Composite precursor was made, using two sheets of (SS) for the skins and a foamable precursor of AISI 10 placed in middle. Great importance in the manufacture of such a composite lies in surface finishing, consisting in the middle removal of the surface oxide layer by mechanical and chemical treatments. As shown in Fig. 2 (a-b) as a function of the procedure of preparation, bad or good preliminary bonding have been obtained. During the second step, the composite precursor was then foamed in the oven at 640 °C. In this step the pore walls at the interface make a metallurgical joint with the steel surface, as shown by the concentration profile of the chemical elements at the interface (Fig. 4, Fig. 5)
Fatigue assessment of Ti-6Al-4V titanium alloy laser welded joints in absence of filler material by means of full-field techniques
No full textThe aim of this research activity was to study the fatigue behavior of laser welded joints of titanium alloy, in which the welding was performed using a laser source and in the absence of filler material, by means of unconventional full field techniques: Digital Image Correlation (DIC), and Infrared Thermography (IRT). The DIC technique allowed evaluating the strain gradients around the welded zone. The IRT technique allowed analyzing the thermal evolution of the welded surface during all the fatigue tests. The fatigue limit estimated using the Thermographic Method corresponds with good approximation to the value obtained from the experimental fatigue tests. The obtained results provided useful information for the development of methods and models to predict the fatigue behavior of welded T-joints in titanium alloy. © 2018, Gruppo Italiano Frattura. All rights reserved
Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082
No full textThis paper describes a three-dimensional numerical model based on finite volume method to simulate heat transfer and fluid flow in laser–tungsten inert gas (TIG) hybrid welding process. To simplify the model and reduce the calculation time, keyhole dynamics are not considered; instead, a new modified volumetric heat source model is presented for the laser source to take into account the effect of the keyhole on the heat transfer into the workpiece. Due to the presence of arc current, an appropriate electromagnetic model based on the Maxwell equations are also solved to calculate electromagnetic forces in the weld pool. The results of computer simulation, including temperature, current density, electromagnetic, and melted material velocity field, are presented here. Furthermore, several dimensionless numbers are employed to recognize the importance of fluid flow driving forces in the weld pool. It is deduced that the fluid flow has an important effect on the weld pool shape. It is also founded that among the driving forces, Marangoni force is dominant fluid force in the weld pool. Besides, calculated results of hybrid welding process are compared with those of TIG and laser welding processes. The weld pool depth is relatively the same, but the width of the weld pool is highly larger in hybrid welding than lone laser welding. Eventually, the presented model is validated by comparison between calculated and experimental weld pool shape. It is founded that there is a good agreement as the capability of this model can be proved. © 2014, Springer-Verlag London
Laser beam welding of a Ti–6Al–4V support flange for buy-to-fly reduction
No full textTitanium and its alloys are increasingly being used in aerospace, although a number of issues must be addressed. Namely, in the framework of welding to produce complex parts, the same mechanical strength and a reduced buy-to-fly ratio are desired in comparison with the same components resulting from machining. To give grounds to actual application of autogenous laser beam welding, Ti–6Al–4V L- and T-joints have been investigated in this paper, as they are a common occurrence in general complex components. Discussions in terms of possible imperfections, microstructure, and microhardness have been conducted. Then, a real part consisting of a support flange for aerospace application has been chosen as a valuable test-article to be compared with its machined counterpart both in terms of strength and buy-to-fly. The feasibility and the effectiveness of the process are shown. © 2017 by the authors. Licensee MDPI, Basel, Switzerland
Electron beam welding of IN792 DS: Effects of pass speed and PWHT on microstructure and hardness
No full textElectron Beam (EB) welding has been used to realize seams on 2 mm-thick plates of directionally solidified (DS) IN792 superalloy. The first part of this work evidenced the importance of pre-heating the workpiece to avoid the formation of long cracks in the seam. The comparison of different pre-heating temperatures (PHT) and pass speeds (v) allowed the identification of optimal process parameters, namely PHT = 300 °C and v = 2.5 m/min. The microstructural features of the melted zone (MZ); the heat affected zone (HAZ), and base material (BM) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD), and micro-hardness tests. In the as-welded condition; the structure of directionally oriented grains was completely lost in MZ. The γ' phase in MZ consisted of small (20-40 nm) round shaped particles and its total amount depended on both PHT and welding pass speed, whereas in HAZ, it was the same BM. Even if the amount of γ' phase in MZ was lower than that of the as-received material, the nanometric size of the particles induced an increase in hardness. EDS examinations did not show relevant composition changes in the γ' and phases. Post-welding heat treatments (PWHT) at 700 and 750 °C for two hours were performed on the best samples. After PWHTs, the amount of the ordered phase increased, and the effect was more pronounced at 750 °C, while the size of γ' particles in MZ remained almost the same. The hardness profiles measured across the joints showed an upward shift, but peak-valley height was a little lower, indicating more homogeneous features in the different zones. © 2017 by the authors
Welding of IN792 DS superalloy by electron beam
No full textNi-based superalloys are widely used in the components of aeronautic engines and gas turbines operating at the highest temperatures. During the service life, surface cracks may form in these mechanical parts; therefore, their repairing by welding is of great technological relevance. Seams have been realized by means of electron beam welding (EBW) on plates of IN792 DS superalloy with material pre-heating. They are free of macro-defects like cracks and pores; however, microstructural changes are observed in molten (MZ) and heat affected (HAZ) zones. The amount of γ' phase in MZ is smaller than that in the base metal, and the particles are very fine with an average size of 20 nm that leads to an increase of hardness. In HAZ particle, coarsening takes place as a consequence of heating; therefore, hardness slightly decreases with respect the base metal. X-ray Photoelectron Spectroscopy analyses carried out inside and outside the MZ, and the results show that the distribution of chemical elements remains homogeneous in the sample. Auger electron spectroscopy line scans with higher lateral resolution evidenced that the center of MZ is depleted of Mo and rich of Cr. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd
Pensiero monodico, pensiero binario e terzità nella società ipermoderna.
No full textStarting from some singer-songwriter’s lyrics and from a novelist’s book, the author analyses the most recurring forms of thought in the hyper-modern society: the binary thought, based on a Schizoid-paranoid logic, and the monodic thought. The binary thought leads the person to a choice between two alternative options, opposed at a first glance, but which in fact legitimise each other and leave out any third option. The monadic thought is the psychic reflection of the lacanian «capitalist discourse» and it keeps the subject into a spiral of «jouissance», which is opposed to desire and from which it is impossible to get out. They are two dynamics of thought flattening the mind, impeding the mentalization, crystallizing the intrapsychic and intersubjective fields and, in the political sphere, depriving the democracy of its real sense
- …
