51 research outputs found
Peck drilling of CFRP/titanium stacks: effect of tool wear on hole dimensional and geometrical accuracy
No full textThe effect of tool wear on dimensional and geometrical accuracy of holes machined by peck drilling in carbon fibre reinforced plastic (CRFP) and titanium (Ti) stacks is studied. Coated and uncoated tungsten carbide drills of both fine and ultra-fine microstructures are employed to assess the importance of grain size and coating on hole accuracy. Hole profiles show two maxima: one at the hole entry and the other at the CFRP/Ti interface. Hole cylindricity as function of tool wear shows a minimum. It firstly decreases due to flank wear and subsequent reduction of the drill diameter. Then the rise of tool instability prevails with the result that an increase of the cylindricity with tool wear is brought about. Less wear-resistant drills attain this minimum in a shorter time of cutting
Effect of different surface treatments on titanium dental implant micro-morphology
No full textBackground: Titanium dental implants are today widely used with osseointegration mainly dependently on the implant surface properties. Different processing routes lead to different surface characteristics resulting, of course, in different in situ behaviors of the implants. Materials: The effect of different treatments, whether mechanical or chemical, on the surface morphology of titanium implants were investigated. To this aim, various experimental methods, including roughness analysis as well scanning electron microscope (SEM) observations, were applied. Results: The results showed that, in contrast to the mechanical treatments, the chemical ones gave rise to a more irregular surface. SEM observations suggested that where commercial pure titanium was used, the chemical treatments provided implant surfaces without contaminations. In contrast, sandblasted implants could cause potential risks of surface contamination because of the presence of blasting particles remnants. Conclusions: The examined implant surfaces showed different roughness levels in relation to the superficial treatment applied. The acid-etched surfaces were characterized by the presence of deeper valleys and higher peaks than the sandblasted surfaces. For this reason, acid-etched surfaces can be more easily damaged by the stress produced by the peri-implant bone during surgical implant placement
A comparison between wet and cryogenic drilling of CFRP/Ti stacks
No full textThis paper compares conventional and cryogenic cooling in the deep hole drilling of CRFP/Ti stacks. Various parameters are taken into account to find if the use of cryogenic coolant is justified by the improvement of the final results. Both the thrust and the torque were acquired continuously during the machining operations and compared both in average and distribution. The use of a cryogenic coolant brings a reduction in thrust force and torque without any sensible drawback. Overall the results prove that cryogenic drilling is a suitable technology for CFRP/Ti stack drill
Stationary Shoulder Friction Stir Processing: Influence of Tool Wear on Surface Properties
No full textLo scomunicatore di Tibor Déry: un episodio della fortuna di Ambrogio tra religione e politica
No full textL'articolo studia le singolari modalità con cui lo scrittore ungherese Tibor Déry presenta, nel suo romanzo "Lo scomunicatore" (1966, tradotto in italiano per l'editore Feltrinelli nel 1969) la figura di Sant'Ambrogio vescovo di Milano e 'Principe della Chiesa'. Attraverso una rappresentazione assai personale delle strutture sociali della tarda romanità e dei rapporti fra Chiesa e Impero, Déry sviluppa una coperta e tagliente denuncia del sistema poliziesco e vessatorio vigente nell'Ungheria comunista in cui viveva
Study of the Linear Friction Welding process of dissimilar Ti-6Al-4V – stainless steel joints
No full textLinear friction welding (LFW) is an innovative joining method that can be used to obtain high strength joints between dissimilar materials. A key factor that influences the joints performances are the intermetallic compounds that could be formed during the welding process. These intermetallics are brittle and could compromise the mechanical performances of the joint. This paper deals with the analysis of the LFW process of dissimilar titanium-stainless steel joints. Two different types of joints were studied: AISI 304 – Ti6Al4V and AISI 316 Ti6Al4V. Particular attention was paid to characterizing the intermetallic compounds using Scanning electron microscopy, Electron Probe microanalysis and X-ray diffractometry. Zones with different microstructure were observed. Due to the diffusive phenomena occurring during the welding Kirkendall effect and several intermetallics were observed. Moreover it was found that the joint with AISI 316 formed brittle intermetallic compounds that lead to the crack formation close to the weld line
Romolo Augustolo: caduta e ‘rigenerazione’ di un impero tra Dürrenmatt e Manfredi
No full textAlla luce di un confronto con le fonti tardoantiche greche e latine, l'articolo esamina come venga presentata la figura di Romolo Augustolo, considerato convenzionalmente l'"ultimo imperatore romano", in recenti 'riscritture' delle sue vicende: il testo teatrale "Romolo il Grande" di Friedrich Duerrenmatt (1949) e il romanzo "L'ultima legione" di Valerio Massimo Manfredi (2002)
On the performances and wear of WC-diamond like carbon coated tools in drilling of CFRP/Titanium stacks
No full textThe use of hybrid structures made of CFRP and titanium alloys is growing more and more in the last years in the aerospace industry due to the high strength to weight ratio. Because of their very different characteristics, the mechanical fastening represent the most effective joining technique for these materials. As a consequence, drilling process plays a key role in the assembly. The one shot drilling, i.e. the contemporary drilling of the stack of the two materials, seems to be the best option both in terms of time saving and assembly accuracy. Nevertheless, due to the considerable different machinability of fiber reinforced plastics and metallic materials, the one shot drilling is a critical process both for the holes quality and for the tools wear. This research was carried out to study the effectiveness of new generation tools in the drilling of CFRP/Titanium stacks. The tools are made of sintered grains of tungsten carbide (WC) in a binder of cobalt and coated with Diamond like carbon (DLC), and are characterized by a patented geometry; they mainly differ in parent WC grain size and binder percentage. Both the cutting forces and the wear phenomena were accurately investigated and the results were analyzed as a function of number of holes and their quality. The results show a clear increase of the cutting forces with the number of holes for all the used drilling tools. Moreover, abrasive wear phenomena that affect initially the tools coating layer were observed. © 2016 Author(s)
Study of the Metallurgy of a Dissimilar Ti-6Al-4V – Stainless Steel Linear Fiction Welded Joints
No full textThis paper investigates the metallurgy of a dissimilar Ti-6Al-4V-stainless steel linear friction welded joint. In particular two different stainless steels were considered: AISI 304 and AISI 316. These two alloys differ in the molybdenum (Mo) content. Metallographic observations, EDS analysis and Vickers Microhardness measurements were carried out, particular attention was focused on the study of the intermetallic compounds and on the microstructures of the different zones produced by the welding process. As is usual for solid state welding processes, three different zones can be identified: the parent material, the heat affected zone (HAZ) and the thermo-mechanical affected zone (TMAZ), furthermore a very thin interface zone, rich of intermetallic compounds, was also observed. In this zone diffusive phenomena also occurred resulting in a variation of the alpha phase content on the titanium side. In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was observed. Moreover, it was observed that in the weld region, exposure to supertransus temperatures (995°C) combined with hotdeformation working and rapid cooling after joining induced the recrystallization of a martensitic beta grain structure. Concerning the joint between Ti-6Al-4V and AISI 316 some cracks were observed within the weld line, due to the presence of brittle intermetallics compounds in this zone. The formation of these intermetallics was promoted by the presence of Molybdenum
Gli spazi del fugitivus nell’ impero romano
No full textMoving from the analysis of two essays on slavery, written by Dio Chrysostomus at the end of the I Century A. D., the Author tries to retrace the cultural and juridical context of the phenomenon of the flight of slaves in the High Roman Empire.A partir del análisis de dos textos sobre la esclavitud escritos por Dión Crisóstomo a finales del siglo I d. C., el autor intenta definir el contexto cultural y jurídico del fenómeno de la huida de esclavos durante el Alto Imperio.Desideri Paolo. Gli spazi del fugitivus nell’ impero romano. In: Los espacios de la esclavitud y la dependecia desde la antigüedad. Madrid, 28-30 novembre 2012. Actats del XXXV coloquio del GIREA. Homenaje a Domingo Placido. Besançon : Presses Universitaires de Franche-Comté, 2015. pp. 385-393. (Actes des colloques du Groupe de recherche sur l'esclavage dans l'antiquité, 35
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