323,137 research outputs found
Fatigue behavior of single crystal superalloy bars joined by capacitor discharge welding
No full textThis work concerns single crystal Ni-based superalloy welded through the capacitor discharge welding (CDW) process. The static and fatigue behavior of CMSX-4 type single crystal alloy has been analyzed, performing mechanical tests on square specimens in order to establish in detail the superalloy behavior at the expected service stresses. Tests have been conducted both at room and working temperatures (800°C), comparing base material and capacitor discharge welded joints. The material microstructure has been observed with optical and scanning electron microscopy in order to characterize welding parameters effects on the weld characteristics, analyzing base material and as-welded specimens; this way, the CDW process has been studied to perform butt joint with the better characteristics ad achieving sound welds. Microstructural modifications and the heat affected zones have been observed in the welded section as well as the interaction between weld material and parent metal. The research activities have been conducted in the frame of AWFORS project, financed by the European community
On Safety Assessment and Base Isolation of Heavy Non-structural Monolithic Objects
No full textAbstractUnder seismic actions heavy non-structural objects, which are usually placed at the top of existing constructions, may constitute a danger to human lives and a considerable loss for world heritage. In this contribution, safety assessment of non-structural monolithic objects is discussed through the illustration of a case study, which concerns seismic protection of eleven ancient marble decorative pinnacles placed at the top of a three-arched masonry city gate in Ferrara (ITALY). A method for assessing the safety of the underlying masonry structure under the action of seismic excitations is outlined and the amplification of the ground motions due to the presence of such structure is evaluated
A scanner for in situ X-ray radiography of large paintings: the case of “Paolo and Francesca” by G. Previati
No full textA scanner for digital radiography of large paintings has been designed and developed, aimed to in situ performances. We report here the application to “Paolo and Francesca” (260×230cm2), masterpiece by the Italian divisionist painter Gaetano Previati (1909). The scanner has given the whole radiography in 1137 X-ray shots, which were corrected for X-ray inhomogeneities and finally processed, minimizing the visual impact of the frame structure. The original version of the painting has been brought to the light, and it appears to be a further step in the evolution of the theme frequently experienced by the artist
Influence of groundwater flow on the estimation of subsurface thermal parameters
No full textWe investigated the influence of groundwater flow on the thermal tests performed in borehole heat exchangers to infer the underground thermal properties. Temperature–time signals were simulated with a moving line source (MLS) model under different hypotheses of Darcy velocity. Periodic and random noise was included in the synthetic data obtained with this model in order to mimic high-frequency disturbances caused by several possible sources (e.g. equipment instability and changes in environmental conditions during the experiment) that often occur in real signals. The subsurface thermal conductivity, the Darcy velocity and the borehole thermal resistance were inferred by minimising the root-mean-square error between the synthetic dataset and the model. The calculated thermal and hydraulic parameters were consistent with the “a priori” values. The optimisation procedure results were then tested with the infinite line source (ILS) model. For a Darcy velocity exceeding 10−7 m s−1, ILS largely overestimates thermal conductivity. The approach relying on the MLS model was finally tested with real temperature–time data and produced reliable estimates of thermal conductivity, Darcy velocity and borehole thermal resistance. The inferred groundwater flow was cross checked by means of an independent method based on the analysis of temperature–depth logs recorded under thermal equilibrium conditions. Such a test validates the Darcy velocity inferred with the MLS approach
Data mining and knowledge discovery resources for astronomy in the web 2.0 age
No full textThe emerging field of AstroInformatics, while on the one hand appears crucial to face the technological challenges, on the other is opening new exciting perspectives for new astronomical discoveries through the implementation of advanced data mining procedures. The complexity of astronomical data and the variety of scientific problems, however, call for innovative algorithms and methods as well as for an extreme usage of ICT technologies. The DAME (DAta Mining & Exploration) Program exposes a series of web-based services to perform scientific investigation on astronomical massive data sets. The engineering design and requirements, driving its development since the beginning of the project, are projected towards a new paradigm of Web based resources, which reflect the final goal to become a prototype of an efficient data mining framework in the data-centric era. © 2012 SPIE
Caratterizzazione meccanica e microstrutturale per il repair di leghe aeronautiche saldate con tecnica CDW
No full textLe tendenze attuali sulle possibili procedure produttive e di repair di componenti aeronautici in superlega vertono sull’utilizzo di sistemi di laser cladding e processi di saldatura avanzata. Tra le tecniche di saldatura, quella capacitiva denominata Capacitor Discharge Welding (CDW) si rivela particolarmente adeguata in quanto consente, dopo la rimozione della parte danneggiata, l’applicazione di una nuova pala senza la sostituzione dell’intero blocco, evitando lavorazioni aggiuntive e con l’ottenimento di ottime proprietà meccaniche. Il processo CDW consente di ottenere cordoni di saldatura di piccolissimo spessore, effetti di intaglio minimi ed una buona caratteristica strutturale e di forma del materiale saldato. Nel presente lavoro è stato analizzato il comportamento meccanico statico, a fatica ed a creep delle superleghe Inconel 718 e TiAl6V4 prima e dopo la giunzione CDW su particolari provini cilindrici saldati di testa, soggetti anche a specifici trattamenti termici. Le prove sono state eseguite sia a temperatura ambiente che ad alta temperatura sul materiale base e sul materiale sottoposto a tecnica di saldatura CDW, confrontando i risultati ottenuti. E’ stata inoltre analizzata la microstruttura delle leghe mediante osservazione al microscopio ottico e al microscopio elettronico a scansione (SEM). La tecnica è stata infine impiegata anche per la saldatura di provini complessi quali mock-up di turbina aeronautica, con risultati al momento non del tutto soddisfacent
Experimental investigation of shape memory polymer strips
No full textShape memory polymers (SMPs) represent a technologically important class of stimuli-responsive materials whose key feature lies in the shape change exhibited during a suitable thermo-mechanical loading program. Historically, the advancement of the SMP field has been closely associated with its practical potential. In this work an experimental investigation on a particular shape memory polyurethane, named DESMOPAN DP 2795A and produced by Bayer Material Sciences, is presented. The tests were carried out in the laboratories of the Institut für Angewandte Mechanik, RWTH Aachen University. The goal of this experimental work is addressed towards a better understanding of the mechanical behavior of a new polymeric material, in order to assess the basis for future constitutive modeling
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