1,721,178 research outputs found
Study of high strain rate effect on sheet formability based on Nakazima test
No full textThe knowledge of the sheet metals formality is important for the success of the manufacturing processed based on plastic deformation. Even though many industrial processes take place at relatively high speeds, higher than the quasi-static regime ones, few studies are present in the literature on the evaluation of the formability at high speed. In this framework, the present paper aims at studying the effect of the high strain rate on the formability of AA6082 aluminium alloy, characterized by a thickness of 1 mm. An experimental equipment, based on the Nakazima test, mounted on a direct tension-compression Split Hopkinson Bar, has been developed in order to define the formability under dynamic loading conditions. The high strain rate behaviour of the alloy has been compared with the one obtained in quasi-static condition
La tutela amministrativa del segreto di Stato e delle informazioni classificate
No full textIl presente commento illustra le principali novita` introdotte dal d.P.C.M. 22 luglio 2011 in materia di tutela amministrativa del Segreto di Stato e delle informazioni classificate, nel piu` generale quadro della disciplina del sistema di informazione e sicurezza previsto dalla legge 3 agosto 2007, n. 214. La prima parte del commento esamina la struttura organizzativa della cd. Organizzazione nazionale per la sicurezza, sottolineandone il carattere composito e complesso, non solo per la dinamicita` del rapporto tra politica e amministrazione, ma anche per l’integrazione di soggetti privati nel sistema della sicurezza. La seconda parte del commento si concentra sugli aspetti di funzionamento, analizzando i principali strumenti di tutela delle informazioni classificate (in particolare, i provvedimenti di Nos e di Nosi ed i sistemi tecnici di sicurezza), nonche ́ le modalita` di compatibilita` di tale disciplina con il principio generale della trasparenza dell’azione amministrativa e con il diritto di accesso ai documenti amministrativi
Reuse of Composite Prepreg Scraps as an Economic and Sustainable Alternative for Producing Car Components
No full textIn the present paper, an innovative process for the reuse of carbon fiber prepreg scraps, based on a zero-waste approach, was proposed in order to recovery scraps produced during cutting operations of virgin prepreg rolls. Unfortunately, during the prepreg transformation, about 75% of the materials is discarded due to the inefficiency of the cutting phase. Nevertheless, this prepreg can be reused, in a closed loop system, to produce second life products. In this research, the environmental and economic benefits of implementing a recovery system for prepreg scraps were investigated exploiting Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) techniques. The LCA technique was used to compare the environmental impact of the innovative reclaiming process with the one obtained by the manufacturing process based on the use of virgin prepreg. Typical compression molding process was modeled for both the scenarios and the environmental performances were evaluated exploiting the Cumulative Energy Demand indicators. Moreover, the LCC analysis of the two alternatives was performed for evaluating the economic sustainability of the recycling process
Tensile behavior and formability of pre‐painted steel sheets
No full textThe present work aims at studying the tensile behavior and formability of pre‐painted steel sheets. To this purpose, uniaxial tensile and hemispherical punch tests were performed in order to analyze the deformation behavior of pre‐painted sheets under uniaxial stretching and biaxial balanced stretching conditions, respectively. Tests were interrupted in order to obtain different strain levels until fracture; at each strain level reached, the occurrence of superficial damages on the paint coating was detected; thinning of the different layers of the pre‐painted sheet was also measured. It was observed that the degree of damage on the paint coating depends on the loading condition; in particular, under uniaxial stretching, the paint coating is able to follow the steel sheet during deformation up to the onset of the necking, whilst, under biaxial balanced stretching, coating exhibits superficial damages before fracture of the sheet
Evaluation of Friction at High Strain Rate using the Split Hopkinson Bar
No full textThe present work aims at studying the influence of strain rate on the frictional behaviour of AA7075 aluminium alloy in the O-annealed temper state. To this purpose, ring compression tests were performed both under quasi-static and dynamic loading conditions. The high strain rate tests were carried out by means of the Split Hopkinson Tension-Compression Bar in the direct version. In both cases, hollow cylindrical samples, characterised by an initial outer diameter to inner diameter to height ratio of 6:3:2, were tested under dry condition and by lubricating with molybdenum disulphide grease. The different frictional behaviour exhibited by AA7075-O under quasi-static and dynamic loading conditions can be attributed to the strain rate effect both on the plastic flow behaviour of the deformed material, and on the thickness of the lubricant film
High-speed deformation of pinless fswed thin sheets in aa6082 alloy
No full textThe high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High Strain Rate Behaviour of AA7075 Aluminum Alloy at Different Initial Temper States
No full textThe aim of this work is to study the mechanical properties of alloy AA7075 in both T6
and O temper states, in terms of visco-plastic and fracture behavior. Tension and compression tests
were carried out starting from the quasi-static loading condition 10-3 up to strain rates as high as 2 x
103 s-1. The high strain rate tests were performed using a Split Hopkinson Tension-Compression Bar
(SHTCB) apparatus. The tensile specimens were also subjected to micro-fractography analysis by
Scanning Electronic Microscope (SEM) to evaluate the characteristics of the fracture. The results
show a different behavior for the two temper states: AA7075-O showed a significant sensitivity to
strain rate, with a ductile behavior and a fracture morphology characterized by coalescence of
microvoids, whilst AA7075-T6 is generally characterized by a less ductile behaviour, both as
elongation at break and as fracture morphology. Brittle cleavage is accentuated with increasing
strain rate. The Johnson-Cook viscoplastic model wad also used to fit the experimental data with an
optimum matching
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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