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Analysis of stainless steel welded joints: a comparison between destructive and non-destructive techniques
No full textCUTTING OF THIN METAL SHEETS USING ND:YAG LASERS WITH DIFFERENT PULSE DURATION
No full textAn experimental investigation on the laser cutting of thin metal sheets using a Q-switched diode pumped Nd:YAG laser and a conventional lamp pumped Nd:YAG laser with pulse duration of 150 ns and 0.3 ms respectively is described in this paper. Using the laser with short pulses the lower single pulse energy was not sufficient to remove the material along the entire thickness of the sheet in a single laser scan and multi-passes were required. However, short pulses with higher peak power densities allowed to produce precise cuts with a smaller width than long pulses. These two cutting processes by a multi-passes laser scan (using short pulses of 150 ns) and by a single laser scan (using long pulses of 0.3 ms) were compared in terms of laser energy, machining time and process performance. It was also observed that, when using short pulses, the groove geometry was different depending on the number of passes and the material removal rate due to the laser scan significantly decreases when the groove depth
DALLE MACRO ALLE MICRO LAVORAZIONI LASER VARIANDO LA DURATA DELL'IMPULSO
No full textAttualmente le lavorazioni laser possono essere suddivise in due gruppi: le macro lavorazioni, in cui si utilizzano laser di elevata potenza per operazioni di taglio, saldatura e trattamento termico, e le micro lavorazioni, in cui il materiale viene lavorato con laser di medio/bassa potenza che però generano elevate potenze di picco su zone di dimensioni molto piccole. In questo articolo sarà evidenziata l’influenza della riduzione della durata degli impulsi sulla lavorazione passando dalle macro alle micro lavorazioni laser. In particolare, saranno analizzate le differenze in termini di densità di potenza laser e di passaggi di stato del materiale sottoposto alla radiazione laser. Saranno inoltre forniti esempi pratici di lavorazioni meccaniche con asportazione di materiale realizzate con due differenti laser a Nd:YAG, operanti in regime impulsato e caratterizzati da una durata degli impulsi rispettivamente dell’ordine dei millisecondi e dei nanosecondi. I due laser sono stati impiegati per tagliare e forare sottili lamiere di diversi materiali, quali: AISI 430 e 304, acciaio armonico, titanio ed acciaio C6
Analysis of Composites with Infrared Thermography
No full textThe aim of this study was a non-destructive evaluation of composites through their behaviour under thermal stimulation. Such behaviour was monitored by infrared thermography. Several specimens were fabricated involving: glass/epoxy with inclusion of foreign materials; carbon/epoxy with backdrilled holes; carbon/epoxy with impact damage; Glare® failed in bearing way. The obtained results prove that infrared thermography is capable of detecting the materials inhomogeneities and/or damage listed above. In particular, lock-in thermography is capable of supplying useful information about: the distribution of the adhesive thickness in composite structures; the distribution of the paint thickness; the behaviour under load of aluminium layers and glass fibres in Glare®
Application of lockin thermography in nondestructive evaluation of adhesively bonded aluminum joints
No full textAdvantages and Limitations of Lamp Pumped Nd:YAG Lasers for Micro-cutting of Shape Memory Alloys
No full textThis paper deals with laser micro-cutting of shape memory alloys, which is currently used in the manufacturing of micro components such as miniaturized actuators in robotic systems and coronary stents in medicine. The influence of the laser pulse energy on the characteristics of micro-cuts produced in 400 μm thick sheets of nickel-titanium alloy, by means of a flash lamp pumped Nd:YAG laser, was investigated. Experimental results showed that micro-cuts produced using this laser are characterized by a narrow kerf width, cut surfaces with a high perpendicularity and low roughness, and the absence of dross in the bottom side when the pulse duration is reduced to 0.25 ms. In particular, it was found that the minimum kerf width is approximately 60 μm and the Ra values of cut surfaces are in the range of 1-2 μm. Since a single laser scan is sufficient to produce micro-cuts, when using such lasers it is also possible to achieve shorter machining times than the ones obtainable by ultra short pulse lasers, which still have the advantage to induce negligible heat affected zones
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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