1,720,969 research outputs found
Mechanical Behavior of Aluminum Sandwiches Made by Laser Welding
No full textAluminium sandwiches are interesting subcomponents for lightweight structures applied in rail cars for high speed. A method to realize aluminium sandwiches consists in welding sheets to elementary extruded profiles. Laser welding is the production technology that promises the better features in terms of quality and productivity. Thanks to concentrate energy and very small Heat Input (HI), the laser welding process minimizing the wide of the Heat Affected Zone (HAZ) and the distortions and allow high welding speed. In this work laser technique was applied to join a mock-up of a large aluminium sandwich panel. The mechanical behaviour of the assembled panel was investigated in the two main orthogonal direction of load by four point bending tests. Elastic-plastic FE Analysis confirm the results of bending tests and it is possible to appreciate the quality of welding process that produce joint strength and ductile. In fact in the both load direction it's possible to evaluate the plastic deformation on the welded beam without visible cracks in the welds. The data about the mechanical features of the welds for the FE analysis, about the 80% of the base materials, was achieved by tensile test on elementary but joint. The SEM fractography of the butt joint shows dimples in all the surface of the fracture, confirming the good quality and ductility of welds also in presence of some little micro porosity. The present paper is based on the achievements of the TRAIN Consortium within the research project SIFEG (Integrated freight transport rail-road), granted by the Italian Ministry of Economic Development for the Program "Industria 2015 - Mobilità Sostenibile". © 2015 The Authors. Published by Elsevier Ltd
Welding of high-resilience martensitic stainless steel for hydrodynamic components in innovative seacraft: a comparison of traditional and HDE technologies
No full textFor the designer, the production of innovative seacraft involves the use of atypical materials at the shipyard. This article presents a comparison between traditional (SMAW) and innovative [LBW, electron beam welding (EBW)] welding technologies to illustrate the feasibility and suitability – also in economic terms – of the penetration of new welding technologies in the shipbuilding sector. In particular, the material considered for the production of submerged bearing components in an innovative submerged-wing hydrofoil is X4CrNiMo13-4, a martensitic stainless steel presenting improved resilience chosen by the shipbuilding company (Rodriquez Cantieri Navali), above all, on account of its high mechanical strength. In order to avoid costly PWHT, which, given the large size of the components, has a heavy influence on production costs, welding procedure specifications were developed using an austenitic filler material that, while inducing a limited reduction in performance in the melt zone, allows for conspicuous economic advantages. Research has shown how EBW technology undoubtedly allows for better results, while – although it would be more suitable for large-size components – LBW technology requires a more critical optimization of parameters. © 2013, © 2013 Taylor & Francis
Laser welding of aluminum foam sandwich panels [Saldatura laser di pannelli sandwich in schiuma di alluminio]
No full textThe paper describes the results about the laser and laser-TIG welding of Aluminum Foam Sandwich. The panels used are produced by powder metallurgy technology and this permits to have a metallurgical bonding between skin and core. So, this material is completely metallic and has an excellent stability even in case of fire. These features allow to choose the ASF as new lightweight material for structural components also in the field of transport. One of the limitations relating to this type of materials is the maximum available size (2.5 × 1.2 m), which requires the development of special processes of junction with low heat input to reduce, as much as possible, the dimension of the area affected by the welding process. It should be considered the fact that it is possible to weld only the skins of the sandwich, so a discontinuity in the core remains intrinsic to the welding process. Therefore, it is appropriate to employ a transition element in the welding line to achieve a link between the two skins. The troubleshooting about the laser welding regards both: the common difficulties in the laser welding of the aluminum alloys of the skin and some other problems due to the presence of eutectic alloys in the core than we can't remove completely
Superlega IN792 DS: Ottimizzazione della saldatura EB e laser e dei trattamenti post saldatura
No full textNickel-based superalloys are widely used in the fabrication of high temperature components (discs and vanes) of aeronautical turbines and power plants. Their structure consists, quite simply, of two phases: a disordered matrix (phase ã) reinforced by a second ordered intermetallic phase precipitation, i.e: Ni3 (Al, Ti) phase ã'. In service operation, the nickel superalloy mechanical parts are subject to surface cracking. Given the high cost production, their repair by welding/remelting with material adduction can be a valid solution for the life extension of the components. This paper presents the results of electron beam and laser beam repair welding optimization through re-melting tests analysis conducted on 2 mm thick plates obtained from a directionally solidified IN792 ingot (DS). The results show how, both with EBW and LBW, a preheating (PHT) at 300 °C is necessary to avoid hot cracking initiation followed by a subsequent post-weld heat treatment (PWHT) for stress relieving. For both techniques, the microstructure shows how the ratio between ã'/ã phases goes from 70/30 of the base material to 30/70 of the fused zone (ZF). It has been possible to realize crack-free remelting, however the laser technique (LBW) remains more susceptible to the porosity compared to the electron beam welding (EBW). © 2018 Instituto Italiano della Saldatura. All rights reserved
Processi di fabbricazione di profilati estrusi rinforzati con schiuma metallica
Get PDFIl presente report descrive le fasi di calibrazione del forno di schiumatura per la realizzazione di compositi metallo-metallo costituiti da un profilato in Alluminio AA6060 e da un core in schiuma metallica ottenuto mediante la schiumatura di un precursore commerciale Alulight eutettico di tipo AlSi10 contente lo 0.8% in peso di agente schiumante (TiH2). Il primo capitolo riguarda l’analisi dei parametri di controllo, temperatura e tempo, e la loro correlazione (anche mediante Design of Experiment) con i dati di risposta, principalmente espansione e densità, considerando un piano sperimentale fattoriale con tre livelli di tempi di schiumatura, due livelli di temperatura e due condizioni di raffreddamento, effettuato con due repliche. In particolare, le due repliche sono state effettuate in due punti distinti del forno, evidenziando differenze sostanziali in funzione della temperatura rilevata nel piattello del crogiolo. Con i dati derivanti dall’analisi di immagine e dall’analisi DOE (riferita anche alle misure di espansione mediante sensore laser) sono stati effettuati test di schiumatura in cilindri estrusi, di diametro 30 mm, altezza 40 mm e spessore di parete 2 mm, con l’obiettivo di raggiungere una densità del core di 0.55 g/cm3 +/- 0.05 g/cm3. I parametri per questi test sono stati definiti considerando i limiti imposti dalla temperatura massima (per evitare la fusione o l’eccessivo rammollimento dell’estruso) e utilizzando tempi ottimizzati in funzione delle maggiori masse in gioco, rispetto alla schiumatura di semplici granuli di precursore. Ulteriori test preliminari sono stati realizzati su campioni cilindrici di lunghezza 120 mm: questi hanno tuttavia indicato la necessità di modificare il set up di prova, con un affinamento dei parametri di processo possibile solo mediante l’impiego di un sistema di carico, scarico e raffreddamento automatico dei campioni (descritto nel report RdS/2012/099 e in fase di acquisizione)
Fabbricazione e qualificazione di componenti saldati e progettazione di componenti in AFS
Get PDFQuesto report è suddiviso in tre capitoli. Il primo capitolo riporta l’ottimizzazione di processi di saldatura laser e laser arco individuato come possibile tecnica di saldatura per componenti di grande dimensione. Nel corso del primo anno infatti sono state effettuate ottimizzazioni sui processi di saldatura sia Electron Beam Welding sia Laser Welding. Se è vero che come dimostrato dalla prove meccaniche e dalla correlazione con le prove non distruttive del report Rds/2012/101 la saldatura EBW rappresenta un benchmark, la tecnologia che più industrialmente applicabile su componenti di grosse dimensioni è la tecnologia laser. In particolare la tecnologia laser TIG che è stata ulteriormente affinata nel corso di questo secondo anno. Il secondo capitolo riporta i risultati di qualifica, in termini di prove di compressione e prove di flessione, sul materiale tal quale e sui giunti saldati di campioni di AFS. Lo scopo è oltre a valutare la resistenza ultima a schiacciamento ed a flessione anche la determinazione dei dati salienti ( E, G, Sr, v) utili al progettista per la progettazione con questa nuova classe di materiali. Il terzo capitolo riguarda la scelta è l’analisi di un “case study” effettuato con la collaborazione del consorzio CALEF, in cui è stato scelto e successivamente riprogettato un componente, il pavimento flottante delle carrozze ferroviarie, per valutare quali vantaggi possono essere conseguiti dall’impiego dei pannelli AFS
Mechanical Behavior of Aluminum Sandwiches Made by Laser Welding
No full textAbstractAluminium sandwiches are interesting subcomponents for lightweight structures applied in rail cars for high speed. A method to realize aluminium sandwiches consists in welding sheets to elementary extruded profiles. Laser welding is the production technology that promises the better features in terms of quality and productivity. Thanks to concentrate energy and very small Heat Input (HI), the laser welding process minimizing the wide of the Heat Affected Zone (HAZ) and the distortions and allow high welding speed. In this work laser technique was applied to join a mock-up of a large aluminium sandwich panel. The mechanical behaviour of the assembled panel was investigated in the two main orthogonal direction of load by four point bending tests.Elastic-plastic FE Analysis confirm the results of bending tests and it is possible to appreciate the quality of welding process that produce joint strength and ductile. In fact in the both load direction it's possible to evaluate the plastic deformation on the welded beam without visible cracks in the welds. The data about the mechanical features of the welds for the FE analysis, about the 80% of the base materials, was achieved by tensile test on elementary but joint. The SEM fractography of the butt joint shows dimples in all the surface of the fracture, confirming the good quality and ductility of welds also in presence of some little micro porosity.The present paper is based on the achievements of the TRAIN Consortium within the research project SIFEG (Integrated freight transport rail-road), granted by the Italian Ministry of Economic Development for the Program “Industria 2015 – Mobilità Sostenibile”
Welding of automotive aluminum alloys by laser wobbling processing
No full textThe scope of this paper is to examine the improvement from laser welding by an innovative beam wobbling head towards the welding of tailored blanks parts, widely used in automotive to develop different stiffness aluminum components. For this purpose, butt joints and overlapping joints were produced from sheets made out of two industrial grades, i.e. AA-6082 T6 and AA-5754 H111 of different thickness. The technique was evaluated both with and without the use of a filler wire (AA-5556). The qualification of the welding process encompassed Non Destructive Testing (NDT) and mechanical testing. The results indicate that butt joints tend to fail within the base material (BM) of sheet with smaller thickness. On the contrary, the shear tests on lap joints highlighted a rupture mode occurring in the heat affected zone (HAZ) of the thin sheet. Remarkably, the wobbling process generally allows avoiding porosity when combined with an optimized set of welding parameters. Yet, a residual porosity was always detected in lap joints, varying with the size of the fused zone. © 2017 Trans Tech Publications, Switzerland
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
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