1,720,960 research outputs found
Friction stir welding of AA 2198 T3 rolled sheets in butt configuration[Saldatura in configurazione testa a testa di lamiere in lega 2198 T3 mediante procedimento friction stir welding]
No full textFriction-stir welding (FSW) is a solid-state joining process where, in contrast to the fusion welding, the material to be welded does not reach the melting point. Due to its interesting features, a lot of research activities have been carried out on FSW of different materials. In particular, FSW of AA 2198 aluminium alloy has gained wide interest for the fabrication of lightweight structures requiring a high strength-to-weight ratio and a good corrosion resistance. In this study, rolled plates of AA 2198 T3 aluminium alloy are friction-stir welded in butt configuration varying two fundamental process parameters: rotational and welding speeds. An empirical model based on regression analysis is developed to predict the mechanical strength, in particular yield and tensile strength, of the joints as function of the process parameters under investigation. For the development of the empirical model, a 32 full factorial designs with the yield and tensile strength as observed responses is used. Statistical tools such as analysis of variance, F tests, Mallows' CP, coefficient of determination etc. are used to build and to validate the developed models. By using the desirability function approach, the optimum process parameters to simultaneously obtain maximum possible yield and tensile strength are found within the investigated range. The developed models can be effectively used to predict the stationary forces and the mechanical proprieties of the joints at 95% confidence level. Finally, to validate the possible use of FSWof 2198 in the in the aerospace industry, joints welded using the optimum process parameters before identified are tested under stress corrosion cracking and fatigue. Results show that, unlike the base material, the optimized joints are not attacked by pitting if subjected to a tensile stress in a corrosive environment; furthermore, their fatigue life is comparable to that of the base material and longer than that showed by joints welded using traditional techniques, as MIG or TIG
Superplastic forming of Friction Stir processed magnesium alloys for aeronautical applications: a Modeling approach
No full textMagnesium alloys are attractive for lightweight structural applications in the transportation industry because of their low density and high specific strength and stiffness [1]. With an ultrafine-grained microstructure, they exhibit superplasticity at relatively low temperatures and high strain rates [2]. Friction stir processing (FSP) was used to obtain a microstructure with ultrafine grains in the magnesium alloy AZ31. In this project, microstructures obtained using different rotational speeds are studied. Free bulge forming of the FSP processed AZ31 sheets are carried out to evaluate the superplastic behaviour [3]. The model and the evolution equations have been implemented into a commercial finite element modeling (FEM) code and different simulations are conducted to correlate the experimental and numerical results for the model validation [4]. The purpose of this study is to investigate the effect of the microstructure on the superplastic forming behaviour using free bulge forming and FE simulations
Bending behaviour of sandwich panels with aluminium foam core
No full textThe bending behavior of hybrid sandwich panels, with aluminum foam core, and carbon fiber reinforced thermoset resin face sheets, have been investigated. The effect of core and face sheets thickness and span , on 3-point bending test, has been evaluated for the sandwich panels .
Core yielding and indentation failure modes, influenced by the core properties, have been identified and analytical models to evaluate the maximum load have been applied. The failure mode map has been constructed, which illustrates the dominant failure mode for practical beam design. In order to simulate the different failure modes, FE analysis has been pointed out
FSW of T joints in overlap configuration: process optimization in joining dissimilar aluminium alloys for the aeronautic application
No full textThe effect of welding parameters on the mechanical properties of friction stir-welded dissimilar aluminium alloys in overlap joint configuration was studied. Both the welding configuration and the materials chosen were a typical skin-stringer configuration, widely used for aeronautical fuselage panels. Mechanical properties were evaluated by means of both hoop stress and T-pull test. Results show that there is a great dependence of the hoop stress resistance from welding parameters; conversely, T-pull tests do not show the same dependence. The present work demonstrates the suitability of the x in lap configuration for joining dissimilar aluminium alloys
Effect of welding parameters on morphology and mechanical properties of Ti-6Al-4V laser beam welded butt joints
No full textThe influence of welding speed and laser power on weld quality of 1.6 mm thick Ti-6Al-4V sheets autogenously laser beam welded in butt configuration using a Nd-YAG laser was studied. The joint quality was characterized in terms of weld morphology, microstructure and mechanical properties. An underfill defect, controlling the whole weld geometry, was observed both at the weld face and root surface. In dependence of the specific heat input, this defect showed a maximum, which separates two different welding regimes: keyhole welding, at low heat input, and a welding regime where heat conduction around the keyhole is predominant, at high heat input. Influence of the underfill radius on the weld fatigue life was also assessed
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Manufacturing method for thermoplastic composites containing wood flour
No full textLaminates of high density polyethylene (HDPE) reinforced with wood flour and long hemp fibres have been manufactured adopting a process consisting of two steps. In the first step, pellets of wood flour/HDPE composite, i.e. wood plastic composite (WPC), were compounded by extrusion; in the second step, laminates of WPC and WPC reinforced with hemp fibres were manufactured by compression molding. The properties of the obtained composite materials, measured by means of flexural tests, dynamic mechanical analysis (DMA) and creep tests, have been compared with the matrix (HDPE) properties. Mechanical properties of the WPC increase with the weight percent of wood flour, but WPC reinforced by unidirectional long hemp fibres present the best properties also at high temperature
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