1,720,962 research outputs found
Plastic flow behavior of twinning induced plasticity steel from low to warm temperatures
Full text linkThis work investigates the tensile behavior of twinning induced plasticity (TWIP) steel under room to warm temperatures. Stress-strain flow curves have been obtained from steady-state uniaxial tensile tests performed at different temperatures, that is, from 20 to 800 °C, and different engineering strain rates, 0.003 and 0.5 s-1. The yield and ultimate tensile strength, elongation at fracture, reduction of area, strain hardening exponent and strain hardening rate have been defined to describe the plastic behavior of TWIP steel. It has been found that the plastic flow behavior of TWIP steel is characterized by negative strain rate sensitivity and strain hardening, at temperatures from 20 to 300 °C, until the twinning mechanism occurs. At these temperatures, dynamic strain aging starts at the beginning of plastic deformation, with the appearance of fluctuations in the work hardening rate and local strain rate. Pronounced local serrations also appear at 300 °C and 0.003 s-1. Plastic deformation is mainly driven by dislocation gliding at 550 and 800 °C, and mechanical twins are absent. As a result, negative strain rate sensitivity and local serrations disappear in the stress-strain curves. Creep also contributes notably to plastic deformation at 800 °C, as was also observed on the fracture surfaces of tensile samples. Mechanical twins were only visible for the lower temperatures. The grains in the sample tested at 800 °C and 0.003 s-1 were fully recrystallized
Friction stir welding of aluminum alloys and steels: Issues and solutions
No full textWelding of aluminum alloys and steels by conventional fusion welding technology is difficult because of their different mechanical, chemical, and physical properties. Alternatively, friction stir welding (FSW) could be a solution as materials are joined in a solid state. However, FSW has some issues and drawbacks. The possible formation of brittle Al–Fe intermetallic compounds deteriorates mechanical joint strength. Improper process parameters, such as rotational and welding speed, could generate insufficient and/or inadequate materials intermixing. Therefore, defects like incomplete penetration, tunnel, surface grooves, surface galling, and kissing bond can form. Tool geometry (e.g. tool pin profile and shoulder) drives the uniformity of heat input and intermixing pattern inside weld joint. Tool wear is not capable of producing a homogenous heat and an adequate intermixing, thus voids and/or flashes can occur. To overcome the above-mentioned issues, a proper selection of process parameters, tool geometry and materials should be employed to ensure an adequate heat input and intermixing to join successfully aluminum and steel sheets. This article is a short review about the main issues related to FSW of aluminum and steels sheets and possible solutions
Global-local characterization and numerical modeling of TWB laser welded joints
No full textSheet forming of tailor welded blanks (TWBs) of advanced high strength steels is complex because of the notable differences in mechanical properties, and hence in formability, of base metals, heat affected zones and weld seam. In this work, an accurate characterization of the mechanical behavior of these regions in TWBs made of a DP and TRIP steel was carried out. Micro-samples, machined from base metals and fusion zone were employed to retrieve the local constitutive laws up to fracture. At the same time, macro-samples, extracted throughout the welded joint were tested to assess the weldment overall behavior. Along with global load-displacement data, strain and displacement fields of the joint were evaluated, using a Digital Image Correlation technique. An FE simulation of the entire joint was setup, using the previously identified material properties. In a comparison between the FE model and experiments, good results were obtained both at a global and local level, up to fractur
Main Issues in Quality of Friction Stir Welding Joints of Aluminum Alloy and Steel Sheets
Full text linkJoining of aluminum alloys through friction stir welding (FSW) is effectively employed in several industries (e.g., aeronautics and aerospace) since it guarantees proper weld strength as compared to other joining technologies. Contrarily, dissimilar FSW of aluminum alloys and steels often poses important issues in the selection of welding parameters due to the difficulty to join different materials. Improper welding parameters give rise to the formation of intermetallic compounds, and internal and external defects (e.g., tunnel formation, voids, surface grooves, and flash). Intermetallic compounds are brittle precipitates of Al/Fe, which chiefly initiate crack nucleation, whereas internal and external defects mainly act as stress concentration factors. All these features significantly reduce joint strength under static and dynamic loading conditions. With reference to the literature, the influence of main welding parameters (rotational speed, welding speed, tool geometry, tilt angle, offset distance, and plunge depth) on the formation of intermetallic compounds and defects in FSW of aluminum alloys and steels is discussed here. Possible countermeasures to avoid or limit the above-mentioned issues are also summarily reported
Fiber laser-MAG hybrid welding of DP/AISI 316 and TWIP/AISI 316 dissimilar weld
Full text linkIn this paper, TWinning-Induced Plasticity (TWIP), Dual Phase (DP) and austenitic stainless (AISI 316) steels were joined together by hybrid laser/arc welding with an austenitic steel filler. Microstructural and mechanical characterization of welded joints was carried out by optical microscopy, microhardness, tensile and bend tests. The heat affected zone (HAZ) at the TWIP side was fully austenitic and exhibited a grain coarsening; at the DP side, new martensite formed close to the fusion zone and other phase transformations occurred moving toward the base metal; at the AISI 316 side, stringers of untreated ferrite δ inside the austenitic matrix was observed. All the tensile welded specimens broke within austenitic stainless steel. TWIP/AISI 316 welds exhibited a greater tensile strength than DP/AISI 316 ones. The bending tests confirmed the ductility of both sorts of joints
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
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