1,720,962 research outputs found
Replacement of Nitrided 33CrMoV Steel with ESR Hot Work Tool Steels for Motorsport Applications: Microstructural and Fatigue Characterization
No full textIn this work tensile strength, fatigue resistance and fracture toughness of two electroslag remelted (ESR) tool steels and of 33CrMoV12 ESR steel (both in quenched and tempered condition, as well as nitrided condition) were evaluated. The role of hardness, residual stresses and inclusion sizes on the fatigue behavior was investigated. Tool steels have a tensile strength between about 1900 and 2300 MPa, fracture toughness between 35 and 33 MPa root m, while fatigue strength ranges between 725 and 992 MPa. The tensile strength and fracture toughness of the 33CrMoV12 ESR are, respectively, 1365 MPa and about 150 MPa root m. Nitriding induces a significant increase in fatigue strength from 560 to 980 MPa. These results highlight that appropriate ESR tool steels could replace nitrided steels
The influence of cooling rate on microstructure, tensile and fatigue behavior of heat-treated Al-Si-Cu-Mg alloys
No full textAl-Si-Mg alloys are commonly employed for the production of automotive castings. In view of the recent stringent emissions standards and consequent engine downsizing, these components must withstand higher temperatures and stresses than in the past. In this regard, the heat treatable quaternary Al-Si-Cu-Mg alloys gained particular interest in recent years, due to their superior mechanical properties and higher thermal stability. The present research activity was addressed to evaluate the influence of cooling rate on microstructure and consequently on room temperature tensile and fatigue behaviour of the A354 and C355 alloys. Samples for mechanical tests were produced under controlled cooling rates, in order to induce different secondary dendrite arm spacing (SDAS) values, classified as fine (20-25μm) and coarse (50-70μm). The experimental results showed that the cooling rate strongly influences the type, size and morphology of intermetallic particles. The presence of coarse intermetallic phases, mostly Fe-based, observed in coarse SDAS specimens, was reported to strongly affect ultimate tensile strength (UTS), elongation to failure and fatigue strength of both the investigated alloys. A correlation between UTS and fatigue resistance was found, independent of microstructural coarseness
Tensile behaviour of a hot work tool steel manufactured via Laser Powder Bed Fusion: effect of an innovative high pressure heat treatment
Full text linkThe combination of outstanding mechanical strength of tool steels and design freedom ensured by Additive Manufacturing (AM) processes is of a great interest for automotive applications. However, AM techniques produce peculiar defects, which affect the resulting mechanical behavior. For this reason, safety critical AM components are often subjected to hot isostatic pressing (HIP) to heal process defects. At the same time, tool steels require a proper quenching and tempering (QT) heat treatment to achieve high hardness and strength.
In the present work, the effect of an innovative high pressure heat treatment (HPHT) on the tensile properties of a hot work tool steel produced via Laser Powder Bed Fusion (LPBF) was investigated. LPBF samples were subjected to two post-process heat treatments: a conventional quenching and tempering heat treatment performed in vacuum (CHT), and an innovative HPHT combining HIP e QT in a single step, to heal LPBF defects and obtain high mechanical properties. HPHT featured the same quenching and tempering cycle of CHT but it was performed under high pressure in a HIP furnace and with longer austenitizing time to promote defect closure. Tensile tests indicated no significant effect on proof and tensile strength for HPHT compared to CHT, but a significant reduction of elongation after fracture. Fractographic analyses and fracture mechanics calculations indicated that both CHT and HPHT specimens failed via crack propagation from large LPBF defects when the stress intensity factor reached the material fracture toughness. Fractographic analyses indicated an incomplete defect closure during HPHT due to the presence of an oxide film on the inner surface of defects, thus justifying the same failure mechanism and strength of CHT samples. Instead, it was proposed that the reduced elongation could arise from coarsened grains due to the longer austenitizing
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Mo Addition to the A354 (Al–Si–Cu–Mg) Casting Alloy: Effects on Microstructure and Mechanical Properties at Room and High Temperature
Full text linkCast aluminum alloys are widely used in the automotive field for the production of complex engine parts. However, the mechanical properties of heat-treatable alloys (e.g., Al–Si–Mg or Al–Si–Cu–Mg) are negatively affected by prolonged exposure to temperatures higher than about 200 °C. To date, several researchers have proposed the addition of alloying elements, such as Sc or Hf, for enhancing the high temperature behavior of cast Al alloys, while Mo has not been widely investigated. The present study aimed to assess the effects of Mo addition on microstructure, mechanical properties, and thermal stability of the A354 alloy. Samples of A354 alloy with different amount of Mo (in the range 0.1 to 0.8 wt %) were produced. The casting conditions and heat treatment parameters were optimized by means of optical and scanning electron microscopy, thermal analysis and hardness tests. Tensile tests highlighted that Mo induces a moderate increase of yield strength at room temperature (about 10%), but no appreciable improvement in the performance of the alloy at 250 °C was observed
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