1,720,972 research outputs found
Study of anelastic phenomena in materials of engineering interest
Full text linkMechanical spectroscopy (MS) studies absorption spectra of mechanical energy under the conditions of applied periodic external mechanical field, this technique is a powerful tool for the study of materials. In particular, it is shown that such a technique can help the mechanical characterisation of materials.
The elastic and anelastic properties of the material have been investigated by
using a vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations mode of cantilevered mounted reed samples for a wide range of materials of engineering interest
Single crystal PWA 1483 superalloy: Dislocation rearrangement and damping phenomena
No full textThe structural stability of the single-crystal PWA 1483 superalloy has been investigated by internal friction (IF) and dynamic modulus measurements from room temperature to 1073 K. The examined samples were in the solubilized state. The vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations has been employed. Frequency was similar to 350 Hz. IF spectra recorded in successive test runs on the same samples show a Q(-1) maximum (M1) above 623 K, whose intensity and position change from one run to another: in correspondence with M1 the modulus undergoes a slow decrease followed by a sudden increase. Sometimes another maximum (M2) has been observed at lower temperature (similar to 523 K). After each run the values of the modulus and of Q(-1) change indicating that a progressive irreversible transformation occurs. Damping phenomena have been attributed to the rearrangement of dislocation structures in the disordered matrix. This rearrangement modifies the density and the average distance of pinning points. This explanation is supported by transmission electron microscopy (TEM) observations. (C) 2009 Elsevier B.V. All rights reserved
Anelastic phenomena and Cr2N precipitation in a high nitrogen austenitic steel
No full textInternal friction (IF) and dynamic modulus measurements on a high nitrogen (0.8 wt%) austenitic
steel in the temperature range from room temperature to 800 °C have been carried out by using a
vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural
vibrations in the frequency range of kHz.
The IF spectrum of the as-prepared material shows a broad peak superimposed to an exponentially
increasing background. The discontinuous precipitation of Cr2N phase changes the characteristics of
the peak. The results have been discussed by considering interstitial-substitutional (i-s) interactions
Elastic and anelastic behaviour of Ti6Al4V-SiCf composites produced by HIP and RDB
No full textThe Ti6Al4V-SiCf composite is a promising material for applications in aeronautical engines including turbine components. Sheets of Ti6Al4V-SiCf have been produced by two different routes: Hot Isostatic Pressing (HIP) and Roll Diffusion Bonding (RDB), a new process developed at C.S.M. This work reports the elastic and anelastic characterization of the materials carried out by internal friction (IF) and dynamic modulus experiments. IF spectra of HIP and RDB composites are similar. They exhibit a relaxation peak superimposed to an exponentially increasing background. The peak is due to C-Al and C-V pairs re-orientation in the phase matrix around the fibres. The background, is higher for the RDB composite owing to its higher dislocation density and smaller grain size. Long-term isothermal tests performed at different temperatures evidenced a progressive increase of the dynamic modulus E and decrease of the damping factor Q-1: higher the temperature greater the variation. According to the Granato-Lücke dislocation string model the phenomenon has been explained by considering the interstitial atoms diffusion to dislocations which progressively reduces the mean distance between pinning points
High temperature damping behaviour of Ti6Al4V-SiCf composite
No full textThe Ti6Al4V–SiCf composite, reinforced by unidirectional SiC fibres (SCS-6), has been investigated by internal friction (IF) and dynamic modulus measurements in the temperature range 300–1173K. Experiments
have been carried out by using a vibrating reed technique with electrostatic excitation and
frequency modulation detection of flexural vibrations in the frequency range from 600 to 1800 Hz.
For comparison the monolithic Ti6Al4V alloy has been submitted to the same experiments.
The IF spectrum of the composite exhibits a relaxation peak at about 870K superimposed to an exponentially
increasing background. The peak, not present in the spectrum of matrix alloy, has activation
energy H= 186 kJ mol−1 and relaxation time tau0 = 2.3×10−15 s.
The peak has been explained by an interstitial-substitutional pair reorientation mechanism in the
phase of Ti6Al4V matrix around the fibres
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
Microstructural investigation on tungsten for applications in future nuclear fusion reactors
No full textTungsten is a promising armour material for plasma facing components of nuclear fusion reactors.
Two materials with different density and purity have been examined by optical microscopy, X-ray
diffraction (XRD), instrumented indentation tests (FIMEC) and mechanical spectroscopy.
For both the materials yield stress and elastic modulus strictly depend on the residual porosity.
Moreover, the material with higher porosity (≈ 9%) is not stable and remarkable modulus variations
are observed during heating.
The IF spectrum exhibits a relaxation Q-1 peak superimposed to an exponentially increasing
background. The peak is a single Debye peak with activation energy H = 74.86 kJ mol-1 and preexponential
factor τ0 = 1.76 x 10-9 s that has been ascribed to dislocation interaction with intrinsic
point defects (autointerstitial and substitutional)
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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