1,720,960 research outputs found
Micromechanistic analysis of toughened carbon fibre composite laminate failure by high resolution synchrotron computed tomography
No full textSynchrotron Radiation Computed Tomography (SRCT) allows for non-destructive identification of fracture mechanisms in materials at very high resolutions. In this work, carbon fibre reinforced plastics (CFRPs) were imaged using SRCT to ascertain fracture micro-mechanisms under both quasi-static Mode I and Mode II dominated loading conditions. This, combined with previous work on impacted coupons, provides mechanistic comparison between the different loading conditions on similar material systems. Initial findings have identified particle/matrix debonding, crack bridging and ligamented behaviour as reported previously, but have emphasized micro-cracks and the extent to which particle/matrix debonding occurs ahead of the crack tip under both Mode I and Mode II loading conditions. Such work is intended to support both material development and more accurate structural performance simulation for the toughened materials that are being increasingly used as primary structures in aerospace applications
Interlaminar toughening mechanisms: in situ growth and modelling
No full textModelling composite toughness and what mechanisms are responsible for added toughness has been less tackled within the composites community. With the advances of computational resources and the development of arbitrary cracking models, such as the Augmented Finite Element Method (AFEM), more complex microstructures can now be tackled with multiple interacting cracks. It has been established that Mode I crack propagation in particle-toughened interlayers within a CFRP laminate involve a process zone rather than a distinct crack tip. This involves multiple cracks forming ahead of the main crack that then coalesce and leave behind bridging ligaments that provide traction across the crack flanks. Preliminary idealised 2D AFEM models are presented in this work, that highlight the effects of the relative role of neat resin to ply interface cohesive properties, and the fraction of ‘idealised de-bonds’/discontinuities, in keeping the crack path within the interlayer. 4- dimensional time-resolved Computed Tomography (CT) experiments complement the abstract models, with the chronology of damage events and resultant crack paths being directly identified in different toughened microstructures. Additionally, quantification of the bridging behaviour elucidated micromechanical differences between the systems, with the number of bridging ligaments and the total bridged area being quantified and compared to macro-scale toughness. This work is intended to improve understanding around interlaminar toughness, and lead to the development and validation of physically representative micro-mechanical model
Micro-mechanistic analysis of in situ crack growth in toughened carbon/epoxy laminates to develop micro-mechanical fracture models
No full textMode I and Mode II crack growth through particle-toughened CFRPs (Carbon Fibre Reinforced Plastics) have been captured using in situ and ex situ Synchrotron Radiation Computed Tomography (SRCT) and Synchrotron Radiation Computed Laminography (SRCL). These experiments were used to provide non-destructive identification of fracture mechanisms at representative stress states for two different material geometries. The local micro-structure prior to crack propagation, the location of particle/matrix de-bonding events, the formation of bridging ligaments, and the evolution of the resultant crack path was identified and related to the local micro-structure. Such data is invaluable to the development and validation of physically representative micro-mechanical models for these material systems that are increasingly being used in primary aerospace structures
Three-dimensional deformation mapping of Mode I interlaminar crack extension in particle-toughened interlayers
Full text linkThis paper presents the first use of Digital Volume Correlation (DVC) on Carbon Fibre Reinforced Plastics (CFRPs) to quantify the strain fields ahead of a Mode I delamination. DVC is a relatively novel tool that can be used to measure displacements and strains occurring inside materials under load. In conjunction with Computed Tomography (CT), the technique has been applied to porous materials, with results providing strain data for validation of Finite Element (FE) models. However, the application of the technique to laminated materials has been limited, with studies often requiring fiducial markings required for volume correlation. In this work, crack propagation steps were captured at a 325 nm voxel resolution using Synchrotron Radiation Computed Tomography (SRCT). The material systems investigated featured different crack bridging mechanisms such as; particle-bridges, resin ligaments, and fibre-bridges. An assessment of noise and sub-volume size on the strain measurement determined that the optimal sub-volume size was 150 voxels with 50% overlap. This provided a spatial resolution of 48.8 ?m for strain and a corresponding strain resolution ranging between 220 and 690 ?? for the repeated reference scans. A rigid body translation study confirmed that specimen movements perpendicular to the fibre orientation support the ‘real’ physical displacements. However, along the fibre direction, the correlation was poor, with correct displacements being detected only within the particle-toughened interlayers. The study demonstrates that strain measurements can be made perpendicular to the fibre direction across the interlayer, which could be used to validate future FE models of these poorly understood particle-toughened interlayer
Interlaminar fracture micro-mechanisms in toughened carbon fibre reinforced plastics investigated via synchrotron radiation computed tomography and laminography
Full text linkSynchrotron Radiation Computed Tomography (SRCT) and Synchrotron Radiation Computed Laminography (SRCL) permit 3D non-destructive evaluation of fracture micro-mechanisms at high spatial resolutions. Two types of particle-toughened Carbon Fibre Reinforced Polymer (CFRP) composites were loaded to allow crack growth in Modes I and II to be isolated and observed in standard and non-standard specimen geometries. Both materials failed in complex and distinct failure modes, showing that interlaminar fracture in these materials involves a process zone rather than a singular crack tip. The work indicates that incorporating particle/resin, fibre/interlayer and neat resin failure is essential within models for material response, since the competition between these mechanisms to provide the energetically favourable crack path influences the macro-scale toughness. The work uniquely combines the strengths of SRCT and SRCL to compare failure micro- mechanisms between two specimen geometries, whilst assessing any edge effects and providing powerful insight into the complex micro-mechanical behaviour of these materials
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
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