1,720,988 research outputs found
Increased impact toughness of mass polymerized ABS by tuning polymer orientation via vibration injection moulding
No full textIn many sectors, stretching from house hold appliances to the automotive industry, acrylonitrile
butadiene styrene (ABS) is applied for its promising material properties. More recent developments in
the industrial production process of this polymer have provided improved stability of the raw material by
using a continuous polymerization process, called mass polymerization. The ABS polymer resulting from
this process, named mABS, is however slightly different in morphological characteristics as it rather
mimics high impact polystyrene (HIPS) than the more conventional used emulsion polymerized ABS
(eABS). These morphological characteristics make mABS more prone to processing related deviations
in part performance and final product morphology. Hence, this research covers the effect of flow induced
orientation on impact performance of mABS parts. To emphasize the effect of orientation, parts were
produced using regular injection moulding and compared to specimens made by the novel method of
vibration injection moulding, which applies a much higher amount of shear during processing and thus
increased orientation within the final product.
Impact specimens were cut from platelet samples in the parallel and perpendicular direction respective
to the flow path. Differences in morphological orientation of the rubber phase were determined via
scanning electron microscopy (SEM) imaging. A distinct layered structure, providing increased
orientation, was observed for the vibration injection moulded samples. This higher orientation caused a
higher resistance against impact deformation applied in the perpendicular direction. For impact applied
parallel to the oriented rubber phase however, no difference for increased orientation was established.
This research could therefore draw similar conclusions as found in research covering performance of
HIPS. It can thus be concluded that a higher degree of orientation within mABS parts can positively
contribute to part performance, depending on the direction of deformation.
Comparing mABS to the more conventional eABS, it should be stressed that anisotropy after processing
mABS is indeed high. This might cause altered product performance upon altering the used ABS type
without considering process adaptations
Mechanical characterisation and fibre morphology analysis in ABS and short carbon fibre composites : influence of different polymer processing techniques
No full textPolymer composites have attracted considerable interest due to their potential to enhance mechanical
properties of polymers or advanced applications. Yet, challenges exist including complex mechanical
behaviour and poor affinity between reinforcement material and polymer matrix. This study investigates
the influence of various processing methods on the mechanical properties of acrylonitrile butadiene
styrene (ABS) reinforced with 15 wt% short carbon fibres (sCF), focusing mainly on fibre morphology.
By analysing injection moulding (IM), fused filament fabrication (FFF) and compression moulding (CM),
this research aims to elucidate the relationship between the processing method, fibre orientation and
mechanical properties. Improved affinity is achieved through nitric acid surface treatment. Scanning
electron and optical microscopy are used to analyse the morphology, revealing insights into void
presence and fibre roughness, length, distribution and orientation. Additionally, mechanical properties
are assessed through impact, tensile and flexural tests. Significant differences in morphology among
ABS/sCF composites produced by different methods are revealed. Microscopy images show that in IM
parts, fibres are highly aligned in the shear layer but exhibit a more varying orientation in the core, with
minimal voids. FFF parts exhibit excellent sCF alignment but show voids between different layers,
whereas CM parts display varying fibre orientations and small air inclusions. These differences notably
affect the mechanical properties. Test bars produced via IM demonstrate superior stiffness, tensile
strength and tensile strain at break, followed by FFF (which shows very high impact strength), while CM
parts exhibit the least favourable properties, partly due to their isotropic nature and random sCF
orientation. These outcomes can be immediately linked to the resulting morphologies. The findings of
this work highlight the critical role of processing methods and fibre morphology in determining composite
performance
Enhancing thermal conductivity of ABS and short carbon fibre composites : influence of processing techniques on carbon fibre orientation
No full textPolymer composites play a significant role in the transition to a sustainable future due to their exceptional
material properties. By adding fillers to a matrix, thermal properties can be improved, allowing for
broader application of lightweight materials. This study focuses specifically on acrylonitrile butadiene
styrene (ABS) in combination with 15 w% short carbon fibres (sCF), which form a composite with
improved thermal conductivity. Although most research has focused on compression moulding, this
study examines other relevant techniques including extrusion-fused filament fabrication (FFF) and
injection moulding. To ensure superior material properties, the adhesion between the matrix and the
fibre is investigated, by comparing the compatibility between the matrix and untreated fibres, and matrix
and fibres that have undergone a surface treatment with nitric acid. Based on optical microscopy and
SEM, it could observed that fewer air voids were visible in the pellet with the treated fibre. Consequently,
the treated fibre showed significantly better adhesion to the matrix. The SEM images showed that the
treated fibres did not have increased surface roughness. Therefore, the improvement is due to the
formation of functional groups. Furthermore, the fibre length distribution of the untreated and treated
fibre after compounding showed that the treated fibre underwent less fibre breakage then the untreated
fibres, as a result of the improved adhesion protecting the fibres. The improvement in thermal
conductivity measured by the Transient Plane Source (TPC) method, is mainly influenced by fibre
orientation and not by fibre length, as the fibre length distributions for the three processing techniques
did not show significant differences. In contrary to literature, compression moulding resulted in
anisotropic properties due to high pressure and low temperature, which aligned the fibres and increased
the in-plane thermal conductivity to 1.737 ± 0.045 W/(m∙K) compared to the thermal conductivity of ABS
(0.1818 ± 0.0004 W/(m∙K)), while the through-plane conductivity decreased to 0.053 ± 0.007 W/(m∙K)
due to entrapped voids in the material. For single screw extrusion followed by FFF, the fibres were
aligned in the flow direction due to the shear forces present, resulting in an increased thermal
conductivity of 1.532 ± 0.018 W/(m∙K). In the through-plane direction, a decrease of 0.166 ± 0.002
W/(m∙K) was observed due to the weak adhesion between the layers. Finally, injection moulding showed
the smallest increase in thermal conductivity in the in-plane direction, due to the less alignment of the
fibres in the core layer, where shear is minimal. It should be noted that the in-plane thermal conductivity
at the end of the 1A tensile test bar showed a greater increase, namely 1.126 ± 0.013 W/(m∙K), whereas
at the gate the in-plane thermal conductivity was 0.999 ± 0.003 W/(m∙K). However, it shows the greatest
in-crease in through-plane thermal conductivity, namely 0.199 ± 0.001 W/(m∙K), which is more important
for most applications such as a heat exchanger
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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