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Kerrosten välisen leikkausjännityksen testaus ei-yhdensuuntaisesti lujitetuissa komposiiteissa
Get PDFOne of the most detrimental failure types in composite materials is delamination, a fracture that starts
to propagate between the individual fibre-reinforced layers of the composite. Delamination can be
caused by different forces but in this thesis the focus point is in delamination caused by interlaminar
shear. Interlaminar shear strength, ILSS, is a value that is often used for comparing different composite
materials to each other and basically tells how well the composite can resist interlaminar shear forces
before breaking.
This thesis primarily focuses on experimental testing of non-unidirectionally reinforced laminates in
order to find out their interlaminar shear strenght. The testing is done by three point bending according
to standard ASTM D2344 that defines the rules for the ILSS testing. Two main types of test specimens
are tested: aramid and glass-fibre-reinforced specimens. The glass-fibre-reinforced laminates have two
lay-ups, which are being compared to find out how the ILSS behaviour changes with different lay-up.
To determine the stresses in different parts of the composite specimen during bending in detail, finite
element models of the glass-fibre-reinforced laminates with both lay-ups were created.
Based on the experimental results, the delaminations happened often at the lower interface of the
laminates, where the fibre direction changed. This was confirmed with the simulations, which showed
peak stresses at the interface. The wet testing conditions and the elevated temperature during testing
both had a negative effect on the ILSS values as well as the behaviour of the laminates during ILSStesting.
Ageing in a water-sulphuric-acid immersion decreased the average ILSS values but did not
affect the ILSS behaviour and the specimens delaminated in an interlaminar way. Simulated critical
shear stresses were 14-24% lower than the values based on the ASTM standard. The simulated pure
lay-up-induced decrease in shear stress between the two laminates was 34-58% (depending on the
free-edge-effects), which is higher than suggested by the experiments (21-26%).Yksi tyypillisimmistä vauriomuodoista komposiittirakenteissa on delaminaatio, murtuma, joka saa
alkunsa yksittäisten kuitulujitettujen kerrosten välissä, kun kerrokset irtoavat toisistaan. Delaminaatio
voi aiheutua monesta tekijästä, mutta tässä diplomityössä pääpaino on delaminaatiolla, joka saa
alkunsa kerrostenvälisestä leikkausvoimasta. Kerrostenvälinen leikkauslujuus (ILSS) on arvo, jota
käytetään usein, kun halutaan vertailla erilaisia komposiitteja toisiinsa ja se käytännössä kertoo, kuinka
hyvin komposiitti kykenee vastustamaan kerrostenvälistä leikkausvoimaa, ennen kuin se murtuu.
Tämä diplomityö keskittyy ensisijaisesti ILSS-arvojen mittaamiseen sellaisilla laminaateilla, joissa
kuitukerrokset eivät ole yhdensuuntaisia. Kokeellinen testaus suoritetaan ILSS:n mittaamiseen
kehitetyn standardin, ASTM D2344, perusteella. Koekappaleina käytetään kahdenlaisia laminaatteja,
joista ensimmäiset ovat lasikuitulujitettuja, toiset aramidilujitettuja. Testeissä käytetyissä
lasikuitulujitetuissa laminaateissa on kahdenlaista laminointia, joita verrataan keskenään, jotta voidaan
nähdä miten erilaiset kerrosjärjestykset vaikuttavat käyttäytymiseen ILSS-testeissä. Tarkempaa
analyysia varten molemmista laminoinneista luotiin simulaatiomalli. Näin oli mahdollista selvittää,
minkä kerrosten väliin leikkausjännityspiikit muodostuvat.
Kokeelliset testit osoittivat, että useimmiten koekappaleet delaminoituivat alemmasta rajapinnasta,
jossa lujitekuitujen suunta muuttuu. Tämä pystyttiin osoittamaan myös simulaatioilla, joissa alempaan
rajapintaan muodostui suurimmat jännityspiikit. Laminaattien testaaminen kosteana ja korotetussa
lämpötilassa heikensi ILSS-arvoja sekä ILSS-käyttäytymistä testeissä. Laminaattien ikäännyttäminen
vesi-rikkihappo -upotuksessa ennen testaamista heikensi ILSS-arvoja, mutta ILSS käyttäytyminen
pysyi hyvänä, ja laminaatit hajosivat delaminoitumalla. Simuloidut kriittiset leikkausjännitykset olivat 14-
24 % matalammat kuin ASTM standardin mukaan lasketut jännitykset. Simuloitu puhtaasti
laminoinnista johtuva ero eri laminaattien välillä oli 34-58 % (riippuen reunaefektistä), mikä on
suurempi kuin kokeissa havaittu ero (21-26 %)
MTBE:n reaktoreiden syrjäytysten optimointi
Get PDFOpinnäytetyö tehtiin Neste Oyj:n Porvoon öljyjalostamolla ja tarkoituksena oli optimoida MTBE-yksikön reaktoreiden syrjäytysprosesseja. Tavoitteena oli etsiä hidastavia tekijöitä, taulukoida syrjäytysvaiheiden ajankäyttöä ja laatia reaktorin katalyytin vaihdosta prosessikaavio. Hidastavien tekijöiden pohjalta etsittiin ratkaisuja nopeuttaa katalyytinvaihtoa muuttamatta prosessia. Prosessikaavion tarkoituksena oli selkeyttää katalyytinvaihtoprosessin rooleja, vastuita ja etenemistä työntekijöille.
Opinnäytetyössä esimerkkisyrjäytyksenä käytettiin marraskuussa 2019 alkanutta katalyytinvaihtoa reaktorille DC-1901. Syrjäytysvaiheiden kesto taulukoitiin, jotta pystyttiin vertailemaan eri vaiheiden viemää aikaa. Syrjäytykset ennen katalyytin vaihtoa veivät selvästi enemmän aikaa kuin vaihdon jälkeiset syrjäytykset. Tämä johtuu turvallisuudesta, koska reaktorin hiilivetyvedyttömyys ja metanolittomuus ovat kriittisen tärkeää avattaessa reaktori ja laskettaessa sen sisältämä neste viemäriin. Ajankäytön perusteella ja syrjäytysvirtauksia tutkimalla laskettiin likimääräiset tilavuudet tuotetuille syrjäytysseoksille.
Tulosten perusteella syrjäytysten suurimpia hidasteita ovat epäonnistunut katalyytin kuivaus, reaktoreiden metanolitäytön hitaus, syrjäytyslinjojen tukokset ja erotuskolonnien operointiongelmista johtuva rajoitettu syrjäytysnopeus. Paras keino syrjäytysten nopeuttamiseen olisi erilliset syrjäytyssäiliöt, joihin syrjäytysnopeus olisi rajoittamaton. Virtauksen varmistamiseksi vesimetanolisyrjäytyslinjaan voitaisiin sijoittaa suodatin syrjäytysautomaatin tukkeutumisen estämiseksi. Reaktoreiden metanolitäyttöjen nopeuttaminen olisi mahdollista rakentamalla metanolipumpuille omat minimikierrot tai vaihtamalla pumput tehokkaampiin. Katalyyttien kuivauksen helpottamiseen voitaisiin suunnitella kiinteä typpikuumennin, jolla saataisiin parempi kuivaustulos. Uudistusten kannattavuus on kuitenkin laskettava, jotta niiden toteuttaminen olisi järkevää.The objective of this thesis was to optimize liquid replacement processes for reactors in MTBE unit. The goal was to find the delaying factors of the changing catalyst process and to make a process chart to define the stages of the process and clarify the roles and responsibilities involved.
Time used in different replacement processes were calculated from catalyst change which was done for the reactor DC-1901 in November 2019. The data obtained of the time used in different parts of process was arranged into tabular form. Liquid replacement processes before catalyst change took significantly more time than the processes after the catalyst change. To avoid hazardous leaks, it is crucial to have a low hydrocarbon and methanol percentage before opening the reactor and running it empty to the sewer. The approximate volumes of the replacement mixtures caused by the different replacement processes were calculated by the duration of the process and by the data from the process measurements.
According to the results and experience of catalyst changes it seems that the major delays are inflicted by various reasons like unsuccessful catalyst drying, insufficient methanol feed for reactor at point of filling it up, clogged replacement mixture pipes and limited replacement mixture flows caused by operation problems in the separation colons. Separate vessels for the replacement mixtures would free the flow speed in the replacement process. To prevent clogs, it would be useful to add a filter to the water and methanol mixture pipeline. To speed up the reactor’s methanol filling the methanol pumps should be replaced by ones with a bigger output or by installing separate bypass loops and operate the pumps parallel. The best way to ensure better drying results for the catalyst drying is to design a firm nitrogen heater. However, in future it is necessary to calculate the expenses for the reformations to ensure the cost-effectiveness
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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