101,903 research outputs found
Development & assessment of equipment and procedure for continuous ultrasonic welding of thermoplastic composites
No full textUltrasonic welding (USW) is a technique used to bond materials together by heating the bonding surfaces with ultrasound. Its main advantage is the high processing speed, which is in the order of seconds. However, application of this technique with thermoplastic composite (TPC) materials is still limited. One of the areas in which almost no research has been done is continuous ultrasonic welding of TPCs. This MSc thesis therefore explores some possibilities on a continuous variant of the ultrasonic welding process, applicable to TPCs. To do this, a machine was designed and developed which has a single, horizontally moving axis. This machine is able to weld in a straight line, complying to any thickness changes in the material. The design has been tested by comparing welds made with it with welds made on a conventional machine. The machine works correctly, but the frame has to be made stiffer, for which recommendations are made. Research was conducted into multiple-pass welding as well, as it is a potential solution for some of the problems sequential ultrasonic welding is facing. This research consisted of welding lap shear specimens in two separate passes, and comparing the produced weld with a reference (single-pass) weld. It is shown that the welding processes and welds are very similar, which makes current knowledge on ultrasonic welding applicable to multiple-pass welding.Structural Integrity & CompositesAerospace Structures and MaterialsAerospace Engineerin
Optimising Ultrasonic Welding of Carbon Fibre PEKK Composites
No full textThe interest of the aerospace industry in thermoplastic composites has increased over the last years. One of the advantages of using thermoplastics over thermosets is the possibility to use thermoplastic welding as a joining technique. Ultrasonic welding is considered one of the most promising variants: it is very fast, results in high-quality welds, can be applied to any fibre and resin type, is easy to automate and makes use of compact tooling. Therefore, it is a suitable technique for assembly and spot welding. This thesis research aims to improve the current processes for ultrasonic welding at TU Delft, while keeping a close eye on the industrial application. The first part of the research was focussed on the energy directors (EDs): resin protrusions between the substrates that heat up before the bulk material in the laminates. Previous research at TU Delft has mostly used loose EDs, but for industrial purposes it is preferable to integrate the EDs into the laminates. In this research, two production methods were developed that are suitable for moulding slender ED strips onto laminates: the first with aluminium strips with holes, the second with an Invar mould in which slender grooves have been machined. Both were used in combination with neat PEKK foil. An issue that was encountered with both methods is the variability in the thickness of the strips, leading to uneven melting. A comparison was made between the welding process of integrated and loose EDs. Moreover, it was found that the loose energy directors outperformed the integrated energy directors in terms of joint strength. Next, the displacement ceiling was investigated: a maximum in sonotrode travel that occurs before the optimum weld stage has been reached. When this happens, it is more difficult to use displacement as a welding driver to create welds of high strength. It was found that there are two types of displacement ceiling. The first occurs when a single ED strip is used, or the strips are placed far apart and the flow fronts do not merge. The origin possibly lies in changes in impedance and friction of the energy director flow. The second type of ceiling occurs when multiple ED strips flow and merge, which only happens if the spacing between them is small enough. The flow of the EDs pushes into each other, increasing the impedance of the flow and preventing further displacement of the sonotrode. To overcome the displacement ceiling, new displacement-controlled welding strategies have been investigated. First, the vibration phase was stopped before the ceiling had been reached. This resulted in welds of poor quality and strength. By reducing the pressure, the welds could be improved, but not to a satisfactory level. In the second strategy, the welding pressure was increased during the vibration phase. It was found that it is possible to push through the displacement ceiling and use a higher displacement value as the welding driver, which improves the strength of the welds greatly. These results showed significant scatter in the strength, which could be reduced by preventing secondary welding.Structural Integrity and CompositesAerospace Structures and MaterialsAerospace Engineerin
On the effect of flat energy directors thickness on heat generation during ultrasonic welding of thermoplastic composites
No full textThis paper presents a detailed experimental assessment of the effect of the thickness of flat energy directors (ED) on heat generation at the interface during ultrasonic welding. Power and displacement data showed clear differences caused by the change of thickness, related to heat concentration at the weld line during the process. The extent of the heat-affected zone was assessed by welding specimens without consolidation at different stages of the process. It was confirmed through optical microscopy that heat is generated at the interface and transferred to the bulk adherends earlier in the process for thinner ED. The analysis of their fracture surface under optimum welding conditions revealed signs of matrix degradation, leading to less consistent quality, likely due to faster heat generation rate in both the ED and the substrates, and incidentally, higher temperatures surrounding the energy director.</p
Ultrasonic welding of thermoplastic composite coupons for mechanical characterization of welded joints through single lap shear testing
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Ultrasonic welding of CF/PPS composites with integrated triangular energy directors: melting, flow and weld strength development
No full textThis paper presents a fully experimental study on melting, flow and weld strength development during ultrasonic welding of CF/PPS composites with integrated triangular energy directors. The main goal of this research was assessing whether the heating time to achieve maximum weld strength could be significantly reduced as compared to ultrasonic welding with flat energy directors. The main conclusion is that, in the specific case under study, the triangular energy directors did heat up, melt and collapse approximately two times faster than the time it took for the flat energy directors to melt and significantly flow. However the heating time needed to achieve maximum weld strength for the integrated triangular energy directors did not differ drastically from that for flat energy directors. This was caused by the fact that a fully welded overlap was not directly achieved right after the collapsing of the triangular energy directors. Instead a solidified resin-rich interface was created which needed to be re-melted as a whole in order to achieve a fully welded overlap and hence maximum weld strength.</p
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
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
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3346: Samuel G. Freedman, author, 2013
No full textPhotograph of author Samuel G. Freedman, at NT Daily Slash meeting in the Mayborn School of Journalism at UNT
Smart ultrasonic welding of thermoplastic composites
No full textThis paper presents an overview of the latest research on ultrasonic welding of composites performed at the Delft University of Technology. Firstly, we showed that for thermoplastic composites, a simple flat energy director shape, made of a loose film of neat resin, can be used to produce welds of high quality. Furthermore, for single lap shear coupons, it was shown that the use of a microprocessor-controlled welder allows for in-situ monitoring through power and sonotrode displacement data. As a result, a smart ultrasonic welding procedure was designed in which the feedback from the ultrasonic welder was used to define the processing parameters that yield optimum weld quality, significantly decreasing development times. Based on the knowledge developed at a lab-scale level, a welding strategy was developed to demonstrate the assembly of small and medium-sized components. Experimental comparison between ultrasonically spot-welded and mechanically fastened joints into double-lap shear and pull-through configurations further outlined the potential application of this technology, as well as its limitations. While ultrasonic welding is an efficient technique to join thermoplastic composites components, another potential application was shown to be the welding of thermoplastic and thermoset composites, enabled through the very short heating times in the ultrasonic welding process. This opens up new possibilities for ultrasonic welding where optimum design and manufacturing of aircraft parts call for the assembly of dissimilar materials, and could lead to significant costs and weight reduction as compared to mechanical fastening.Structural Integrity & Composite
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