330 research outputs found
Continuous Ultrasonic Welding of Thermoplastic Composites
No full textAerospace EngineeringAerospace Structures & Material
The dangers of single-lap shear testing in understanding polymer composite welded joints
No full textSingle-lap shear (SLS) joints are straightforward to manufacture. This makes them especially attractive for testing polymer composite welded joints. Owing to local heating, which is characteristic of composite welding processes, the production of more geometrically intricate joints (such as double-lap or scarfed joints) or bigger joints (such as end-notched flexure or double cantilever beam) typically entails significant complexity in the design of the welding process. Testing of SLS joints is also uncomplicated and, even though, owing to mixed-mode loading and uneven stress distribution, it does not provide design values, it is widely acknowledged as a valuable tool for comparison. Even so, comparing different aspects of composite welded joints through their corresponding SLS strength values alone can be deceptive. This paper shows that comparison of different welding processes, adherend materials, process parameters or different types of joining techniques through SLS testing is only meaningful when strength values are combined with knowledge on other aspects of the joints such as joint mesostructure, failure modes and joint mechanics. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.Accepted Author ManuscriptAerospace Structures & Computational MechanicsStructural Integrity & Composite
Resistance Welding of Thermoplastic Composites: Process and Performance
No full textCompared to thermoset composites, thermoplastic composites are drawing more and more attention by aircraft industries not only due to their excellent material properties but also due to their potentials to reduce cycle time and structure cost by using low-cost manufacturing technologies such as welding. Resistance welding has been regarded as one of the most promising welding techniques owing to the low energy consumption, simplicity of welding operation and capability for scaling up. Previous researches on resistance welding of thermoplastic composites are mainly focused on understanding the welding mechanisms and characterizing the welding qualities. The research work was aimed to gain deeper knowledge of resistance welding, in both micro-level and macro-level. In micro-level study, the specific properties that influence the welding quality were discussed, such as the surface properties of adherends, the weld line properties and the welding induced voids. In macro-level study, the emphasis was put on improving the current welding process, for both static resistance welding and continuous resistance welding. Micro-level study: 1. Resistance welding of woven fabric reinforced thermoplastic composites was investigated. Both the type of the majority fibres (warp yarns or weft yarns) and the apparent orientation of the majority fibres on the adherend surface were found to influence the failure mode and lap shear strength. Fibre sizing was found to be crucial for a good fibre-matrix adhesion, and therefore it was crucial for a good weld. 2. Other than fibre de-compaction, the residual volatiles inside the adherends was found to be a main cause of the voids in the joints for a welding process performed under a moderate welding pressure. Non-uniform void distribution was observed inside the joints, with void concentrations near the middle of weld overlap. The voids could be reduced by using pre-dried adherends or using a higher welding pressure. 3. A thinner weldline, usually obtained by using a thinner heating element, was found to be preferable to a thicker one. The relatively weaker welding quality near the edges of the joints was found to be a limitation of weld performance, but this could be improved by tailoring heat generation at the weld overlap or creating resin fillets near the edges. Micro-level study: 1. The possibility of using displacement measurement data for process monitoring and processing window definition was investigated, and it showed ability to detect voids generation and resin squeeze flow during welding and to construct processing windows. 2. The process of continuous resistance welding was analysed, and a model was developed to simulate the heat generation and heat transfer during welding.Aerospace Structures and MaterialsAerospace Engineerin
TRADITIONS, INNOVATIONS AND NEW TRENDS IN THE PEDAGOGICAL THEORY AND SCIENTIFIC SCHOOL OF ACADEMICIAN I.F. KHARLAMOV
No full textThe relationship between the development of pedagogical theory and the formation of scientific-pedagogical school, the relationships between traditions and innovations in scientific pedagogy are considered, the basic principles and ideas of educational theory which formed the basis for the creation of the most important and, in fact, the only in the Republic of Belarus scientific-pedagogical school in the field of theory and practice of modern education are examined. Ivan Kharlamov (1920-2003) is doctor of pedagogy, professor, honoured scientific worker of the BSSR (1980), academician of the Academy of Pedagogical Sciences of the USSR (1990), academician of the National Academy of Belarus (1995), foreign member of the Russian Academy of Education (1999), State Prize winner of Belarus (for the textbook “Pedagogy” (2000)). Author of over 300 scientific works, including more than 20 monographs and textbooks; founder of the most powerful pedagogical theory and the most important scientific-pedagogical school in the Republic of Belarus. The comparative analysis of I.F. Kharlamov’s educational theory and J. Edelman’s theory of Neural Darwinism may lead to the discovery of many cognitive phenomena that can transform the theory and practice of modern education and personal development
Diagnostic of manufacturing defects in ultrasonically welded thermoplastic composite joints using ultrasonic guided waves
No full textThis article presents research about the propagation of ultrasonic guided waves in ultrasonically welded thermoplastic composite joints. The goal of the study was to understand the effect of weld manufacturing defects on guided wave transmission across the joint. Triangular energy-directors integrated into the lower composite adherends enabled the production of defective joints in a controlled manner. The produced defect types were unwelded areas and adherend fibre bundle distortion. The reference condition corresponded to the fully welded stage which showed the highest single-lap shear strength. It was possible to detect adherend fibre bundle distortion through the increase in the negative shift of the signal characteristic frequency. Evidence of the presence of unwelded areas was found in the increase of Time-of-Flight of the maximum amplitude Lamb wave group. The sensitivity of the diagnostic parameters was found to be dependent on the ultrasonic guided wave excitation frequency.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Integrity & CompositesAerospace Manufacturing Technologie
Energy directors for Continuous Ultrasonic Welding of thermoplastic composites
No full textUltrasonic Welding (USW) is a rapidly upcoming technology for joining high performance Thermoplastic Composite (TPC) structures in the automotive industry. With the focus shifting from metals to composites for primary structures, USW process is seen as a fast, clean and efficient alternative for the conventional joining methods. Continuous Ultrasonic Welding (CUW) is an innovative, upscaled version of the USW process, where the weld is made over a moving part to create a weld line instead of a single spot. Currently, there has been very limited research done in this field and the technology is in very early stages. The key to success of this technology lies in creating a uniform weld of an acceptable lap shear strength (LSS). Recent research has suggested that using a woven mesh as an energy director (ED) at the interface provides a good uniformity along the weld line, along with an acceptable LSS value. The research shows how the mesh deforms prior to the melting process, creating an intimate contact between the adherends and how this has a positive effect on the weld uniformity. This study uses this data to design and manufacture a new ED that has these beneficial features incorporated in it. The study also uses an expanded mesh as an ED to study the effect of open areas in the weld uniformity. The EDs are used in the CUW process and compared based on their different features. Through this study, a deeper understanding of the behaviour of EDs during a CUW process is established which will be useful for developing new means of optimizing this process.Aerospace 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
No full textprStructural Integrity & Composite
Investigation of Vertically Oriented Carbon Nanotubes Materials at Interlaminar Region of Polyphenylene Sulfide Thermoplastic Composites
No full textThis project investigates the combination of PPS thermoplastic UD and fabric composite materials with novel mass-produced vertically aligned carbon nanotube (VACNT) materials at the interlaminar region. There are two goals for this project, the first is to understand how the VACNT materials can be embedded and consolidated with the use of elevated temperatures and pressures and how that impacts the resulting morphology of the VACNTs. The second is to understand if VACNTs can increase the interlaminar related mechanical properties of the PPS composite materials similar to that seen with thermoset materials. Processes for embedding of VACNTs to a single ply was found to be possible and repeatable, though secondary multi-ply consolidation lead to matting of the VACNTs at the interlaminar layer. Subsequent mechanical testing showed that this matting of VACNTs led to a decrease in shear and compression strengths by 10.6% and 8.5% respectively against control specimens.Aerospace Engineerin
Investigating the use of Fused Deposition Modeling as Energy Director application method for Ultrasonic Welding of Thermoplastic Composites
No full textThe joining of high performance Thermoplastic Composite (TPC) structures by Ultrasonic Welding (USW) is considered a promising alternative for mechanical joining or adhesive bonding methods. The process is fast, clean, and highly automated. In the USW process, an intermediate, unreinforced polymer layer is required at the weld interface to concentrate the heat generation at this weld interface and is called the Energy Director (ED). This research investigates a new method to manufacture and apply this ED at the weld interface, being Fused Deposition Modeling (FDM). With FDM, complex products can be manufactured directly from a Computer Aided Design (CAD) model, without additional mould or special tooling required. The goal is to simultaneously manufacture and adhere a dedicated ED geometry on a consolidated TPC substrate with FDM, such that no additional fixation step of the ED is required before welding. The new technique is successfully applied with a PEEK (Polyether ether Ketone) ED and a consolidated CF/PPS (Carbon fibre/Polyphenylene Sulfide) substrate. The deposited ED has sufficient bonding with the substrate that it remained fixated during handling prior to and during the weld process. This resulted in a successful weld, having similar strength and quality as found with welds having a loose, flat film as ED. A challenge encountered in using FDM as manufacturing method of the EDs, is a non-uniform thickness distribution occurring in the ED. Additional research on the influence of a variation in thickness is done, where it is found to reduce the overall single Lap Shear Strength (LSS), and divide the fracture surface of a single weld in two areas welded to different weld stages.TAPAS2Aerospace Engineerin
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