44 research outputs found
Design and analysis of DLS steel/composite thick-adhernd adhesive joints
No full textThe paper describes experimental and numerical techniques to study the structural design and behaviourof thick-adherend DLS joints that are based on steel /steel and steel/composites and epoxy adhesives, withfocus on long overlap joints. A standard fabrication method was followed to produce 60 specimens of
various dimensions and materials
Fabrication, testing and analysis of steel/composite DLS adhesive joints
No full textThis paper describes experimental and numerical techniques to study the structural design of double lap shear joints that are based on thick-adherend steel/steel and steel/composite, with epoxy adhesive. A standard practical fabrication method was used to produce specimens of various dimensions and materials. These specimens consist of 10 mm steel inner adherend and various outer adherend materials including composite and steel of various thicknesses and overlaps. The composite is largely based on carbon fibre reinforced plastic. The specimens were tested under monotonic tensile loading and the results showed that joint strength depends largely on materials combination and overlap length. The testing also included the use of an advanced imaging system to determine failure initiation and propagation. Two-dimensional finite element analysis (FEA) stress models were applied and showed the importance of modelling the composite layers adjacent to the adhesive bondline in order to account for the critical local stresses. The FEA results also showed that overall shear stress distributions can be used to characterise joint failure. The paper presents the experimental and numerical details with key conclusions
Fabrication, Testing and Analysis of Steel/Composite DLS Adhesive Joints
No full textThis paper aims to provide a guide on the design and fabrication of thick adherend double lap shear joints (DLS), often referred to as butt connections/joints in ship structures including patch repair. The specimens consist of 10mm steel inner adherend and various outer adherend materials including 0/90 WR GFRP and 0/90 UD CFRP laminates and steel. The focus here is on CFRP/steel joint due to availability of test data. The thickness of the outer adherend varies from 3 mm to 6 mm. Shear overlaps of 25-200mm were considered. The overall objectives are (i) to assess the quality of the standard fabrication method, (ii) to determine joint strength and overlap plateau for various specimens with a range of material combinations and (iii) to understand aspects of failure and design of joint under quasi-static loading. The paper presents experimental and numerical details with key conclusions
Asymmetric assembling of iron oxide nanocubes for improving magnetic hyperthermia performance
No full textMagnetic hyperthermia (MH) based on magnetic nanoparticles (MNPs) is a promising adjuvant therapy for cancer treatment. Particle clustering leading to complex magnetic interactions affects the heat generated by MNPs during MH. The heat efficiencies, theoretically predicted, are still poorly understood because of lack of the control of the fabrication of such clusters with defined geometries and thus their functionality. This study aims to correlate the heating efficiency under MH of individually coated iron oxide nanocubes (IONCs) vs. soft colloidal nanoclusters made of small groupings of nanocubes arranged in different geometries. The controlled clustering of alkyl stabilized IONCs is achieved here during the water transfer procedure by tuning the fraction of the amphiphilic copolymer, poly(styrene-co-maleic anhydride) cumene terminated, to the nanoparticle surface. It is found that increasing the polymer-to-nanoparticle surface ratio leads to the formation of increasingly large nanoclusters with defined geometries. When compared to the individual nanocubes, we show here that controlled grouping of nanoparticles—so-called “dimers” and “trimers” comprised of two and three nanocubes, respectively—increases 2 specific absorption rate (SAR) values, while conversely, forming centrosymmetric clusters having more than four nanocubes leads to lower SAR values. Magnetization measurements and Monte-Carlo based simulations support the observed SAR trend, and reveal the importance of the dipolar interaction effect and its dependence on the details of the particle arrangements within the different clusters. individual nanocubes, we show here that controlled grouping of nanoparticles—so-called “dimers” and “trimers” comprised of two and three nanocubes, respectively—increase
The effect of surface preparation on the behaviour of double strap adhesive joints with thick steel adherents
No full textOne of the major factors determining the integrity of an adhesive bond is the preparation of the bonding surfaces. The present study is an experimental investigation of the effect of the surface preparation procedure on the response of a steel-to-steel double strap adhesive joint. Two procedures for preparing the bonding surfaces are investigated, namely grit blasting (GB) and simple sandpaper (SP). The behaviour of the joints, in terms of the force-displacement and strains-displacement responses was monitored and compared for both cases. The joints with SP surface preparation exhibited slightly lower stiffness and lower strength than the joints with GB surface preparation, while the latter failed at a lower displacement. In both cases, failure initiated at the free edges of the joints and the dominating failure mode was interfacial. In addition to the above experimental measurements, results are also presented from the application of a properly modified analytical model. © 2009 Taylor & Francis Group, London
Growth and characterization of nanostructured magnetic materials
No full textThe goal of this thesis is to develop and characterize advanced nanostructured magnetic materials for future applications in nanodevices. The magnetic characterization of materials in the form of thin and multilayered films exhibits new investments of exceptionally great technological interest. More specifically, the development of nanostructured magnetic materials of transition metal-metal oxide type multilayer films was carried out by natural oxidation using the sputtering technique and the study of the magnetic properties both at room temperature and at low and high temperatures. In summary, the structural and magnetic properties of i) Ni-based (Ni/NiO), ii) Co-based (Co/CoO) magnetic multilayers, and iii) the influence of the addition of noble metals such as platinum on Co/CoO and platinum and palladium in Ni/NiO multilayered systems were studied. Experiments with electron microscopy TEM and X-ray diffraction-reflectivity XRD-XRR showed that the samples have excellent layering quality with low roughness. The main results of magnetic measurements with the MOKE magnetometer are summarized in the enhancement of perpendicular magnetic anisotropy after moderate annealing in the Ni-based multilayered system. Low-temperature after field-cooling experiments with the SQUID magnetometer demonstrated important phenomena such as the spin reorientation transition SRT, the large value of the exchange bias EB, and the strong enhancement of the coercive field HC in some systems. As for the Co/CoO multilayer films, they often presented inverted hysteresis loops, in which a successful theoretical attempt to reproduce them was made, while the Co/CoO/Pt systems presented a strong PMA even at room temperature, with large values of exchange field at temperatures of 4–10 K. Nowadays, systems that exhibit perpendicular magnetic anisotropy have a wide range of applications including data storage media on magnetic and magneto-optical disks, which are potential materials for reading heads and sensors in spintronics.Η παρούσα Διδακτορική Διατριβή πραγματεύεται την ανάπτυξη και τον χαρακτηρισμό προηγμένων νανοδομημένων μαγνητικών υλικών κατάλληλα για εφαρμογές σε νανοδιατάξεις. Ο μαγνητικός χαρακτηρισμός υλικών υπό μορφή λεπτών και πολυστρωματικών υμενίων, ανοίγει τις πόρτες σε νέες ιδιότητες με εξαιρετικά μεγάλο τεχνολογικό ενδιαφέρον. Πιο συγκεκριμένα, πραγματοποιήθηκε ανάπτυξη νανοδομημένων μαγνητικών υλικών πολυστρωματικών υμενίων τύπου μεταβατικών μετάλλων-οξειδίου μετάλλου με φυσική οξείδωση χρησιμοποιώντας την τεχνική της ιοντοβολής (sputtering) και μελέτη των μαγνητικών ιδιοτήτων τόσο σε θερμοκρασία δωματίου όσο και σε χαμηλές και σχετικά υψηλές θερμοκρασίες. Συνοπτικά, μελετήθηκαν οι δομικές και μαγνητικές ιδιότητες μαγνητικών πολυστρωματικών υμενίων i) με βάση το νικέλιο (Ni/NiO), ii) με βάση το κοβάλτιο (Co/CoO) και iii) η επίδραση των ευγενών μετάλλων πλατίνας σε Co/CoO και πλατίνας και παλλαδίου σε πολυστρωματικά συστήματα Ni/NiO. Πειράματα με ηλεκτρονική μικροσκοπία ΤΕΜ και περίθλασης-ανακλαστικότητας ακτίνων Χ, XRD-XRR έδειξαν πως τα δείγματα έχουν εξαιρετική ποιότητα διαστρωμάτωσης και επαναληψιμότητα παραγωγής. Τα κυριότερα αποτελέσματα μαγνητικών μετρήσεων με το μαγνητόμετρα ΜΟΚΕ συνοψίζονται στην ενίσχυση της κάθετης μαγνητικής ανισοτροπίας μετά από μέτρια ανόπτηση στο σύστημα πολυστρωματικών υμενίων με βάση το Ni. Πειράματα σε χαμηλές θερμοκρασίες και με ψύξη υπό πεδίο με το μαγνητόμετρο SQUID κατέδειξαν σημαντικά φαινόμενα, όπως τη μετάβαση επαναπροσανατολισμού των σπιν SRT, τη μεγάλη τιμή πόλωσης ανταλλαγής EB και την ισχυρή ενίσχυση του συνεκτικού πεδίου HC σε ορισμένα συστήματα. Όσον αφορά στα πολυστρωματικά υμένια Co/CoO, παρουσίασαν συχνά ανάστροφους βρόχους υστέρησης, στους οποίους πραγματοποιήθηκε επιτυχημένη θεωρητική προσπάθεια αναπαραγωγής τους, ενώ τα συστήματα Co/CoO/Pt παρουσίασαν ισχυρή PMA ακόμα και σε θερμοκρασία δωματίου, με μεγάλες τιμές πόλωσης ανταλλαγής σε θερμοκρασίες 4 – 10 Κ. Συχνά στις μέρες μας, όταν τέτοια συστήματα εμφανίζουν κάθετη μαγνητική ανισοτροπία βρίσκουν πληθώρα εφαρμογών όπως είναι η εγγραφή πληροφορίας σε μαγνητικούς και μαγνητο-οπτικούς δίσκους, ως υποψήφια υλικά σε κεφαλές ανάγνωσης και αισθητήρες, στη σπιντρονική
Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni0.95Fe0.05/NiFeO Multilayers
No full textNi0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) on the magnetic properties of NiFe/NiFeO multilayers is also investigated. Annealing results in the enhancement of perpendicular magnetic anisotropy, mainly due to an increase in the uniaxial volume anisotropy term. Temperature-dependent hysteresis measurements between 4-400 K revealed considerable enhancement of coercivity and appearance of exchange bias effect
LOAD CAPACITY OF SANDWICH PANEL WITH CORE FOAM EVALUATED BY 3-POINT BENDING TEST
No full textThe classification society Bureau Veritas requires a structural assessment of composite materials structures to confirm the compliance with applicable rules, like 3-point bending tests. However, for sandwich panels with a low-density foam core, local phenomena like indentation and wrinkling may occur in the upper face sheet at the loading punch, thus the intended load capacity of the sandwich panel will not be reached. It is then proposed to perform complementary shear tests to capture the behaviour of the core of the sandwich panel. In the present paper, the load capacity in a 3-point bending test is simulated with emphasis on the influence of the constitutive modelling of the core foam, as calibrated against experimental results for shear tests. It is carried out as a benchmark exercise, with participation from three universities. The FE-simulations show that the shear test can be used to accurately model the load capacity of the core foam. However, for the 3-point bending test using specimen with a very high panel length/thickness ratio a large part of the load transfer is done in the upper face sheet with less involvement of shear in the core. Although core fracture is observed in the experiments, both the FE-simulated and experimentally found maximum load agree well with the load capacity as determined from analytical formula for local failure in the upper face sheet. The FE-simulated vertical displacement at maximum load differs though
Safeguarding Our Heritage—The TRIQUETRA Project Approach
No full textCultural heritage (CH) sites are frequently exposed to natural elements, and their exposure becomes particularly precarious with the onset of climate change. This increased vulnerability places these sites at risk of deterioration or complete destruction. Risks such as land deformation, floods, acid rain, and erosion significantly threaten historic monuments, while water-related hazards, significantly influenced by both climate change and human activities, present a particularly grave risk to these invaluable sites. Considerable research efforts have focused on safeguarding CH sites. However, there remains a deficiency in systemic approaches towards identifying and mitigating risks for CH sites. The TRIQUETRA project proposes a technological toolbox and a methodological framework for tackling climate change risks and natural hazards threatening CH in the most efficient way possible. It aims at creating an evidence-based assessment platform allowing precise risk stratification as well as a database of available mitigation measures and strategies, acting as a Decision Support System (DSS) towards efficient risk mitigation and site remediation. TRIQUETRA is a European project that brings together a diverse group of researchers with varied expertise, encompassing university research groups, research institutes, public entities, as well as small and medium-sized enterprises. In this article, TRIQUETRAs overall methodology is presented, and preliminary results concerning risk identification, TRIQUETRAs knowledge base, as well as novel sensors and coatings, are discussed
