Browsing by Author "An, Donglan"

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    Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints
    (Springer Nature, 2020-10-08) Bregar, Tadej; An, Donglan; Gharavian, Somayeh; Burda, Marek; Durazo-Cardenas, Isidro; Thakur, Vijay Kumar; Ayre, David; Słoma, Marcin; Hardiman, Mark; McCarthy, Conor; Nezhad, Hamed Yazdani
    Carbon nanotubes (CNTs) embedded polymers are of increasing interest to scientific and industrial communities for multi-functional applications. In this article, CNTs have been introduced to high-strength epoxy adhesive for enabling in-situ strain sensing in adhesively bonded aluminium-to-aluminium single-lap joints to accurately indicate the onset and propagation of adhesion failure to the evolution of piezo-resistivity in varying mechanical loads. The CNT modified adhesive in bonded joints and the CNT modified adhesive alone have been tested under monothonic and cyclic tensile loads up to ultimate failure. The changes in the piezo-resistivity induced by the CNTs have been monitored in situ with respect to loading. A novel interpretation method has been developed for progressive, instantaneous adhesion failure estimation under cyclic tensile stresses from a resistivity baseline. The method indicates that the in-situ resistivity changes and the rate of the changes with strain, i.e. sensitivity, strongly correlate with the adhesion failure progression, irrespective of the CNT dispersion quality. Moreover, the effect of bond thickness on the evolution of piezo-resistivity and adhesion failure have been studied. It was observed that relatively thin adhesive bonds (0.18mm thickness), possessing higher CNT contact points than thick bonds (0.43mm thicknes), provide 100 times higher sensitivity to varying cyclic loads
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    Strain self-sensing tailoring in functionalised carbon nanotubes/epoxy nanocomposites in response to electrical resistance change measurement
    (SSRN, 2020-10-26) An, Donglan; Nourry, Jim; Gharavian, Somayeh; Thakur, Vijay Kumar; Aria, Adrianus Indrat; Durazo-Cardenas, Isidro; Khaleque, Tasnuva; Nezhad, Hamed Yazdani
    Carbon nanotubes (CNTs) are inherently multifunctional, conductive and possess piezo-resistive characteristics. Aiming at the multi-functionality of materials, nanocomposites made of epoxy resin with embedded CNTs are a promising solution for strain self-sensing applications. A critical parameter to achieve repeatable and reliable measure is the CNTs dispersion state in the resin. This study investigated the effect of CNTs concentration (0.01 wt% and 0.1 wt%), with different loading of surfactant Triton X-100, (0.0%, 0.2%, 0.5% and 1.0%) on strain sensing in terms of sensitivity and linearity based on electrical resistance data. The CNTs were synthesised directly using an injection floating catalyst chemical vapor deposition (ICCVD) process and their quality was characterised by Raman spectroscopy and scanning electron microscopy. Only the epoxy modified with 0.1 wt% CNTs exhibited sufficient piezo-resistivity for the resistance measurements, and those with 0.01 wt% CNTs did not show sufficiently measurable conductivity so were excluded in our study, since their CNTs were highly entangled, and conductive network failed to be established. It was observed that, with 0.1 wt% CNTs, adding 0.5% content of the surfactant improved gauge factor. With more content of the surfactant (1.0 %), surprisingly, we observed a drop of gauge factor by the order of two. Therefore, by comparing the conductivity change between 1.0% and 0.5% surfactant, we postulated that the relatively high content surfactant has reached critical micelle concentration, and negatively affects CNTs dispersion state. The research presented in this article shows that moderate content of surfactant could improve piezo-resistivity gauge factor while excessive surfactant could cause adverse effect.
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    Ultra-thin electrospun nano-fibres for damage tolerant composite laminates
    (Cranfield University, 2019-11-08 12:34) An, Donglan; Lotfian, Saeid; Mesbah, Daria; Ayre, David; Yoosefinejad, Ata; Kumar, Vijay; Yazdani Nezhad, Hamed
    Raw data and calculation of Mode-I fracture toughness at initiation and propagation for different densities of electrospun nanofibres embedded for toughening of composite laminates
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    Ultra-thin electrospun nanofibers for development of damage-tolerant composite laminates
    (Elsevier, 2019-11-05) An, Donglan; Lotfian, Saeid; Mesbah, Daria; Ayre, David; Yoosefinejad, Ata; Thakur, Vijay Kumar; Yazdani Nezhad, Hamed
    The present article overcomes existing challenges in inter-laminar toughening of novel multifunctional fiber-reinforced polymer composites via development and embedment of highly stretched, ultra-thin electrospun thermoplastic nanofibers made of polyamide 6.6. The nanofibers exhibit significant enhancement of the composite laminate's structural integrity with almost zero weight penalty via ensuring a smooth stress transfer throughout the plies and serving tailoring mechanical properties in desired directions, with no interference with geometric features, e.g., thickness. The findings for 1.5 g per square meter electrospun nanofibers have demonstrated, on test coupon specimens, improvements up to 85% and 43% in peak load and crack opening displacement, respectively, with significant improvement (>25%) and no sacrifice of fracture toughness at both initiation and propagation phases. The initial stiffness for the modified specimens was improved by nearly 150%. The enhancement is mainly due to nanofibers contributing to the stiffness of the resin-rich area at the crack tip adjacent to the polytetrafluoroethylene (PTFE) film. Glass fiber-reinforced woven phenolic pre-impregnated composite plies have been modified with the nanofibers (each layer having an average thickness of <1 micron) at 0.5, 1.0, 1.5, 2.0 and 4.0 gsm, electrospun at room temperature on each ply, and manufactured via an autoclave vacuum bagging process. Inter-laminar fracture toughness specimens were manufactured for Mode I (double cantilever beam) fracture tests. It was found that there is threshold for electrospun nanofibers density, at which an optimum performance is reached in modified composite laminates. The threshold is influenced by the plastic deformation mechanism at the crack tip, the fiber bridging between the adjacent plies afforded by the nanofibers, and the density of the electrospun fibers. Such optimum performance was found linked to the nanofibers at a specific density. Excessively increasing above the threshold (herein >2.0 gsm) degrades the adhesion properties (chemical bonding) between glass fibers and the phenolic matrix. The density of nanofibers increases, so does the likelihood of forming a physical barrier between the plies resulting in the loss of resin flow and poor adhesion. Such an effect was evident from microscopic investigations and reduction in fracture toughness data at the initiation and propagation phases.
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    Underpinning Data for Article: Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints
    (Cranfield University, 2020-09-25 19:16) Yazdani Nezhad, Hamed; Bregar, Tadej; An, Donglan; Gharavian, Somayeh; Burda, Marek; Durazo-Cardenas, Isidro; Kumar, Vijay; Ayre, David; Sloma, Marcin; Hardiman, Mark; McCarthy, Conor
    The underpinning data for Research Article on Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints