Browsing by Keyword "Epoxy resins"
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Item Corrosion and environmental degradation of bonded composite repair(2013) Gkikas, G.; Paipetis, A.; Lekatou, A.; Barkoula, N. M.; Sioulas, D.; Canflanca, B.; Florez, S.; SG; POLIMEROSPurpose - Bonded composite patches are ideal for aircraft structural repair as they offer enhanced specific properties, case-tailored performance and excellent corrosion resistance. Bonding minimizes induced stress concentrations unlike mechanical fastening, whilst it seals the interface between the substrate and the patch and reduces the risk of fretting fatigue that could occur in the contact zone. The purpose of this paper is to assess the electrochemical corrosion performance and the environmentally induced mechanical degradation of aerospace epoxy adhesives when carbon nanotubes (CNTs) are used as an additive to the neat epoxy adhesive. Design/methodology/approach - The galvanic effect between aluminium substrates and either plain or CNT enhanced carbon fibre composites, was measured using a standard galvanic cell. Also, rest potential measurements and cyclic polarizations were carried out for each of the studied systems. The effect of the CNT introduction to a carbon fiber reinforced plastic (CFRP) on the adhesion efficiency, before and after salt-spraying for 10, 20 and 30 days, was studied. The adhesion efficiency was evaluated by the single lap joint test. Findings - The corrosion behaviour of the system is polymer matrix type dependent. CNT introduction to a CFRP may induce small scale localized degradation. Originality/value - This paper fulfills an identified need to study how the shear strength and the response to galvanic corrosion are affected by epoxy resins modified by carbon nanotubes.Item Diagnosis of failures in epoxy-mica insulating systems by means of partial discharges analysis and finite element models(Institute of Electrical and Electronics Engineers Inc., 2003) Sorí, S. S.; Caminero, M. C.; Melero, M. G.; Cabanas, M. F.; Kortajarena, A.; Rojas, C. H.; Orcajo, G. A.; GeneralesEoxy-mica insulating systems are widely used in the construction of all type of electrical machines. This kind of insulation is usually built into large machines using a "resin rich" process. This process involves the application of mica paper tapes that have been impregnated with epoxy resin. These pre-impregnated tapes are then consolidated by confining coils in molds while applying heat and pressure or by using an autoclave where the coil is vacuum and pressure treated while it is enclosed in molds and then cored. During the manufacturing processes small defects caused by irregularities or by incorrect control of pressure or temperature during the pressing and curing process can appear in the wrapping of the insulating tape. These small defects which might not be detected during the fabrication process, reduce the coil's useful life and resistance to environmental, mechanical, thermal and electric stresses applied to the machine during its industrial operation. For this reason, this paper presents a preliminary study to obtain the characteristic partial discharge patterns related to different kind of defects in test specimens of mica-epoxy insulating form-wound coils. Several finite element models have been developed in order to obtain the electric field distributions caused by different type of failures in epoxy-mica form-wound coils. The results of this study allowed the construction of a complete set of epoxy-mica specimens where the simulated failures were applied. These specimens have been later tested using partial discharge analysis in order to obtain the discharge pattern related to each type of failure.