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Condition monitoring of damage in the reinforced adhesive joints by CNT and GNP

Omid Sam-Daliri PhD Candidate, School of mechanical engineering, University of Tehran, IRAN Guest researcher at AAU and CTR

Abstract: Nowadays, the employment of adhesives in assembling of similar and dissimilar parts in engineering structures increases considerably. The traditional mechanical fastening approaches, such as bolted and screw joints lead to a stress concentration in the fastening hole which can weaken the joint and cause premature failures. In addition, in metallurgical joints, like the welding joint, defects and residual stresses can be observed around the welding line, induced from heat treatment during the manufacturing process which diminishes the mechanical performance of the welded joint. Hence, adhesive bonding is often used for sensitive structures like in aircraft and naval applications, assembly of tubes in oil and gas industrials, etc. However, a disadvantage of the adhesive joint is its inability to be disassembled for evaluation of underlying damages by nondestructive methods. Non-Destructive Testing (NDT) evaluations are applied for the inspection of adhesive joints, to ensure their integrity after assembly or also used for condition monitoring of the adhesive joints during their service life. Understanding damage in adhesively-bonded joints is further complicated by the difficulty in detecting the onset and progression of joint damage due to delamination or adhesive cracking. The development of strategies for sensing of damage in situ will help to elucidate the initiation and progression of damage and ultimately enable more accurate life prediction and assessment of long-term durability. The emergence of nanotechnology has enabled the tailoring of a variety of functional properties. Recent researches address carbon nanotubes and graphene nanoplates for structural health monitoring of composites, because they have exceptional mechanical stiffness and strength, as well as excellent electrical conductivity and piezoresistivity. In this presentation, we will talk about the results of our experiments which are conducted by the impedance measurement method to analyze the sensing capability of adhesive joints made with carbon nanotube and Graphene nanoplates. Firstly, we will present how to make a smart adhesive with good sensing capability. Then we will use of this adhesive for condition monitoring of single lap adhesive joint and Mode-I fracture energy test (opening mode or DCB test). Also, the correlation between the electrical response and mechanical behavior will be presented. In summary, it has been observed that electrical resistance increases with mechanical strain in single lap adhesive joints due to tunneling effect or contact mechanism on CNT and GNP networks. On Mode-I tests, it has been observed also an increase of electrical resistance with delamination extension along the bonding line. Thus, it is possible to see a clear correlation between impedance response and mechanical behavior for prediction of fracture behavior in SLJ or damage propagation in adhesive joints.

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