PSI - Issue 52

Francisco de Sá Rodrigues et al. / Procedia Structural Integrity 52 (2024) 719–729

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F. de Sa´ Rodrigues et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 3: Cure Monitoring results for the di ff erent spaced IDT finger

monitoring of the adhesive bonding of both CFRP ends is inspected to determine in situ the presence of impurities and defects on the cure monitoring which prevent achieving an uniform bondline. The IDTs were inkjet printed to the Kapton using the same procedure and settings as those described in the previous section. However, for monitoring the adhesive curing between the CFRP surfaces in the single lap joint, a procedure is required for transferring the Kapton printed section to the CFRP surface since, otherwise, this technique would not be applicable to large structure with more complex shapes incapable of fitting in the printer. Previously, the proposed cure monitoring methodology by directly printing on top of the CFRP substrate was validated in single lap joints Bekas et al. (2019) and scarf repaired coupons Bekas et al. (2019). For transferring the inkjet circuit from the substrate to the host surface whilst providing electrical isolation between the carbon fibres and the electric circuits, a thermoplastic film was placed between the printed Kapton layer (with the circuit side facing down) and the substrate. The assembly was heated to the curing thermoplastic’s temperature. After curing is finalized, the thermoplastic is cooled down to room temperature quickly and the Kapton layer is peeled o ff whilst the inkjet printed circuits remain attached to the thermoplastic film. Application of specific temperature conditions in industrial context requires using portable instruments capable of adapting to complex shapes unlike laboratorial ovens. In this work, the Anita Repair console (by GMI Aero) is employed for applying the necessary thermal cycles by placing the heating blankets on the di ff erent components. The employment of heating blankets revealed some challenges associated to the inherent functioning of the com mercial instruments which required circumventing if the inkjet printing procedure is to be applied in large structure. The electric impulses supplied by the Anita console for the heating blanket to follow the programmed curing cycle occurred close to the frequency range of interest for cure monitoring which severely a ff ected the impedance mea surements in the region of interest, as seen in Figure 4, which would render the current procedure unusable given the incapability to accurately distinguish maximum of in the right range. To minimize the influence of the Anita Console in the measurements, the heating blanket was wrapped with Alu minium foil tape (3M 425 Conductive Aluminium Tape) which simulated a Faraday box and erased the electromag netic e ff ects from the heating blanket in the resin’s cure monitoring. Furthermore, a banana connector was attached to the Aluminium and connected to the ground port present in the Impedance Analyzer. 4.1. Anita Console Resonance e ff ect