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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(b)

(a)

Insulation Layer Thermoplastic Kapton

(c)

(d)

Fig. 8: Microscope sections for embedded circuit: (a) laminate section; (b) inkjet circuit detail ; (c) insulating and bonding area ;and (d) insulating and bonding area

an area correspondent to two tracks (two laminae). Location 3 corresponds to a more sensitive area of the patch given it’s proximity to the wire extraction and the generation of peel-stresses from the adhesive. The single impact on this location resulted in the immediate disconnection to the track from the impact event, indicated by the sudden increase in the resistance for both tracks 3 and 4. The results presented in the current impact campaign reinforce the multiple capabilities provided by the embedding of the inkjet printed tracks both for process- and operation-monitoring given the damage detection capabilities for both small and failure events.

6. Conclusion

This work reports on the development of an industrial procedure for bonding inkjet printed circuits for Impedance Spectroscopy during an adhesive’s curing which permits the upscaling of the bonded repair procedure to large struc tures requiring repairs of any shapes given the printing capabilities. Industrial challenges arising from the instrumentation employed for performing the bonded repair in large aircraft structures are highlighted and circumvented with simple workshop solutions. The methodology enabled monitoring the curing process of adhesives by measuring the electrical particle charge transmission during the gelation and vitri fication process of the resin film through Impedance Spectroscopy. The inkjet circuit’s final application was validated on a flat repaired coupon with a consistent trend reported for each laminae’s IDTs which reinforced the achievement of a uniform bondline. Finally, the damage detection capabilities for BVID in the patch area were demonstrated alongside the circuits capabilities to monitor the increase in severity of existing damages by sequential impacts in the same location. The results demonstrated throughout this roadmap show the benefits of implementing embedded inkjet-printed circuits for monitoring the curing of bonded repair patches given its capabilities for ensuring repeatable procedures for monitoring the adhesive’s cure and the capabilities to detect locations where defects prevent uniform curing. Finally, the detection of damages due to impacts on the patch location are also provided by the current solution. This reinforces the employment of bonded repair patches in primary aircraft structures.