PSI - Issue 52

ScienceDirect Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2023) 000–000 Available online at www.sciencedirect.com Available online at www.sciencedirect.com Available online at www.sciencedirect.com Available online at www.sciencedirect.com Procedia Structural Integrity 52 (2024) 719–729 Structural Integrity Procedia 00 (2023) 000–000 Structural Integrity Procedia 00 (2023) 000–000

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© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Professor Ferri Aliabadi Abstract Composite repair solutions are applied to recover the strength and functionality of composite structures in service without having to replace the whole structural part which is impractical for large sections. However, such bonded repairs are still not implemented in primary aircraft structures given the inability to provide repeatable results, ensure uniform bondline and the absence of non destructive testing methods for detecting poor bond. In this paper, a dielectric-based technique is proposed to monitor the curing of composite bonded repairs based on Impedance Spectroscopy using smart patches embedded in the laminate by relying on drop-on demand inkjet printed circuits which provided indicators of the polymer’s curing stage whilst introducing minimal thickness in the bondline. The inkjet printed circuit is bonded to the composite plates using a newly developed procedure for high-level applications. The experimental campaign followed a building block approach to iteratively upscale the information from single printed IDTs in polymeric films to large circuits bonded to repaired composite parts with multiple tracks and IDTs. Numerous parameters were explored with the respective influence on the cure monitoring procedure of the thermoset adhesive layer, like the IDT design, the presence of imperfections at the bondline and instrumentation noise. Finally, the embedded smart patch was successfully employed for the detection of multiple impact damages and respective severity on the repair patch. Keywords: Inkjet printing; Cure Monitoring; Structural Health Monitoring; Electromechanical Impedance Spectroscopy; Composite Step-Sanded Repair; Fracture, Damage and Structural Health Monitoring Smart Patch repair solution for cure monitoring of bonded repairs in composite aircraft structures Francisco de Sa´ Rodrigues a, ∗ , Dimitrios G. Bekas b , Zahra Sharif Khodaei a , Ferri M.H. Aliabadi a a Imperial College London, South Kensington, London SW7 2BX, United Kingdom b Department of Materials Science & Engineering, University of Ioannina, Ioannina, 45110, Greece Abstract Composite repair solutions are applied to recover the strength and functionality of composite structures in service without having to replace the whole structural part which is impractical for large sections. However, such bonded repairs are still not implemented in primary aircraft structures given the inability to provide repeatable results, ensure uniform bondline and the absence of non destructive testing methods for detecting poor bond. In this paper, a dielectric-based technique is proposed to monitor the curing of composite bonded repairs based on Impedance Spectroscopy using smart patches embedded in the laminate by relying on drop-on demand inkjet printed circuits which provided indicators of the polymer’s curing stage whilst introducing minimal thickness in the bondline. The inkjet printed circuit is bonded to the composite plates using a newly developed procedure for high-level applications. The experimental campaign followed a building block approach to iteratively upscale the information from single printed IDTs in polymeric films to large circuits bonded to repaired composite parts with multiple tracks and IDTs. Numerous parameters were explored with the respective influence on the cure monitoring procedure of the thermoset adhesive layer, like the IDT design, the presence of imperfections at the bondline and instrumentation noise. Finally, the embedded smart patch was successfully employed for the detection of multiple impact damages and respective severity on the repair patch. Keywords: Inkjet printing; Cure Monitoring; Structural Health Monitoring; Electromechanical Impedance Spectroscopy; Composite Step-Sanded Repair; Fracture, Damage and Structural Health Monitoring Smart Patch repair solution for cure monitoring of bonded repairs in composite aircraft structures Francisco de Sa´ Rodrigues a, ∗ , Dimitrios G. Bekas b , Zahra Sharif Khodaei a , Ferri M.H. Aliabadi a a Imperial College London, South Kensington, London SW7 2BX, United Kingdom b Department of Materials Science & Engineering, University of Ioannina, Ioannina, 45110, Greece Abstract Composite repair solutions are applied to recover the strength and functionality of composite structures in service without having to replace the whole structural part which is impractical for large sections. However, such bonded repairs are still not implemented in primary aircraft structures given the inability to provide repeatable results, ensure uniform bondline and the absence of non destructive testing methods for detecting poor bond. In this paper, a dielectric-based technique is proposed to monitor the curing of composite bonded repairs based on Impedance Spectroscopy using smart patches embedded in the laminate by relying on drop-on demand inkjet printed circuits which provided indicators of the polymer’s curing stage whilst introducing minimal thickness in the bondline. The inkjet printed circuit is bonded to the composite plates using a newly developed procedure for high-level applications. The experimental campaign followed a building block approach to iteratively upscale the information from single printed IDTs in polymeric films to large circuits bonded to repaired composite parts with multiple tracks and IDTs. Numerous parameters were explored with the respective influence on the cure monitoring procedure of the thermoset adhesive layer, like the IDT design, the presence of imperfections at the bondline and instrumentation noise. Finally, the embedded smart patch was successfully employed for the detection of multiple impact damages and respective severity on the repair patch. Keywords: Inkjet printing; Cure Monitoring; Structural Health Monitoring; Electromechanical Impedance Spectroscopy; Composite Step-Sanded Repair; Fracture, Damage and Structural Health Monitoring Smart Patch repair solution for cure monitoring of bonded repairs in composite aircraft structures Francisco de Sa´ Rodrigues a, ∗ , Dimitrios G. Bekas b , Zahra Sharif Khodaei a , Ferri M.H. Aliabadi a a Imperial College London, South Kensington, London SW7 2BX, United Kingdom b Department of Materials Science & Engineering, University of Ioannina, Ioannina, 45110, Greece Abstract Composite repair solutions are applied to recover the strength and functionality of composite structures in service without having to replace the whole structural part which is impractical for large sections. However, such bonded repairs are still not implemented in primary aircraft structures given the inability to provide repeatable results, ensure uniform bondline and the absence of non destructive testing methods for detecting poor bond. In this paper, a dielectric-based technique is proposed to monitor the curing of composite bonded repairs based on Impedance Spectroscopy using smart patches embedded in the laminate by relying on drop-on demand inkjet printed circuits which provided indicators of the polymer’s curing stage whilst introducing minimal thickness in the bondline. The inkjet printed circuit is bonded to the composite plates using a newly developed procedure for high-level applications. The experimental campaign followed a building block approach to iteratively upscale the information from single printed IDTs in polymeric films to large circuits bonded to repaired composite parts with multiple tracks and IDTs. Numerous parameters were explored with the respective influence on the cure monitoring procedure of the thermoset adhesive layer, like the IDT design, the presence of imperfections at the bondline and instrumentation noise. Finally, the embedded smart patch was successfully employed for the detection of multiple impact damages and respective severity on the repair patch. Keywords: Inkjet printing; Cure Monitoring; Structural Health Monitoring; Electromechanical Impedance Spectroscopy; Composite Step-Sanded Repair; The benefits of incorporating composite materials in next generation aircraft structures involve their improved me chanical performance whilst yielding components with lower weights and manufacturing procedures for more com plex shapes and improved fuel consumption costs. As the aircraft progresses through its normal life cycle, transverse impact events generate delaminations and debondings in the composite material which can compromise its integrity and safe operation. In these situations, the structure requires adequate repair for which bonded solutions do not sat isfy the current requirements for primary aircraft structures given the inability to ensure repeatable bondline and the limitations of current non-destructive technologies for detecting weak bonds. In these locations, bolted solutions are Fracture, Damage and Structural Health Monitoring Smart Patch repair solution for cure monitoring of bonded repairs in composite aircraft structures Francisco de Sa´ Rodrigues a, ∗ , Dimitrios G. Bekas b , Zahra Sharif Khodaei a , Ferri M.H. Aliabadi a a Imperial College London, South Kensington, London SW7 2BX, United Kingdom b Department of Materials Science & Engineering, University of Ioannina, Ioannina, 45110, Greece www.elsevier.com / locate / procedia 1. Introduction 1. Introduction 1. Introduction The benefits of incorporating composite materials in next generation aircraft structures involve their improved me chanical performance whilst yielding components with lower weights and manufacturing procedures for more com plex shapes and improved fuel consumption costs. As the aircraft progresses through its normal life cycle, transverse impact events generate delaminations and debondings in the composite material which can compromise its integrity and safe operation. In these situations, the structure requires adequate repair for which bonded solutions do not sat isfy the current requirements for primary aircraft structures given the inability to ensure repeatable bondline and the limitations of current non-destructive technologies for detecting weak bonds. In these locations, bolted solutions are The benefits of incorporating composite materials in next generation aircraft structures involve their improved me chanical performance whilst yielding components with lower weights and manufacturing procedures for more com plex shapes and improved fuel consumption costs. As the aircraft progresses through its normal life cycle, transverse impact events generate delaminations and debondings in the composite material which can compromise its integrity and safe operation. In these situations, the structure requires adequate repair for which bonded solutions do not sat isfy the current requirements for primary aircraft structures given the inability to ensure repeatable bondline and the limitations of current non-destructive technologies for detecting weak bonds. In these locations, bolted solutions are 1. Introduction The benefits of incorporating composite materials in next generation aircraft structures involve their improved me chanical performance whilst yielding components with lower weights and manufacturing procedures for more com plex shapes and improved fuel consumption costs. As the aircraft progresses through its normal life cycle, transverse impact events generate delaminations and debondings in the composite material which can compromise its integrity and safe operation. In these situations, the structure requires adequate repair for which bonded solutions do not sat isfy the current requirements for primary aircraft structures given the inability to ensure repeatable bondline and the limitations of current non-destructive technologies for detecting weak bonds. In these locations, bolted solutions are ∗ Corresponding author. Tel.: + 44 7712280432; E-mail address: f.rodrigues20@imperial.ac.uk Structural Integrity Procedia 00 (2023) 000–000

∗ Corresponding author. Tel.: + 44 7712280432; E-mail address: f.rodrigues20@imperial.ac.uk ∗ Corresponding author. Tel.: + 44 7712280432; E-mail address: f.rodrigues20@imperial.ac.uk

2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Professor Ferri Aliabadi 10.1016/j.prostr.2023.12.072 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of Professor Ferri Aliabadi. 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of Professor Ferri Aliabadi. ∗ Corresponding author. Tel.: + 44 7712280432; E-mail address: f.rodrigues20@imperial.ac.uk 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of Professor Ferri Aliabadi. 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of Professor Ferri Aliabadi.