title: Circularity-engineering approach for value-retention of high-performance thermoplastic composites by ultrasonic-assisted technologies
Creators: name: Balle, Frank
Publisher: name: Albert-Ludwigs-Universität Freiburg
Year: 2025

description: Over the past decade, the aerospace industry has increasingly focused on recycling end-of-use (EoU) or scrap composites. Traditional recycling methods, however, fail to preserve critical physical properties of the composites, such as fiber length, orientation, and part size [1]. As a result, there is a growing need for a circularity approach that facilitates the recovery and reuse of these materials in high-performance applications. The primary challenge lies in separating the fiber layers from the matrix without causing significant damage, thus allowing the recovered layers to be reused as patches for repairing damaged aerospace composite structures or creating tailored laminates. Preliminary investigations have explored the viability of using power ultrasonics to enable value-retention processes of carbon and glass fiber composites [1-3]. Power ultrasonics provide a means of separating the composite layers through ultrasonic-assisted cutting, followed by the reconsolidation of the separated layers to other components via ultrasonic bonding. This process consists of four key stages to achieve near-complete recovery of high-performance thermoplastic composites: (i) ultrasonic-assisted pre-cracking [4], (ii) ultrasonic layer separation, (iii) layer characterization, and (iv) ultrasonic reconsolidation. Compared to traditional mechanical separation methods, the use of power ultrasonics minimizes damage to fiber bundles and the residual matrix during the layer separation process. Additionally, ultrasonic reconsolidation shows potential for joining the separated layers to tailored or even damaged composite components. The successful optimization of ultrasonic pre-cracking and reconsolidation parameters is crucial for enhancing the mechanical performance of the composite joints. With appropriate parameter adjustments, power ultrasonics hold significant promise as a tool for the recovery and reintegration of EoU or scrap thermoplastic composites in engineering applications.

References:
[1]	Balaji Ragupathi, Matthias Florian Bacher, Frank Balle, 2023. First efforts on recovery of thermoplastic composites at low temperatures by power ultrasonics. Cleaner Materials 8. https://doi.org/10.1016/j.clema.2023.100186

[2]	Balaji Ragupathi, Matthias Florian Bacher, Frank Balle, 2023. Separation and Reconsolidation of thermoplastic glass fiber composites by power ultrasonics. Resources, Conservation and Recycling 198. https://doi.org/10.1016/j.resconrec.2023.107122

[3]	Balaji Ragupathi, Frank Balle, 2024, Characterization of glass-fiber reinforced thermoplastic composite after ultrasonic reconsolidation. European Journal of Materials, Volume 4(1), 2313316. https://doi.org/10.1080/26889277.2024.2313316


[4]	Balaji Ragupathi, Puneeth Jakkula, Michael Rienks, Frank Balle, 2024. Online monitoring of pre-crack initiation in carbon-fiber-reinforced thermoplastic composites by an ultrasonic cutting tool using high-speed optical imaging and infrared thermography. Ultrasonic 143, 107411 https://doi.org/10.1016/j.ultras.2024.107411