Abstract

With the increase of composite deployment in many applications such as aerospace, automotive, and pipelines (to build a pipeline and to be wrapped around corroded steel pipelines to ensure their mechanical integrity), the demand for reliable high-performance composite repair increases. In most cases, composite repairs are applied using adhesives, where an adhesive joint between the structure and the repair is formed. This technique is applied today, but as a temporary solution and for secondary structures.  A major concern about adhesive joints is the low confidence of the joint due to low toughness and failure instability, which leads to catastrophic failure (once a crack initiated in the joint is propagated in an uncontrolled manner). Our objective is here to introduce a new strategy to enhance the toughness and failure stability of adhesive joints by creating crack arrest features during crack propagation.

Our strategy for enhancing the toughness was inspired by the biological adhesion adhesive system, the 𝑀𝑦𝑡𝑖𝑙𝑢𝑠 𝑐𝑎𝑙𝑖𝑓𝑜𝑟𝑛𝑖𝑎𝑛𝑢𝑠 (one of the sea livings), where it exhibits excellent bonding with high adhesion strength and toughness in the deep water due to the presence of wisely distributed voids in the protein bonding layer. Therefore, we mimicked the microstructure of this biological adhesion system, where we embed sacrificial cracks inside the adhesive layer that allows the generation of nonlocal dissipative mechanisms, which increases the fracture energy of the interface. We demonstrated the toughening effects and controlled crack propagation of this bio-inspired adhesive system for the fundamental fracture toughness modes in static and fatigue, mode I¹ and II², and semi-structure, T-joint³. Moreover, we extended this toughening strategy to toughen thermoplastic adhesive tapes, where we achieved a large enhancement in the shear strength and toughness of the tapes with three times longer fatigue life.

References

1. Wagih, A., Tao, R., & Lubineau, G. (2021). Bio-inspired adhesive joint with improved interlaminar fracture toughness. Composites Part A: Applied Science and Manufacturing, 149, 106530.‏
2. Wagih, A., & Lubineau, G. (2021). Enhanced mode II fracture toughness of secondary bonded joints using tailored sacrificial cracks inside the adhesive. Composites Science and Technology, 204, 108605.‏
3. Wagih, A., Hashem, M., & Lubineau, G. (2022). Simultaneous strengthening and toughening of composite T-joints by microstructuring the adhesive bondline. Composites Part A: Applied Science and Manufacturing, 162, 107134.‏

Location: Building 19, Level 3, Hall 1-2.