14 January, 2024
Monday, Jan 22, 2024
11:45 KSA time (GMT +3)
From Brittle to Tough Resilient Adhesive Bonded Joints through Microstructuring the Adhesive Bondline
By Dr. Ahmed Wagih
Senior research scientist at the Mechanics of Composites for Energy and Mobility (MCEM) lab. at King Abdullah University for Science and Technology (KAUST).
Abstract
An adhesive is a material used to join two surfaces permanently/temporarily through adhesive bonding. It can be used to join metals, ceramics, plastics, and dissimilar materials and can be formulated in a conductive material. The use of adhesive bonding has widely increased in the last two decades, both in heavy industries such as aerospace and automotive and light industries such as hygiene, home appliances, and interior decoration. A major concern about adhesive joints is the low confidence of the joint due to its low toughness and brittleness (failure instability), which leads to catastrophic failure (once a crack initiated in the joint is propagated in an uncontrolled manner). The objective here is to introduce a new strategy to enhance the toughness and failure stability of adhesive joints by creating crack arrest features during crack propagation.
The strategy for enhancing the toughness and failure stability 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 allow 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 I [1] and II [2], and semi-structure, T-joint [3]. 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. Additionally, this technique has attracted the adhesive tape industry due to its effectivity and simplicity of implementation in production lines. Currently, we are working together with one of the major players in the adhesive tape industry (Lohmann gmbh &Co) to develop this technology using their production lines. The project is now at the considered technology readiness level (TRL4), where we demonstrated the technology using a pilot line at their R&D facility, and is on its way towards TRL6.
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.