Surface Toughening – An industrial Approach to increase the Robustness of pure adhesive Joints with film adhesives

Bonding is known for its wide range of advantages over bolted joints when joining different materials together. Nevertheless, disadvantages of a bonded joint can quickly occur if the bonded joint is subjected to higher loads. This problem is particularly well known in aviation. Highly loaded components are structurally bonded by a combination of rivets and adhesive in order to underline the advantages of structural adhesive bonding with the safety of the well-known bolted joints. Known as fail-safe design, this concept is damage tolerant and more robust against manufacturing defects through a secured double load path. Especially when joining fiber-reinforced composites, bolts weaken the adherends of the joint and only contribute to load transfer when the brittle adhesive fails [1]. With the help of Surface Toughening [2], a boltless technique for reducing stress concentrations and arresting cracks in adhesive bonded joints is available. This work describes the industrial application of this technique. Starting with coupon tests and a small scale demonstrator to ensure the compatibility with industrial manufacturing processes, such as infusion and prepreg manufacturing, a large scale demonstrator of a 2m CFRP HTP leading edge with hybrid laminar flow control is manufactured by the industrial partner AERnnova. Verifying a simple and cost-effective application of the technology, Surface Toughening enables robust bonded joints with a minimum impact on today's process of adhesive bonding. [1] E. Paroissien, et al., Int. J. Adhes. Adhes.,77,p.183-197,(2017). [2] M.J. Schollerer, et al., J. Adhes., 95:5-7, p.495-514, (2019)