In structural bonds, the interface between adherend and adhesive is nearly two-dimensional making it susceptible to minute quantities of contamination, which can cause weak bonds. No methods currently exist to nondestructively measure the strength of an adhesive bond. For these reasons, government organizations such as the Federal Aviation Administration (FAA) often require redundant load paths in secondary-bonded, primary-structures to achieve certification for civil transport aircraft. To meet this requirement, manufacturers commonly install redundant fasteners (~10<sup>5</sup> fasteners in a twin-aisle airframe with composite fuselage and wings) which add tremendous complexity, time and cost, and significantly reduce performance of the airframe. Under NASA’s Convergent Aeronautics Solutions (CAS) Program, the Adhesive Free Bonding of Composites (AERoBOND) project is investigating reformulated aerospace epoxy matrix resins to enable reflow and diffusion of the resin at the interface during a secondary bonding/cure process. The mixing process eliminates the material discontinuity at the interface, thereby removing the dependence of bond performance on adhesion at a nearly two-dimensional boundary. The AERoBOND interface is equivalent to the interlaminar region obtained during a co-cure process, so joint performance is evaluated by the cohesive properties of the matrix resin, which can be measured, inspected non-destructively, and certified for flight with fewer redundant fasteners. This presentation describes the ongoing development of stoichiometrically-offset epoxy resins to control the degree of cure in composite joints and enable interfacial mixing during secondary bonding/curing. Details on the resin formulation, laminate fabrication, and mechanical testing will also be presented.

Modified epoxy matrix resins for reduced dependence on redundant fasteners in secondary-bonded composite structures

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.