A hybrid bondline concept for bonded composite joints

Abstract

Based on the experience in the past and the occurrence of in-service damages, the authorities restrict today the application of adhesive bonding of composite structures for aircraft applications. However, certification limitations can be overcome if occurring disbonds within a bond are stopped by implemented design features, so called disbond stopping features. Consequently, a novel bondline architecture for bonded composite joints is proposed. By implementing a distinct rather ductile thermoplastic phase, a physical barrier for growing disbonds is obtained and thus a fail-safe design, respectively. Moreover, the joint is established by using two different joining technologies, namely adhesive bonding and thermoset composite welding. A sophisticated manufacturing technique is developed for the hybrid bondline concept to achieve a high strength joint. The joint's quality is examined by means of several analytical methods like microsections, scanning electron microscopy (SEM), and energy-dispersive X-Ray (EDX) analysis. Additionally, the mechanical performance is evaluated by static Double Cantilever Beam (DCB) and Single Lap Shear (SLS) tests.