Investigation of bolted/bonded composite joint behaviour using design of experiments

Abstract Bonded joint technology is still not widely applied in primary aircraft structures due to the difficulty in meeting civil aviation certification requirements. Adding fasteners to create a hybrid fail-safe joint is one of the design features that can be used to meet the current civil aviation substantiation requirements for bonded joints. However, hybrid (bolted/bonded) composite joint technology is currently in early stages of development as compared to bonded or bolted aircraft joints for composites. The aim of this research was to evaluate the effect of several factors quantitatively on the hybrid joints strength by applying the design of experiments (DOE) methodology. The studied factors included adherend thickness, adhesive modulus, adhesive thickness, clamping area and bolt-hole clearance. It was found that the hybrid joints were stronger than the bolted or bonded joints, and the crack arrest capability due to the hybridization was captured experimentally. Finally, the ANOVA results showed that the hybrid joint strength is mainly driven by the adherend thickness, adhesive mechanical properties and bolt-hole clearance.