Composite materials are increasingly used in the aviation industry for various products. They introduce high strength and stiffness, yet low weight. Bonded composites are even more attractive, since usage of such assembly concept may lead to further weight and cost reductions, as well as faster assembly, which is essential in future aviation products. Development of reliable cohesive failure criteria are needed for design of bonded structures to be used by the aviation industry. This study presents a comprehensive testing campaign of bonded composites, conducted for three different bond line thicknesses with a variety of mode mixities. EA 9394 paste adhesive, was investigated. The Mixed Mode Bending (MMB) test specimen was used. FE simulations were executed to obtain the stress distributions in the vicinity of the disbond tips, leading to establishment of a macroscopic stress-based failure envelope for different mode mixities and bond line thicknesses.