Foxtail Wedged Composite Joint Design

The ARMY’s objective is to develop novel composite joints for aircraft skin-to-frame connections. The proposed solution combines a traditional wood joining technique known as wedged mortise and tenon joint (Foxtail Wedged Joint) with advanced carbon fiber technology and the latest composite airframe. The wedge design exploits the most favorable loading conditions for composites by avoiding pure shear forces and working in compression, relying entirely on geometric constraint and does not require through-thickness fasteners or adhesive bonding. The main elements of the innovative joint designs are a 1. new hat stringer design, co-cured with the skin, 2. a frame structure with mating holes for the stringers (similarly to the 787 airframe design) and a self lock wedge mechanism. This joint design is reversible and applicable to both flat and curved geometries. Further it meets all the criteria required with the wedge as the keystone of the design:  Inspectable: wedge can be removed and inspected for physical damage; or through NDT.  Maintainable: wedge is removable and easily replaced during maintenance.  Affordable: joint installation will be much faster as riveting is eliminated.  Durable: wedge design is self-locking, made of a damage tolerant material and replaced based on flight hours.