Increased Stiffener Pull-Off Strength Through Enhanced 2D to 3D Joints

The design and development of a co-cured stiffened skin structure with high strength stiffener to skin joints without the requirement of fasteners is a goal of aircraft designers. Foster-Miller has developed enabling technology that will help designers achieve this goal and to fully realize the potential of advanced composites in airframe design. Lockheed Martin Tactical Aircraft Systems and Foster-Miller have been aggressively addressing these needs to develop innovative stiffener design and attachment technologies. The results achieved to date have demonstrated a 400 to 500% increase in stiffener pull-off strengths over conventional approaches through the use of advanced inserts with Z-Fiber through thickness reinforcement. These increases provide the potential to radically reduce the number of blades or hats required in stiffened skin applications as well as dramatically improving the load transfer from the skin to the stiffener. We propose in Phase I to investigate how the inserts and Z-Fiber interact in a stiffener to develop the understanding required to design the next generation airframe. In addition, we will investigate the use of Z-Fiber with advanced inserts to construct novel hat stiffeners. A Phase II effort will produce a design guide specific to the JSF aircraft.