Truss Reinforced Foam Core Sandwich Structures Using the Z-Fiber Process

Honeycomb sandwich structures used in aircraft are particularly susceptible to impact damage which creates a path for moisture intrusion. Moisture condensing on the exterior is forced into the core during descent causing corrosion, bondline degradation, reduced structural performance. Sandwich structures can be used in primary wing and fuselage components, if improved damage tolerant core materials are developed. Foster-Miller's truss reinforced foam core (TRFC) concept combines the strength of aluminum honeycomb with the resistance to moisture intrusion of closed cell foam. Our concept uses structural foam, reinforced with a network of small diameter truss members about 10 mils in diameter. Analysis predicts shear strength exceeding that of aluminum honeycomb. Our initial tests of this structure show that the truss network dramatically improves the load capacity of the foam sandwich with minimal increase in weight. TRFC sandwich panels are made using Foster-Miller's proprietary z-fiber process. This proven process can be used to produce the desired structures during a standard autoclave cure cycle. Its use will permit fabrication cost reductions relative to honeycomb since it eliminates machining of the honeycomb and secondary bonding of the facesheets. Lockheed will assist in Phase I to insure approaches developed are relevant to future aircraft and integrate with their Robost Composites Structures proposal.