Because of possible failure mechanisms integral ribs are commonly used at the aircraft's lower side where a mainly compressive stress state occurs. An advanced integral rib design with increased safety against cracking initiation, crack grow, and a high remaining resistance after failure can compensate the disadvantages of the common structures to make them applicable also in tension-stressed parts of the upper aircraft side. As an example for a failure mechanism based on crack initiation and crack growth in airplane structures the crashes of several De Havilland COMET I in the 1950s can be regarded. Also, aircraft bodies must show a strong resistance against damage by foreign objects like birds or parts of turbines damaged during a flight. The structures have to show redundant loading paths which can be activated when the primary load path fails. In combination with high residual strength of the structure a failure-proof design must be obtained. This leads to the need for damage-tolerant properties of structures which enable an increasing residual strength. The production of continuously reinforced metallic profiles produced, for example, by composite extrusion offers the possibility to increase this strength by combining the aluminum profile with one or more wires of high strength steel. Embedding the endless wires or wire ropes in aluminum stringer profiles by a composite extrusion process offers the potential to increase not only the profile's strength, but also stiffness and resistance against crack growth in case of failure. Within the project 'Improvement of material and part properties of aircraft ribs by composite extrusion' of the Collaborative Research Center SFB/TR 10, funded by the German Research Foundation (DFG), the process will be transferred to aluminum aircraft stringer profiles in order to analyze the increase in resistance against cracking and crack growth. To analyze the process usability under close-to-market conditions, the project is kindly supported by EADS Innovation Works, Alcan, Alcoa, Alu Menziken, Aleris, Sandvik Materials Technology, and VAC Vacuumschmelze. Each partner supports the project either with material, testing facilities, or process knowledge to develop, produce, and analyze the composite extruded profiles and their behavior in usage when mounted on an aircraft skin.
Improved properties of aircraft stringer profiles by composite extrusion
2007
8 Seiten, 9 Bilder, 7 Quellen
Aufsatz (Konferenz)
Englisch
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