NEW MULTIFUNCTIONAL HYBRID POLYMER COMPOSITES REINFORCED BY CARBON AND STEEL FIBERS

The challenges of society and politics for next generation aircraft are highly ambitious. On top of major improvements in the field of aerodynamic and propulsion technology, significant advancements of the airframe structure are required. Efforts must focus on manufacturing efficiency as well as on breakthrough solutions for damage tolerance and function integration. Compared to aluminum alloys, contemporary CFRP solutions for airframe structures offer poor electrical conductivity. Additional metal elements are necessary to fulfill important electrical functions (e.g., lightning strike protection, electromagnetical shielding, electrical bonding and grounding), compromising CFRP's lightweight potential. Moreover, CFRP shows brittle failure behavior, limiting the structural integrity in crash load cases. The limited damage tolerance against probable impact events also leads to a minimum wall thickness criterion. Against this background, a new hybrid composite material consisting of reinforcing carbon and metal fibers embedded in an epoxy matrix is investigated. Basic idea of this material concept is to merge electrical and load-bearing functions by incorporated highly conductive and ductile stainless steel fibers. The increased density of the composite is overcompensated by eliminating the need for additional electrical system installation items and the enhanced damage tolerance, resulting in a reduced minimum wall thickness. The present study focus on optimizing the electrical and mechanical properties of the composite. Material tests are conducted on unidirectional coupons with different steel fiber volume fractions to demonstrate the potential of this novel hybrid composite.