November 8-12, 2015
The increasing need for efficient passenger aircraft led to the development of innovative lightweight designs and an increasing demand on new lightweight materials such as carbon fiber reinforced plastics (CFRP) in the recent decades. Due to the high weight specific mechanical properties and the relatively high cost of raw materials, semi-finished and manufacturing the use of CFRP is limited on high performance applications, especially for components of the primary structures of aircraft.
Subsequently, fiber reinforced plastics (FRP) are also used in cabin and interior. Due to lower mechanical loads, but high requirements on fire protection, optics, surface and acoustics sandwich structures are used in most cases. Generally, these sandwich structures are made of honey comb cores and top layers based on glass fiber fabrics impregnated by phenolic resin. However, higher complexity of the parts, directly integrated functions and the required surface properties for applying the decorative films or paintings can only be realized by a lot of manufacturing, finishing and assembly steps. In order to meet the increasing demands for lightweight structures for cabin and cargo applications the aerospace industry is working on improvements and developments of new materials, manufacturing processes and construction methods for secondary structures. One auspicious technology is the combination of Sheet Molding Compounds (SMC) with long fiber reinforcements and directed, pre-impregnated continuous fiber reinforcements, which are processed in a single-stage pressing and curing process to produce a new kind of hybrid composite components for aircraft. This hybrid composite technology is characterized by the realization of geometrically complex, highly functional and lightweight components with low process cycle times in the range of 30 to 180 seconds. Depending on the specific requirements and the application thermoset matrix systems based on unsaturated polyester, vinyl ester or epoxy resins can be used. The ability of full automation and the relatively high material usage in the range of 90 percent and higher make this technology economically efficient. In addition, the process obtains the possibility to integrate various functions directly. Coloring and the direct integration of metallic components such as inserts or nuts are only some examples for that. Time and costs for rework assembly and further process steps can be reduced due to the extended possibilities of functional integration and the higher complexity of the components. In addition, an optimized utilization of material and the possibility of using recycled carbon fibers from a pyrolysis process or dry chopped fibers from production waste obtain an increase of resource and energy efficiency. The carbon fibers may be reused as long-fiber reinforcements for veils. Due to the described potentials there are a lot of auspicious applications of this hybrid composite material for future aircraft cabins. Load carrying cabin monuments, highly functional storage systems for hand luggage, complex fittings, holders or brackets are only some exemplary applications. By the integration of continuous fiber reinforcements following the load paths of the appropriate component high lightweight potentials and also structural applications can be realized. However, the high requirements on fire, smoke and toxicity (FST) and the required lightweight specifications of cabin and cargo structures create huge challenges for the material and the process development.
This publication deals with the development of the combination of SMC and pre-impregnated, tailored carbon fiber reinforcements for cabin and cargo applications in aerospace industry. The main focusses are different investigations on the material properties and analyses of the manufacturing procedures of advanced SMC formulations based on unsaturated polyester resin with a high proportion of the inorganic flame retardant additives as well as aluminum trihydrate (ATH). Generally, a high degree of fire resistance additives has negative effects on the fiber-resin adhesion, the impregnation of the fibers and the flow behavior during the compression molding. Nevertheless, the findings on this hybrid composite technology obtain promising possibilities for functional integrations, lightweight constructions and the cost-efficient production of secondary structure aircraft components.
Marc Fette, "High efficient material and process combination for future aircraft applications based on advanced sheet molding compound technologies" in "Composites at Lake Louise (CALL 2015)", Dr. Jim Smay, Oklahoma State University, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/composites_all/20