A. Shanygin
Central Aerohydrodynamic Institute (TsAGI), Zhukovsky, Moscow Region, Russia
Keywords: composite airframes, multidisciplinary design, resins, structure weight estimation, non-conventional concepts.
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The investigation of the main problems of strength for composite structures of different design concepts is the subject of this paper. In this paper the relationship between weight efficiency of composite structures and ultimate strength-strain characteristics of resins was analysed. The following two critical parameters have been chosen as the base parameters for the resin: the value of maximum tensile strain and maximum tensile stress.
The results of investigation of composite aircrafts have shown that using current composite materials containing carbon fibre with characteristics of specific strength ten times higher in comparison with metals has given no significant benefits in structure weight saving. The main reason of it is rather low stress-strain physical characteristics of current resins, which are usually used in composites as binders.
A number of investigations of conventional laminar composite structures described in the paper showed the low efficiency of high-strength carbon fibre and consequently low benefits in weight saving of composite structures not only for tensile parts of airframes but also for those in compession.
It was shown that in order to have significant weight benefits the value of ultimate deformation of the resin must be at least two times more than for current resins (keeping values of the resin ultimate tension stress at the same level of about 6-8kg/mm2). Investigation of alternative "black metal" and "frame" structure concepts has shown that the "frame" concept has more potential in weight saving for current resin and for the resin with ultimate deformation up to 8%.
A short description of the multilevel approach developed for fast and confident estimation of non-conventional airframe weight at the initial stage of designing is included in this paper. The results of the computer modelling of the relationship between the weight of the primary structure and the base parameters of resin for a composite panel of the fuselage unit of a middle-range civil aircraft are included in the paper as an example.
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