Ideology of design of aviation designs from polymeric composite materials
Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
The article is devoted to the design of structures made of composite materials (CM) and contains the problems that arise when designing such structures. It is shown that in all cases of the structure loading, local bulk stress concentrations of stretching-compression (wrinkling) appear in the layers of CM pack in the joint zone of regular part (fixed in composition of CM pack) with the adjacent structure. In this case, the structural strength will mainly depend on the strength of the binder. The dependence of concentration factors is shown. Theoretical formulas for estimation of the joint action of local stress concentrations on the strength of the structure effect do not exist. Stress concentration magnitude in CM layers versus constructive and technological factors, material properties characteristic is shown.
The article presents an empirical formula for the loss of strength in the joint zone in relation to the regular part of the structure estimation. It is shown that actual increase of thickness in the joint zone in comparison with the regular part of the construction depends on the number of fasteners rows. With double-row seam the thickness increases, respectively, by 1,5–3 times, and with triserial — by 1–2 times. It is necessary herewith to take into account the non-uniformity of fasteners rows loading.
The dependence of weight saving by replacing B95 stringer panels with CM structure fr om the volume (area) fraction of joint zones related to the total area of the panel.
The presence of joints reduces possible weight saving of the structure by 35–37%. If the value of the joint zone square fraction is more than 20% of the total CM panel area, implementation of CM by weight criterion loses its meaning.
Optimal structure of CM panels and racks will be the structure, wh ere the strength of the binder fibers corresponds to the strength of bearing layers, which corresponds, for example, to the structure of animal bones.
Keywords:structure, composite material, stress concentration, connection, problems
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