КРАЙОВІ ЕФЕКТИ В БАЛКАХ ІЗ КОМПОЗИТІВ

Beams made of composites are widely used in aircraft structures, various machines and mechanisms. The experience of operation and repair of such objects shows that when designing beams and spars, one must take into account such effects as the influence of thermal stresses and the additional contribution of Poisson's coefficients to the stressed state of beam elements both in the length direction and along the width beam elements. Scientific studies devoted to the assessment of the stress-strain state of load-bearing structures made of composites demonstrate the conclusions that the effects of thermal expansion (contraction) of heterogeneous connected elements and the influence of Poisson's ratios give significant increases in stress. The value of these increases can be up to dozens of percents of the base load (that is, without taking these effects into account).The paper proposes an engineering mathematical model that allows estimating the value of normal and shear stresses from thermal loading and Poisson stresses. An analysis of the distribution of these stresses along the length and width of the beam elements was carried out.When using the structural-technological solution of beams with sub-shoulders, the proposed method allows you to reasonably choose adhesive or binder for reliable connection of the cap with sub-shoulder, as well as more correctly justify the geometric dimensions of the beam elements. Also, this technique can be used to develop new structural and technological solutions for beams and other load-bearing elements (ribs, walls, webs, doublers, overlapping joints of composite parts).Another applied direction of using the developed methodology can be considered the development and optimization of existing technological processes for the production of parts and units of composites, in which the so-called hot polymerization of the binder (at elevated temperatures) is used. The method makes it possible to estimate the level of thermal stresses that occur during the manufacture of the unit.In general, the proposed technique makes it possible to understand the principles of additional stresses occurrence, to estimate their absolute values, and to increase the accuracy of estimating the stress-strain state of beam elements.