Abstract. The paper presents the results of studies on the stress-strain state of composite wing spars with different lay-up structures. The object of research is a U-shaped cross-section composite wing spar. On the basis of the analysis of the stress-strain state, the most favorable structure of a wing spar from the viewpoint of minimizing the risk of stress state and providing the highest stiffness. Recommendations are given on layup structure stacking (compared with typical structures) for more effective perception of external loads by a wing spar.

In this article the results of stress-strain state investigation for composite airplane wing stringer with different layers stacking structures are presented. As an object of research, a stringer made of composite carbon with V-shaped cross-section is considered. Due to the stress-strain state analysis of various stringer structures, the most effective structure for stringer layers stacking is selected, both in the view of providing the most rigidity and optimal perception by the stringer the field of external loads, which are most typical for the conditions of its operation.

Composite materials are now widely used in aircraft manufacturing, rocket production, shipbuilding, the petroleum and chemical industries. Multilayer composites are the most promising from the viewpoint of controlling their physical and mechanical properties, depending on the direction of external forces during operation. By changing the multilayer composite structure (the number of layers, the angles and the sequence of their stacking, the physical and mechanical properties of the composite components), it is possible to control their physical and mechanical characteristics in a given direction. The article presents the results of an analytical, experimental and finite-element exploration of the influence of a unidirectional spatial reinforcement of carbon fiber composite with cross-piercing on its elastic compliance coefficients and strength characteristics. A literature review of methods for determining the elastic characteristics of composite materials (CM) with 3D (spatial) structures is given. Methods of determining elastic characteristics of spatially reinforced composites described in the literature are based on the principle of splitting them into layers, in which a unidirectional layer characterized by nine elastic parameters is taken as the basis: three elastic moduli along the main axes of elastic symmetry E 1 , E 2 , E 3 , three shear moduli G 12 , G 23 , G 13 and three Poisson coefficients ν 12 , ν 23 , ν 13. From the analysis of the literature sources, it has been established that in determining the compliance coefficients of spatially reinforced composite materials, only the volume fraction of the reinforcing material and its elastic characteristics are taken into account. Studies of the stress-strain state of the matrix modified with a piercing thread showed that its elastic characteristics, in addition to the piercing thread volume content, were influenced by the geometrical parameters of the insertion, the elastic characteristics of the piercing thread impregnated with the matrix material, and the stress concentration on its boundary. This influence occurs in all ways of creating spatial structures formed by a system of three threads. The article also presents the results of the experimental determination of the spatially reinforced CM elastic characteristics and its comparison with the theoretical components of the elastic compliance tensor of a unidirectionally reinforced CM.