Modeling the propagation of interlaminar defects in multilayer composite materials requires knowledge of the characteristics of the material under study associated with the fracture processes. The goal of the study is determination of the interlaminar fracture toughness in the case of normal traction (GIc). Finite element modeling of testing was carried out proceeding from the data obtained. The delamination process was modeled using the most common approaches within the finite element method: VCCT (virtual crack closure technique) and CZM (cohesive zone model), wherein the fracture toughness is used as the main parameter for the occurrence of delamination. The obtained data are compared with the experiment. To confirm the correctness of the obtained experimental data on the fracture toughness GIc, modeling of the process of compression testing of a strut-type specimen with a defect in the form of a through-the-width delamination was carried out. This problem includes a nonlinear static solution with buckling and subsequent post-buckling behavior, and, as a result, the spread of the delamination zone. The data obtained using finite element modeling are consistent with the available experimental data.

The paper presents a finite element formulation for solving stability problems of the composite cylindrical shells taking into account momentness and nonlinearity of their subcritical stress-strain state. The nonlinear problem of strength and stability was solved by the finite element methods and the Newton-Kantorovich linearization. Critical loads were determined in the process of solving the geometrically nonlinear problem using the Sylvester criterion. Finite elements of the composite cylindrical shells with natural curvature previously developed on the basis of Timoshenko’s hypothesis were used. Their rigid motions were explicitly identified in the movement approximation. Stability of a circular cylindrical shell made of the polymer composite material was studied under combined loading with torque, transverse force and internal pressure. Interaction curves of the external loads were obtained. Influence was determined of monolayers laying methods, nonlinearity of deformation and internal pressure on the critical loads of the shell buckling and the weight efficiency of composite shells in comparison with the metal ones.

The topological optimization method was used to synthesize bionic structures for the promising small aircraft compartment made of aluminum alloy. Topological optimization was performed on the basis of the ESO-SIMP method using the ANSYS Workbench software tools. Influence of the design parameters, in particular, of the shell thickness, on the strength and weight characteristics of the compartment bionic structures after topological optimization was studied under the external loads action.

Currently, polymer composite materials are widely used in the modern aircraft structures. Their application significantly reduces the weight of the structure, while maintaining its strength and stiffness characteristics. A large number of works have been published on the study of the strength of such structures, but the issues of strength and stability during their nonlinear deformation remain unresolved. There is a small number of works on the study of strength and stability of thin-walled shells made of polymer composite materials. The latter is especially necessary for thin-walled aircraft fuselage structures, where the loss of composite skin stability is unacceptable. The problem of determining the influence of the stacking order of monolayers in a skin on the strength and stability of composite material shells under nonlinear deformation remains unsolved. Methods for calculating the strength and stability of thin-walled composite structures, regarding the nonlinearity of the initial stress-strain state, are not well developed. Therefore, the development of reliable and efficient methods for calculating shells made of composite materials is an urgent task. The article describes solving the problem of strength and stability of cylindrical composite shells under arbitrary loading using finite element methods and Newton-Kantorovich linearization. Critical loads have been determined in the course of solving a geometrically nonlinear problem using the Sylvester criterion. The stability of a circular cylindrical shell made of a polymer composite material has been studied under combined loading by a bending moment and a transverse force. The influence of the nonlinearity of deformation, methods of stacking monolayers on the shell critical loads has been determined.

Abstract. The change of the global climate is most pronounced in the Arctic, where the air temperature increases 2 to 3 times faster than the global average. This process is associated with an increase in the concentration of greenhouse gases in the atmosphere. There are publications predicting the sharp increase in methane emissions into the atmosphere due to permafrost thawing. Therefore, it is important to study how the air composition in the Arctic changes in the changing climate. In the Russian sector of the Arctic, the air composition was measured only in the surface atmospheric layer at the coastal stations or earlier at the drifting stations. Vertical distributions of gas constituents of the atmosphere and aerosol were determined only in a few small regions. That is why the integrated experiment was carried out to measure the composition of the troposphere in the entire Russian sector of the Arctic from on board the Optik Tu-134 aircraft laboratory in the period of ​​​​​​​4 to 17 September of 2020. The aircraft laboratory was equipped with contact and remote measurement facilities. The contact facilities were capable of measuring the concentrations of CO2, CH4, O3, CO, NOx​​​​​​​, and SO2, as well as the disperse composition of particles in the size range from 3 nm to 32 µm, black carbon, and organic and inorganic components of atmospheric aerosol. The remote facilities were operated to measure the water transparency in the upper layer of the ocean, the chlorophyll content in water, and spectral characteristics of the underlying surface. The measured data have shown that the ocean continues absorbing CO2. This process is most intense over the Barents and Kara seas. The recorded methane concentration was increased over all the Arctic seas, reaching 2090 ppb in the near-water layer over the Kara Sea. The contents of other gas components and black carbon were close to the background level. In bioaerosol, bacteria predominated among the identified microorganisms. In most samples, they were represented by coccal forms, less often spore-forming and non-spore-bearing rod-shaped bacteria. No dependence of the representation of various bacterial genera on the height and the sampling site was revealed. The most turbid during the experiment was the upper layer of the Chukchi and Bering seas. The Barents Sea turned out to be the most transparent. The differences in extinction varied by more than a factor of 1.5. In all measurements, except for the Barents Sea, the tendency of an increase in chlorophyll fluorescence in more transparent waters was observed.