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The main, well-known scientific results were obtained by outstanding scientist Yu. N. Rabotnov in the field of creep theory, hereditary elasticity, damage mechanics, technical theory of shells. However, in the last years of his life, the academician Yu. N. Rabotnov was keen on some problems in the field of mechanics of fiber-reinforced composite materials. He proposed new, original strength criteria, simplified methods for ply-by-ply calculation of composite laminates. One of Yu. N. Rabotnov's scientific passions were connected with description of specific fracture modes of layered fibrous composites having the types of delamination and splitting. On the base of energy fracture criterion, it's possible to estimate the scale effect of strength – the dependence of critical stresses on the absolute sizes of composite members. Such models of specific fracture modes make it possible to estimate the danger of such technological defects as thin polymeric film between composite layers. [ABSTRACT FROM AUTHOR]

The stability of axially functionally graded (AFG) heavy columns was analyzed. Consideration in stability analysis of the column is given to the free vibration and bucking problems. The mass density and Young's modulus of the AFG heavy column vary along the column axis through a power-law function. Unified modeling of the differential equations with the associated boundary conditions governing the deformed shape of the free vibrations and buckling of the column was developed. Using a combination of direct numerical integration method and numerical solution method of nonlinear equation, differential equations were solved to calculate the natural frequency and the critical buckling load. Calculation results for the natural frequency and buckling load compare well with the FEM results. As a result of numerical experiments, the effects of material and geometric properties on the natural frequency and the buckling load were reported and discussed in detail. [ABSTRACT FROM AUTHOR]

The paper aims to develop a unified modeling to analyze the free vibrations and buckling of laterally functionally graded material columns. The columns of rectangular cross-section, in which the mass density and Young's modulus vary along the depth as a power-law function, were considered. The differential equation governing a mode shape of a deformed column was derived with the relevant boundary conditions, including the effect of rotatory inertia. The computation results for the natural frequencies and buckling load were compared well with those available in the open scientific literature. The effects of geometrical and material properties on natural frequencies and buckling loads with the mode shapes are highlighted. [ABSTRACT FROM AUTHOR]

In the present research, the optimum paths and orientations for curvilinear and straight fibers of variable-and constant-stiffness composite cylindrical shells subjected to an external hydrostatic pressure and bending were found. For this purpose, a linear variation in the fiber orientation was considered for the curvilinear fibers. A genetic algorithm program written in the Python language was developed and linked to the ABAQUS finite-element code and used in an optimization process. The optimization was performed for several aspect ratios of the length-to-diameter of composite cylindrical shells. The buckling pressure of the variable-stiffness composite cylindrical shell increased by about 30℅ in comparison with that of the constant-stiffness composite cylindrical shell under an external hydrostatic pressure. The gaps and overlaps were modeled using a Pythonbased program and the ABAQUS software to investigate their effects on the buckling load of variable-stiffness cylindrical shells under external pressure loads. [ABSTRACT FROM AUTHOR]

For several years, kites have been representing an innovative technology in the maritime sector to reduce the fuel consumption through an auxiliary propulsion or producing energy onboard. Regarding the continuous increase in kite sizes, one of the main objectives is to determine whether a leading-edge inflatable kite and its components will be able to withstand the pressure field induced by the aerodynamic load. Therefore, an accurate identification of stress fields in them is required by designers. For this aim, a fluid-structure interaction method was developed by coupling a 3D nonlinear lifting-line model with the Abaqus™ 2017 finite-element software tools. Within this framework, a structural analysis was performed for a kite made of a woven fabric by employing the thin-layer finite-element technique for its weak bending properties. This modeling method is new and is not available in the Abaqus™. [ABSTRACT FROM AUTHOR]

The 3D nonaxisymmetric local stability loss problem is studied for a hollow cylinder, made of a viscoelastic composite material, under the axial compression. The criterion of an infinitesimal initial imperfection is employed, and the evolution of this imperfection is investigated by 3D geometrically nonlinear exact equations of viscoelasticity theory. The corresponding nonlinear problem is solved by the boundary perturbation method. The material of the cylinder is modeled as a viscoelastic transversely isotropic medium. Numerical results for the critical time and critical compressive forces are presented, discussed, and compared with those obtained by approximate shell theories. [ABSTRACT FROM AUTHOR]