Annotation: The paper proposes a method for investigating structural strength and determining structural failure loads by computer-aided simulation and nondestructive testing. The methodology is grounded on general ratios of elastoplasticity in increments based on the Lagrangian approach and the principle of virtual translations, taking into account the geometrically nonlinear nature of structural deformation under intense loading. The baseline technique for numerical simulation was the fi nite element method. The methodology for structural strength investigation includes three steps. The fi rst step involves studying the structure in the form of a spatially two-dimensional shell-like model. An analysis of the calculated values of the model’s stress and strain is performed based on the results of the computational experiment, and the critical regions within the structure are determined, where these parameters reach their peak values. The second step yields detailed three-dimensional models of those critical regions within the structure. These models incorporate the geometrical (including the actual thicknesses of the elements) and physical specifi cs of the structure. The results of numerical experiments are applied in an analysis of the refi ned stress and strain values of the three-dimensional models, and the minimum structural failure load is determined. In the third step, strain gauges are installed in the determined critical regions, and the structure’s strength is tested using a nondestructive load. A predicted structural failure load is found by comparing the strain and translation values obtained from the test results with the outputs of computational experiments. The development of the mentioned methodology encompassed an investigation of stress and strain at diff erent internal pressures for an oxidizer tank of a launch vehicle’s fi rst stage, a quantitative estimation of the tank’s strength, and the determination of the structural failure load and regions where a structural failure is likely to start. This paper demonstrates that the results of a tank strength analysis using a criterion of a maximum stress are closest to experimental data.

Annotation: One of the tasks of the development tests conducted on a launch pad is verification of its strength properties. The tests are carried out after the launch pad was manufactured and assembled on-site as well as during the whole operating period (if necessary). Load mode was chosen in consideration of cost and possibility of providing the required loading conditions. Two modes of creating the required test load were examined: usage of weights with corresponding mass (load simulators) or special devises (which have smaller mass as compared with load simulators). The descriptions, basic characteristics, advantages and disadvantages of composite and bulk weights and pad loading device are given. This article studies the pad loading device under development. This device enables to conduct static nondestructive tests on the launch pad in order to check its strength after manufacturing and during the whole operating period. The device consists of the load-bearing frame, hydraulic system, locks, control system and measurement system. Advantages of the pad loading device include low materials consumption, low cost in comparison with composite weights (with large load values), provision of the required modes for applying and removing the test load, controlled separate loading of each support of the launch pad, high mobility, short duration of testing, possibility of using launch pads of other rocket complexes with lower or equal test load values for testing. Therefore, the pad loading device enables to achieve the required test load values while having considerably smaller dimensions and mass as compared with composite weights and bigger functional possibilities as compared with bulk weights. Small overall dimensions and operability reduce the number of needed personnel and equipment.

Annotation: New theoretical results were obtained in definition of the stability longitudinal stress of the stiffened cylindrical shells both with internal and external arrangement of the stiffened stacks. They were obtained due to application of the dynamic approach to the solution of the refined equilibrium equations, introduction of the Qfactor of the structural elements into the system of equations, definition and application of the forces and moments in the calculation, that act in the sections of the joint bending of the shell and elements of stiffening. Expressions are given, which define the process of stability loss, including parameters of wave generation and amplitude of shell oscillation from the moment of application of the axial compressive force P0 up to the moment of snap action. With dynamic approach to the solution of the problem of the shell’s longitudinal stability the achievement of the first zero frequency by one of the higher modes of bending oscillations of the shell will indicate the loss of stability under the impact of the axial compressive force P0. This process is most obvious during testing of the absolutely flexible shells, which permit multiple loading. In the initial step of shell loading with axial compressive force P0, high-frequency bending oscillations with m, n ˃˃ 1 modes and low amplitudes occur. With a rise in force P0 oscillation frequency begins to drop, and amplitude to increase, with oscillatory mode remaining unchanged. There is a snap action when zero frequency is achieved for the first time by one of the oscillatory modes. This fact allowed formulation of the basic principles of nondestructive method for estimation of the critical stability stress of the flight-ready shell, main point of which is in the comparison of the theoretical curve of the frequency drop due to force P0 action on the structure versus the actual curve of the frequency drop of the flight-ready structure under the impact of the same values of P0 in the elastic range.