1. Methods for structural strength investigations of rocketry.

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.