Hud M. Evaluation of the durability of thin-walled cylindrical shells during transportation by air

The first section analyzes the literature data on the assessment of the load of long thin-walled shells during transportation by land and water transport. The existing methods of experimental research of accelerations, measurements and statistical processing are analyzed. It is established that to ensure the integrity of the LV during transportation by aircraft, it is necessary to investigate the range of loads during transportation, the shape and frequency of natural oscillations by analytical and numerical methods, taking into account the influence of geometric dimensions, fastening method and shell strengthening. Criteria of admissible fatigue durability of elements of a design of LV are defined. The stress threshold for the D16AT aluminum alloy is determined In the second section, a finite element model of the first stage of launch vehicle (LV) in the form of reinforced and smooth cylindrical shells is developed. Using the modal analysis of the FEM, the natural frequencies and forms of oscillations of the smooth shell - the model of the first stage of the launch vehicle - were studied. The influence of the presence of amplifying elements (stringers) on the natural frequencies of the cylindrical shell is determined. The nature of the change in the frequencies of the natural oscillations of the reinforced shell depending on the type of fastening and the change in the area of the reinforcing elements is revealed. An original method of transition from a full-size shell of the first stage of LV to a model shell of the first stage of LV has been developed. According to the results of the modal analysis, the natural frequency values of the cylindrical stringer-reinforced thin-walled model structure of the first stage of the launch vehicle are obtained. It is found that the natural frequencies of the model structure exceed by several orders of magnitude the values of the natural oscillations taken as the basis of the first stage of the LV. In the third section the methodology of experimental researches of the forced oscillations of the stringer-reinforced cylindrical shell on the basis of the STM-100 servohydraulic test machine is developed. Based on the application of affinity similarity, an experimental model of the first stage of LV in the form of a shell reinforced with stringers and frames, as well as a platform for its attachment and a system for reading oscillation parameters when tested on the basis of servo-hydraulic test machine STM-100. The parameters and amplitude of forced oscillations of the reinforced model shell with and without filler were investigated experimentally. Based on the obtained experimental data, the ultimate stresses of the reinforced scale shell with filler are determined. Using the fatigue curve for the D16AT alloy, the number of cycles to failure is determined depending on the frequency of forced oscillations of the filled reinforced model shell at a constant amplitude external load. In the fourth section, for the full-size reinforced cylindrical thin-walled shell using the ANSYS software package, the influence of natural oscillations on the SSS of the shell material is investigated. It was found that the nature of the stress change is curvilinear and inversely proportional to the natural frequency of the reinforced cylindrical shell. However, in contrast to the value of normal stresses σy, the values of the tangential stresses τxy exceed the yield strength of the material D16AT. It is found that the places of stress concentrations σx, σy, σz are the vertices of transverse and longitudinal waves. The places of concentration of tangential stresses τxy, τxz are the places of change of the direction of displacements. The maximum values of stresses in a thin-walled reinforced cylindrical shell under the action of natural oscillations are determined. The scientific novelty of the obtained results is that: the method of scaling is developed and the geometric and physical parameters of the model of the first stage of LV in the form of a reinforced cylindrical shell are substantiated; The natural frequencies of the cylindrical, stringer-reinforced thin-walled model structure of the first stage of the launch vehicle were studied; a mathematical model of a cylindrical thin-walled smooth shell has been developed, on the basis of which the natural oscillation frequencies of an unreinforced cylindrical shell have been determined; the method of computer modeling was further developed and the main regularities of the flow of frequencies and amplitudes of natural oscillations on the stress-strain state of the reinforced cylindrical shell for a large number of modes were revealed; the technique of experimental researches of influence of frequency and amplitude of loading on the forced fluctuations of the cylindrical shell strengthened by stringers is developed.