Analysis of the Cyclic Strength of Technical Systems under Complex Operating Loading Conditions

Abstract

The main cyclic thermomechanical and relevant time-variable vibration and aero-hydrodynamic loadings affect modern energy facilities and space, air, water, and land transport during their operation. The total number of loading cycles with allowance for the operating time turns out to vary within very wide limits. It has been shown that a general time range of loads affecting the aforementioned objects appears to be very complex in terms of load levels, frequencies, and action times. Taking into account a wide variation of service impacts in the loading level, frequency, and total number of loading cycles, the general analysis of the resistance to deformation, damage, and fracture of highly loaded modern technical objects has been carried out. The results obtained have shown that, under combined mechanical, vibration, and aero-hydrodynamic loadings, the limit state, by the cyclic strength criteria with the use of the rule of linear summation of damage expressed in deformation parameters, will be attained earlier than in the case when only the main thermomechanical loading is taken into account. To substantiate the strength and operating life of the investigated objects, standard and unified mechanical isothermal tests for static and cyclic loading have been performed to determine the basic mechanical properties of a material, and special mechanical programmed tests with variable modes simulating complex operational thermomechanical, vibration, and aero-hydrodynamic impacts have been carried out. The results of these tests are used in the computational and experimental estimations of the strength and durability for the corresponding spectra of operational loads. A refined verification calculation of the cyclic strength and durability is becoming increasingly relevant for modern machines operating under the conditions of increasing speeds of movement, operating pressures with increased levels of pulsation, and accompanying mechanical oscillations, vibrations, and aero-hydroacoustic impacts.