Numerical Analysis of Fatigue Life of Structural Elements under Thermopulsations

The problem of parrying parametric non-stationary thermomechanical effects of critical engineering infrastructure objects arising in the operating modes of these objects is considered. The problem of obtaining strength and resource estimates is solved. A mathematical model of the mechanics of damaged environment (MDE) is developed for studying the processes of thermoviscoplastic deformation and damage accumulation. The model takes into account material degradation by coupled joint mechanisms of low-cycle fatigue and long-term strength. The model is formed by relations for cyclic thermoviscoplastic behavior of the material up to the process of destruction; equations of damage accumulation kinetics; strength criterion of damaged material. Thermoviscoplastic is based on the concepts of yield surfaces, creep, and the principle of gradient vectors of plastic deformation and creep strain rates to the corresponding surface at the loading point. The model describes the main effects of the process of cyclic thermoviscoplastic deformation of the material for arbitrary complex loading trajectories. A scalar damage parameter is used in the kinetic equations of damage accumulation. The model is based on energy principles and takes into account the main effects of formation, growth and merging of microdefects under arbitrary complex loading conditions. The condition of reaching a critical value by damage is taken as the strength criterion. The presented calculations of thermoviscoplastic deformation and damage accumulation are compared with the data of full-scale experiments. In the example, an analysis of thermal fatigue of a structural element is carried out. A welded joint under thermomechanical loading is investigated for a pressure vessel with stress concentrators. The performance of the presented model for assessing the fatigue life of structures under multiaxial disproportionate paths of combined thermomechanical loading is shown.