Evaluation of service life of heat-resistant alloys under cyclic thermomechanical loading

The problem of evaluating strength and service life of critical engineering facilities, whose operating properties are characterized by multi-parametric non-stationary thermomechanical effects is discussed in the paper. The main degradation mechanisms of structural materials (metals and alloys) specific to these objects are considered. The main requirements to the mathematical models of fatigue damage accumulation are formulated. The basic physical laws of complex thermoplastic deformation and fatigue damage accumulation in structural materials (metals and their alloys) for various modes of combined thermomechanical loading and their main difference from isothermal fatigue processes are considered. In the modern mechanics of damaged media (MDM), a mathematical model is developed which describes the processes of thermoplastic cyclic deformation and fatigue damage accumulation in structural alloys under multiaxial disproportionate modes of combined thermomechanical loading. A MDM model consists of three interrelated parts: defining relations of thermal plasticity accounting for their dependence on failure process, evolution equations of fatigue damage accumulation and a strength criterion of damaged material. It is shown that for certain parameters of equations of cyclic thermal plasticity, using a single point on the experimental fatigue curve, the parameters of evolution equations of damage accumulation can be determined which are used for a high-accuracy computational reconstruction of low-cycle fatigue curves for various complex deformation trajectories. The results of numerical modeling of thermoplastic cyclic deformation and fatigue damage accumulation in heat-resistant alloys (Haynes188) under combined thermomechanical loading are presented. Particular attention is paid to the issues of modeling the process of thermoplastic cyclic deformation and fatigue damage accumulation for complex processes of deformation accompanied by the rotation of the main sites of stress and strain tensors.