MODELLING OF DAMAGE ACCUMULATION PROCESSES AT PLANE STRESS STATE

An approach to modeling the processes of damage accumulation during creep is proposed- The case of the stress state in a structural element is characterized by the presence of areas with different stress levels is considered. As a result of aging, oxidation, and other high-temperature degradation processes in zones with low stress levels, the rate of accumulation of hidden damage may increase, which is not reflected in the classical formulations of Damage Mechanics. A description of the evolution equation for the scalar damage parameter is provided, in which the parameters included in it are the functions of the stress values, which at a given time before the finishing of hidden damage accumulation are destructive. The mathematical formulation of the problem and its finite element formulation are performed for the case of a plane stress state. Numerical modeling of damage accumulation processes in plates with circular notches made of heat-resistant alloy CMSX-4 is carried out. The distributions of the damage parameter along the plate obtained using the classical Kachanov-Rabotnov damage parameter equation and the one proposed in this work for a wide range of stresses are compared. It is shown that taking into account a different, increased rate of damage accumulation in areas with a low level of stresses in the analysis of long-term strength leads to a significant reduction in the time to completion of hidden damage accumulation. It is demonstrated that in the case of using the modified evolution equation, the zone with a high level of damage is distributed throughout the volume of the plate, which may indicate further rapid fracture. The proposed approach to modifying the evolution equation for the damage parameter can be used in the case when there is an information about the real value of the time to fracture in operational conditions with the subsequent execution of a cycle of numerical experiments to obtain the characteristics of the long-term strength curve, which will be incorporated into the modified evolution equation.