Comparative analysis of variants of plasticity theories under cyclic loading

Based on the results of the experimental investigations of the samples made of stainless steels SS304, 12X18H9 and 12X18H10T subject to a hard (controlled deformations) and soft (controlled stresses) cyclic loadings under uniaxial tension-compression and normal temperature we carried out a comparative analysis of the adequacy of the currently used variants of the plasticity theories which belong to flow theories with a combined hardening. The loads that include the sequences of cyclic and monotonic loads as wells as placing and ratcheting of the plastic hysteresis loop are considered. The loads are applied until fracture, i.e. the emergence of macrocracks with a length of 1 mm. Within the scope of our analysis we have considered the following variants of theories including the models of Korotkih, Bondar and Chaboche. For each model, a set of material functions is given on basis of which the calculations of the kinetics of the stress-strain state of the cyclic loading processes are made. By comparing the results of the calculations and experiments, it has been shown that the description of the cyclic loop placing and ratcheting processes is possible only within the Bondar and Chaboche models with a certain advantage of the modified Bondar model, which enables an adequate description of the nonstationary cyclic loading and nonlinear damage accumulation. It is shown that the modified Bondar model - including the third type of microvoltage (Ono-Wang) and kinetic equations of damage accumulation - provides the most adequate (in comparison with other models) description of the kinetics of the stress-strain state and fracture under nonstationary nonsymmetric cyclic loading processes. It can be recommended for practical computations of the kinetics of the stress-strain state and the design life affected by an arbitrary load action.