Some features of monotonic and cyclic loadings. Experiment and modeling

Having analyzed the experimental studies of samples of 12X18H10T stainless steel with a hard (controlled deformation) deformation process including sequences of monotonic and cyclic loading modes, under uniaxial tension-compression and normal temperature, we found some features and differences of isotropic and anisotropic hardening processes under monotonic and cyclic loads. To describe these features in the framework of the plasticity theory (Bondar model) belonging to the class of flow theories with combined hardening, the criterion of changing the direction of plastic deformation and the memory surface allowing the separation of monotonic and cyclic deformations is introduced in the plastic strain tensor space. For the description of transient processes from monotonic to cyclic and from cyclic to monotonic ones, the evolutionary equations are formulated for the parameters of isotropic and anisotropic hardening. The basic experiment, on the basis of which the material functions are determined, consists of three stages, i.e. cyclic loading, monotonic loading and subsequent cyclic up to destruction. The method of material functions identification according to the results of the basic experiment is given. For stainless 12X18H10T steel, the material functions at room temperature were determined on the basis of the basic experiment and the identification method. The comparison of the calculated and experimental results for the stainless steel under rigid loading, was made and consisted of a sequence of five stages: cyclic, monotonic, cyclic, monotonic and cyclic up to destruction, are given. The calculated and experimental kinetics of the stress-strain state throughout the deformation process are compared. Changes in the range and average stress of the cycle at the stages of cyclic stress are analyzed. At these stages there is a landing hysteresis loop. A reliable agreement between the calculated and experimental results was obtained. A sufficiently adequate description by the theory of the processes of change in the kinetics, range and average stress of a cycle under hard loading suggests the possibility of a more adequate description and processes of soft loading, especially in non-stationary asymmetric loading conditions.