A Study On The Uniaxial Ratcheting Behavior Of Austenitic Stainless Steel Z2CND18.12N

In this study, a series of uniaxial tensile tests, strain cyclic test and uniaxial ratcheting tests were conducted at room temperature on Z2CND18.12N austenitic stainless steel used for the auxiliary piping in the fist loop system of pressurized water reactor. The experimental results showed that at room temperature (1) this material displayed viscoplastic characteristic: the stress-strain response was rate dependent; (2) after cyclic hardening for the first few cycles, slowly evolving cyclic softening was observed until cyclic stabilizing---in general, it is a material with the cyclic hardening feature; (3) the uniaxial ratcheting strain level increased with the increasing mean stress and stress amplitude, decreased with the increasing loading rate, and was more sensitive to lower loading rate; (4) under the same loading condition, the ratcheting strain level of specimen after aging was higher than that without aging; (5) loading history had great influence on the ratcheting behavior: under the constant loading rate, lower loading level after higher loading history led to the shakedown of ratcheting; under the constant loading level, higher loading rate after loading history with lower loading rate also resulted in the shakedown of ratcheting. In the contrary cases, ratcheting strain continued to accumulate, at a higher level than those under the same loading condition without loading historyWithin the framework of unified viscoplasticity, combined with the isotropic hardening rule, a new model was constructed on the basis of Ohno-Wang II kinetic hardening rule to describe both the strain cyclic behavior and the uniaxial ratcheting behavior of Z2CND18.12N stainless steel at room temperature. Parameters of the new model were determined according to a simple procedure. The predicted results showed acceptable agreement with the experimental results.