RATCHETTING IN CYCLIC PLASTICITY .1. UNIAXIAL BEHAVIOR

This paper is concerned with the phenomenon of cyclic creep, or ratcheting of metals cyclically loaded in the plastic range (ratcheting here describes the cyclic accumulation of deformation). Part I is concerned with time-independent ratcheting under uniaxial loading; Part II addresses various ratcheting mechanisms under biaxial loading. In the uniaxial case, a systematic set of stress-controlled cyclic experiments was conducted on 1020 and 1026 (heat-treated) carbon steels, in which the effect of the cycle amplitude and mean stress on the rate of ratcheting was established. Three rate-independent cyclic plasticity models are critically reviewed with respect to their performance in predicting the rate of ratcheting measured experimentally. A modification of the Dafalias-Popov model is outlined in which the linear bounds are allowed to "translate" in the direction of the cyclic creep at the rate of ratcheting. With this modification, the model is shown to improve the simulation of ratcheting in all ranges of parameters tested experimentally.