On material immanent ratchetting of two-phase materials under cyclic purely thermal loading

The paper analyses specific features of the response of two-phase materials with different thermomechanical properties of the phases to purely thermal cycling. It is shown that even without mechanical loading both shakedown a nd ratchetting regimes are possible. A short review is given of the phenome na and various models of shakedown and ratchetting under cyclic thermomecha nical loading. Three structural models for the description of a special two -phase material, namely the duplex stainless steel, under purely thermal lo ading are discussed: a simple two-bar model, a composite cylinder model and micromechanical finite element models with duplex topologies. These models account for different features of the deformation process during thermal c ycling and are used as basis for the analysis of thermal ratchetting. Resul ts of numerical simulations are presented for various material conditions a nd modelling schemes. Conditions for material immanent ratchetting are derived and verified by nu merical experiments. It is shown that a temperature-dependence of the yield stresses of the two phases, which exhibits an intersection of the correspo nding curves within the temperature interval of the cyclic thermal load, en forces this sort of ratchetting, lacking intersection of the yield stress-t emperature curves indicates, on the other hand, a lesser or lacking tendenc y for material immanent ratchetting. Comparisons with results of laboratory experiment are also presented, and the tendencies derived from the microme chanical models are verified.