Modelling of the deformation process under thermo-mechanical fatigue conditions

A method enabling a description of materials behaviour in the fatigue process has been developed. This paper presents some elements of the method and examples of thermo-mechanical fatigue characteristics determined for selected parameters of fatigue tests. Fatigue examinations of the P91 steel, which is used in polish power industry, were carried out. The main problem addressed in the paper is the description of a deformation process under the conditions of mechanical and thermal interactions. An appropriate model has been developed to this end. A model presentation enables extensive investigations of the influence of various types of relations between the fatigue process parameters on changes of the uniaxial stress-strain characteristics. Characteristics of the thermal cycle in thermo-mechanical fatigue conditions, i.e. courses of stress changes as a function of mechanical strain, determined on the model base have been presented for chosen shift angles in the mechanical strain cycle phase in relation to the thermal one. So far, experimental verification of the stress-strain characteristics' course for a selected value of the phase shift angle has been made.