Features of Development of the Process of Thermal Fatigue of Metals and Methods of Its Assessment

Analysis of published results of thermal fatigue studies carried out by various methods of thermocycling testing is presented. The widely used Coffin’s method and its feasibility for describing the dependence of the durability on the plastic deformation in a cycle (ε_pl) is considered. It is shown that the range of the variation of ε_pl provided by the method is too narrow for covering the processes occurring in the materials during operation of the articles. This fact is confirmed by evaluation of ε_pl in testing of corset samples at the I. I. Polzunov Scientific and Development Association on Research and Design of Power Equipment, the test portion of which repeats the shape of failure areas frequently occurring in actual articles due to thermal fatigue. It is shown that during the testing process, cracks appear already in the first loading cycles and are a manifestation of the structural changes in the material. This is a result of an excessively high ε_pl, which is confirmed by a theoretical estimation. It is recommended to use a similar approach to simulate thermal fatigue in articles and to vary the plastic strain in them by changing the shape of the shoulders of corset samples without changing the thermal regime in testing.