The strain range partitioning method was applied to a creep-fatigue life prediction of the rotor of the permanent magnet type eddy current retarder, which is a braking system equipped in heavy trucks. Transient heat transfer analysis and elastic-plastic-creep thermal stress analysis were conducted with a three-dimensional finite element model in order to evaluate the inelastic strain caused by repetition of braking. On the basis of analytical results and creep-fatigue properties of rotor steels, creep-fatigue life of the rotor was predicted by the strain range partitioning method and creep-fatigue damage rule based on the strain range partitioning concept. The predicted lives were well corresponded with those in thermal cycle tests with the actual retarder. Furthermore, in order to increase the braking torque and extend the life of the rotor, the new rotor steel was developed. The developed steel has lower electrical resistivity and higher strength at high temperature than the conventional rotor steel. It was found that the developed steel rotor has higher braking torque and longer creep-fatigue life than those of the conventional steel rotor.
